Protein kinase C phosphorylates ribosomal protein S6 kinase betaII and regulates its subcellular localization.
The ribosomal protein S6 kinase (S6K) belongs to the AGC family of Ser/Thr kinases and is known to be involved in the regulation of protein synthesis and the G(1)/S transition of the cell cycle. There are two forms of S6K, termed S6Kalpha and S6Kbeta, which have cytoplasmic and nuclear splice variants. Nucleocytoplasmic shuttling has been recently proposed for S6Kalpha, based on the use of the nuclear export inhibitor, leptomycin B. However, the molecular mechanisms regulating subcellular localization of S6Ks in response to mitogenic stimuli remain to be elucidated. Here we present data on the in vitro and in vivo phosphorylation of S6Kbeta, but not S6Kalpha, by protein kinase C (PKC). The site of phosphorylation was identified as S486, which is located within the C-terminal nuclear localization signal. Mutational analysis and the use of phosphospecific antibodies provided evidence that PKC-mediated phosphorylation at S486 does not affect S6K activity but eliminates the function of its nuclear localization signal and causes retention of an activated form of the kinase in the cytoplasm. Taken together, this study uncovers a novel mechanism for the regulation of nucleocytoplasmic shuttling of S6KbetaII by PKC-mediated phosphorylation.
Valovka
Taras
T
Ludwig Institute for Cancer Research, London W1W 7BS, United Kingdom.
Verdier
Frederique
F
Cramer
Rainer
R
Zhyvoloup
Alexander
A
Fenton
Timothy
T
Rebholz
Heike
H
Wang
Mong-Lien
ML
Gzhegotsky
Miechyslav
M
Lutsyk
Alexander
A
Matsuka
Genadiy
G
Filonenko
Valeriy
V
Wang
Lijun
L
Proud
Christopher G
CG
Parker
Peter J
PJ
Gout
Ivan T
IT
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D001665:Binding Sites; D002460:Cell Line; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D008934:Mitogens / Q000494:pharmacology; D008969:Molecular Sequence Data; D010656:Phenylephrine / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000201:enzymology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection
D005231:Fatty Acids, Unsaturated; D007328:Insulin; D007527:Isoenzymes; D008934:Mitogens; D011994:Recombinant Proteins; D010656:Phenylephrine; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C448959:ribosomal protein S6 kinase, 70kD, polypeptide 2; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; C038753:leptomycin B