Wnt-TCF7-SOX9 axis promotes cholangiocarcinoma proliferation and pemigatinib resistance in a FGF7-FGFR2 autocrine pathway

Cholangiocarcinoma (CCA) is a type of highly malignant tumor originating from bile ducts. The prognosis of CCA is poor and the treatment options are limited. The biomarker study of CCA has made little progresses in recent years because of the difficulty to obtain CCA specimens. SOX9 is an important regulator of cholangiocyte proliferation and differentiation. We performed mRNA sequencing of CCA, retrieved TCGA data, and detected SOX9 expression in a large CCA cohort. With WNT3A stimulation, SOX9 expression and transcription was elevated by TCF7. Moreover, SOX9 was substantially up-regulated in CCA tissues and was identified as a prognostic biomarker of CCA. With mRNA sequencing and in vitro/vivo validation, we demonstrated that SOX9 enhanced the transcription and expression of FGF7 and FGFR2. FGF7 was significantly up-regulated in the bile and serum of CCA patients, and may promote CCA proliferation by activating FGFR2 in an autocrine pathway. co-expression of FGF7 and FGFR2 was a more sensitive marker for poor prognosis. SOX9-induced overexpression of FGF7 and FGFR2 was the key reason of SOX9-involved pemigatinib resistance. In conclusion, SOX9 and FGF7 were prognostic biomarkers of CCA. WNT3A-TCF7-SOX9 axis could induce pemigatinib resistance in two independent pathways: (1)SOX9 directly promotes FGFR2 transcription and expression; (2)SOX9 elevates FGF7 expression, which could be secreted from CCA cells and activates FGFR2 phosphorylation in an autocrine pathway.