Increased expression of germinal center-associated nuclear protein (GANP) is associated with malignant transformation of melanocytes

Background: Germinal center-associated nuclear protein (GANP) is a newly cloned molecule that is up-regulated in the germinal center B cells. Although GANP functions in the regulation of DNA repair during replication and survival of B cells, little is known about its expression in melanocytic cells. Objectives: To investigate whether GANP and phosphorylated-GANP (P-GANP) are expressed in cultured human melanocytes and melanoma cells and in benign and malignant melanocytic lesions. In addition, we aim to determine whether GANP and P-GANP are associated with malignant transformation of melanocytic lineage. Methods: GANP and P-GANP expression in cultured melanocytic cells was analyzed by immunostaining and in vitro kinase assay. GANP and P-GANP expression in melanocytic lesions was analyzed by immunohistochemistry. Results: GANP and P-GANP were up-regulated in cultured melanoma cells compared to melanocytes. GANP and P-GANP were restricted to nucleus of melanocytes but co-expressed in cytoplasm of melanoma cells. On the other hand, GANP and P-GANP were widely expressed at various levels in melanocytic nevi and melanoma lesions with nuclear and cytoplasmic staining pattern. Melanoma cells showed a stronger intensity of GANP and P-GANP than melanocytic nevus cells, however the staining intensity in primary melanoma lesions was not associated with any clinicopathological variables. Cytoplasmic GANP and P-GANP expression was associated with MCM3 and Ki67 expression. Conclusions: These data suggest, for the first time, that GANP and P-GANP are up-regulated in cultured melanoma cells compared to melanocytes and also they are widely expressed in benign and malignant melanocytic tumor cells.