Identification of the elements regulating the expression of the cell adhesion molecule MCAM/MUC18 - Loss of AP-2 is not required for MCAM expression in melanoma cell lines

The cell adhesion molecule melonoma cell adhesion molecule (MCAM)/MUC18/CD1 46 is specifically up-regulated on tumors of neuroectodermal origin and in animal models confers metastatic capacity to human melanoma cells, To ident ify critical regions regulating MCAM expression in melanomas, 1 kilobase of the MCAM 5' region was analyzed for promoter activity and transcription fa ctor binding in 1 glioma, 1 carcinoma, and 4 melanoma cell lines. The minim al MCAM promoter (-106/+22 base pair (bp)) consists of 4 Sp-l sites, two AP -2 elements, one cAMP responsive element, and the initiator surrounding the transcriptional start site. Analysis of mutated constructs indicated that the cAMP-responsive element is a major transcriptional activator in the maj ority of cell Lines. Site-directed mutagenesis revealed that, in AP-2 expre ssing cells, the AP-2 site within the core promoter (-23 bp) has an inhibit ory influence on MCAM expression while the AP-2 sites at -131 and -302 bp a re activating. Functional AP-2 was observed in both MCAM positive and MCAM negative melanoma cell lines indicating that expression of MCAM does not re quire loss of this transcription factor. Furthermore, all MCAM: constructs were strongly expressed in MCAM negative as well as MCAM positive cells, in dicating that the expression of this gene is not controlled solely by the p resence of transactivating factors binding to the investigated region.