Regulation of cyclin-dependent kinase 4 during adipogenesis involves switching of cyclin D subunits and concurrent binding of p18INK4c and p27Kip1.
Terminal differentiation of many cell lineages involves an exit from the mitotic cycle and entry into, and maintenance of, a permanent state of G1 arrest. We found that during terminal differentiation of mouse 3T3-L1 preadipocytes, the level of cyclin-dependent kinase 4 (CDK4) remained constant, but the subunit composition of the CDK4 complex underwent a dynamic rearrangement. As 3T3-L1 cells differentiated, the levels of cyclin D1 and cyclin D1-CDK4 complexes declined to negligible levels. Meanwhile, cyclins D2 and D3 levels and their associations with CDK4 increased transiently and persistently, respectively, with cyclin D3 becoming the predominant cyclin partner of CDK4 in mature adipocytes. At least five CDK inhibitors are expressed during the differentiation program of 3T3-L1 cells. Both p15INK4b and p16INK4a continuously declined to undetectable levels immediately after differentiation induction. p21 was transiently expressed during the exit of 3T3-L1 cells from mitotic clonal expansion and then decreased to undetectable levels in mature adipocytes. The level of p27KiP1 and p27-CDK4 complexes remain high during differentiation and in mature adipocytes. Distinctly, there is a remarkable induction of p18INK4c mRNA and protein that was not seen in the closely related nondifferentiating 3T3-C2 cell line, suggesting that p18 induction in 3T3-L1 cells is related to cell differentiation, not cell cycle arrest. The pRb kinase activity of cyclin D3 and CDK4 was not detected in quiescent 3T3-L1 cells and was then induced as the cells entered the mitotic clonal expansion phase. Unexpectedly, cyclin D3 and CDK4 pRb kinase activity remained high after 3T3-L1 cells completed their mitotic division and was still readily detectable in mature adipocytes. Our study reveals an active regulation, rather than passive inhibition, of CDK4 activity during adipocyte differentiation. Two central features of this complex regulation are switching of activating cyclin D subunits and concurrent binding by the p18 and p27 CDK inhibitors.
Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, 27599, USA.
D E
DE
Phelps
Y
Y
Xiong
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology* / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D056741:Cyclin D; D051358:Cyclin-Dependent Kinase 4; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050763:Cyclin-Dependent Kinase Inhibitor p18; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D004791:Enzyme Inhibitors; D005656:Fungal Proteins / Q000378:metabolism; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D020409:Molecular Motor Proteins; D010766:Phosphorylation; D011233:Precipitin Tests; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D025521:Tumor Suppressor Proteins
D002352:Carrier Proteins; C493961:Cdkn1b protein, mouse; C493968:Cdkn2b protein, mouse; C493972:Cdkn2c protein, mouse; D018797:Cell Cycle Proteins; D056741:Cyclin D; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050763:Cyclin-Dependent Kinase Inhibitor p18; D016213:Cyclins; D004791:Enzyme Inhibitors; D005656:Fungal Proteins; C075341:KIP2 protein, S cerevisiae; D008869:Microtubule-Associated Proteins; D020409:Molecular Motor Proteins; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D029701:Saccharomyces cerevisiae Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D011494:Protein Kinases; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases