ECTO-ATP DIPHOSPHOHYDROLASE CD39 IS OVEREXPRESSED IN DIFFERENTIATED HUMAN MELANOMAS/

Ecto-ATPase activities of melanocytes and human melanoma cell lines di ffering in the stage of progression were compared. A dramatic increase in ecto-ATPase activity above the level of normal melanocytes,vas dem onstrated in the differentiated melanomas and was followed by a gradua l decrease with tumor progression. The characteristics of this enzymat ic activity were consistent with CD39/ecto-ATP diphosphohydrolase (ATP Dase) which was found to be the major ecto-ATP-hydrolysing enzyme in m elanomas. Indeed, the expression of CD39 and the level of CD39 mRNA fo llowed a similar pattern. Since CD39 is known to regulate homotypic ad hesion and, supposedly, affects the disaggregation step, we suggest th at overexpression of CD39 may enable tumor cells to reduce contacts wi th T-lymphocytes and escape from immunological recognition. (C) 1998 F ederation of European Biochemical Societies.