Physiology and Experimental Medicine Program, The Hospital for Sick Children, University of Toronto, Canada.
Glycobiology. 2010 May;20(5):603-16. doi: 10.1093/glycob/cwq010. Epub 2010 Jan 24.
We recently established that the subunit of cell surface-residing elastin receptor, neuraminidase-1 (Neu1), can desialylate adjacent insulin-like growth factor 1 receptors (IGF-1R) of arterial smooth muscle cells, thereby quenching their proliferative response to insulin-like growth factor II. In this study, we explored whether Neu1 would also desialylate the insulin receptors (IR), as well as the IGF-1R on rat skeletal L6 myoblasts, and whether desialylation of IR and IGF-1R would affect a net proliferative effect of insulin. First, we found that physiological (0.5-1 nM) and high therapeutic (10 nM) insulin concentrations induced a modest increase in proliferation rate of cultured L6 myoblasts. While IR kinase inhibitor could abolish the mitogenic effect of these insulin concentrations, the observed more pronounced proliferative response to supraphysiological concentration (100 nM) of insulin could be eliminated only by specific inhibition of IGF-1R. Then, we found that treatment of L6 cells with mouse-derived Neu1 or with Clostridium perfringens neuraminidase caused desialylation of IR, which coincided with a significant increase of their proliferative response to lower (0.5-10 nM) concentrations of insulin. In contrast, experimental desialylation of IGF-1R coincided with elimination of the heightened proliferative response of L6 myoblasts to 100 nM insulin. Importantly, we also found that inhibition of endogenous Neu1 abolished the increase in proliferation of L6 cells induced by 1 and 10 nM of insulin, but amplified the proliferative effect of 100 nM insulin. We therefore conclude that desialylation of both IR and IGF-1R by Neu1 controls the net proliferative response of skeletal myoblasts to insulin.
我们最近发现，细胞表面驻留弹性蛋白受体的亚基，神经氨酸酶-1（Neu1），可以去唾液酸化动脉平滑肌细胞中相邻的胰岛素样生长因子 1 受体（IGF-1R），从而抑制其对胰岛素样生长因子 II 的增殖反应。在这项研究中，我们探讨了 Neu1 是否也会去唾液酸化胰岛素受体（IR）以及大鼠骨骼肌 L6 成肌细胞上的 IGF-1R，以及 IR 和 IGF-1R 的去唾液酸化是否会影响胰岛素的净增殖效应。首先，我们发现生理浓度（0.5-1 nM）和高治疗浓度（10 nM）的胰岛素会适度增加培养的 L6 成肌细胞的增殖率。虽然 IR 激酶抑制剂可以消除这些胰岛素浓度的促有丝分裂作用，但观察到的对超生理浓度（100 nM）胰岛素的更明显增殖反应只能通过特异性抑制 IGF-1R 来消除。然后，我们发现用鼠源性 Neu1 或产气荚膜梭菌神经氨酸酶处理 L6 细胞会导致 IR 的去唾液酸化，这与它们对较低浓度（0.5-10 nM）胰岛素的增殖反应显著增加相一致。相比之下，IGF-1R 的实验性去唾液酸化与 L6 成肌细胞对 100 nM 胰岛素的增殖反应的消除相一致。重要的是，我们还发现内源性 Neu1 的抑制消除了 1 和 10 nM 胰岛素诱导的 L6 细胞增殖的增加，但放大了 100 nM 胰岛素的增殖效应。因此，我们得出结论，Neu1 对 IR 和 IGF-1R 的去唾液酸化控制了骨骼肌成肌细胞对胰岛素的净增殖反应。
