SREBP

The mammalian target of rapamycin complex 1 (mTORC1), a master regulator of cell growth and proliferation, is aberrantly activated in cancer, genetic tumor syndromes and obesity. Much progress has been made to understand the upstream pathways that regulate mTORC1, most of which converge upon its negative regulator, the Tuberous Sclerosis Complex (TSC) 1-TSC2 complex. However, the cell intrinsic consequences of aberrant mTORC1 activation remain poorly characterized. Using systems in which mTORC1 is constitutively activated by genetic loss of TSC1 or TSC2 and pharmacologically inhibited by treatment with an mTORC1-specific inhibitor rapamycin, we have identified that mTORC1 controls specific aspects of cellular metabolism, including glycolysis, the pentose phosphate pathway, and de novo lipogenesis. Induction of the pentose phosphate pathway and de novo lipogenesis is achieved by activation of a transcriptional program affecting metabolic gene targets of sterol regulatory element-binding protein (SREBP). We have demonstrated that mTORC1 stimulates the accumulation of processed, active SREBP, although details of the molecular mechanism remain to be elucidated.