MOLECULAR-CLONING OF THE HUMAN GLUCOSE-REGULATED PROTEIN ERP57 GRP58,A THIOL-DEPENDENT REDUCTASE - IDENTIFICATION OF ITS SECRETORY FORM AND INDUCIBLE EXPRESSION BY THE ONCOGENIC TRANSFORMATION/

Recently it was shown that putative phospholipase C-alpha cDNA does no t code for an isotype of the phospholipase C superfamily but for one o f the glucose-regulated proteins (GRPs), ERp57/GRP58. We have isolated human ERp57/GRP58 cDNA from human placenta. Sequence analysis showed that ERp57/GRP58 has two Trp-Cys-Gly-His-Cys-Lys motifs completely con served among the mammals. Bacterially expressed recombinant ERp57/GRP5 8 protein contained a thiol-dependent reductase activity which was com pletely abolished when Ser residues were substituted for Cys residues in both of the two motifs. Furthermore, we have identified a soluble f orm of ERp57/GRP58 by Western blotting and biosynthetic labeling. In v -onc transformants of normal rat kidney cells, the expression level of ERp57/GRP58 was elevated at the protein level. In NIH3T3 cells transf ormed with v-src, activated c-src (Y527F) or c-src, the expression lev el of ERp57/GRP58 was upregulated in proportion to their transforming abilities. These results indicate that a soluble form of ERp57/GRP58 e xists and that this protein may control both extracellular and intrace llular redox activities through its thiol-dependent reductase activity . Moreover, it is likely that ERp57/GRP58 is involved in the oncogenic transformation.