Identification by differential display of a protein phosphatase-2A regulatory subunit preferentially expressed in malignant melanoma cells

We described the occurrence of 4 transcripts differentially displayed betwe en syngeneic murine B16F10 (metastatic melanoma) and Melan-a (immortalised melanocytes) cell lines. We now report that one such transcript, which is B 16F10-specific, represents a protein phosphatase-2A B' regulatory subunit. No expression of this transcript was detected in the weakly metastatic B16F 1 by Northern blotting. Moreover, the transcript was not expressed by spont aneously immortalised, non-tumorigenic, melanocytes (Melan-Ab and Melan-a2) , nor was it expressed by ras-transformed, tumourigenic melanocytes (Melan- Ab-LTR-ras). Cloning of the 5'-end region of this transcript (termed band 8 A) from B16F10 cells revealed an intracisternal A-particle insertion, inclu ding the long terminal repeat region, which could account for the observed high expression in B16F10 cells. Single cell clones of B16F10 manifested an experimental metastasis capacity, which correlated with band 8A expression with the lowest expressors being least metastatic. The human homologue of the B' regulatory subunit, B56 gamma, is expressed preferentially at the mR NA level in human melanoma cell lines compared with normal epidermal melano cytes. In situ hybridisation studies on human clinical samples detected hig h expression of this gene in a number of malignant melanomas, Our results i mply strongly that this protein phosphatase-2A regulatory subunit may have a role in melanoma tumour progression. Int. J, Cancer 82:709-713, 1999. (C) 1999 Wiley-Liss, Inc.