Melnikova I N, Bounpheng M, Schatteman G C, Gilliam D, Christy B A
Institute of Biotechnology, University of Texas Health Science Center, San Antonio, Texas, 78245-3207, USA.
Exp Cell Res. 1999 Feb 25;247(1):94-104. doi: 10.1006/excr.1998.4330.
Id proteins are helix-loop-helix (HLH) transcription factors that lack DNA-binding domains. These proteins form inactive heterodimers with basic HLH (bHLH) factors, inhibiting their DNA-binding and transcriptional activities. Consistent with a proposed role for Id proteins as inhibitors of terminal differentiation, Id1 and Id3 have been shown to negatively regulate myogenesis in cultured muscle cells. Here we have investigated the possibility that Id2 and/or Id4 can act in a similar manner. Surprisingly, while overexpression of Id2 resulted in inhibition of differentiation of Sol 8 myoblast cells, overexpression of Id4 did not. Sol 8 cells stably transfected with Id4 showed no apparent changes in expression of muscle-specific genes upon differentiation. DNA-binding activities present at the muscle creatine kinase (MCK) enhancer E-box and transcription of the MCK enhancer were not altered in Id4-overexpressing cells, compared with vector-transfected cells. Id2 is also a more potent inhibitor of protein/DNA complex formation at the MCK-R enhancer E-box than Identified in vitro. Therefore, our data support the notion that members of the Id family might be involved in the regulation of distinct developmental pathways.
Id蛋白是缺乏DNA结合结构域的螺旋-环-螺旋（HLH）转录因子。这些蛋白与碱性HLH（bHLH）因子形成无活性的异二聚体，抑制它们的DNA结合和转录活性。与Id蛋白作为终末分化抑制剂的假定作用一致，Id1和Id3已被证明在培养的肌肉细胞中负向调节肌生成。在此，我们研究了Id2和/或Id4是否能以类似方式发挥作用的可能性。令人惊讶的是，虽然Id2的过表达导致Sol 8成肌细胞分化受到抑制，但Id4的过表达却没有。稳定转染Id4的Sol 8细胞在分化时肌肉特异性基因的表达没有明显变化。与载体转染细胞相比，在Id4过表达细胞中，肌肉肌酸激酶（MCK）增强子E盒处的DNA结合活性以及MCK增强子的转录均未改变。与体外鉴定的情况相比，Id2也是MCK-R增强子E盒处蛋白/DNA复合物形成的更有效抑制剂。因此，我们的数据支持这样一种观点，即Id家族成员可能参与不同发育途径的调控。
