Glycogen synthase kinase-3β regulates cyclin D1 proteolysis and subcellular localization

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作者：

JA Diehl，M Cheng，MF Roussel，CJ Sherr

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摘要：

The activities of cyclin D-dependent kinases serve to integrate extracellular signaling during Gphase with the cell-cycle engine that regulates DNA replication and mitosis. Induction of D-type cyclins and their assembly into holoenzyme complexes depend on mitogen stimulation. Conversely, the fact that D-type cyclins are labile proteins guarantees that the subunit pool shrinks rapidly when cells are deprived of mitogens. Phosphorylation of cyclin D1 on a single threonine residue near the carboxyl terminus (Thr-286) positively regulates proteasomal degradation of D1. Now, we demonstrate that glycogen synthase kinase-3β (GSK-3β) phosphorylates cyclin D1 specifically on Thr-286, thereby triggering rapid cyclin D1 turnover. Because the activity of GSK-3β can be inhibited by signaling through a pathway that sequentially involves Ras, phosphatidylinositol-3-OH kinase (PI3K), and protein kinase B (Akt), the turnover of cyclin D1, like its assembly, is also Ras dependent and, hence, mitogen regulated. In contrast, Ras mutants defective in PI3K signaling, or constitutively active mitogen-activated protein kinase-kinase (MEK1) mutants that act downstream of Ras to activate extracellular signal-regulated protein kinases (ERKs), cannot stabilize cyclin D1. In direct contrast to cyclin D1, which accumulates in the nucleus during Gphase and exits into the cytoplasm during S phase, GSK-3β is predominantly cytoplasmic during Gphase, but a significant fraction enters the nucleus during S phase. A highly stable D1 mutant in which an alanine is substituted for the threonine at position 286 and that is refractory to phosphorylation by GSK-3β remained in the nucleus throughout the cell cycle. Overexpression of an active, but not a kinase-defective, form of GSK-3β in mouse fibroblasts caused a redistribution of cyclin D1 from the cell nucleus to the cytoplasm. Therefore, phosphorylation and proteolytic turnover of cyclin D1 and its subcellular localization during the cell division cycle are linked through the action of GSK-3β.

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关键词：

Animals Mice 3T3 Cells Proteasome Endopeptidase Complex Phosphothreonine Cysteine Endopeptidases Glycogen Synthase Kinases Glycogen Synthase Kinase 3 Cyclins Fluorescent Antibody Technique