Blaschuk K L, Holland P C
Montreal Neurological Institute, McGill University, Quebec, Canada.
Dev Biol. 1994 Aug;164(2):475-83. doi: 10.1006/dbio.1994.1217.
The expression of alpha 5 beta 1 integrin was examined in either cloned or fluorescence-activated cell-sorted satellite cells derived from human biceps muscle. Removal of serum and factors required for muscle cell growth and proliferation both induced terminal differentiation and resulted in a coordinate downregulation of mRNA transcripts encoding alpha 5 and beta 1 integrin subunits. A corresponding downregulation of the alpha 5 subunit occurred at the protein level. Treatment of cultures with 5-bromo-2'-deoxyuridine (BUdR), a thymidine analog which inhibits muscle cell differentiation, resulted in increased expression of alpha 5 integrin subunit at both the mRNA and protein levels. However, levels of alpha 5 subunit message and protein were still markedly downregulated on removal of serum and growth factors from BUdR-treated cultures, indicating that downregulation of alpha 5 beta 1 integrin during myogenesis does not require and is not a consequence of muscle cell terminal differentiation. Downregulation of alpha 5 integrin subunit expression could be prevented by maintenance of cells in medium supplemented with serum and growth factors, although no single defined component of this medium could on its own prevent the downregulation of alpha 5 integrin subunit expression. Collectively, these results suggest that downregulation of alpha 5 beta 1 integrin expression is not a consequence of muscle cell terminal differentiation, but is dependent on a combination of exogenous growth factors which are also required for muscle cell growth and proliferation.
在源自人二头肌的克隆卫星细胞或经荧光激活细胞分选的卫星细胞中检测了α5β1整合素的表达。去除肌肉细胞生长和增殖所需的血清和因子，既诱导了终末分化，又导致编码α5和β1整合素亚基的mRNA转录物协同下调。α5亚基在蛋白质水平上相应下调。用5-溴-2'-脱氧尿苷（BUdR）处理培养物，BUdR是一种抑制肌肉细胞分化的胸苷类似物，导致α5整合素亚基在mRNA和蛋白质水平上的表达增加。然而，从经BUdR处理的培养物中去除血清和生长因子后，α5亚基的信息和蛋白质水平仍显著下调，这表明在肌生成过程中α5β1整合素的下调并不需要肌肉细胞终末分化，也不是其结果。通过将细胞维持在补充有血清和生长因子的培养基中，可以防止α5整合素亚基表达的下调，尽管该培养基中没有单一的特定成分能够单独防止α5整合素亚基表达的下调。总体而言，这些结果表明，α5β1整合素表达的下调不是肌肉细胞终末分化的结果，而是取决于外源性生长因子的组合，这些生长因子也是肌肉细胞生长和增殖所必需的。
