MECHANISMS OF HUMAN CELL SENESCENCE

关于人细胞生长刺激的分子细节的知识 肿瘤抑制基因的生长抑制， 促进了对人类细胞机制的分子研究 衰老此外，关于潜在的新信息 肌肉分化的分子基础导致了新的假设 关于衰老细胞的细胞周期中的一个阻滞。 与这一提议相关的是观察到， 肿瘤抑制蛋白视网膜母细胞瘤p110（Rb），在G1期， 细胞周期可能导致细胞生长抑制活性的丧失， 蛋白质，相反，蛋白质的去磷酸化在G2/M 细胞周期的一个阶段似乎恢复了生长抑制活性 Rb蛋白质。我们已经证明， 通过I型蛋白的过度表达，使Rb在G1期去磷酸化 磷蛋白磷酸酶导致细胞周期停滞，与 Rb蛋白的作用。在肌肉分化过程中，我们和其他人 我假设碱性螺旋-环-螺旋蛋白MyoD的作用是 维持Rb蛋白处于磷酸化不足的状态，从而 有助于肌细胞的生长停滞表型。衰老 细胞生长停滞，仅含有低磷酸化形式的 Rb蛋白。我们假设在多种遗传成分中 负责细胞衰老，至少有一个影响 Rb的磷酸化状态，并通过cDNA表达克隆结合 通过单细胞生长抑制试验， 可以鉴定衰老，包括参与Rb调节的那些。 为此，我们希望1）测试低磷酸化Rb蛋白在 衰老表型的维持，2）采用cDNA表达克隆 在衰老的单细胞测定中， 衰老的分子基础; 3）探讨 在（2）中鉴定的基因。

Knowledge regarding the molecular details of human cell growth stimulation by protooncogenes and growth suppression by tumor suppressor genes has facilitated molecular investigation into the mechanism of human cell senescence. Moreover, new pieces of information regarding the potential molecular basis of muscle differentiation have led to new hypotheses regarding one of the blockages in the cell cycle of the senescent cells. Pertinent to this proposal are the observations that the phosphorylation of the tumor suppressor protein, retinoblastoma p110 (Rb), in G1 phase of the cell cycle likely results in the loss of growth suppressor activity of the protein and, conversely, the dephosphorylation of the protein in G2/M phase of the cell cycle appears to restore the growth suppression activity of the Rb protein. We have shown that the apparent premature dephosphorylation of Rb in G1 phase by overexpression of type I phosphoprotein phosphatase results in cell cycle arrest, consistent with this role of the Rb protein. During muscle differentiation, we and others have hypothesized that the basic helix-loop-helix protein, MyoD, acts to maintain the Rb protein in an underphosphorylated state, thereby contributing to the growth arrest phenotype of the muscle cell. Senescent cells are growth arrested and contain only the hypophosphorylated form of the Rb protein. We hypothesize that of the multiple genetic components responsible for cellular senescence, at least one affects the phosphorylation state of Rb, and that by cDNA expression cloning combined with single cell assays of growth inhibition, genetic elements which cause senescence can be identified, including those involved in Rb regulation. For this we wish to 1) test the role of hypophosphorylated Rb protein in maintenance of the senescent phenotype, 2) employ cDNA expression cloning in single cell assay's of senescence to identify genes underlying the molecular basis of senescence, and 3) explore the mechanism of action of the genes identified in (2).