Chondroitin sulfate E activates IL-6/STAT3 signaling to drive androgen-independent growth in castration-resistant prostate cancer.

[BACKGROUND] Castration-resistant prostate cancer (CRPC) remains a major clinical challenge, as tumor growth persists despite androgen receptor (AR) pathway inhibition. Glycosaminoglycans, particularly chondroitin sulfate (CS), are increasingly recognized as modulators of oncogenic signaling. However, the contribution of distinct sulfation motifs to therapeutic resistance is poorly understood. Here, we identify the CS-E motif as a critical regulator of IL-6/STAT3 signaling and a driver of hormone-independent growth in CRPC.

[METHODS] Transcriptomic profiling (RNA-seq), real-time PCR, and flow cytometry were employed to assess CS sulfation changes in C4-2 prostate cancer cells under androgen-deprived conditions. Because reliable tools to detect CS-E have been lacking, we engineered a novel mutant lectin (Cochlin B8) with selective affinity for CS-E. This innovation enabled precise monitoring and functional characterization of CS-E on the surface of cancer cells. Functional studies combined GALNAC4S-6ST knockdown, pharmacological inhibition with Chst15-IN-1, and signaling assays to examine effects on IL-6/STAT3 activation and cell proliferation.

[RESULTS] Androgen deprivation induced upregulation of GALNAC4S-6ST and enhanced CS-E biosynthesis on the cell surface. Elevated CS-E facilitated IL-6 binding to the cell surface, potentiated STAT3 phosphorylation, and sustained androgen-independent proliferation. Genetic or pharmacological inhibition of GALNAC4S-6ST significantly reduced CS-E levels, impaired IL-6 binding, attenuated STAT3 activation, and selectively suppressed proliferation under hormone-depleted conditions (IC₅₀ = 1.39 µM under androgen-deprived conditions vs. 4.46 µM under androgen-replete conditions). These effects were specific to IL-6/STAT3, with no detectable impact on AR-independent EGFR or WNT signaling pathways.

[CONCLUSIONS] This study reveals a previously unrecognized mechanism whereby CS-E sustains CRPC progression by selectively enhancing IL-6/STAT3 signaling when AR signaling is suppressed. Importantly, the development of Cochlin B8 overcomes a major technical barrier in CS-E research, providing a novel tool for its specific detection and functional analysis. Targeting CS-E biosynthesis represents a promising therapeutic strategy to counter resistance and improve prostate cancer treatment.