Oral keratinocyte-mediated inflammation and epithelial disruption: A narrative review on IRF6 signaling and oral carcinogenic risk.

Introduction
Head and neck cancer (HNC) represents the sixth most common malignancy worldwide.1,2 Among the various subtypes, oral squamous cell carcinoma (OSCC) accounts for most cases.
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While tobacco smoking and excessive alcohol consumption remain the most prominent and well-established risk factors for OSCC,1,3 a growing subset of patients, classified as non-smoking and non-drinking (NSND), develop the disease in the absence of these traditional exposures. In such cases, alternative etiological factors such as chronic trauma and dysbiosis of the oral microbiome have been proposed.
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The oral epithelium functions as a critical interface between the host and the external environment. Oral keratinocytes, the predominant cell type in this barrier, play a dual role: they provide a physical defense against external insults and contribute to immune surveillance. This immunological function is largely mediated by pattern recognition receptors, particularly Toll-like receptors (TLRs), which enable keratinocytes to detect microbial components and initiate immune responses.5,6 Upon activation, TLRs orchestrate a finely balanced immune reaction by regulating the production of pro-inflammatory and anti-inflammatory mediators.
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Specifically, TLR activation induces the expression of cytokines, chemokines, and type I interferons (IFNs), which collectively guide the epithelial immune response.
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TLR signaling in oral keratinocytes occurs via two main adaptor-dependent pathways: Myeloid differentiation primary response 88 (MyD88) and TIR-domain-containing adapter-inducing interferon-β (TRIF).
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The MyD88-dependent pathway involves the recruitment of interleukin-1 receptor-associated kinase 1 (IRAK1), which subsequently activates nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and members of the interferon regulatory factor (IRF) family.
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Among these, IRF6 has emerged as a key transcriptional regulator at the intersection of epithelial biology and immune function. Beyond its established role in epithelial differentiation and proliferation, IRF6 has been implicated in the regulation of cell-cell junctions and the modulation of inflammatory responses.
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Previously, we proposed a model in which IRF6 by acting downstream of TLR2 and the MyD88–IRAK1 axis regulates the expression of inflammatory mediators in oral keratinocytes. Notably, IRF6 activation leads to the induction of CC chemokine ligand 5 (CCL5), a potent chemoattractant involved in T cell recruitment and activation; therefore, epithelial immune signaling can be directly linked to broader inflammatory processes.
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This narrative review aims to synthesize current knowledge regarding the molecular mechanisms governing inflammation in the oral epithelium, with a particular focus on IRF6 signaling, CCL5 regulation, the impact of hypoxic microenvironments on epithelial behavior as well as oral keratinocyte biology and chronic inflammation-related carcinogenesis. To do so, literature included in this review was identified through structured searches in multiple databases (PubMed, Scopus, and Embase) up to June 2025, with additional references retrieved from key publications. Given the narrative nature of this review, a systematic evidence synthesis or meta-analysis was not performed; rather, studies that contributed to the proposed mechanistic framework linking IRF6 signaling to oral carcinogenic risk were critically selected. By integrating these key pathways, we propose a conceptual framework that connects keratinocyte function to chronic inflammation and oral disease progression. Understanding these molecular circuits may unveil novel therapeutic targets and offer translational insights into the pathogenesis of OSCC.

Oral epithelium
The oral mucosa consists of two layers: the stratified oral epithelium and the underlying connective tissue, which houses the vascular, lymphatic, and neural networks essential for epithelial support and regeneration.
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The oral epithelium functions as a specialized barrier that protects the body from chemical, mechanical, and microbial insults encountered in the oral environment. This protection is mediated through both structural and immunological mechanisms.
