IGFS AND SKELETAL MUSCLE CELL DIFFERENTIATION

胰岛素样生长因子（IGFs）的独特之处在于它们是 只有已知的有丝分裂原，当没有其他血清成分时，刺激 骨骼肌细胞的增殖和分化。 IGFs的促有丝分裂和分化机制- 然而，由于这些事件， 在这个组织中是相互排斥的。 本提案中 我们将研究IGF-I最初抑制的机制， 随后刺激肌细胞生成素基因转录，我们将 评估cdk 4/cdk 6抑制剂p19在介导 IGF-I反应从增殖到分化的转变。 我们 将测试三个假设：1）早期抑制和随后的 IGF-I对肌细胞生成素基因转录的刺激作用是介导的 通过包含在5'侧翼的IGF应答元件（或多个元件）， 2）IGF-I对肌细胞生成素基因的早期抑制作用， 肌细胞生成素的转录由Ras/MAP激酶途径介导， IGF-I对生肌蛋白转录后续刺激作用是 由磷脂酰肌醇（PI）-3激酶途径介导;和3） 在对IGF-I的初始促有丝分裂反应期间，p19表达增加 在S期成肌细胞中，限制进一步的细胞周期进入并引起IGF- 从刺激细胞增殖到促进细胞周期 退出和刺激分化。 我们提出以下具体建议： 目的，在小鼠骨骼肌细胞中进行：1）鉴定 肌细胞生成素基因的调节部分中的区域， 赋予IGF-I的早期抑制和晚期刺激作用， 肌细胞生成素转录，并检查核蛋白的相互作用 2）鉴定IGF-I受体信号传导 介导早期抑制和后续刺激的途径 肌细胞生成素基因转录;和3）评估肌细胞生成素基因转录的潜在作用。 cdk 4/cdk 6抑制剂p19介导IGF-I应答的转换 骨骼肌成肌细胞的增殖到分化。 这些研究 应该进一步了解IGFs的机制， 影响骨骼肌成肌细胞增殖的决定， 区分。 此外，这些IGF反应元件的研究， 信号通路和细胞周期调控成分可能有更多的 对理解IGFs作用机制的一般意义 调节多种组织中的增殖和分化。

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.