Transcriptional activation of the cyclin D1 gene is mediated by multiple cis-elements, including SP1 sites and a cAMP-responsive element in vascular endothelial cells.

In an attempt to examine the mechanisms by which transcriptional activity of the cyclin D1 promoter is regulated in vascular endothelial cells (EC), we examined the cis-elements in the human cyclin D1 promoter, which are required for transcriptional activation of the gene. The results of luciferase assays showed that transcriptional activity of the cyclin D1 promoter was largely mediated by SP1 sites and a cAMP-responsive element (CRE). DNA binding activity at the SP1 sites, which was analyzed by electrophoretic mobility shift assays, was significantly increased in the early to mid G(1) phase, whereas DNA binding activity at CRE did not change significantly. Furthermore, Induction of the cyclin D1 promoter activity in the early to mid G(1) phase depended largely on the promoter fragment containing the SP1 sites, whereas the proximal fragment containing CRE but not the SP1 sites was constitutively active. Finally, the increase in DNA binding and promoter activities via the SP1 sites was mediated by the Ras-dependent pathway. The results suggested that the activation of the cyclin D1 gene in vascular ECs was regulated by a dual system; one was inducible in the G(1) phase, and the other was constitutively active.