Linker Phosphorylation of Smad3 as a Driver of Cholangiocarcinoma Progression and Chemotherapy Resistance

Cholangiocarcinoma (CCA) is the second most prevalent primary liver cancer, with an increasing incidence in the western world. Despite significant differences in their molecular pathogenesis, CCA patients are traditionally classified based on the anatomic location of the tumor and receive similar chemotherapies. Aberrant phospho-Smad (pSmad) signaling has been suggested as one mechanism underpinning the malignant switch of TGFβ in multiple tumor entities. However, how alternative Smad phosphorylation and variant downstream signaling contributes to CCA progression and therapy response remains elusive. To address this, we assessed Smad3 phosphorylation patterns in liver tissue of CCA patients and patient-derived CCA cell lines and functionally correlated the findings with tumorigenesis and disease prognosis. We observed increased cell numbers with linker phosphorylated Smad3 (pSmad3L) in CCA areas and an inverse correlation with Smad3 C-terminal phosphorylation (pSmad3C), as compared to adjacent tissue. Given the involvement of several kinases in pSmad signaling, we performed a kinase screen using known inhibitors as well as a newly-synthesized small molecule. The results show that Erk/p38 MAPKs as well as GSK3b are involved in Smad3L phosphorylation in CCA. Consistent with this, modulation of signaling and rebranching the pathway from pSmad3L to pSmad3C reduces CCA cell proliferation and migration, and re-sensitizes CCA cells to more efficient chemotherapy. Our findings suggest pSmad3L signaling as a new targetable molecular mechanism underlying CCA progression and chemotherapy resistance

Publication History

Article published online:
20 January 2025