Structurally, it forms a physical shield via stratification and intercellular junctions. Histologically, the oral epithelium is predominantly composed of keratinocytes that differentiate progressively as they migrate from the basal layer to the superficial surface. The basal layer contains proliferative, undifferentiated cells, while the suprabasal layers undergo morphological and biochemical transitions culminating in terminal differentiation. These layers are classically defined as the basal, spinous, granular (or intermediate), and superficial layers, with the degree of keratinization varying according to anatomical site and function.
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In regions such as the buccal mucosa, the epithelium is non-keratinized and stratified, tailored for flexibility and resilience.
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The thickness of this mucosa ranges from approximately 0.3 mm in the mandibular canine area to 6.7 mm in the maxillary tuberosity, reflecting site-specific functional adaptations.
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Notably, the oral epithelium exhibits a high turnover rate, which is essential for barrier renewal and microbial resistance.12,16 In particular, the buccal mucosa demonstrates rapid regeneration, with a reported renewal cycle of 6–7 days—faster than the turnover of 5–11 days for keratinized sites like the gingiva on primate models.17–19
The other key feature of the oral epithelium structure is the presence of cell junctions. Epithelial cells develop polarity through specialized cell-to-cell contact structures known as epithelial junctions. These junctional complexes consist of tight junctions, desmosomes and adherens junctions. Tight junctions serve as barriers to both paracellular and intramembrane diffusion, controlling the permeability of the epithelial layer by regulating the movement of lipids and proteins between the apical and basolateral membranes. Key proteins involved in the formation of tight junctions include the transmembrane proteins claudin and occludin, which localize within these structures and mediate the connection between the basolateral membranes of adjacent cells.20,21
Desmosomes regulate permeability; however, this can be affected by factors such as hypoxia, medications, radiation, and bacterial dysbiosis.
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These junctions connect the lateral walls of keratinocytes, while hemidesmosomes anchor keratinocytes to the basement membrane.
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Keratins play a fundamental role in these junctions. In fact, defects in keratin 5 (K5) and K14 lead to cytoskeletal loss in basal keratinocytes, causing epidermolysis bullosa simplex, a condition characterized by blistering lesions following minor trauma.
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Desmosomes are also interconnected through desmosomal cadherins, including desmogleins and desmocollins, which facilitate strong intercellular adhesion.
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Similarly, mature adherens junctions are established through calcium-dependent interactions between cadherin molecules on neighboring epithelial cells. E-cadherin, the primary adhesion protein in epithelial adherens junctions, serves as a membrane anchor for the actin cytoskeleton by interacting with P120-catenin, α-catenin, and β-catenin. This cadherin-catenin complex not only reinforces cell-cell adhesion but also plays a crucial role in the dynamic regulation of adherens junctions under various physiological conditions.
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Immunologically, the oral epithelium regulates tolerance or activation in response to microbial antigens through signaling pathways and immune cell interactions.5,27 These intercellular junctions strengthen the immune barrier that protects the oral epithelium from mechanical and chemical injuries by resisting both physiological and pathogenic mechanical stress. However, oral mucosal immunity relies not only on the physical properties of cell junctions but also on a network of signaling proteins produced by keratinocytes, which interact with the basement membrane and immune system cells, particularly antigen-presenting cells (APCs).17,28

Toll-like receptors
Toll-like receptors (TLRs), members of the pattern recognition receptor family, are wide class of receptors involved in innate and adaptive immune responses.
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TLRs bind numerous antigens by recognizing conserved pathogen-associated molecular patterns (PAMPs) or Damage-associated molecular patterns (DAMPS), to which the oral cavity is constantly exposed, and triggering inflammatory responses during tissue damage.29,30 Once activated, TLRs coordinated expression of genes involved in specific signaling pathways in the regulation of innate and adaptive immunity and tissue repair and regeneration. To do so, TLRs are coupling in its cytoplasmatic domain to adaptor molecules including myeloid differentiation factor 88 (MyD88), TIR domain-containing protein (TIRAP), and TIR domain-containing adaptor inducing interferon-β-related adaptor molecule (TRAM). This potentially leads to the activation of two main pathways, the MyD88-dependent (used by all TLRs except TLR3) and the MyD88-independent TRAM/TRIF pathway (used by TLR3 and some signals of TLR4).
