Tuberous Sclerosis Complex Proteins 1 and 2 Control Serum-Dependent Translation in a TOP-Dependent and -Independent Manner

Abstract

The tuberous sclerosis complex (TSC) proteins TSC1 and TSC2 regulate protein translation by inhibiting the serine/threonine kinase mTORC1 (for mammalian target of rapamycin complex 1). However, how TSC1 and TSC2 control overall protein synthesis and the translation of specific mRNAs in response to different mitogenic and nutritional stimuli is largely unknown. We show here that serum withdrawal inhibits mTORC1 signaling, causes disassembly of translation initiation complexes, and causes mRNA redistribution from polysomes to subpolysomes in wild-type mouse embryo fibroblasts (MEFs). In contrast, these responses are defective in Tsc1^−/− or Tsc2^−/− MEFs. Microarray analysis of polysome- and subpolysome-associated mRNAs uncovered specific mRNAs that are translationally regulated by serum, 90% of which are TSC1 and TSC2 dependent. Surprisingly, the mTORC1 inhibitor, rapamycin, abolished mTORC1 activity but only affected ∼40% of the serum-regulated mRNAs. Serum-dependent signaling through mTORC1 and polysome redistribution of global and individual mRNAs were restored upon re-expression of TSC1 and TSC2. Serum-responsive mRNAs that are sensitive to inhibition by rapamycin are highly enriched for terminal oligopyrimidine and for very short 5′ and 3′ untranslated regions. These data demonstrate that the TSC1/TSC2 complex regulates protein translation through mainly mTORC1-dependent mechanisms and implicates a discrete profile of deregulated mRNA translation in tuberous sclerosis pathology.

SUPPLEMENTAL MATERIAL

We thank David Kwiatkowski for kindly providing WT, Tsc1-null, and Tsc2-null MEFs and TSC2 reconstituted Tsc2-null MEFs. We are grateful to the Genome Analysis Core for TaqMan analysis. We thank Mike Fried, Pablo Rodriguez-Viciana, Tanja Tamgüney, Christina Spevak, and Clodagh O'Shea for critical and helpful comments on the manuscript.

This study was supported by Grants from the U.S. Department of Defense Tuberous Sclerosis Research Program (TS030017 and TS050054).