RNF43 induces the turnover of protease‐activated receptor 2 in colon cancer

Post‐translational modification of G‐protein coupled receptors (GPCRs) plays a central role in tissue hemostasis and cancer. The molecular mechanism of post‐translational regulation of protease‐activated receptors (PARs), a subgroup of GPCRs is yet understudied. Here we show that the cell‐surface transmembrane E3 ubiquitin ligase ring finger 43 (RNF43) is a negative feedback regulator of PAR2, impacting PAR2‐induced signaling and colon cancer growth. RNF43 co‐associates with PAR2, promoting its membrane elimination and degradation as shown by reduced cell surface biotinylated PAR2 levels and polyubiquitination. PAR2 degradation is rescued by R‐spondin2 in the presence of leucine‐rich repeat‐containing G‐protein‐coupled receptor5 (LGR5). In fact, PAR2 acts jointly with LGR5, as recapitulated by increased β‐catenin levels, transcriptional activity, phospho‐LRP6, and anchorage‐independent colony growth in agar. Animal models of the chemically induced AOM/DSS colon cancer of wt versus Par2/f2rl1 KO mice as also the ‘spleen‐liver’ colon cancer metastasis, allocated a central role for PAR2 in colon cancer growth and development. RNF43 is abundantly expressed in the Par2/f2rl1 KO‐treated AOM/DSS colon tissues while its level is very low to nearly null in colon cancer adenocarcinomas of the wt mice. The same result is obtained in the ‘spleen‐liver’ model of spleen‐inoculated cells, metastasized to the liver. High RNF43 expression is observed in the liver upon shRNA ‐Par2 silencing. “Limited‐dilution‐assay” performed in mice in‐vivo, assigned PAR2 as a member of the cancer stem cell niche compartment. Collectively, we elucidate an original regulation of PAR2 oncogene, a member of cancer stem cells, by RNF43 ubiquitin ligase. It impacts β‐catenin signaling and colon cancer growth.