IGFS AND SKELETAL MUSCLE CELL DIFFERENTIATION

胰岛素样生长因子(IGF)的独特之处在于它们是 只有已知的有丝分裂原，在没有其他血清成分的情况下，刺激 骨骼肌细胞的增殖和分化。 IGF既能有丝分裂又能分化的机制- 然而，由于这些事件，在骨骼肌中促进作用尚不清楚 被认为在这个组织中是相互排斥的。在本建议书中 我们将研究IGF-I最初抑制和 随后刺激肌生成素基因转录，我们将 评价CDK4/CDK6抑制物p19在细胞周期调控中的作用 IGF-I反应由增殖向分化的转变。我们 将检验三个假说：1)早期抑制和后续抑制 胰岛素样生长因子-I对肌生成素基因转录的促进作用 通过包含在5‘侧翼的一个或多个IGF反应元件 2)胰岛素样生长因子-I的早期抑制作用 肌生成素的转录由Ras/MAP激酶途径介导，而 IGF-I随后对肌生成素转录的刺激作用是 由磷脂酰肌醇(PI)-3激酶途径介导； 在对IGF-I的最初促有丝分裂反应中，p19的表达增加 在S期成肌细胞中，限制了细胞周期的进一步进入，并导致胰岛素样生长因子-1 I从刺激增殖转向促进细胞周期 退出和刺激分化。我们提出了以下具体建议 目的，将在小鼠骨骼肌细胞中实现：1)鉴定 肌生成素基因调控部分的区域(S) 胰岛素样生长因子-I的早期抑制和晚期刺激作用 肌生成素转录，并检测核蛋白之间的相互作用 2)鉴定IGF-I受体信号传导途径 介导早期抑制和随后刺激的通路 以及3)评估肌生成素基因转录的潜在作用。 CDK4/CDK6抑制剂p19在介导胰岛素样生长因子-I反应中的作用 骨骼肌母细胞增殖分化的研究。这些研究 应该进一步加深我们对IGFS的机制的理解 影响骨骼肌成肌细胞增殖或增殖的决定 差异化。此外，这些对IGF反应元件的研究， 信号通路和细胞周期调节成分可能有更多 理解IGFS的机制的一般含义 调节多种组织的增殖和分化。

The insulin-like growth factors (IGFs) are unique in that they are the only known mitogens that, when free of other serum components, stimulate both the proliferation and differentiation of skeletal muscle cells. The mechanisms by which IGFs can be both mitogenic and differentiation- promoting in skeletal muscle, however, are unclear since these events are believed to be mutually exclusive in this tissue. In this proposal we will examine the mechanisms by which IGF-I initially inhibits and subsequently stimulates myogenin gene transcription, and we will evaluate the potential role of the cdk4/cdk6 inhibitor p19 in mediating the switch in IGF-I response from proliferation to differentiation. We will test three hypotheses: 1) The early inhibitory and subsequent stimulatory effects of IGF-I on myogenin gene transcription are mediated by an IGF response element (or elements) contained in the 5' flanking region of the myogenin gene; 2) The early inhibitory effect of IGF-I on myogenin transcription is mediated by the Ras/MAP kinase pathway, while the subsequent stimulatory effect of IGF-I on myogenin transcription is mediated by the phosphatidylinositol (PI)-3 kinase pathway; and 3) During the initial mitogenic response to IGF-I, p19 expression increases in S phase myoblasts, limiting further cell cycle entry and causing IGF- I to switch from stimulating proliferation to promoting cell cycle exit and stimulating differentiation. We propose the following specific aims, to be carried out in murine skeletal muscle cells: 1) Identify the region(s) in the regulatory portion of the myogenin gene which confer the early inhibitory and late stimulatory effects of IGF-I on myogenin transcription, and examine the interaction of nuclear proteins with this region or regions; 2) Identify the IGF-I receptor signaling pathways which mediate the early inhibition and subsequent stimulation of myogenin gene transcription; and 3) Assess the potential role of the cdk4/cdk6 inhibitor p19 in mediating the switch in IGF-I response from proliferation to differentiation in skeletal myoblasts. These studies should further our understanding of the mechanisms by which IGFs influence the decision of skeletal myoblasts to proliferate or differentiate. In addition, these studies of IGF response elements, signaling pathways, and cell cycle regulatory components may have more general implications for understanding the mechanisms by which IGFs regulate proliferation and differentiation in a variety of tissues.