Sasaoka Toshiyasu, Kikuchi Kosei, Wada Tsutomu, Sato Akira, Hori Hiroyuki, Murakami Shihou, Fukui Kazuhito, Ishihara Hajime, Aota Rina, Kimura Ikuko, Kobayashi Masashi
Department of Clinical Pharmacology, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan.
Endocrinology. 2003 Sep;144(9):4204-14. doi: 10.1210/en.2003-0190.
Src homology domain 2 (SH2)-containing inositol phosphatase 2 (SHIP2) possesses 5-phosphatase activity and an SH2 domain. The role of SHIP2 in platelet-derived growth factor (PDGF) and IGF-I signaling was studied by expressing wild-type (WT-) and a catalytically defective (Delta IP-) SHIP2 into rat aortic smooth muscle cells by adenovirus-mediated gene transfer. PDGF- and IGF-I-induced tyrosine phosphorylation of their respective receptors and phosphatidylinositol 3-kinase (PI3-kinase) activity were not affected by the expression of either WT- or Delta IP-SHIP2. SHIP2 possessed 5'-phosphatase activity to hydrolyze the PI3-kinase product phosphatidylinositol 3,4,5-trisphosphate in vivo. Akt and glycogen synthase kinase 3beta are known to be downstream molecules of PI3-kinase, leading to the antiapoptotic effect. Overexpression of WT-SHIP2 inhibited PDGF- and IGF-I-induced phosphorylation of these molecules and the protective effect of poly(ADP-ribose) polymerase degradation, whereas these phosphorylations and the protective effect were enhanced by the expression of Delta IP-SHIP2, which functions in a dominant negative fashion. Regarding the Ras-MAPK pathway, PDGF- and IGF-I-induced tyrosine phosphorylation of Shc was not affected by the expression of either WT- or Delta IP-SHIP2, whereas both expressed SHIP2 associated with Shc. Importantly, PDGF and IGF-I stimulation of Shc/Grb2 binding, MAPK activation, and 5-bromo-2'-deoxyuridine incorporation were all decreased in both WT- and Delta IP-SHIP2 expression. These results indicate that SHIP2 plays a negative regulatory role in PDGF and IGF-I signaling in vascular smooth muscle cells. As the bifunctional role, our results suggest that SHIP2 regulates PDGF- and IGF-I-mediated signaling downstream of PI3-kinase, leading to the antiapoptotic effect via 5-phosphatase activity, and that SHIP2 regulates the growth factor-induced Ras-MAPK pathway mainly via the SH2 domain.
含Src同源结构域2（SH2）的肌醇磷酸酶2（SHIP2）具有5-磷酸酶活性和一个SH2结构域。通过腺病毒介导的基因转移将野生型（WT-）和催化缺陷型（Delta IP-）SHIP2表达至大鼠主动脉平滑肌细胞中，研究SHIP2在血小板衍生生长因子（PDGF）和胰岛素样生长因子-I（IGF-I）信号传导中的作用。PDGF和IGF-I诱导的各自受体的酪氨酸磷酸化以及磷脂酰肌醇3-激酶（PI3-激酶）活性不受WT-或Delta IP-SHIP2表达的影响。SHIP2在体内具有5'-磷酸酶活性，可水解PI3-激酶产物磷脂酰肌醇3,4,5-三磷酸。已知Akt和糖原合酶激酶3β是PI3-激酶的下游分子，可导致抗凋亡作用。WT-SHIP2的过表达抑制了PDGF和IGF-I诱导的这些分子的磷酸化以及聚（ADP-核糖）聚合酶降解的保护作用，而Delta IP-SHIP2的表达增强了这些磷酸化和保护作用，Delta IP-SHIP2以显性负性方式发挥作用。关于Ras-MAPK途径，PDGF和IGF-I诱导的Shc酪氨酸磷酸化不受WT-或Delta IP-SHIP2表达的影响，而两种表达的SHIP2均与Shc相关。重要的是，在WT-和Delta IP-SHIP2表达中，PDGF和IGF-I对Shc/Grb2结合、MAPK激活和5-溴-2'-脱氧尿苷掺入的刺激均降低。这些结果表明SHIP2在血管平滑肌细胞的PDGF和IGF-I信号传导中起负调节作用。作为双功能作用，我们的结果表明SHIP2在PI3-激酶下游调节PDGF和IGF-I介导的信号传导，通过5-磷酸酶活性导致抗凋亡作用，并且SHIP2主要通过SH2结构域调节生长因子诱导的Ras-MAPK途径。