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TLR activation on epithelial cells has been shown to induce the production of several cytokines, chemokines, and antimicrobial peptides.
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Genetic disruption of TLRs and adaptor molecules of the TLR pathway has been associated with tumor development and progression in mice.
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TLRs—particularly TLR2 and TLR4—have been widely studied in oral mucosal diseases.34,35 However, TLR2 is of interest since it had been reported as tumoral suppressor, its lack led to increase cell proliferation and decreased apoptosis in a mouse model,
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it plays a role in Treg expansion and their suppressive capacity,
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and its expression increases in OSCC keratinocytes vs its healthy control.

Interferon regulatory factor 6 (IRF6)
IRF6 is a member of the Interferon Regulatory Factor (IRF) family that comprises nine transcription factors involved in various biological processes.37,38 IRF6 has been extensively studied in the context of craniofacial formation defects.
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If fact, mutations in IRF6 are known to cause Van der Woude Syndrome (VWS) and Popliteal Pterygium Syndrome (PPS).38,39 Patients with VWS are at higher risk of wound healing complications following surgical repair.
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IRF6 is unique among IRF family members due to its epithelial-specific expression and its central role in regulating keratinocyte differentiation.41–43 Unlike most IRFs, which are broadly expressed in immune cells, IRF6 is largely restricted to epithelial tissues. However, given its close genetic similarity to IRF5 and IRF7, evidence suggests that IRF6 may assume analogous functions to these factors within epithelial cells,
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particularly in innate immune signaling. Beyond immunity, IRF6 controls epithelial cell cycle dynamics: its phosphorylation targets the protein for ubiquitination and proteasomal degradation.
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Reduced IRF6 expression results in elevated Cyclin D3 levels, a key G1-phase marker, underscoring its role in cell cycle arrest. However, IRF6 alone is insufficient to fully regulate proliferation, as its stability depends on an inductive environment that prevents degradation.
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These findings align with research in cancer cells, where IRF6 acts as a tumor suppressor.
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IRF6 expression is downregulated in squamous cell carcinomas, where it is associated with invasive tumor cell behavior
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and epithelial-mesenchymal transition (EMT) in breast cancer.
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Restoring IRF6 expression halts cell cycle progression and proliferation.41,49 IRF6 has also been implicated in the development of vulvar squamous cell carcinoma arising from vulvar lichen sclerosus
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and as a prognostic marker for cervical neoplastic stages
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and gastric cancer, where it predicts poorer outcomes.
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More recently, IRF6 has also been recognized for its role in innate immunity where it plays a role in TLR signaling, regulating the activation of type I interferons and contributing to NFκB signaling in response to pathogenic stimuli.
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It also functions as a tumor suppressor studied in various cancers.41,46–48,50,51 Additionally, it contributes to immune responses through TLR signaling pathways in oral keratinocytes.42,54 The interplay between TLR3 and IRF6 in wound healing suggests a functional connection regulated within keratinocytes.
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Specifically, activation of IRF6 via the MyD88-IRAK1 pathway induces the production of CCL5, a chemokine dependent on TLR2 signaling in epithelial cell lines.43,56 CCL5 plays a crucial role in T-cell activation and the production of other pro-inflammatory cytokines.
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Notably, IRF6 mediates cytokine inflammatory responses in oral keratinocytes exposed to the periodontal pathogen Porphyromonas gingivalis, leading to enhanced differentiation of basal layer keratinocytes.
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These findings highlight an innate immune role for IRF6, previously attributed solely to other IRF family members.

C-C motif chemokine ligand 5 (CCL5)
CCL5, also known as RANTES (Regulated upon Activation, Normal T cell Expressed and Secreted), is part of the C-C motif chemokine family, which also includes CCL3 (macrophage inflammatory protein-1α, MIP-1α) and CCL4 (MIP-1β).
