A role for an alternatively spliced Id3 isoform in vascular lesions?

Abstract

Alterations in proliferation, migration, and function of vascular smooth muscle cells (SMCs) are important in the formation of atherosclerotic and restenotic lesions.1 Although of tremendous clinical importance, the precise molecular mechanisms controlling the proliferation and differentiation of SMCs are not completely understood. Regulation of growth and differentiation in skeletal and cardiac muscle involves a class of transcription factors called helix-loop-helix (HLH) proteins, but the situation in smooth muscle is less clear. The study by Matsumura et al2 in this issue of Arteriosclerosis, Thrombosis, and Vascular Biology investigates a particular HLH protein in vascular SMCs in culture and in vivo after vascular injury. HLH transcriptional regulatory proteins are implicated in control of cell growth and terminal differentiation in a number of cell types.3 The HLH motif mediates dimer formation among HLH proteins. Most HLH proteins contain a region of basic amino acids adjacent to the HLH domain that constitutes the DNA-binding domain; heterodimers or homodimers of basic HLH (bHLH) proteins generally bind to a conserved DNA binding site (E-box). A subfamily of HLH proteins ( I nhibitor of D NA binding [Id] proteins) contain an HLH dimerization domain but lack the basic region and thus are not able to bind DNA.4 Id proteins interact with selected DNA-binding bHLH proteins and negatively regulate their transcriptional activity by preventing formation of functional DNA-binding dimers. Although other potential Id protein functions and interactions have been described,4 this dominant …