A novel genome‐wide in vivo screen for metastatic suppressors in human colon cancer identifies the positive WNT ‐ TCF pathway modulators TMED 3 and SOX 12

The progression of tumors to the metastatic state involves the loss of metastatic suppressor functions. Finding these, however, is difficult as in vitro assays do not fully predict metastatic behavior, and the majority of studies have used cloned cell lines, which do not reflect primary tumor heterogeneity. Here, we have designed a novel genome‐wide screen to identify metastatic suppressors using primary human tumor cells in mice, which allows saturation screens. Using this unbiased approach, we have tested the hypothesis that endogenous colon cancer metastatic suppressors affect WNT ‐ TCF signaling. Our screen has identified two novel metastatic suppressors: TMED 3 and SOX 12, the knockdown of which increases metastatic growth after direct seeding. Moreover, both modify the type of self‐renewing spheroids, but only knockdown of TMED 3 also induces spheroid cell spreading and lung metastases from a subcutaneous xenograft. Importantly, whereas TMED 3 and SOX 12 belong to different families involved in protein secretion and transcriptional regulation, both promote endogenous WNT ‐ TCF activity. Treatments for advanced or metastatic colon cancer may thus not benefit from WNT blockers, and these may promote a worse outcome. image Two novel metastatic suppressors TMED 3 and SOX 12, derived from an innovative, unbiased, in vivo , sh RNA genome‐wide screen, are shown to be positive modulators of WNT signaling. Their suppression causes an increase in metastasis from a primary tumor. A novel, unbiased, in vivo , sh RNA genome‐wide screen for metastatic suppressors has been developed with primary human cancer cells. The screen can reach saturation and can be modified, for instance, to include cell competition as well as positive metastatic modulators. Using primary human colon cancer cells, two novel in vivo metastatic suppressors are described derived from the screen, TMED 3 and SOX 12, belonging to multigene families involved in Golgi‐to‐ ER trafficking and transcriptional regulation, respectively. In addition to independent functions, both are positive modulators of WNT signaling as their knockdown results in repressed WNT ‐ TCF targets. Repression of WNT signaling in human colon cancer xenografts promotes metastases in vivo .