INVOLVEMENT OF 70-KD HEAT-SHOCK PROTEINS IN PEROXISOMAL IMPORT

This report describes the involvement of 70-kD heat-shock proteins (hs p70) in the import of proteins into mammalian peroxisomes. Employing a microinjection-based assay (Walton, P. A., S. J. Gould, J. R. Feramis co, and S. Subramani. 1992. Mel. Cell Biol. 12:531-541), we demonstrat e that proteins of the hsp70 family were associated with proteins bein g imported into the peroxisomal matrix. Import of peroxisomal proteins could be inhibited by coinjection of antibodies directed against the constitutive hsp70 proteins (hsp73). In a permeabilized-cell assay (We ndland and Subramani. 1993. J. Cell Biol. 120:675-685), antibodies dir ected against hsp70 proteins were shown to inhibit peroxisomal protein import. Inhibition could be overcome by the addition of exogenous hsp 70 proteins. Purified rat liver peroxisomes were shown to have associa ted hsp70 proteins. The amount of associated hsp70 was increased under conditions of peroxisomal proliferation. Furthermore, proteinase prot ection assays indicated that the hsp70 molecules were located on the o utside of the peroxisomal membrane. Finally, the process of heat-shock ing cells resulted in a considerable delay in the import of peroxisoma l proteins. Taken together, these results indicate that heat-shock pro teins of the cytoplasmic hsp70 family are involved in the import of pe roxisomal proteins.