Cameron Angus J, Procyk Katarzyna J, Leitges Michael, Parker Peter J
Protein Phosphorylation Laboratory, Cancer Research UK, London Research Institute, Lincoln's Inn Fields Laboratories, 44 Lincoln's Inn Fields, WC2A 3PX London, United Kingdom.
Int J Cancer. 2008 Aug 15;123(4):769-79. doi: 10.1002/ijc.23560.
Protein kinase C alpha (PKCalpha) has been implicated in tumor development with high levels of PKCalpha expression being associated with various malignancies including glioblastomas and tumors of the breast and prostate. To account for its upregulation in these cancers, studies have suggested that PKCalpha plays a role in promoting cell survival. Here we show by siRNA depletion in U87MG glioma cells that a critical threshold level of PKCalpha protein expression is essential for their growth in the presence of serum and for their survival following serum deprivation. Derivation of PKCalpha wt and KO mouse embryo fibroblast cell lines confirms a role for PKCalpha in protecting cells from apoptosis induced by serum deprivation. Notably, PKCalpha was found to mediate chemo-protection in these fibroblastic cell lines. In U87MG cells PKCalpha does not confer chemoprotection though this likely reflects growth arrest associated with its depletion. To determine the requirements for catalytic function, comparison was made between distinct classes of PKC inhibitors. In contrast to loss of PKCalpha protein, inhibition of PKC kinase activity in glioma cell lines does not significantly inhibit growth or survival. Conversely, inhibition with calphostin C, which targets the regulatory domain of PKC, potently inhibits proliferation and induces apoptosis. Evidence is presented that it is the fully phosphorylated, folded form of PKCalpha that confers this activity-independent behaviour. These results indicate an essential pro-proliferative and pro-survival role for PKCalpha in glioma but question the use of ATP competitive inhibitors as therapeutics, either alone, or in combination with chemotoxic agents.
蛋白激酶Cα（PKCα）与肿瘤发展有关，PKCα的高表达与包括胶质母细胞瘤以及乳腺和前列腺肿瘤在内的各种恶性肿瘤相关。为了解释其在这些癌症中的上调，研究表明PKCα在促进细胞存活中发挥作用。在这里，我们通过在U87MG胶质瘤细胞中进行小干扰RNA（siRNA）敲低实验表明，PKCα蛋白表达的关键阈值水平对于它们在有血清存在时的生长以及血清剥夺后的存活至关重要。PKCα野生型和敲除型小鼠胚胎成纤维细胞系的衍生证实了PKCα在保护细胞免受血清剥夺诱导的凋亡中的作用。值得注意的是，发现PKCα在这些成纤维细胞系中介导化学保护作用。在U87MG细胞中，PKCα不赋予化学保护作用，尽管这可能反映了与其敲低相关的生长停滞。为了确定催化功能的要求，对不同类别的PKC抑制剂进行了比较。与PKCα蛋白缺失相反，在胶质瘤细胞系中抑制PKC激酶活性不会显著抑制生长或存活。相反，用靶向PKC调节域的钙泊三醇C抑制可有效抑制增殖并诱导凋亡。有证据表明，赋予这种不依赖活性行为的是完全磷酸化、折叠形式的PKCα。这些结果表明PKCα在胶质瘤中具有重要的促增殖和促存活作用，但质疑单独或与化学毒性剂联合使用ATP竞争性抑制剂作为治疗药物的可行性。