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This chemokine plays a crucial role in immune responses by acting as a potent chemoattractant for various immune cells and modulating inflammatory pathways.
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The primary receptor for CCL5 is C-C chemokine receptor type 5 (CCR5). However, it can also interact with CCR1, CCR3, CCR4, CD44, and GPCR-independent pathways.
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Notably, dipeptidyl peptidase IV (DPPIV/CD26) enzymatically modifies CCL5 by removing the first two amino acids from its N-terminus, which enhances its affinity for CCR5 while diminishing its binding to CCR1 and CCR3.61,62 Additionally, this post-translational modification has been shown to influence Ca²⁺ release, further affecting intracellular signaling pathways.
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These enzymatic alterations may contribute to the specificity of CCL5’s function in different immune contexts, potentially fine-tuning immune cell recruitment and activation.
CCL5 is a target gene regulated by NFκB and is produced by a variety of cell types, including T lymphocytes, macrophages, platelets, synovial fibroblasts, tubular epithelial cells, and tumor cells.
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Due to the widespread expression of its receptors, CCL5 exerts a broad immunological influence by recruiting monocytes, mast cells, dendritic cells, natural killer (NK) cells, eosinophils, basophils, CD4+ and CD8+ T cells, and B cells to sites of inflammation or infection.
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Given its strong chemoattractant properties, CCL5 is implicated in various inflammatory diseases, autoimmune disorders, and cancer progression.
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In chronic inflammatory conditions, elevated levels of CCL5 contribute to sustained immune cell infiltration, amplifying tissue damage and disease pathology.
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Additionally, in the tumor microenvironment, CCL5 has been associated with tumor growth, immune evasion, and metastasis, making it a potential target for therapeutic intervention.
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IRF6 as a regulator of epithelial differentiation and EMT in chronic inflammation
This review underscores the pivotal role of oral keratinocytes in regulating inflammatory responses within the oral mucosa. The differentiation status of these cells directly influences the integrity of epithelial junctions, the magnitude of inflammatory responses, and the expression of key regulatory molecules such as IRF6, NFκB, and CCL5.
In addition to its established role in epithelial morphogenesis, IRF6 has been identified as a regulator of immune responses in keratinocytes. It promotes terminal differentiation, suppresses proliferation, and negatively regulates p63 by repressing pro-proliferative genes while upregulating differentiation markers (e.g. Transglutaminase 1 (TGM1), Involucrin (IVL), and Keratin 13 (KRT13)).42,46,65,66 IRF6 has also been implicated in tumor suppression through its interaction with factors such as Maspin and by modulating epithelial differentiation pathways.48,49 Notably, Ke et al.
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demonstrated that IRF6 regulates EMT-related genes, including Transforming Growth Factor Beta-3 (TGFβ3) and snail family transcriptional repressor 2 (SNAI2), during palatal development, highlighting its broader role in epithelial plasticity.
EMT, characterized by the loss of apicobasal polarity, decreased E-cadherin expression, and acquisition of mesenchymal markers like vimentin and fibronectin68,69 occurs during embryonic development, wound repair, and cancer progression.
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Previous findings support the role of IRF6 in regulating EMT in oral keratinocytes.
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Girousi et al.
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showed that IRF6-deficient keratinocytes exhibited disorganized colony architecture, reduced E-cadherin at junctions, delayed migration, and impaired stratification in both 2D and 3D models. These alterations suggest increased epithelial reactivity and permeability, conditions that can promote chronic inflammation.42,71 Moreover, irf6 knockout keratinocytes demonstrated significantly impaired calcium-induced differentiation, with reduced expression of those markers previously mentioned, TGM1, IVL, and KRT13,
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suggesting a potential shift toward EMT. As expected, this calcium-induced differentiation response was absent in IRF6-ablated keratinocytes. However, although partial rescue was achieved by ectopic IRF6 expression, low levels of exogenous IRF6 were insufficient to restore IVL and TGM1 expression, suggesting that a threshold level of IRF6 is required for full functional activity.
