Lodén M, Nielsen N H, Roos G, Emdin S O, Landberg G
Department of Pathology, Umeå University, Sweden.
Oncogene. 1999 Apr 22;18(16):2557-66. doi: 10.1038/sj.onc.1202488.
The cell cycle machinery is regulated by cyclin dependent kinases and sets of activating and inhibitory proteins. The G1-S control mechanism is often deregulated in tumours supposedly leading to increased kinase activity, phosphorylation of substrates and subsequent S phase entrance. Increased kinase activity has been proposed to be essential in cell cycle aberrations, but few studies have actually shown enhanced kinase activity related to specific cell cycle defects in primary tumours. In the present study we have determined the cyclin E dependent kinase activity (cyclin E(kinase)) in 59 primary breast cancers, using an H1-kinase assay, and related the activity to the expression of cyclin E, p27 and p21. In a subgroup of 48 tumours, we further characterized the association between cyclin E(kinase), in vivo phosphorylation of the retinoblastoma protein (pRb) and proliferation. The cyclin E(kinase) correlated significantly with cyclin E content and inversely with p27 and p21 expression. P27, but not p21, was associated with low cyclin E(kinase) in specimens with normal/low levels of cyclin E. At elevated cyclin E levels, suppression of cyclin E(kinase) seemed to require high levels of both p21 and p27. The cyclin E(kinase) correlated with the phosphorylation status of pRb as well as with proliferation. Surprisingly, pRb phosphorylation did not correlate with proliferation. Our results support that pRb is a substrate for cyclin E(kinase) in primary breast cancer and that deregulation of cyclin E and p27 act through increased CDK-kinase activity, but cyclin E associated events beside pRb phosphorylation might be rate-limiting for entrance into S phase.
细胞周期机制受细胞周期蛋白依赖性激酶以及一系列激活和抑制蛋白的调控。G1-S 控制机制在肿瘤中常常失调,据推测这会导致激酶活性增加、底物磷酸化以及随后进入 S 期。有人提出激酶活性增加在细胞周期异常中至关重要,但实际上很少有研究表明原发性肿瘤中与特定细胞周期缺陷相关的激酶活性增强。在本研究中,我们使用 H1-激酶检测法测定了 59 例原发性乳腺癌中细胞周期蛋白 E 依赖性激酶活性(细胞周期蛋白 E(激酶)),并将该活性与细胞周期蛋白 E、p27 和 p21 的表达相关联。在 48 个肿瘤的亚组中,我们进一步表征了细胞周期蛋白 E(激酶)、视网膜母细胞瘤蛋白(pRb)的体内磷酸化与增殖之间的关联。细胞周期蛋白 E(激酶)与细胞周期蛋白 E 含量显著相关,与 p27 和 p21 的表达呈负相关。在细胞周期蛋白 E 水平正常/较低的标本中,p27 而非 p21 与低细胞周期蛋白 E(激酶)相关。在细胞周期蛋白 E 水平升高时,抑制细胞周期蛋白 E(激酶)似乎需要高水平的 p21 和 p27。细胞周期蛋白 E(激酶)与 pRb 的磷酸化状态以及增殖相关。令人惊讶的是,pRb 磷酸化与增殖不相关。我们的结果支持 pRb 是原发性乳腺癌中细胞周期蛋白 E(激酶)的底物,并且细胞周期蛋白 E 和 p27 的失调通过增加的 CDK 激酶活性起作用,但除 pRb 磷酸化之外的细胞周期蛋白 E 相关事件可能是进入 S 期的限速因素。