Upstream regions of the hamster desmin and vimentin genes regulate expression during in vitro myogenesis

Varying lengths of the hamster desmin and vimentin promoter regions were fused to the bacterial chloramphenicol acetyl-transferase gene. These constructs were transfected into two different myogenic cell lines, T984 and C2C12. In both cell lines an increase in endogenous desmin expression takes place upon myogenesis. A region between -89 and +25 bp relative to the desmin transcription initiation site directs high-level tissue- and stage-specific expression upon in vitro myogenesis. At the myoblast stage, C2C12 cells appeared to express both desmin and vimentin, whereas in T984 myoblasts only vimentin expression was detected. Although vimentin is expressed during all stages of myogenesis, a strong decrease in vimentin expression occurs during differentiation of C2C12 cells. Vimentin--CAT constructs followed the endogenous expression pattern, showing that this down-regulation is mediated by 5' flanking sequences. Vimentin promoter activity is modulated by at least two separate regions, both in myogenic and in non-myogenic cell lines.