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These findings emphasize IRF6’s critical function in maintaining epithelial stability and suggest that its dysregulation may drive inflammation-associated epithelial remodeling and predispose tissues to malignant transformation.

Chronic inflammation and hypoxia: The dual role of CCL5 in oral carcinogenesis
Chronic inflammation and cancer are closely linked.72,73 The interaction between IRF6 and TLR2 signaling provides new insights into the mechanisms by which oral keratinocytes regulate immune responses. In epithelial cells, stimulation with Lipopolysaccharide (LPS) and Fibroblast Stimulating Lipopeptide 1 (FSL-1) activated CCL5 expression, a process directly influenced by the phosphorylation status of IRF6.
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Simultaneously, TLR activation also triggers NFκB signaling, supporting the role of oral keratinocytes as key coordinators of the inflammatory response. The interplay between IRF6, CCL5, and NFκB reveals a tightly coordinated regulatory mechanism that amplifies and sustains inflammation within the oral mucosa.
NFκB plays a central role by establishing a positive feedback loop that amplifies inflammatory signaling. It regulates the transcription of numerous genes involved in inflammation, including pro-inflammatory cytokines (IL-1, IL-2, IL-6, TNFα), chemokines (IL-8, MIP-1α, MCP-1, CCL5), adhesion molecules (ICAM, VCAM, E-selectin), inducible enzymes (COX-2, iNOS), and EMT-related transcription factors such as Snail.74,75 Taking together, these responses contribute to tissue remodeling, hypoxia, and the potential activation of EMT, linking chronic inflammation to disease progression and possibly malignant transformation.75,76 Inflammatory mediators such as soluble factors, oxidative stress or hypoxia can foster the acquisition of EMT-like features in cancer cells and reduce the susceptibility of carcinoma cells to lymphocytes, natural killer cells, lymphokine activated killer.
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Hypoxia is a hallmark of both physiological and pathological conditions. Tissues exposed to the external environment—such as those in the upper airway—naturally experience fluctuating oxygen levels. In pathological contexts, however, hypoxia tends to become more severe, particularly in inflamed tissues where edema, vasculitis, and the recruitment of oxygen-consuming immune cells exacerbate oxygen deprivation.
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The transcription factor hypoxia-inducible factor 1-alpha (HIF-1α) is the principal regulator of cellular adaptation to hypoxia. It activates a broad range of genes involved in survival, metabolism, and inflammation.
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Members of the HIF transcription factor family are essential for cancer cell adaptation to hypoxic environments, as their activation leads to the reprogramming of metabolic pathways, protein synthesis, and cell cycle progression.
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The transition from chronic inflammation to malignancy is a complex process that involves multiple factors. Within the oral cavity, one of these key factors is microbial dysbiosis. Olsen and Yilmaz
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reported an association between periodontitis and increased risk of oral, gastrointestinal, and pancreatic cancers, suggesting that chronic inflammation and dysbiosis are significant drivers of orodigestive carcinogenesis. Porphyromonas gingivalis, a key pathogen in periodontal disease, has been specifically linked to gingival squamous cell carcinoma.
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Interestingly, LPS of P. gingivalis—previously shown to induce IRF6-mediated differentiation—also triggers CCL5 expression.
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These reports provide evidence to link microbial stimuli to inflammatory signaling and epithelial transformation.
Of the highlighted chemokines previously, CCL5 is of interest since it plays a key role in immune responses by acting as a potent chemoattractant for various immune cells and by modulating inflammatory signaling pathways.58,59 IRF6 was found to influence the regulation of CCL5,
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a notable finding given CCL5’s established function in T cell recruitment and its involvement in sustaining chronic inflammation.
