p27 cytoplasmic localization is regulated by phosphorylation on Ser10 and is not a prerequisite for its proteolysis.
The activity of the cyclin-dependent kinase inhibitor p27 is controlled by its concentration and subcellular localization. However, the mechanisms that regulate its intracellular transport are poorly understood. Here we show that p27 is phosphorylated on Ser10 in vivo and that mutation of Ser10 to Ala inhibits p27 cytoplasmic relocalization in response to mitogenic stimulation. In contrast, a fraction of wild-type p27 and a p27(S10D)-phospho-mimetic mutant translocates to the cytoplasm in the presence of mitogens. G1 nuclear export of p27 and its Ser10 phosphorylation precede cyclin-dependent kinase 2 (Cdk2) activation and degradation of the bulk of p27. Interestingly, leptomycin B-mediated nuclear accumulation accelerates the turnover of endogenous p27; the p27(S10A) mutant, which is trapped in the nucleus, has a shorter half-life than wild-type p27 and the p27(S10D) mutant. In summary, p27 is efficiently degraded in the nucleus and phosphorylation of Ser10 is necessary for the nuclear to cytoplasmic redistribution of a fraction of p27 in response to mitogenic stimulation. This cytoplasmic localization may serve to decrease the abundance of p27 in the nucleus below a certain threshold required for activation of cyclin-Cdk2 complexes.
Rodier
G
G
Institut de recherches cliniques de Montréal, University of Montreal, Montreal, Quebec, Canada H2W 1R7.
Montagnoli
A
A
Di Marcotullio
L
L
Coulombe
P
P
Draetta
G F
GF
Pagano
M
M
Meloche
S
S
D000409:Alanine / Q000235:genetics; D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000096:biosynthesis*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D003593:Cytoplasm / Q000378:metabolism*; D004789:Enzyme Activation; D004958:Estradiol / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D015151:Immunoblotting; D008856:Microscopy, Fluorescence; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D021381:Protein Transport; D051381:Rats; D012694:Serine / Q000235:genetics / Q000378:metabolism*; D013629:Tamoxifen / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis*; D025801:Ubiquitin / Q000378:metabolism
D000935:Antifungal Agents; C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D004965:Estrogen Antagonists; D005231:Fatty Acids, Unsaturated; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin; D013629:Tamoxifen; D050760:Cyclin-Dependent Kinase Inhibitor p27; D012694:Serine; D004958:Estradiol; D000409:Alanine; C038753:leptomycin B