Musgrove E A, Swarbrick A, Lee C S, Cornish A L, Sutherland R L
Cancer Research Program, Garvan Institute of Medical Research, St Vincent's Hospital, Sydney, New South Wales, Australia.
Mol Cell Biol. 1998 Apr;18(4):1812-25. doi: 10.1128/MCB.18.4.1812.
The steroid hormone progesterone regulates proliferation and differentiation in the mammary gland and uterus by cell cycle phase-specific actions. In breast cancer cells the predominant effect of synthetic progestins is long-term growth inhibition and arrest in G1 phase. Progestin-mediated growth arrest of T-47D breast cancer cells was preceded by inhibition of cyclin D1-Cdk4, cyclin D3-Cdk4, and cyclin E-Cdk2 kinase activities in vitro and reduced phosphorylation of pRB and p107. This was accompanied by decreases in the expression of cyclins D1, D3, and E, decreased abundance of cyclin D1- and cyclin D3-Cdk4 complexes, increased association of the cyclin-dependent kinase (CDK) inhibitor p27 with the remaining Cdk4 complexes, and changes in the molecular masses and compositions of cyclin E complexes. In control cells cyclin E eluted from Superdex 200 as two peaks of approximately 120 and approximately 200 kDa, with the 120-kDa peak displaying greater cyclin E-associated kinase activity. Following progestin treatment, almost all of the cyclin E was in the 200-kDa, low-activity form, which was associated with the CDK inhibitors p21 and p27; this change preceded the inhibition of cell cycle progression. These data suggest preferential formation of this higher-molecular-weight, CDK inhibitor-bound form and a reduced number of cyclin E-Cdk2 complexes as mechanisms for the decreased cyclin E-associated kinase activity following progestin treatment. Ectopic expression of cyclin D1 in progestin-inhibited cells led to the reappearance of the 120-kDa active form of cyclin E-Cdk2 preceding the resumption of cell cycle progression. Thus, decreased cyclin expression and consequent increased CDK inhibitor association are likely to mediate the decreases in CDK activity accompanying progestin-mediated growth inhibition.
类固醇激素孕酮通过细胞周期阶段特异性作用调节乳腺和子宫中的细胞增殖与分化。在乳腺癌细胞中，合成孕激素的主要作用是长期生长抑制并使细胞停滞于G1期。孕激素介导的T-47D乳腺癌细胞生长停滞之前，体外会抑制细胞周期蛋白D1-Cdk4、细胞周期蛋白D3-Cdk4和细胞周期蛋白E-Cdk2激酶活性，并降低pRB和p107的磷酸化水平。这伴随着细胞周期蛋白D1、D3和E表达的降低，细胞周期蛋白D1-Cdk4和细胞周期蛋白D3-Cdk4复合物丰度的降低，细胞周期蛋白依赖性激酶（CDK）抑制剂p27与其余Cdk4复合物结合增加，以及细胞周期蛋白E复合物分子量和组成的变化。在对照细胞中，细胞周期蛋白E从Superdex 200洗脱时呈现两个峰，分别约为120 kDa和约200 kDa，120 kDa峰显示出更高的细胞周期蛋白E相关激酶活性。孕激素处理后，几乎所有细胞周期蛋白E都处于200 kDa的低活性形式，该形式与CDK抑制剂p21和p27相关；这种变化先于细胞周期进程的抑制。这些数据表明，这种高分子量、与CDK抑制剂结合的形式优先形成，以及细胞周期蛋白E-Cdk2复合物数量减少，是孕激素处理后细胞周期蛋白E相关激酶活性降低的机制。在孕激素抑制的细胞中异位表达细胞周期蛋白D1导致细胞周期蛋白E-Cdk2的120 kDa活性形式在细胞周期进程恢复之前重新出现。因此，细胞周期蛋白表达降低以及随之而来的CDK抑制剂结合增加，可能介导了孕激素介导的生长抑制过程中CDK活性的降低。
