Insulin and IGF-1 are regulators of cell growth and metabolism. Despite considerable progress in understanding the molecular mechanisms underlying these effects, except for members of the FoxO family, many regulators of the transcriptional effects of these hormones remain poorly understood. To identify new components of IR/IGF1R signaling, we created brown preadipocyte lines in which both endogenous IR and IGF1R genes had been deleted and then reconstituted these cells with normal IR, IGF1R or chimeric receptors containing the extracellular domain of IR fused to intracellular domain of IGF1R and vice versa. Mass spectroscopic proteomic analysis revealed a number of proteins co-precipitated with each receptor construct, in both ligand stimulation-dependent and -independent manners. Among the proteins that associated with both receptors and chimeric receptors in a ligand-dependent manner was FoxK1. In contrast to FoxO1, the transcription factor FoxK1 was translocated from the cytoplasm to the nucleus after insulin stimulation, a pattern that is reciprocal to that of FoxO1 after insulin stimulation. We show that FoxK1 and FoxK2 are phosphorylated in two major domains and that translocation to the nucleus is dependent on the Akt-mTOR mediated phosphorylation, while their localization to the cytoplasm in the basal state is dependent on GSK3 phosphorylation. Knockdown of FoxK1 and FoxK2 in a mouse hepatocyte cell line causes marked alteration of the transcription of genes associated with apoptotic pathway and down-regulation of genes involved in control of cell cycle and metabolism. This resulted in decreased cell proliferation and altered mitochondrial fatty acid metabolism in these cells. Thus, insulin stimulates the reciprocal translocation of FoxKs and FoxO1 between the cytoplasm and nucleus turning off FoxO1-regulated genes and turning on FoxK-regulated genes resulting in an elaborate balance in insulin regulation of metabolism, growth and cell survival.
M. Sakaguchi: None. W. Cai: None. C. Wang: None. T.M. Batista: None. E. Araki: Speaker's Bureau; Self; Astellas Pharma US, Inc., MSD K.K., Kowa Pharmaceuticals America, Inc., Sanofi, Novo Nordisk Inc.. Research Support; Self; Astellas Pharma US, Inc., MSD K.K., Ono Pharmaceutical Co., Ltd., Shionogi & Co., Ltd., Takeda Pharmaceuticals U.S.A., Inc., Daiichi Sankyo Company, Limited, Nippon Boehringer Ingelheim Co. Ltd., Novartis Pharma K.K., Novo Nordisk Inc., Sanofi, Mitsubishi Tanabe Pharma Corporation, Sumitomo Dainippon Pharma Co., Ltd., Taisho Toyama Pharmaceutical Co. C. Kahn: Advisory Panel; Self; CohBar, ERX Therapeutics, AntriaBio, Inc.. Board Member; Self; Kaleio Biosciences.