Cyclic AMP stimulates MEG3 gene expression in cells through a cAMP-response element (CRE) in the MEG3 proximal promoter region

MEG3 is a human maternally expressed gene that potentially acts as a non-coding RNA. Our laboratory found that a cDNA isoform of MEG3, MEG3a, inhibits cell proliferation. MEG3 is highly expressed in the normal human pituitary but not expressed in clinically non-functioning pituitary tumors, suggesting that this imprinted gene may be involved in pituitary tumorigenesis. Previously we demonstrated that hypermethylation of the MEG3 promoter region is associated with the loss of MEG3 expression in pituitary tumors, potentially by blocking the binding of transcription factors to their cis-elements. To further investigate the cis- and trans-factors that are important for the regulation of MEG3, we have characterized the human MEG3 promoter. A single transcription initiation site was identified by 5′ RACE. Up to 5 kb of the 5′-flanking region of MEG3 gene was cloned into a reporter plasmid. Deletion and mutation analysis suggest that a cAMP response element (CRE), located between −69 and −49 of the MEG3 proximal promoter region, is critical for promoter activity. Consistent with this finding, Northern blot analysis demonstrate that elevated intracellular cAMP levels stimulate MEG3 expression in human fibroblasts in culture. Furthermore, gel shifting, ChIP analysis, and co-transfection experiments show that CREB directly binds to the CRE site and stimulates MEG3 promoter activity. Therefore, MEG3 is a downstream target gene of cAMP. Together with the anti-proliferative function of cAMP, our data suggest that MEG3 may interact with the cAMP-dependent signaling pathway to be involved in the control of cell proliferation and other cAMP-related physiological functions.