title: Microtubule-associated protein/microtubule affinity-regulating kinase 4 (MARK4) is a negative regulator of the mammalian target of rapamycin complex 1 (mTORC1).
abstract: The mammalian target of rapamycin (mTOR) is a central cell growth regulator. It resides in two protein complexes, which in mammals are referred to as mTORC1 and mTORC2. mTORC1, which is directly inhibited by rapamycin, promotes cell growth by stimulating protein synthesis and inhibiting autophagy. A wide range of extra and intracellular signals, including growth factors, nutrients, energy levels, and various stress conditions, regulates mTORC1. Dysregulation of mTORC1 contributes to many human diseases, including cancer, cardiovascular disease, autoimmunity, and metabolic disorder. In this study, we identified MARK4, an AMP-activated kinase-related kinase, as a negative regulator of mTORC1. In Drosophila S2 cells and mammalian cells, knockdown of MARK family member increased mTORC1 activity, whereas overexpression of MARK4 in mammalian cells significantly inhibited mTORC1 activity. Interestingly, MARK4 selectively inhibits mTORC1 activation by Rag GTPases, which are involved in amino acid signaling, but does not inhibit the effect of Rheb, which directly binds to and activates mTORC1. In addition, we found that MARK4 phosphorylates Raptor, a key component of mTORC1, and this phosphorylation may interfere with Raptor-Rag interaction. Our data demonstrate MARK4 as a new negative regulator of mTORC1.
authors.affiliation: Department of Pharmacology and Moores Cancer Center, University of California San Diego, La Jolla, California 92093, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.forename: Kun-Liang
authors.initials: KL
authors.lastname: Guan
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000818:Animals; D004331:Drosophila melanogaster; D005347:Fibroblasts / Q000166:cytology; D020558:GTP Phosphohydrolases / Q000378:metabolism; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D034622:RNA Interference; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D046912:Multiprotein Complexes; C483047:MARK4 protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D020558:GTP Phosphohydrolases