Salvatori G, Lattanzi L, Puri P L, Melchionna R, Fieri C, Levrero M, Molinaro M, Cossu G
Istituto di Istologia ed Embriologia Generale, Fondazione A. Cesalpino, Universitá di Roma La Sapienza, Italy.
Cell Growth Differ. 1997 Feb;8(2):157-64.
The temperature-conditional mutant tsA58 of SV40 large T antigen (Tag) increases the proliferation rate and the number of cell divisions in primary murine and human myogenic cells when expressed under permissive conditions (i.e., at 33 degrees C in medium containing high levels of serum). Under these conditions, Tag also prevents terminal differentiation. Under nonpermissive conditions (i.e., at 39 degrees C in medium containing low levels of serum) in which Tag is largely inactive, proliferation is arrested, and differentiation occurs. However, even at a permissive temperature, the removal of serum induced myosin expression and the fusion of myogenic cells, which continued to express functional Tag. Although Tag was complexed with pRb, as expected from a functional protein, proliferation was nevertheless arrested, and differentiation was induced. Consistent with these findings, the exposure of Tag-expressing differentiated myotubes to serum at 33 degrees C did not reinduce DNA synthesis in these cells. Thus, in myogenic cells, temperature-conditional mutants of Tag stimulate proliferation in the presence of serum but neither prevent terminal differentiation in the absence of serum nor induce DNA synthesis once complete withdrawal from the cycle has occurred.
SV40 大 T 抗原（Tag）的温度条件突变体 tsA58 在允许条件下（即在含有高水平血清的培养基中 33 摄氏度）表达时，可提高原代小鼠和人成肌细胞的增殖速率及细胞分裂次数。在这些条件下，Tag 还可阻止终末分化。在非允许条件下（即在含有低水平血清的培养基中 39 摄氏度），此时 Tag 基本无活性，增殖停止，分化发生。然而，即使在允许温度下，去除血清也会诱导肌球蛋白表达及成肌细胞融合，而成肌细胞仍持续表达功能性 Tag。尽管 Tag 与 pRb 结合，这是功能性蛋白的预期结果，但增殖仍会停止，且会诱导分化。与这些发现一致的是，在 33 摄氏度下将表达 Tag 的分化肌管暴露于血清中并不会在这些细胞中重新诱导 DNA 合成。因此，在成肌细胞中，Tag 的温度条件突变体在有血清存在时刺激增殖，但在无血清时既不阻止终末分化，也不会在完全退出细胞周期后诱导 DNA 合成。
