Characterization of a conserved C-terminal motif (RSPRR) in ribosomal protein S6 kinase 1 required for its mammalian target of rapamycin-dependent regulation.
The mammalian target of rapamycin, mTOR, is a Ser/Thr kinase that promotes cell growth and proliferation by activating ribosomal protein S6 kinase 1 (S6K1). We previously identified a conserved TOR signaling (TOS) motif in the N terminus of S6K1 that is required for its mTOR-dependent activation. Furthermore, our data suggested that the TOS motif suppresses an inhibitory function associated with the C terminus of S6K1. Here, we have characterized the mTOR-regulated inhibitory region within the C terminus. We have identified a conserved C-terminal "RSPRR" sequence that is responsible for an mTOR-dependent suppression of S6K1 activation. Deletion or mutations within this RSPRR motif partially rescue the kinase activity of the S6K1 TOS motif mutant (S6K1-F5A), and this rescued activity is rapamycin resistant. Furthermore, we have shown that the RSPRR motif significantly suppresses S6K1 phosphorylation at two phosphorylation sites (Thr-389 and Thr-229) that are crucial for S6K1 activation. Importantly, introducing both the Thr-389 phosphomimetic and RSPRR motif mutations into the catalytically inactive S6K1 mutant S6K1-F5A completely rescues its activity and renders it fully rapamycin resistant. These data show that the N-terminal TOS motif suppresses an inhibitory function mediated by the C-terminal RSPRR motif. We propose that the RSPRR motif interacts with a negative regulator of S6K1 that is normally suppressed by mTOR.
Schalm
Stefanie S
SS
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Tee
Andrew R
AR
Blenis
John
J
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017124:Conserved Sequence; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011494:Protein Kinases / Q000502:physiology*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000737:chemistry* / Q000378:metabolism; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D058570:TOR Serine-Threonine Kinases
D011494:Protein Kinases; C546842:MTOR protein, human; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1; D020123:Sirolimus