The unique 5 '-flanking region of the human basic calponin gene

Calponin has been implicated in the regulation of smooth muscle contraction . Basic calponin, one of the calponin isoforms, is expressed exclusively in smooth muscle cell (SMC)-rich tissues, and is considered to be a phenotypi c marker of differentiated SMC. To define the molecular mechanism of SMC-sp ecific gene transcription in humans, we isolated and characterized the 5'-f lanking region of this gene. Sequence analysis revealed that several putati ve cis-acting elements were clustered within a 500-bp sequence upstream of the transcription start site. However, the 1.9-kb promoter region obtained herein lacked a completely matched consensus sequence of the CArG bos that is commonly identified in the promoter region of other SMC-specific genes. A luciferase assay demonstrated that the 1.9-kb promoter region was suffici ent to drive a basal transcriptional activity not only in human vascular sm ooth muscle cells (VSMC) but also in HeLa cells. In particular, the sequenc e between positions -1,906 and -867 had a significantly higher transcriptio nal activity in VSMC than in HeLa cells. In contrast, the promoter activity was drastically decreased between positions -327 and -257 in both types of cells. These results indicate that the sequence spanning from position -32 7 to -257 contains an essential domain involved in the basal transcriptiona l activity of the human basic calponin gene, and that the distal region of the 1.9-kb 5'-flanking sequence presented herein mag play a pivotal role in the phenotypic modulation of VSMC.