CYTOPLASMIC ACCUMULATION OF THE 52 KDA RO SS-A NUCLEAR AUTOANTIGEN INTRANSFECTED CELL-LINES/

The 60 kDa Ro/SS-A (Ro60) autoantigen is thought to reside predominant ly in the nucleus; however, the intracellular localization of 52 kDa R o/SS-A (Ro52) in normal cells is controversial, probably due to its lo w abundance. Therefore, we studied the intracellular expression and lo calization of the human Ro52 following transfection of a human Ro52 cD NA into cultured cell lines. Immunofluorescence staining of human (HEp -2) and mouse (LTA-5) cell transfectants with affinity-purified anti-R o52 antibodies revealed that Ro52 antigen was most abundant in the cyt oplasm and present to a lesser extent in the nucleus. This relative lo calization was supported by a preponderance of the Ro52 antigen in the cytoplasmic rather than nuclear fraction of enucleated cell lines det ected by immunoblotting. In contrast to the Ro52 autoantigen, Ro60 and La autoantigens were mainly expressed in the nucleus of transfected c ells under similar circumstances, indicating distinct localization of the intracellular pools of these autoantigens. The findings indicate t hat the Ro52 autoantigen lacks intrinsic signals required for nuclear localization and suggest that a significant pool of this autoantigen r esides in the cytoplasm. Ro52 may therefore rely upon an association w ith other molecules for any specific nuclear transport. (C) Academic P ress Limited