Cyclin-Dependent Kinase Inhibitor suppresses the growth in oral squamous cell carcinoma cells

细胞周期蛋白依赖性蛋白激酶(CDK)在细胞内调控细胞周期中起着重要作用。CDK阻滞剂(黄烷醇和罗司匹林)通过抑制CDK抑制肿瘤的体内外生长。众所周知，这些药物可以抑制CDK2、CDK4和CDK7的活性，减少细胞周期蛋白Dl的表达，并诱导细胞凋亡。然而，CDK抑制剂对口腔鳞状细胞癌(OSCC)细胞的抑制作用及其介导的细胞毒作用机制尚未完全阐明。本研究旨在研究CDK抑制剂对口腔鳞状细胞癌细胞株的作用，并探讨其介导细胞凋亡的机制。发现CDK抑制剂以时间和剂量依赖的方式抑制所有5种口腔鳞癌细胞的生长，并降低CDKs的活性。在所有细胞以及亚G1DNA含量、DNA片段化和PARP裂解的细胞中都观察到了诱导凋亡的现象。未观察到细胞凋亡调节因子Bcl2的表达水平变化。而在CDK抑制剂作用下，Bclxl表达下调，Bclxs表达上调。CDK抑制剂处理后口腔鳞癌细胞中细胞周期蛋白A、细胞周期蛋白B和细胞周期蛋白D1的表达也显著降低。我们还发现，CDK激活酶和CDC25C的表达水平降低，而磷酸化的p34CDK2在Thr 14和Tyr 15：失活状态下上调，表明CDK抑制剂在体外对口腔鳞癌具有生长抑制活性。CDK抑制剂不仅可以直接抑制CDKs，还可以抑制CDKs的激活途径，激活BclX的凋亡途径。

Cyclin-dependent kinases (CDKs) play an essential role in intracellular control of cell cycle. CDK inhinitors (Flavopiridol and Roscpvitine) that inhibits tumor growth in vitro and in vivo by because of the inhibiting CDKs. These agents are known to inhibit CDK2, CDK4 and CDK7 activities, to diminish cyclin Dl expressions, and to induce apoptosis. However, effects of CDK inhibitors against oral squamous cell carcinoma (OSCC) cells and mechanisms of these agents mediated cytotoxicity have not been fully elucidated.In this study, we have investigated effects of CDK inhibitors in OSCC cell lines and studied mechanisms of CDK inhibitors mediated-apoptosis. CDK inhibitors were found to inhibit the growth of all five OSCC cells in time and dose-dependent manner and to diminish CDKs activities. Induction of apoptosis was observed in all cells, as well as cells with sub-Gl DNA contents, DNA fragmentations, and PARP cleavages. No alternation of expression levels of Bcl-2, an apoptosis regulator was observed. In contrast, Bcl-XL was down regulated and Bcl-Xs was up regulated after being exposed to CDK inhibitors. CDK inhibitors treatments also resulted in remarkable reductions of cyclin A, cyclin B, and cyclin Dl expressions in OSCC cells. We also found that expression levels of CDK Activation Kinase and CDC25C were reduced, and p34 CDK2 that phosphorylated in Thr 14 and Tyr 15: inactive form were up-regulated after CDK inhibitors exposure.Our data indicate that CDK inhibitors has growth inhibition activities against OSCC in vitro. CDK inhibitors not only inhibits CDKs directly, but it also inhibits CDKs activation pathway and activates Bcl-X apoptotic pathway.