Department of Diagnostic and Biological Sciences, University of Minnesota, Minneapolis, Minnesota, United States of America.
PLoS One. 2013 Jul 9;8(7):e69395. doi: 10.1371/journal.pone.0069395. Print 2013.
Malignant transformation results in abnormal cell cycle regulation and uncontrolled growth in head and neck squamous cell carcinoma (HNSCC) and other cancers. S100A8/A9 (calprotectin) is a calcium-binding heterodimeric protein complex implicated in cell cycle regulation, but the specific mechanism and role in cell cycle control and carcinoma growth are not well understood. In HNSCC, S100A8/A9 is downregulated at both mRNA and protein levels. We now report that downregulation of S100A8/A9 correlates strongly with a loss of cell cycle control and increased growth of carcinoma cells. To show its role in carcinogenesis in an in vitro model, S100A8/A9 was stably expressed in an S100A8/A9-negative human carcinoma cell line (KB cells, HeLa-like). S100A8/A9 expression increases PP2A phosphatase activity and p-Chk1 (Ser345) phosphorylation, which appears to signal inhibitory phosphorylation of mitotic p-Cdc25C (Ser216) and p-Cdc2 (Thr14/Tyr15) to inactivate the G2/M Cdc2/cyclin B1 complex. Cyclin B1 expression then downregulates and the cell cycle arrests at the G2/M checkpoint, reducing cell division. As expected, S100A8/A9-expressing cells show both decreased anchorage-dependent and -independent growth and mitotic progression. Using shRNA, silencing of S100A8/A9 expression in the TR146 human HNSCC cell line increases growth and survival and reduces Cdc2 inhibitory phosphorylation at Thr14/Tyr15. The level of S100A8/A9 endogenous expression correlates strongly with the reduced p-Cdc2 (Thr14/Tyr14) level in HNSCC cell lines, SCC-58, OSCC-3 and UMSCC-17B. S100A8/A9-mediated control of the G2/M cell cycle checkpoint is, therefore, a likely suppressive mechanism in human squamous cell carcinomas and may suggest new therapeutic approaches.
恶性转化导致头颈部鳞状细胞癌（HNSCC）和其他癌症的细胞周期调控异常和失控生长。S100A8/A9（钙卫蛋白）是一种参与细胞周期调控的钙结合异二聚体蛋白复合物，但具体的机制和在细胞周期控制和癌生长中的作用尚不清楚。在 HNSCC 中，S100A8/A9 的 mRNA 和蛋白水平均下调。我们现在报告 S100A8/A9 的下调与细胞周期控制的丧失和癌细胞生长的增加密切相关。为了在体外模型中显示其在致癌作用中的作用，我们在 S100A8/A9 阴性的人癌细胞系（KB 细胞，HeLa 样）中稳定表达 S100A8/A9。S100A8/A9 的表达增加了 PP2A 磷酸酶活性和 p-Chk1（Ser345）磷酸化，这似乎信号抑制有丝分裂 p-Cdc25C（Ser216）和 p-Cdc2（Thr14/Tyr15）的抑制性磷酸化，从而使 G2/M Cdc2/细胞周期蛋白 B1 复合物失活。然后，细胞周期蛋白 B1 的表达下调，细胞周期在 G2/M 检查点停滞，减少细胞分裂。正如预期的那样，S100A8/A9 表达的细胞显示出锚定依赖性和非依赖性生长以及有丝分裂进展均减少。使用 shRNA 沉默 TR146 人 HNSCC 细胞系中的 S100A8/A9 表达会增加生长和存活，并减少 Thr14/Tyr15 处的 Cdc2 抑制性磷酸化。S100A8/A9 的内源性表达水平与 HNSCC 细胞系 SCC-58、OSCC-3 和 UMSCC-17B 中 p-Cdc2（Thr14/Tyr14）水平的降低密切相关。因此，S100A8/A9 介导的 G2/M 细胞周期检查点控制是人类鳞状细胞癌中一种可能的抑制机制，并可能提示新的治疗方法。
