Distinct regulatory mechanism for p70 S6 kinase beta from that for p70 S6 kinase alpha

Citation
T. Minami et al., Distinct regulatory mechanism for p70 S6 kinase beta from that for p70 S6 kinase alpha, GENES CELLS, 6(11), 2001, pp. 1003-1015
Citations number
38
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Molecular Biology & Genetics
Journal title
GENES TO CELLS
ISSN journal
1356-9597 → ACNP
Volume
6
Issue
11
Year of publication
2001
Pages
1003 - 1015
Database
ISI
SICI code
1356-9597(200111)6:11<1003:DRMFPS>2.0.ZU;2-K
Abstract
Background: A novel ribosomal S6 kinase, termed p70 S6 kinase beta (p70 bet a), has a highly homologous amino acid sequence to that of p70/p85 S6 kinas e (p70 alpha). This includes the critical phosphorylation sites, Thr(252), Ser(394) and Thr(412) in p70 alpha1, which correspond to Thr(241), Ser(383) and Thr(401) in p70 beta1, respectively. However, the regulatory mechanism for p70 beta remains to be elucidated. Results: We report here the expression and the mechanism of in vivo regulat ion of p70 beta. Two isoforms, p70 beta1 and p70 beta2, were expressed in a variety of tissues at a different level. p70 beta1 was mainly targeted to the nucleus, whereas p70 beta2 dispersed throughout the cytoplasm including nucleoplasm. The kinase activity of p70 beta1 was less sensitive to the in hibition induced by rapamycin, wortmannin and amino acid withdrawal than th at of p70 alpha. The portion of p70 beta activity inhibited by rapamycin wa s rescued by the rapamycin-resistant mutant of the mammalian target of rapa mycin (mTOR). Mutational analysis revealed that the phosphorylation of Thr 241 and Thr(401) in p70 beta1 was indispensable for the kinase activity. In contrast, a p70 beta1 mutant in which Ser(383) was substituted with Gly (S 383G) still retained nearly the half maximal activity. Sequential phosphory lation of wild-type and S383G mutant of p70 beta1 with mTOR and 3-phosphoin ositide-dependent protein kinase 1 (PDK1) in vitro synergistically activate d their kinase activities. Conclusion: These results indicate that p70 beta is regulated by the mTOR- and PDK1-signalling pathways through a synergistic interaction between phos phorylated Thr(241) and Thr(401), while Ser(383) plays minor role in their activation mechanism. Activated p70 beta may be less sensitive to dephospho rylation mediated by putative phosphatases activated by rapamycin, amino ac id withdrawal, and probably wortmannin.