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This regulatory relationship suggests that IRF6 may be involved in suppressing inflammation-induced EMT, particularly under chronic inflammatory conditions or in the early stages of tumorigenesis. However, the role of CCL5 remains complex and context dependent. While CCL5 can act as an immune-protective factor in certain settings, its overexpression has also been associated with poor prognosis in others. Notably, CCL5 expression is often enhanced under hypoxic conditions,
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which are common in inflamed or tumorigenic tissues. Therefore, the function of CCL5 appears to vary depending on the microenvironment and disease stage. A deeper understanding of this dual role will be essential for improving the diagnosis and treatment of oral potentially malignant disorders (OPMDs) and for preventing the malignant transformation of chronic inflammatory conditions.
The ability of cells to adapt their metabolic activity under hypoxic conditions helps explain the activation of distinct signaling pathways in both physiological and pathological contexts. For example, CCL5 has been identified as an immune-protective factor contributing to immune surveillance in solid tumors.
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However, overexpression of the CCR5/CCL5 axis has also been linked to poor clinical outcomes in OSCC, including regional lymph node metastasis and decreased overall survival.
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The CCL5/CCR5 axis also contributes to the stabilization and accumulation of HIF-1α, although this effect is highly dependent on the oxygen levels present in the microenvironment.
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Under conditions, HIF-1α is hydroxylated by prolyl hydroxylases (PHDs) and subsequently ubiquitinated by the von Hippel-Lindau (VHL) protein, leading to its proteasomal degradation. In contrast, under hypoxic conditions, reduced oxygen availability inhibits PHD activity, resulting in HIF-1α stabilization and accumulation.
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Once stabilized, HIF-1α forms a transcriptional complex that binds to hypoxia response elements (HREs) in the promoters of target genes. This complex activates the expression of genes involved in metabolic reprogramming (e.g. GLUT1), angiogenesis (e.g. VEGF), and regulation of the inflammatory profile.59,83
This mechanism is particularly relevant in oral submucous fibrosis (OSF), another OPMD characterized by persistent hypoxia and epithelial atrophy. OSF has been described as an “overhealing wound,” in which vascular collapse and excessive fibrotic remodeling generate a chronically hypoxic microenvironment that drives malignant potential.84,85 The resulting epithelial atrophy and loss of barrier function render the mucosa more vulnerable to physical and chemical insults, further increasing susceptibility to malignant transformation.
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A translational framework for chronic inflammation-driven epithelial disruption in oral mucosa
Building on the findings presented in this review and the current scientific literature, we propose a model wherein the oral mucosa, under physiological and normoxic conditions, maintains a highly regulated keratinocyte differentiation program. This culminates in the terminal differentiation of keratinocytes, marked by nuclear loss in the stratum corneum (Figure 1(a)). In this state, the epithelium forms an effective physical and immunological barrier, reinforced by strong intercellular junctions and elevated E-cadherin expression (Figure 1(b)).
Well-differentiated keratinocytes also exhibit immunocompetence. Upon exposure to microbial or danger-associated signals such as LPS or FSL-1, TLR2 is activated, triggering the MyD88–IRAK1 signaling cascade. This leads to the phosphorylation of IRF6 and parallel activation of NFκB. Both transcription factors translocate into the nucleus, where they induce the expression of inflammatory mediators such as CCL5. IRF6 activation simultaneously represses the proliferative marker p63 and promotes the expression of differentiation-associated genes including TGM1, Involucrin, Keratin 13, TGFβ3, and SNAI2, thereby maintaining epithelial integrity (Figure 1(b)).
