SMAD4 Palmitoylation Drives a Metabolic-Transcriptional Circuit to Promote Tumorigenesis and Confers Radiosensitivity in Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by frequent SMAD4 inactivation and profound lipid metabolic rewiring, yet how these processes intersect especially in SMAD4 PDAC remains elusive. Here, we identify palmitoylation as a previously unrecognized post-translational modification of SMAD4. Combining biochemical labeling, mutagenesis, and functional assays, we demonstrate that SMAD4 is palmitoylated at cysteine 363 by the acyltransferase ZDHHC22 and depalmitoylated by APT2. Mechanistically, palmitoylation enhances SMAD4 protein stability, facilitates the interaction of SMAD4 with importins, and amplifies subsequent transcriptional output, leading to direct upregulation of the key fatty acid biosynthetic enzyme FASN. Consequently, elevated palmitic acid levels in turn reinforce SMAD4 palmitoylation, establishing a self-amplifying SMAD4 palmitoylation-FASN-palmitic acid positive feedback loop that drives PDAC tumor growth. Intriguingly, SMAD4 palmitoylation sensitizes PDAC cells to radiotherapy both in vitro and in vivo, revealing a dual role between tumor progression and treatment responses. Notably, clinically relevant SMAD4 mutants (R361C and R361H) exhibit enhanced palmitoylation, underscoring the pathological relevance of this mechanism for tumorigenesis. Collectively, these findings unveil a metabolic-transcriptional circuit wherein palmitoylation bridges lipid metabolism with SMAD4-driven oncogenesis, and posit SMAD4 palmitoylation as a therapeutic vulnerability in pancreatic cancer.