Different nuclear/cytoplasmic distributions of RET finger protein in different cell types.

The RET finger protein (RFP), which belongs to the B box zinc finger protein family, has a tripartite motif consisting of a Ring finger, a B box finger and a coiled-coil domain. The RET finger protein becomes oncogenic when its tripartite motif is fused with the tyrosine kinase domain of the RET protein. This study examined the RFP expression in normal and tumor tissues by immunohistochemistry. RFP was detected in the nuclei of various cells, including peripheral and central neurones, hepatocytes, adrenal chromaffin cells and male germ cells. Among them, RFP was expressed at high levels in male germ cells such as primary spermatocytes and round spermatids, and formed a perinuclear cap structure in primary spermatocytes. On the other hand, high levels of cytoplasmic expression of RFP were observed in some plasma cells as well as solitary plasmacytoma and multiple myeloma. These results suggested that different nuclear/cytoplasmic distributions of RFP might play a role in the regulation of growth or differentiation of different cell types.