A CRE that binds CREB and contributes to PKA-dependent regulation of the proximal promoter of human RAB25 gene.

RAB25 plays an important role in tumor progression and aggressiveness; altered RAB25 expression may cause human cancer. As the underlying mechanism of RAB25-mediated carcinogenesis in various tumor types progressively comes to light, RAB25 is expected to represent a novel therapeutic target. However, the regulation of RAB25 expression per se has not yet been described. Here we have firstly identified and characterized the human RAB25 promoter. Using PCR-based chromatin accessibility and chromatin immunoprecipitation (ChIP) assays, an open chromatin conformation (-173/+17) was detected around the transcription start site of the RAB25 gene. Deletion constructs of the 5' flanking region were fused to a luciferase reporter gene. After transient transfection in gastric cancer cell line AGS, a CRE (-67/-58) binding CREB was identified in the core promoter region. Electrophoretic mobility shift (EMSA) and ChIP assays demonstrated that CREB binds to the core promoter. Deletion of CREB consensus sequence resulted in the total loss of the promoter activity. Moreover, we have also found forskolin, PKA activator, could enhance open chromatin accessibility, by which to expose the CRE and facilitate phosphorylation of CREB, which in turn recruits co-factor CBP and Brg I and then results in a more open chromatin configuration associated with local histone modification, finally heightening RAB25 expression and strengthening its promoter activity. Therefore, the present study delineates the fundamental elements of a core promoter structure that will be helpful for future studies regarding the regulation of RAB25 gene.