TMED9-gated CNIH4 and TGFa signaling promotes pro-metastatic states in human primary colon cancer cells

How cells in primary tumors initially become pro-metastatic is not understood. A previous genome-wide RNAi screen uncovered colon cancer metastatic suppressor and WNT promoting functions of TMED3, a member of the p24 ER-to-Golgi protein secretion family. Repression of WNT signaling upon knock-down (kd) of TMED3 might thus be sufficient to drive metastases. However, searching for transcriptional influences on other family members here we find that TMED3 kd leads to enhanced TMED9, that TMED9 acts downstream of TMED3 and that TMED9 kd compromises metastasis. Importantly, TMED9 pro-metastatic function is linked to but distinct from the repression of TMED3-WNT-TCF signaling. Functional rescue of the migratory deficiency of TMED9 kd cells identifies TGFa as a mediator of TMED9 pro-metastatic activity. Moreover, TMED9 kd compromises the membrane localization, and thus function, of TGFa. Analyses in three colon cancer cell types highlight a TMED9-dependent gene set that includes CNIH4, a member of the CORNICHON family of TGFa exporters. Our data indicate that TGFA and CNIH4, which display predictive value for disease-free survival, promote colon cancer cell metastatic behavior and suggest that TMED9 pro-metastatic function involves the modulation of the secretion of TGFa ligand. Finally, TMED9/TMED3 antagonism impacts WNT-TCF and GLI signaling, where TMED9 primacy over TMED3 leads to the establishment of a positive feedback loop together with CNIH4, TGFa and GLI1 that enhances metastases. We suggest that primary colon cancer cells can transition between two states characterized by secretion-transcription regulatory loops gated by TMED3 and TMED9 that modulate their metastatic proclivities. Overall design: CC14 and CC36, two primary colon cancer cells, were treated with control or shTMED9 expressing lentivirus. In addition, CC14 cells were also treated with shTMED3 expressing lentivirus. All the experiments were run in triplicates totaling 15 Samples.

15

Mishra S, Bernal C, Silvano M, Anand S, Ruiz I Altaba A