Boney C M, Sekimoto H, Gruppuso P A, Frackelton A R
Department of Pediatrics, Brown University and Rhode Island Hospital, Providence, Rhode Island 02903, USA.
Cell Growth Differ. 2001 Jul;12(7):379-86.
Insulin-like growth factor-I (IGF-I) stimulates proliferation and differentiation of many cell types, including preadipocytes. We have previously shown that IGF-I stimulates proliferation of 3T3-L1 preadipocytes through activation of the extracellular regulated kinase (ERK)-1 and -2 mitogen-activated protein kinase (MAPK) pathway, and that IGF-I-stimulated MAPK is predominantly downstream of Shc, not IRS-1 phosphorylation. The Src family of nonreceptor tyrosine kinases has been shown to mediate the mitogenic effects of other growth factors that also activate Shc and the ERK-1 and -2 MAPKs. Although Src family kinases (SFK) have been implicated in IGF-I action, no specific role for SFKs in IGF-I regulation of mitogenesis has been previously demonstrated. We studied the role of SFKs in IGF-I mitogenic signaling in 3T3-L1 preadipocytes. The SFK-selective inhibitor PP1 completely inhibited both IGF-I-stimulated DNA synthesis and MAPK activation in proliferating 3T3-L1 cells. PP1 inhibited IGF-I phosphorylation of Shc but not of IRS-1. In addition, IGF-I activation of MAPK was inhibited in proliferating cells transiently transfected with a dominant-negative c-Src. Finally, the kinetics of SFK and MAPK activation by IGF-I suggest that SFKs may act upstream of MAPK. IGF-I activation of SFK members c-Src and Fyn occurred within 1 min of treatment, and activity was back to baseline by 10 min. Our previous studies found that IGF-I activation of MAPK peaked at 5 min and was also back to baseline by 10 min. Our results are the first to demonstrate that SFKs mediate IGF-I mitogenic signaling in 3T3-L1 cells and add to the growing body of evidence that SFKs play a crucial role in IGF-I action.
胰岛素样生长因子-I（IGF-I）可刺激包括前脂肪细胞在内的多种细胞类型的增殖和分化。我们之前已经表明，IGF-I通过激活细胞外调节激酶（ERK）-1和-2丝裂原活化蛋白激酶（MAPK）途径来刺激3T3-L1前脂肪细胞的增殖，并且IGF-I刺激的MAPK主要位于Shc的下游，而非IRS-1磷酸化的下游。非受体酪氨酸激酶的Src家族已被证明可介导其他生长因子的促有丝分裂作用，这些生长因子也可激活Shc以及ERK-1和-2 MAPK。尽管Src家族激酶（SFK）与IGF-I的作用有关，但此前尚未证明SFK在IGF-I对有丝分裂的调节中具有特定作用。我们研究了SFK在3T3-L1前脂肪细胞IGF-I促有丝分裂信号传导中的作用。SFK选择性抑制剂PP1完全抑制了增殖的3T3-L1细胞中IGF-I刺激的DNA合成和MAPK激活。PP抑制了Shc的IGF-I磷酸化，但未抑制IRS-1的磷酸化。此外，在用显性负性c-Src瞬时转染的增殖细胞中，IGF-I对MAPK的激活受到抑制。最后，IGF-I激活SFK和MAPK的动力学表明，SFK可能在MAPK的上游起作用。IGF-I对SFK成员c-Src和Fyn的激活在处理后1分钟内发生，活性在10分钟时恢复到基线。我们之前的研究发现，IGF-I对MAPK的激活在5分钟时达到峰值，并且在10分钟时也恢复到基线。我们的结果首次证明，SFK介导3T3-L1细胞中IGF-I的促有丝分裂信号传导，并进一步证明了SFK在IGF-I作用中起关键作用的证据越来越多。
