Hyperactivated mTORC1 downregulation of FOXO3a/PDGFRα/AKT cascade restrains tuberous sclerosis complex-associated tumor development

Abstract

Hyperactivation of mammalian target of rapamycin complex 1 (mTORC1), caused by loss-of-function mutations in either the TSC1 or TSC2 gene, leads to the development of tuberous sclerosis complex (TSC), a benign tumor syndrome with multiple affected organs. mTORC1-mediated inhibition of AKT constrains the tumor progression of TSC, but the exact mechanisms remain unclear. Herein we showed that loss of TSC1 or TSC2 downregulation of platelet-derived growth factor receptor α (PDGFRα) expression was mediated by mTORC1. Moreover, mTORC1 inhibited PDGFRα expression via suppression of forkhead box O3a (FOXO3a)-mediated PDGFRα gene transcription. In addition, ectopic expression of PDGFRα promoted AKT activation and enhanced proliferation and tumorigenic capacity of Tsc1- or Tsc2-null mouse embryonic fibroblasts (MEFs), and vice versa. Most importantly, rapamycin in combination with AG1295, a PDGFR inhibitor, significantly inhibited growth of TSC1/TSC2 complex-deficient cells in vitro and in vivo. Therefore, downregulated FOXO3a/PDGFRα/AKT pathway exerts a protective effect against hyperactivated mTORC1-induced tumorigenesis caused by loss of TSC1/TSC2 complex, and the combination of rapamycin and AG1295 may be a new effective strategy for TSC-associated tumors treatment.