THE 170-KDA GLUCOSE-REGULATED STRESS PROTEIN IS AN ENDOPLASMIC-RETICULUM PROTEIN THAT BINDS IMMUNOGLOBULIN

Anoxia, glucose starvation, calcium ionophore A23187, EDTA, glucosamin e, and several other conditions that adversely affect the function of the endoplasmic reticulum (ER) induce the synthesis of the glucose-reg ulated class of stress proteins (GRPs). The primary GRPs induced by th ese stresses migrate at 78 and 94 kDa (GRP78 and GRP94). In addition, another protein of similar to 150-170 kDa (GRP170) has been previously observed and is coordinately induced with GRP78 and GRP94. To charact erize this novel stress protein, we have prepared an antisera against purified GRP170. Immunofluorescence, Endoglycosidase H sensitivity, an d protease resistance of this protein in microsomes indicates that GRP 170 is an ER lumenal glycoprotein retained in a pre-Golgi compartment. Immunoprecipitation of GRP170 with our antibody coprecipitates the GR P78 (also referred to as the B cell immunoglobulin-binding protein) an d GRP94 members of this stress protein family in Chinese hamster ovary cells under stress conditions. ATP depletion, by immunoprecipitation in the presence of apyrase, does not affect the interaction between GR P78 and GRP170 but results in the coprecipitation of an unidentified 6 0-kDa protein. In addition, GRP170 is found to be coprecipitated with immunoglobulin (Ig) in four different B cell hybridomas expressing sur face IgM, cytoplasmic Ig light chain only, cytoplasmic Ig heavy chain only, or an antigen specific secreted IgG. In addition, in IgM surface expressing WEHI-231 B cells, anti-IgM coprecipitates GRP78, GRP94, as well as GRP170; antibodies against GRP170 and GRP94 reciprocally copr ecipitate GRP94/GRP170 as well as GRP78. Results suggest that this 170 -kDa GRP is a retained ER lumenal glycoprotein that is constitutively present and that may play a role in immunoglobulin folding and assembl y in conjunction or consecutively with GRP78 and GRP94.