Regulation of tumor growth and metastasis of human melanoma by the CREB transcription factor family

The purpose of this study was to determine the role of CREB and its associa ted proteins in melanoma progression. We used MeWo human melanoma cells tra nsfected with a dominant negative construct of CREB, KCREB. KCREB has a mut ation in its DNA-binding domain and can not bind the CRE element. Expressio n of KCREB yields proper heterodimerization with CREB and its associated pr oteins, but the proteins associated with KCREB do not confer the same degre e of transcriptional activity as they would in the case of wild-type CREB. Here, we demonstrate that expression of KCREB in MeWo melanoma cells leads to a decrease in their tumorigenicity and metastatic potential in nude mice . We identified two mechanisms that explain at least partially this effect of KCREB. The first, is one in which CREB and its associated proteins play an essential role in invasion. We showed that the invasive properties of KC REB-transfected MeWo cells were reduced due to the downregulation of the CR E-dependent expression of the type IV collagenase MMP-2 and the adhesion mo lecule MCAM/MUC18. In the second mechanism, CREB and its associated protein s act as survival factors for human melanoma cells. Here we demonstrated th at expression of KCREB in MeWo cells rendered them susceptible to apoptosis induced by thapsigargin, which in turn increased the intracellular level o f Ca2+. Thapsigargin induced CREB and ATF-1 phosphorylation and activated C RE-dependent transcription in MeWo cells. Collectively, our data demonstrat e that CREB and its associated proteins play an important role in tumor gro wth and metastasis of human melanoma.