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Differential requirement of CAAX-mediated posttranslational processing for Rheb localization and signaling

Oncogene volume 29, pages 380–391 (2010)Cite this article

Abstract

The Rheb1 and Rheb2 small GTPases and their effector mTOR are aberrantly activated in human cancer and are attractive targets for anti-cancer drug discovery. Rheb is targeted to endomembranes via its C-terminal CAAX (C=cysteine, A=aliphatic, X=terminal amino acid) motif, a substrate for posttranslational modification by a farnesyl isoprenoid. After farnesylation, Rheb undergoes two additional CAAX-signaled processing steps, Ras converting enzyme 1 (Rce1)-catalyzed cleavage of the AAX residues and isoprenylcysteine carboxyl methyltransferase (Icmt)-mediated carboxylmethylation of the farnesylated cysteine. However, whether these postprenylation processing steps are required for Rheb signaling through mTOR is not known. We found that Rheb1 and Rheb2 localize primarily to the endoplasmic reticulum and Golgi apparatus. We determined that Icmt and Rce1 processing is required for Rheb localization, but is dispensable for Rheb-induced activation of the mTOR substrate p70 S6 kinase (S6K). Finally, we evaluated whether farnesylthiosalicylic acid (FTS) blocks Rheb localization and function. Surprisingly, FTS prevented S6K activation induced by a constitutively active mTOR mutant, indicating that FTS inhibits mTOR at a level downstream of Rheb. We conclude that inhibitors of Icmt and Rce1 will not block Rheb function, but FTS could be a promising treatment for Rheb- and mTOR-dependent cancers.

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Acknowledgements

We thank Yoel Kloog, Saïd Sebti, and Andrew Hamilton for inhibitors, Lawrence Quilliam and Mark Philips for providing plasmid constructs, Stephen Young for MEF cell lines deficient in Rce1 and Icmt, and the UNC Michael Hooker Microscopy Facility for imaging assistance. This research was supported by grants from the National Institutes of Health to CJD (CA042978), ADC (CA109550), CJD and ADC (CA67771), and FT (CA41996). ABH was supported by a Department of Defense Breast Cancer Research Program predoctoral fellowship (BC061107).

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Authors and Affiliations

  1. Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA

    A B Hanker, A D Cox & C J Der

  2. Department of Pharmacology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA

    N Mitin, R S Wilder, A D Cox & C J Der

  3. Department of Radiation Oncology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA

    R S Wilder & A D Cox

  4. Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA

    E P Henske

  5. Department of Microbiology, Immunology, and Molecular Genetics, Jonsson Comprehensive Cancer Center, University of California at Los Angeles, Los Angeles, CA, USA

    F Tamanoi

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Correspondence to C J Der.

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Hanker, A., Mitin, N., Wilder, R. et al. Differential requirement of CAAX-mediated posttranslational processing for Rheb localization and signaling. Oncogene 29, 380–391 (2010). https://doi.org/10.1038/onc.2009.336

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