CD109 Drives Stemness and Chemoresistance in Colorectal Cancer via LRRC8A/AKAP12/PKCα-Mediated STAT3 Activation and WNT Signaling.

Colorectal cancer (CRC) is the third most prevalent type of cancer worldwide, with a poor survival rate at the metastatic stage. Here, we identify CD109-a negative regulator of TGFβ signaling-as a key driver of stemness and drug resistance through modulation of Wnt signaling in advanced CRC. CD109 expression strongly correlates with TGFβ levels in patient tumors and is enriched in the aggressive CRIS-B subtype, where it associates with poor clinical outcome. CD109 silencing reduced STAT3 phosphorylation and cell proliferation, without affecting migration or invasion. Moreover, global expression analysis revealed downregulation of various hallmarks of cancer stemness (i.e. LGR5 expression), together with increased TGFβ signaling and cellular senescence. Mechanistically, CD109 interacts with LRRC8A, a subunit of the volume-regulated anion channel (VRAC), which associates with AKAP12 to activate PKCα and promote STAT3 phosphorylation. This CD109/LRRC8A/AKAP12/PKCα axis sustains Wnt signaling, stemness, and drug resistance. Consistently, co-expression of CD109/LRRC8A/AKAP12 correlates with poor prognosis in CRC patients. Genetic or pharmacological disruption of this CD109/LRRC8A/AKAP12/PKCα axis impaired STAT3 signaling, reduced LGR5 expression and Wnt signaling, and sensitized cells to chemotherapy. In vivo, CD109 or LRRC8A knockdown significantly impaired liver homing and metastatic colonization in mouse models, showing stronger effects in Swiss nude mice than in highly immunodeficient NSG mice. Collectively, these findings support CD109 as a central regulator for STAT3-driven stemness and chemoresistance in advanced CRC, via the LRRC8A/AKAP12/PKCα axis, and highlight its potential value as a therapeutic target in metastatic disease.