Cyclin-dependent kinase inhibitors and JNK act as molecular switches, regulating the choice between growth arrest and apoptosis induced by galectin-8
Cyclin-dependent kinase inhibitors and JNK act as molecular switches, regulating the choice between growth arrest and apoptosis induced by galectin-8
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DOI：
10.1074/jbc.m502060200
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发表时间：
2005-05-13
影响因子：
4.8
通讯作者：
Zick, Y
中科院分区：
文献类型：
--
作者：
Arbel-Goren, R;Levy, Y;Zick, Y
半乳糖凝集素-8是一种哺乳动物β -半乳糖苷结合凝集素，作为细胞外基质蛋白与整合素形成高亲和力相互作用。在这里，我们证明了可溶性半乳糖凝集素-8抑制细胞周期进程并诱导生长停滞。这些影响不能归因于对细胞粘附的干扰，但可以归因于细胞周期蛋白依赖性激酶抑制剂p21的细胞含量增加了4-5倍，这在H1299细胞与半乳糖凝集素-8孵育4小时后已经很明显。在p21水平升高之前，JNK和蛋白激酶B （PKB）活性增加了3-5倍。因此，JNK抑制剂SP600125和PKB上游激活剂磷脂酰肌醇3-激酶抑制剂wortmannin抑制了p21细胞含量的增加。此外，JNK的上游激酶调节因子SEK1的显性抑制形式的过表达抑制JNK的激活和p21的积累。当p21的表达被环己亚胺抑制时，半乳糖凝集素-8引导细胞凋亡，这包括诱导聚（adp -核糖）聚合酶裂解。事实上，与亲代HTC细胞相比，半凝集素-8诱导的HTC细胞（p21-null）凋亡率高出2倍。由于半乳糖凝集素-8的过度表达会降低DNA合成的速率，因此只有在过度表达生长因子受体（如胰岛素受体）的细胞中才能产生稳定的过表达和分泌半乳糖凝集素-8的菌落。这些结果暗示半乳糖凝集素-8通过上调p21作为细胞生长的调节剂。这一过程包括JNK的激活，增强p21的合成，结合PKB的激活，抑制p21的降解。凝集素的这些作用取决于蛋白-糖的相互作用，当凝集素-8作为可溶性配体存在或在细胞中过度表达时，就会引起凝集素-8的这些作用。
Galectin-8, a mammalian beta-galactoside binding lectin, functions as an extracellular matrix protein that forms high affinity interactions with integrins. Here we demonstrated that soluble galectin-8 inhibits cell cycle progression and induces growth arrest. These effects cannot be attributed to interference with cell adhesion but can be attributed to a 4-5-fold increase in the cellular content of the cyclin-dependent kinase inhibitor p21, which was already evident following a 4-h incubation of H1299 cells with galectin-8. The increase in p21 levels was preceded by a 3-5-fold increase in JNK and protein kinase B (PKB) activities. Accordingly, SP600125, the inhibitor of JNK, and wortmannin, the inhibitor of phosphatidylinositol 3-kinase, which is the upstream activator of PKB, inhibited the increase in the cellular content of p21. Furthermore, overexpression of a dominant inhibitory form of SEK1, the upstream kinase regulator of JNK, inhibited both JNK activation and p21 accumulation. When p21 expression was inhibited by cycloheximide, galectin-8 directed the cells toward apoptosis, which involves induction of poly(ADP-ribose) polymerase cleavage. Indeed, galectin-8-induced apoptosis was 2-fold higher in HTC (p21-null) cells when compared with parental HTC cells. Because overexpression of galectin-8 attenuates the rate of DNA synthesis, stable colonies that overexpress and secrete galectin-8 can be generated only in cells overexpressing a growth factor receptor, such as the insulin receptor. These results implicate galectin-8 as a modulator of cellular growth through up-regulation of p21. This process involves activation of JNK, which enhances the synthesis of p21, combined with the activation of PKB, which inhibits p21 degradation. These effects of the lectin depended upon protein-sugar interactions and were induced when galectin-8 was present as a soluble ligand or when it was overexpressed in cells.