Cyclin F-dependent degradation of RBPJ inhibits IDH1R132H-mediated tumorigenesis

Cyclin F is a substrate recognition subunit of Skp1-Cul1-F-box protein (SCF) E3 ubiquitin ligase complex. Although there have been reports describing the role of cyclin F in the genotoxic stress response, its function under conditions of altered metabolic homeostasis remain unexplored. Here we report that cyclin F is induced upon metabolic stress in a FOXO1-dependent manner. Under metabolic stress conditions, cyclin F mediated polyubiquitylation of RBPJ at Lys315, leading to its proteasomal degradation. RBPJ regulated the expression of IDH1, which is often mutated to an oncogenic form IDH1R132H in cancers. Thus metabolic stress-induced cyclin F attenuated the oncogenic functions of IDH1R132H in an RBPJ-dependent manner. Studies in mouse tumor models indicated that abrogation of cyclin F expression facilitates IDH1R132H-mediated tumorigenesis and metastasis. Additionally, increased IDH1R132H levels correlated with reduced cyclin F levels in increasing grades of glioma. These findings highlight a novel aspect of cyclin F functions in inhibiting tumorigenesis and provide mechanistic insights into regulation of IDH1R132H.

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