Mettus Richard V, Rane Sushil G
Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Oncogene. 2003 Nov 20;22(52):8413-21. doi: 10.1038/sj.onc.1206888.
Cyclin-dependent kinase 4 (Cdk4) and Cdk6, and later Cdk2, in association with their specific cyclin partners, regulate the G1 to S phase cell cycle transition of mammalian cells by phosphorylation of retinoblastoma (Rb) family proteins. Phosphorylation of Rb results in the release of S-phase specific transcription factors; cell cycle-promoting gene expression, and advancement of the cell cycle. Loss of Cdk4 by homologous-targeted disruption leads to a delay in S-phase entry in serum-stimulated mouse embryo fibroblast (MEF) cultures. Homozygous Cdk4-deficient mice display defects in weight gain, fertility and hypoproliferation of specific endocrine cells of the pituitary and pancreas, the latter of which results in a diabetes-like phenotype. In contrast, inheritance of the p16(Ink4a)-insensitive Cdk4(R24C) mutation leads to spontaneous transformation of MEF cultures in vitro and, in vivo, hyperproliferative disorders that progress to cancer. In this manuscript, we report characterization of the abnormal pancreatic development, reduced growth and infertility in Cdk4 mutant mice. We observe that, whereas Cdk4 is dispensable for early pancreatic development, normal Cdk4 expression is critical for optimal growth of the organism. Also, we observe that loss of Cdk4 may result in insulin insensitivity, implicating an additional role of Cdk4 in beta-cell function, in addition to its role in beta-cell proliferation. Further, we demonstrate that loss of Cdk4 leads to an age-dependent defect in spermatogenesis and disruption in the timing of the estrus cycle. Taken together, our results indicate that the overall defects in growth, fertility and pancreatic development in Cdk4-deficient mice may be a combination of cell-type specific defects and altered glucose metabolism, as a result of defects in postnatal pancreatic development.
细胞周期蛋白依赖性激酶4（Cdk4）和Cdk6，以及随后的Cdk2，与其特定的细胞周期蛋白伙伴结合，通过磷酸化视网膜母细胞瘤（Rb）家族蛋白来调节哺乳动物细胞从G1期到S期的细胞周期转换。Rb的磷酸化导致S期特异性转录因子的释放；促进细胞周期的基因表达以及细胞周期的推进。通过同源靶向破坏使Cdk4缺失会导致血清刺激的小鼠胚胎成纤维细胞（MEF）培养物进入S期延迟。纯合Cdk4缺陷小鼠在体重增加、生育能力以及垂体和胰腺特定内分泌细胞的增殖不足方面表现出缺陷，后者导致类似糖尿病的表型。相比之下，对p16（Ink4a）不敏感的Cdk4（R24C）突变的遗传会导致体外MEF培养物的自发转化，以及在体内导致进展为癌症的过度增殖性疾病。在本手稿中，我们报告了Cdk4突变小鼠胰腺发育异常、生长减缓及不育的特征。我们观察到，虽然Cdk4对于胰腺早期发育并非必需，但正常的Cdk4表达对于生物体的最佳生长至关重要。此外，我们观察到Cdk4的缺失可能导致胰岛素不敏感，这意味着Cdk4除了在β细胞增殖中的作用外，在β细胞功能中还有额外作用。此外，我们证明Cdk4的缺失会导致精子发生的年龄依赖性缺陷以及发情周期时间的紊乱。综上所述，我们的结果表明，Cdk4缺陷小鼠在生长、生育能力和胰腺发育方面的总体缺陷可能是细胞类型特异性缺陷和葡萄糖代谢改变的综合结果，这是由于出生后胰腺发育缺陷所致。