Under the persistent inflammatory stimuli present in oral lichen planus (OLP) and other potentially malignant disorders (OPMDs), sustained CCL5 expression and immune cell infiltration can lead to reduced IRF6 expression (Figure 2(a)). This may result from epigenetic modifications or a compensatory tissue repair response. The downregulation of IRF6 contributes to decreased E-cadherin and other differentiation-related proteins, weakening epithelial cohesion and barrier function (Figure 2(b) and (e)). Poorly differentiated keratinocytes at the epithelial surface may exhibit heightened reactivity, further amplifying inflammation (Figure 2(b)).
Chronic inflammation also fosters a hypoxic and acidic microenvironment (Figure 2(b)), exacerbated by external factors such as tobacco smoking, alcohol consumption, trauma, and microbial dysbiosis (Figure 2(b)). These conditions support the growth of lactate-producing bacteria, contributing to tissue acidification and perpetuation of inflammation. Hypoxia also promotes proteasomal degradation of IRF6, further reducing its regulatory influence on p63 and epithelial differentiation. Simultaneously, pro-inflammatory and adhesion molecules such as ICAM, VCAM, COX-2, iNOS, and E-selectin become upregulated, driving further epithelial damage (Figure 2(e)).
In parallel, reduced oxygen availability inhibits the activity of prolyl hydroxylases, resulting in the stabilization of hypoxia-inducible factor 1α (HIF-1α). Stabilized HIF-1α translocates into the nucleus, where it binds hypoxia-responsive elements (HREs) and activates the transcription of genes involved in metabolic reprogramming (e.g. GLUT1), angiogenesis (e.g. VEGF), and immune regulation. These changes contribute to the induction of EMT (Figure 2(c)), characterized by the loss of apicobasal polarity, downregulation of epithelial markers, and increased keratinocyte invasiveness, ultimately promoting malignant transformation and progression to OSCC (Figure 2(d)).
Taken together, this model elucidates the molecular and cellular mechanisms through which chronic inflammation disrupts keratinocyte homeostasis and promotes epithelial remodeling. By focusing on the TLR2-IRF6-CCL5 axis and the impact of hypoxia, this framework highlights potential therapeutic targets to restore epithelial integrity and immune balance in OPMDs.
Future studies should focus on validating this model using patient-derived tissues, assessing dynamic IRF6 and CCL5 expression profiles, and evaluating therapeutic interventions such as IRF6 supplementation or CCL5/CCR5 antagonism (e.g. Maraviroc). These insights may contribute to early diagnosis, better prognostication, and prevention of malignant transformation in chronic inflammatory oral diseases.

Future perspectives
This review has outlined a mechanistic framework in which chronic inflammation, hypoxia, and epithelial plasticity converge to destabilize oral keratinocyte homeostasis. The TLR2–IRF6–CCL5 axis, together with hypoxia-induced stabilization of HIF-1α, emerges as a central pathway linking persistent inflammatory signaling to impaired differentiation, EMT, and malignant progression. While this framework provides a valuable lens for understanding the molecular underpinnings of oral carcinogenesis, it also underscores broader clinical implications where knowledge remains incomplete. One example is OSF, an OPMD characterized by progressive fibrosis, vascular collapse, and epithelial atrophy. OSF has been described as an “overhealing wound,” where recurrent trauma and chronic irritation lock the mucosa in a cycle of perpetual repair.
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Hypoxia is an obligatory feature of this process, driving both fibrotic remodeling and malignant risk. More recently, hypoxia-driven epigenetic modifications, such as DNA methylation, histone alterations, and microRNA dysregulation, were shown to sustain myofibroblast activation and accelerate disease progression.
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Gene–gene crosstalk, including PTEN with TGF-β and NFκB, further reinforce fibrosis and carcinogenic risk. Within the model proposed here, OSF exemplifies how hypoxia reduces IRF6 activity while amplifying CCL5 expression, fostering a pro-inflammatory, EMT-prone epithelial state. Therefore, OSF is not only a fibrotic disorder but also a clinically relevant model for studying inflammation- and hypoxia-driven carcinogenesis.
Another key aspect highlighted in this review is the link between IRF6 and microbial signaling. We focused on the capacity of IRF6 to induce CCL5 expression, a relationship that becomes particularly pronounced following TLR2 stimulation, a pathway engaged by specific microbial ligands. This emphasizes the role of pathogens and their metabolites in promoting oral carcinogenesis. Indeed, recent human studies have identified distinct microbiome profiles associated with oral cancer.86,87 Dysbiotic microbial communities, particularly in an atrophic and hypoxic epithelium, may compromise barrier integrity, heightening susceptibility to malignant transformation.
From a translational standpoint, the concept of field cancerization across the aerodigestive tract is also relevant. Clinical evidence indicates a two-way relationship between head and neck cancers and esophageal carcinoma, with patients affected by one malignancy at higher risk of developing a second primary tumor in contiguous mucosa.
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This suggests that dysregulated epithelial signaling—potentially involving IRF6 instability and sustained CCL5 expression—may not be restricted to the oral cavity but reflect a broader vulnerability across mucosal fields. Such insights highlight the importance of developing integrated surveillance strategies for patients with oral cancer and OPMDs, extending beyond the primary lesion to adjacent mucosal sites.
Despite these advances, important uncertainties and limitations remain. Most investigations of IRF6 in keratinocyte biology and cancer have relied on in vitro models, with limited validation in patient-derived tissues. Interestingly, IRF6 has also been recently associated with ovarian cancer development and progression,
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reinforcing IRF6 broader relevance in oncogenesis. However, its specific role in oral cancer remains unclear. The dynamic regulation of IRF6 phosphorylation, its degradation under hypoxic conditions, and its interaction with CCL5 in human OPMDs and OSCC require systematic study. Moreover, while modulation of IRF6 activity appears promising as a therapeutic strategy, it is unlikely to be sufficient on its own. Effective interventions will likely need combinatorial approaches targeting IRF6 alongside hypoxia signaling, microbial dysbiosis, and chronic inflammation.
Moving forward, advancing this framework will require closer collaboration between researchers and clinicians. Studies using patient-derived tissues are essential to validate the IRF6–CCL5–TLR2 axis and clarify its clinical relevance in oral cancer. Only by integrating molecular insights with real-world clinical data can we determine whether targeting this pathway offers tangible benefits for diagnosis, prognosis, and therapy in chronic inflammatory oral diseases.

Conclusion
Oral keratinocytes are increasingly recognized as active regulators of immune responses and epithelial integrity, particularly under chronic inflammatory conditions. This review proposes a mechanistic model in which IRF6 functions as a central mediator linking epithelial differentiation, immune signaling, and inflammation resolution in the oral mucosa. Through its regulation of p63 and downstream effectors like CCL5, IRF6 maintains a homeostatic balance between epithelial renewal and immune activation.
Chronic inflammation is a key contributor to epithelial dysfunction and malignant transformation in the oral cavity. This review proposes a model in which oral keratinocytes act not only as structural components but also as active regulators of immune signaling, primarily through the TLR2–IRF6–CCL5 axis. Under homeostatic conditions, IRF6 supports terminal differentiation and immune balance. However, in the presence of sustained inflammation, hypoxia, and environmental stressors, IRF6 expression is diminished, leading to impaired epithelial integrity, exaggerated inflammatory responses, and activation of EMT-associated pathways.
By integrating molecular pathways of inflammation, differentiation, and hypoxic adaptation, the proposed model offers a conceptual framework for understanding disease progression in oral potentially malignant disorders (OPMDs). It also points toward novel therapeutic targets, including IRF6 stabilization and CCR5/CCL5 pathway modulation, with potential to prevent malignant transformation.
Further research using patient-derived tissues and in vivo models is warranted to validate this model and explore its translational applications. These efforts may ultimately contribute to improved diagnostic, prognostic, and therapeutic strategies for managing chronic inflammatory oral diseases and reducing oral cancer risk.