mTORC2 mediate FLCN-induced HIF2α nuclear import and proliferation of clear cell renal cell carcinoma

Abstract

Clear cell renal cell carcinoma (ccRCC), as the most important type of renal carcinoma, has a high incidence and easy metastasis. Folliculin (FLCN) was identified as a tumor suppressor gene. Its deletions and mutations are associated with a potential risk of kidney cancer. At present, the specific molecular mechanism of FLCN-induced proliferation, invasion and migration in clear cell renal cell carcinoma remains elusive.In this study, we demonstrated that FLCN controled cell proliferation, invasion and migration through PI3K/mTORC2 pathway. FLCN combined with HIF2α in various normal and cancerous renal cells, and mTORC2 mediate FLCN effectively alleviated the deterioration of renal cancer cells by degrading HIF2α. Silencing of FLCN showed promotion of HIF2α protein expression, which in turn led to an increase in downstream target genes Cyclin D1 and MMP9. Moreover, when interfering with siFLCN, HIF2α degradation rate was delayed, and the time of entry into the nucleus was advanced. Taken together, our study illustrated that mTORC2 promoted the specific molecular mechanism of HIF2α by down-regulated FLCN, and might be a new therapeutic target against renal cancer progression. Abbreviations:FLCN: folliculin VHL: Von Hippel -Lindau MMP9: matrix metalloproteinase 9 CHX: cycloheximide ccRCC: clear cell renal cell carcinoma IntroductionRenal cell carcinoma is a malignant tumor originating in the renal tubular epithelial system, and most of which are clear cell renal cell carcinoma (~75%) 1 . Cell viability is important for various physiological processes such as embryonic development, angiogenesis, and tumor proliferation, invasion and metastasis. Birt-Hogg-Dubé syndrome is caused by inactivating mutations of FLCN, a tumor suppressor gene which encodes folliculin 2 . Common causes of Birt-Hogg-Dubé syndrome are lung cyst, spontaneous pneumothorax, skin fibrofolliculomas and renal cancer 3 . It is also reported that inactivation of FLCN is an initial step in the development of renal tumors in BHD 4 . Work by Sok Kean Khoo and Laura S. Schmidt have confirmed a tumor suppressor role for FLCN [5][6][7] . Similarly the FLCN-deficient animal models 8 showed activated mTOR and its downstream pathway effectors 9 . These paper suggested that FLCN-deficient kidney tumors showed activation of mTOR and AKT 10 . And this regulation mechanism is also established in humans 2,11,12 .Hypoxia-inducible factor (HIF) is a crucial mediator of hypoxic adaptation. Previous studies have shown that renal tumor-associated gene VHL plays a decisive role in regulating HIF expression 13,14 . Similarly, research data also shows that there are many links between FLCN and HIF1α 8,15 . Our pretest result indicated that the FLCN gene acts as a regulator of renal tumors and its knockdown resulted in a significant increase in HIF2α protein levels. Cyclin D1 and MMP9 have been identified as HIF2α-regulated genes which can mediate cancer cell proliferation and invasion [16][17][18] .In this study, we hypothesized that FLCN may regulate HIF2α through bindi...

FLCN Regulates HIF2α Nuclear Import and Proliferation of Clear Cell Renal Cell Carcinoma

“…81773107) and a project funded by the Jiangsu Collaborative Innovation Center for Cancer Personalized Medicine to LG. This manuscript has been released as a pre-print at bioRxiv (Zhao et al, 2020 ).…”