Masamha Chioniso Patience, Benbrook Doris Mangiaracina
Departments of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, 73104, USA.
Cancer Res. 2009 Aug 15;69(16):6565-72. doi: 10.1158/0008-5472.CAN-09-0913. Epub 2009 Jul 28.
D- and E-type cyclins mediate G(1)-S phase cell cycle progression through activation of specific cyclin-dependent kinases (cdk) that phosphorylate the retinoblastoma protein (pRb), thereby alleviating repression of E2F-DP transactivation of S-phase genes. Cyclin D1 is often overexpressed in a variety of cancers and is associated with tumorigenesis and metastasis. Loss of cyclin D can cause G(1) arrest in some cells, but in other cellular contexts, the downstream cyclin E protein can substitute for cyclin D and facilitate G(1)-S progression. The objective of this study was to determine if a flexible heteroarotinoid anticancer compound, SHetA2, regulates cell cycle proteins and cell cycle progression in ovarian cancer cells. SHetA2 induced cyclin D1 phosphorylation, ubiquitination, and proteasomal degradation, causing G(1) arrest in ovarian cancer cells despite continued cyclin E2 expression and independently of p53 and glycogen synthase kinase-3beta. Cyclin D1 loss inhibited pRb S780 phosphorylation by cyclin D1-cdk4/6 and released p21 from cyclin D1-cdk4/6-p21 protein complexes to form cyclin E2-cdk2-p21 complexes, which repressed phosphorylation of pRb S612 by cyclin E2-cdk2 and ultimately E2F-DP transcriptional activity. G(1) arrest was prevented by overexpression or preventing degradation of cyclin D1 but not by restoration of pRb S612 phosphorylation through p21 knockdown. In conclusion, we show that loss of cyclin D1 in ovarian cancer cells treated with SHetA2 is sufficient to induce G(1) cell cycle arrest and this strategy is not impeded by the presence of cyclin E2. Therefore, cyclin D1 is a sufficient therapeutic target in ovarian cancer cells.
D型和E型细胞周期蛋白通过激活特定的细胞周期蛋白依赖性激酶（cdk）介导G1-S期细胞周期进程，这些激酶使视网膜母细胞瘤蛋白（pRb）磷酸化，从而减轻对E2F-DP转录激活S期基因的抑制。细胞周期蛋白D1在多种癌症中常过度表达，并与肿瘤发生和转移相关。细胞周期蛋白D的缺失可导致某些细胞出现G1期停滞，但在其他细胞环境中，下游的细胞周期蛋白E蛋白可替代细胞周期蛋白D并促进G1-S期进程。本研究的目的是确定一种柔性杂芳维甲酸类抗癌化合物SHetA2是否能调节卵巢癌细胞中的细胞周期蛋白和细胞周期进程。SHetA2诱导细胞周期蛋白D1磷酸化、泛素化和蛋白酶体降解，尽管细胞周期蛋白E2持续表达且独立于p53和糖原合酶激酶-3β，仍导致卵巢癌细胞出现G1期停滞。细胞周期蛋白D1的缺失抑制了细胞周期蛋白D1-cdk4/6对pRb S780的磷酸化，并使p21从细胞周期蛋白D1-cdk4/6-p21蛋白复合物中释放出来，形成细胞周期蛋白E2-cdk2-p21复合物，该复合物抑制细胞周期蛋白E2-cdk2对pRb S612的磷酸化，并最终抑制E2F-DP的转录活性。过表达或阻止细胞周期蛋白D1的降解可防止G1期停滞，但通过敲低p21恢复pRb S612磷酸化则不能。总之，我们表明，用SHetA2处理的卵巢癌细胞中细胞周期蛋白D1的缺失足以诱导G1期细胞周期停滞，且该策略不受细胞周期蛋白E2存在的阻碍。因此，细胞周期蛋白D1是卵巢癌细胞中一个充分的治疗靶点。
