Gosens Reinoud, Dueck Gordon, Rector Edward, Nunes Raquel O, Gerthoffer William T, Unruh Helmut, Zaagsma Johan, Meurs Herman, Halayko Andrew J
Departments of Physiology, University of Manitoba, Winnipeg.
Am J Physiol Lung Cell Mol Physiol. 2007 Nov;293(5):L1348-58. doi: 10.1152/ajplung.00346.2007. Epub 2007 Sep 14.
Muscarinic receptors and platelet-derived growth factor (PDGF) receptors synergistically induce proliferation of airway smooth muscle (ASM), but the pathways that regulate these effects are not yet completely identified. We hypothesized that glycogen synthase kinase-3 (GSK-3), a kinase that represses several promitogenic signaling pathways in its unphosphorylated form, is cooperatively inhibited by PDGF and muscarinic receptors in immortalized human ASM cell lines. PDGF or methacholine alone induced rapid GSK-3 phosphorylation. This phosphorylation was sustained only for PDGF; however, methacholine potentiated PDGF-induced sustained GSK-3 phosphorylation. Synergistic effects of methacholine also were observed on PDGF-induced retinoblastoma protein (Rb) phosphorylation and cell proliferation. Suppression of GSK-3 inhibitory function using SB 216763 also augmented PDGF-induced Rb phosphorylation and cell cycle progression; this synergy was similar in magnitude to that seen for methacholine with PDGF. GSK-3 phosphorylation induced by methacholine required PKC, since it was abolished by GF 109203X and Gö 6976; however, inhibition of PKC had no effect on cell responses to PDGF. PKC inhibition also specifically abolished the synergistic effect of methacholine on PDGF-induced GSK-3 phosphorylation and cell proliferation. Collectively, these results show that GSK-3 plays a key repressive role in ASM cell proliferation. Moreover, muscarinic receptors mediate PKC-dependent GSK-3 inhibition, and this appears to be a primary mechanism underpinning augmentation of PDGF-induced cell growth.
毒蕈碱受体与血小板衍生生长因子（PDGF）受体协同诱导气道平滑肌（ASM）增殖，但调节这些作用的信号通路尚未完全明确。我们推测，糖原合酶激酶-3（GSK-3），一种以未磷酸化形式抑制多种促有丝分裂信号通路的激酶，在永生化人ASM细胞系中被PDGF和毒蕈碱受体协同抑制。单独使用PDGF或乙酰甲胆碱可迅速诱导GSK-3磷酸化。这种磷酸化仅在PDGF作用下持续存在；然而，乙酰甲胆碱可增强PDGF诱导的GSK-3持续磷酸化。乙酰甲胆碱对PDGF诱导的视网膜母细胞瘤蛋白（Rb）磷酸化和细胞增殖也有协同作用。使用SB 216763抑制GSK-3的抑制功能也增强了PDGF诱导的Rb磷酸化和细胞周期进程；这种协同作用的程度与乙酰甲胆碱和PDGF的协同作用相似。乙酰甲胆碱诱导的GSK-3磷酸化需要蛋白激酶C（PKC），因为它被GF 109203X和Gö 6976消除；然而，抑制PKC对细胞对PDGF的反应没有影响。PKC抑制也特异性地消除了乙酰甲胆碱对PDGF诱导的GSK-3磷酸化和细胞增殖的协同作用。总的来说，这些结果表明GSK-3在ASM细胞增殖中起关键的抑制作用。此外，毒蕈碱受体介导PKC依赖性的GSK-3抑制，这似乎是增强PDGF诱导的细胞生长的主要机制。
