Ma Cuiling, Wang Jian, Gao Ying, Gao Tian-Wen, Chen Gang, Bower Kimberly A, Odetallah Mohammed, Ding Min, Ke Zunji, Luo Jia
Department of Microbiology, Immunology and Cell Biology, West Virginia University School of Medicine, Robert C. Byrd Health Sciences Center, Morgantown, WV, USA.
Cancer Res. 2007 Aug 15;67(16):7756-64. doi: 10.1158/0008-5472.CAN-06-4665.
Glycogen synthase kinase 3beta (GSK3beta) is a multifunctional serine/threonine kinase. We showed that the expression of GSK3beta was drastically down-regulated in human cutaneous squamous cell carcinomas and basal cell carcinomas. Due to its negative regulation of many oncogenic proteins, we hypothesized that GSK3beta may function as a tumor suppressor during the neoplastic transformation of epidermal cells. We tested this hypothesis using an in vitro model system, JB6 mouse epidermal cells. In response to epidermal growth factor (EGF) or 12-O-tetradecanoylphorbol-13-acetate (TPA), the promotion-sensitive JB6 P+ cells initiate neoplastic transformation, whereas the promotion-resistant JB6 P- cells do not. JB6 P- cells expressed much higher levels of GSK3beta than JB6 P+ cells; JB7 cells, the transformed derivatives of JB6, had the least amount of GSK3beta. The activity of GSK3beta is negatively regulated by its phosphorylation at Ser9. EGF and TPA induced strong Ser9 phoshorylation in JB6 P+ cells, but phosphorylation was seen at a much lesser extent in JB6 P- cells. EGF and TPA-stimulated Ser9 phosphorylation was mediated by phosphoinositide-3-kinase (PI3K)/Akt and protein kinase C (PKC) pathways. Inhibition of GSK3beta activation significantly stimulated activator protein-1 (AP-1) activity. Overexpression of wild-type (WT) and S9A mutant GSK3beta in JB6 P+ cells suppressed EGF and TPA-mediated anchorage-independent growth in soft agar and tumorigenicity in nude mice. Overexpression of a kinase-deficient (K85R) GSK3beta, in contrast, potentiated anchorage-independent growth and drastically enhanced in vivo tumorigenicity. Together, these results indicate that GSK3beta plays an important role in skin tumorigenesis.
糖原合酶激酶3β（GSK3β）是一种多功能丝氨酸/苏氨酸激酶。我们发现，在人皮肤鳞状细胞癌和基底细胞癌中，GSK3β的表达显著下调。由于其对许多致癌蛋白具有负调控作用，我们推测GSK3β在表皮细胞的肿瘤转化过程中可能作为一种肿瘤抑制因子发挥作用。我们使用体外模型系统JB6小鼠表皮细胞来验证这一假设。响应表皮生长因子（EGF）或12 - O - 十四酰佛波醇 - 13 - 乙酸酯（TPA）时，促癌敏感的JB6 P +细胞会启动肿瘤转化，而促癌抗性的JB6 P -细胞则不会。JB6 P -细胞中GSK3β的表达水平比JB6 P +细胞高得多；JB7细胞是JB6的转化衍生物，其GSK3β含量最少。GSK3β的活性通过其丝氨酸9位点的磷酸化受到负调控。EGF和TPA在JB6 P +细胞中诱导强烈的丝氨酸9磷酸化，但在JB6 P -细胞中的磷酸化程度要小得多。EGF和TPA刺激的丝氨酸9磷酸化由磷脂酰肌醇 - 3 -激酶（PI3K）/Akt和蛋白激酶C（PKC）途径介导。抑制GSK3β激活可显著刺激活化蛋白 - 1（AP - 1）活性。在JB6 P +细胞中过表达野生型（WT）和S9A突变型GSK3β可抑制EGF和TPA介导的软琼脂中不依赖贴壁的生长以及裸鼠中的致瘤性。相比之下，过表达激酶缺陷型（K85R）GSK3β可增强不依赖贴壁的生长并显著提高体内致瘤性。总之，这些结果表明GSK3β在皮肤肿瘤发生中起重要作用。
