The epithelial-mesenchymal transcription factor SNAI1 represses transcription of the tumor suppressor miRNA let-7 in cancer

Wang, H.; Chirshev, E.; Hojo, N.; Suzuki, T.; Bertucci, A.; Pierce, M.; Perry, C.; Wang, R.; Zink, J. I.; Glackin, C.; Ioffe, Y.; Unternaehrer, J.

doi:10.1101/2020.11.04.368688

bioRxiv · 10.1101/2020.11.04.368688

The epithelial-mesenchymal transcription factor SNAI1 represses transcription of the tumor suppressor miRNA let-7 in cancer

Wang, H.·Chirshev, E.·Hojo, N.·Suzuki, T.·Bertucci, A.·Pierce, M.·Perry, C.·Wang, R.·Zink, J. I.·Glackin, C.·Ioffe, Y.·Unternaehrer, J.

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Abstract

We aimed to determine the mechanism of epithelial-mesenchymal transition (EMT)-induced stemness in cancer cells. Cancer relapse and metastasis are caused by rare stem-like cells within tumors. Studies of stem cell reprogramming have linked let-7 repression and acquisition of stemness with the EMT factor, SNAI1. The mechanisms for the loss of let-7 in cancer cells are incompletely understood. In four carcinoma cell lines from breast cancer, pancreatic cancer and ovarian cancer and in ovarian cancer patient-derived cells, we analyzed stem cell phenotype and tumor growth via mRNA, miRNA, and protein expression, spheroid formation, and growth in patient-derived xenografts. We show that treatment with EMT-promoting growth factors or SNAI1 overexpression increased stemness and reduced let-7 expression, while SNAI1 knockdown reduced stemness and restored let-7 expression. Rescue experiments demonstrate that the pro-stemness effects of SNAI1 are mediated via let-7. In vivo, nanoparticle-delivered siRNA successfully knocked down SNAI1 in orthotopic patient-derived xenografts, accompanied by reduced stemness and increased let-7 expression, and reduced tumor burden. Chromatin immunoprecipitation demonstrated that SNAI1 binds the promoters of various let-7 family members, and luciferase assays revealed that SNAI1 represses let-7 transcription. In conclusion, the SNAI1/let-7 axis is an important component of stemness pathways in cancer cells, and this study provides a rationale for future work examining this axis as a potential target for cancer stem cell-specific therapies. Novelty and ImpactThis study provides new insight into molecular mechanisms by which EMT transcription factor SNAI1 exerts its pro-stemness effects in cancer cells, demonstrating its potential as a stem cell-directed target for therapy. In vitro and in vivo, mesoporous silica nanoparticle-mediated SNAI1 knockdown resulted in restoration of let-7 miRNA, inhibiting stemness and reducing tumor burden. Our studies validate in vivo nanoparticle-delivered RNAi targeting the SNAI1/let-7 axis as a clinically relevant approach.

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Wang, H., Chirshev, E., Hojo, N., Suzuki, T., Bertucci, A., Pierce, M., Perry, C., Wang, R., Zink, J. I., Glackin, C., Ioffe, Y., Unternaehrer, J.. 2020-11-05. The epithelial-mesenchymal transcription factor SNAI1 represses transcription of the tumor suppressor miRNA let-7 in cancer. https://doi.org/10.1101/2020.11.04.368688

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