Departments of Pediatrics & Biochemistry and Molecular Biology, Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia, Canada.
Int J Cancer. 2012 Jul 15;131(2):357-66. doi: 10.1002/ijc.26368. Epub 2011 Nov 2.
Resistance of carcinoma cells to anoikis, apoptosis that is normally induced by detachment of nonmalignant epithelial cells from the extracellular matrix, is thought to be critical for carcinoma progression. Molecular mechanisms that control anoikis of nonmalignant and cancer cells are understood poorly. In an effort to understand them we found that detachment of nonmalignant intestinal epithelial cells triggers upregulation of Chk2, a pro-apoptotic protein kinase that has never been implicated in anoikis and has been thought to kill cells mainly under the conditions compromising genome integrity. We found that enforced downregulation of Chk2 protects intestinal epithelial cells from anoikis. Chk2 can kill cells by stabilizing p53 tumor suppressor protein or via p53-independent mechanisms, and we established that Chk2-mediated anoikis of intestinal epithelial cells is p53-independent. We further found that, unlike nonmalignant intestinal epithelial cells whose anoikis is triggered by detachment-induced Chk2 upregulation, intestinal epithelial cells carrying oncogenic ras, a known inhibitor of anoikis, remain anoikis-resistant in response to enforced Chk2 upregulation. By contrast, drugs, such as topoisomerase I inhibitors, that can kill cells via Chk2-indpendent mechanisms, efficiently triggered anoikis of ras-transformed cells. Thus, oncogenic ras can prevent Chk2 from triggering anoikis even when levels of this protein kinase are elevated in cancer cells, and the use of therapeutic agents that kill cells in a Chk-2-independent, rather than Chk-2-dependent, manner could represent an efficient strategy for overcoming ras-induced anoikis resistance of these cells. We conclude that Chk-2 is an important novel component of anoikis-promoting machinery of intestinal epithelial cells.
癌细胞对失巢凋亡（anoikis）的抵抗能力被认为是癌细胞发展的关键，失巢凋亡是指正常情况下非恶性上皮细胞从细胞外基质中分离时所诱导的细胞凋亡。然而，控制非恶性和癌细胞失巢凋亡的分子机制尚未完全清楚。为了理解这些机制，我们发现非恶性肠道上皮细胞的分离会触发 Chk2 的上调，Chk2 是一种促凋亡的蛋白激酶，它从未被牵涉到失巢凋亡中，并且被认为主要在破坏基因组完整性的情况下杀死细胞。我们发现，强制下调 Chk2 可以保护肠道上皮细胞免受失巢凋亡。Chk2 可以通过稳定 p53 肿瘤抑制蛋白或通过非 p53 依赖的机制杀死细胞，我们确定 Chk2 介导的肠道上皮细胞失巢凋亡是 p53 非依赖的。我们进一步发现，与非恶性肠道上皮细胞不同，非恶性肠道上皮细胞的失巢凋亡是由分离诱导的 Chk2 上调触发的，而携带致癌 ras（一种已知的失巢凋亡抑制剂）的肠道上皮细胞在受到强制 Chk2 上调时仍然保持失巢凋亡抗性。相比之下，像拓扑异构酶 I 抑制剂这样的药物可以通过 Chk2 独立的机制杀死细胞，能够有效地触发 ras 转化细胞的失巢凋亡。因此，即使在癌细胞中 Chk2 蛋白激酶的水平升高，致癌 ras 也可以阻止 Chk2 触发失巢凋亡，并且使用能够以 Chk-2 非依赖而不是 Chk-2 依赖的方式杀死细胞的治疗剂可能代表克服这些细胞中 ras 诱导的失巢凋亡抗性的有效策略。我们的结论是，Chk2 是肠道上皮细胞促进失巢凋亡的新的重要组成部分。
