Kulik G, Klippel A, Weber M J
Department of Microbiology and Cancer Center, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
Mol Cell Biol. 1997 Mar;17(3):1595-606. doi: 10.1128/MCB.17.3.1595.
We have found that insulin-like growth factor I (IGF-I) can protect fibroblasts from apoptosis induced by UV-B light. Antiapoptotic signalling by the IGF-I receptor depended on receptor kinase activity, as cells overexpressing kinase-defective receptor mutants could not be protected by IGF-I. Overexpression of a kinase-defective receptor which contained a mutation in the ATP binding loop functioned as a dominant negative and sensitized cells to apoptosis. The antiapoptotic capacity of the IGF-I receptor was not shared by other growth factors tested, including epidermal growth factor (EGF) and thrombin, although the cells expressed functional receptors for all the agonists. However, EGF was antiapoptotic for cells overexpressing the EGF receptor, and expression of activated pp60v-src also was protective. There was no correlation between protection from apoptosis and activation of mitogen-activated protein kinase, p38/HOG1, or p70S6 kinase. On the other hand, protection by any of the tyrosine kinases against UV-induced apoptosis was blocked by wortmannin, implying a role for phosphatidylinositol 3-kinase (PI3 kinase). To test this, we transiently expressed constitutively active or kinase-dead PI3 kinase and found that overexpression of activated phosphatidylinositol 3-kinase (PI3 kinase) was sufficient to provide protection against apoptosis. Because Akt/PKB is believed to be a downstream effector for PI3 kinase, we also examined the role of this serine/threonine protein kinase in antiapoptotic signalling. We found that membrane-targeted Akt was sufficient to protect against apoptosis but that kinase-dead Akt was not. We conclude that the endogenous IGF-I receptor has a specific antiapoptotic signalling capacity, that overexpression of other tyrosine kinases can allow them also to be antiapoptotic, and that activation of PI3 kinase and Akt is sufficient for antiapoptotic signalling.
我们发现胰岛素样生长因子I（IGF-I）能够保护成纤维细胞免受UV-B光诱导的凋亡。IGF-I受体的抗凋亡信号传导依赖于受体激酶活性，因为过表达激酶缺陷型受体突变体的细胞不能被IGF-I保护。在ATP结合环中含有突变的激酶缺陷型受体的过表达起到了显性负性作用，使细胞对凋亡敏感。所测试的其他生长因子，包括表皮生长因子（EGF）和凝血酶，均不具备IGF-I受体的抗凋亡能力，尽管细胞表达了所有激动剂的功能性受体。然而，EGF对过表达EGF受体的细胞具有抗凋亡作用，并且活化的pp60v-src的表达也具有保护作用。抗凋亡作用与丝裂原活化蛋白激酶、p38/HOG1或p70S6激酶的激活之间没有相关性。另一方面，任何一种酪氨酸激酶对UV诱导的凋亡的保护作用均被渥曼青霉素阻断，这意味着磷脂酰肌醇3激酶（PI3激酶）发挥了作用。为了验证这一点，我们瞬时表达了组成型活性或激酶失活的PI3激酶，发现活化的磷脂酰肌醇3激酶（PI3激酶）的过表达足以提供抗凋亡保护。因为Akt/PKB被认为是PI3激酶的下游效应物，我们还研究了这种丝氨酸/苏氨酸蛋白激酶在抗凋亡信号传导中的作用。我们发现膜靶向的Akt足以保护细胞免受凋亡，但激酶失活的Akt则不能。我们得出结论，内源性IGF-I受体具有特定的抗凋亡信号传导能力，其他酪氨酸激酶的过表达也可使其具有抗凋亡能力，并且PI3激酶和Akt的激活足以进行抗凋亡信号传导。
