RING-dependent tumor suppression and G2/M arrest induced by the TRC8 hereditary kidney cancer gene

TRC8/RNF139 and von Hippel-Lindau (VHL) both encode E3 ubiquitin (Ub) ligases mutated in clear-cell renal carcinomas (ccRCC). VHL, inactivated in nearly 70% of ccRCCs, is a tumor suppressor encoding the targeting subunit for a Ub ligase complex that downregulates hypoxia-inducible factor-alpha. TRC8/RNF139 is a putative tumor suppressor containing a sterol-sensing domain and a RING-H2 motif essential for Ub ligase activity. Here we report that human kidney cells are growth inhibited by TRC8. Inhibition is manifested by G2/M arrest, decreased DNA synthesis and increased Apoptosis and is dependent upon the Ub ligase activity of the RING domain. Tumor formation in a nude mouse model is inhibited by TRC8 in a RING-dependent manner. Expression of TRC8 represses genes involved in Cholesterol and fatty acid biosynthesis that are transcriptionally regulated by the sterol response element binding proteins (SREBPs). Expression of activated SREBP-1a partially restores the growth of TRC8-inhibited cells. These data suggest that TRC8 modulation of SREBP activity comprises a novel regulatory link between growth control and the Cholesterol/lipid homeostasis pathway.