The principal target of rapamycin-induced p70s6k inactivation is a novel phosphorylation site within a conserved hydrophobic domain
Pearson, R.B.; Dennis, P.B.; Han, J.W.; Williamson, N.A.; Kozma, S.C.; Wettenhall, R.E.; Thomas, G.
EMBO Journal 14(21): 5279-5287
1995
ISSN/ISBN: 0261-4189 PMID: 7489717 Document Number: 452335
The immunosuppressive agent rapamycin induces inactivation of p70-s6k with no effect on other mitogen-activated kinases. Here we have employed a combination of techniques, including mass spectrometry, to demonstrate that this effect is associated with selective dephosphorylation of three previously unidentified p70-s6k phosphorylation sites: T229, T389 and S404. T229 resides at a conserved position in the catalytic domain, whose phosphorylation is essential for the activation of other mitogen-induced kinases. However, the principal target of rapamycin-induced p70-s6k inactivation is T389, which is located in an unusual hydrophobic sequence outside the catalytic domain. Mutation of T389 to alanine ablates kinase activity, whereas mutation to glutamic acid confers constitutive kinase activity and rapamycin resistance. The importance of this site and its surrounding motif to kinase function is emphasized by its presence in a large number of protein kinases of the second messenger family and its conservation in putative p70-s6k homologues from as distantly related organisms as yeast and plants.