Inhibition of protein tyrosine phosphatase receptor type F suppresses Wnt signaling in colorectal cancer.

Wnt signaling dysregulation promotes tumorigenesis in colorectal cancer (CRC). We investigated the role of PTPRF, a receptor-type tyrosine phosphatase, in regulating Wnt signaling in CRC. Knockdown of PTPRF decreased cell proliferation in patient-derived primary colon cancer cells and established CRC cell lines. In addition, the rate of proliferation as well as colony formation ability were significantly decreased in tumor organoids grown in 3D, whereas the number of differentiated tumor organoids were markedly increased. Consistently, knockdown of PTPRF resulted in a decrease in the expression of genes associated with cancer stem cells downstream of Wnt/β-catenin signaling. Treating PTPRF knockdown cells with GSK3 inhibitor rescued the expression of Wnt target genes suggesting that PTPRF functions upstream of the β-catenin destruction complex. PTPRF was found to interact with LRP6 and silencing PTPRF largely decreased the activation of LRP6. Interestingly, this PTPRF-mediated activation of Wnt signaling was blocked in cells treated with clathrin endocytosis inhibitor. Furthermore, knockdown of PTPRF inhibited xenograft tumor growth in vivo and decreased the expression of Wnt target genes. Taken together, our studies identify a novel role of PTPRF as an oncogenic protein phosphatase in supporting the activation of Wnt signaling in CRC.