The 56-59-kilodalton protein identified in untransformed steroid receptor complexes is a unique protein that exists in cytosol in a complex with both the 70- and 90-kilodalton heat shock proteins.
It has previously been shown that 9S, untransformed progestin, estrogen, androgen, and glucocorticoid receptor complexes in rabbit uterine and liver cytosols contain a 59-kDa protein [Tai, P. K., Maeda, Y., Nakao, K., Wakim, N. G., Duhring, J. L., & Faber, L. E. (1986) Biochemistry 25, 5269-5275]. In this work we show that the monoclonal antibody KN 382/EC1 raised against the rabbit 59-kDa protein reacts with 9S, untransformed glucocorticoid receptor complexes in cytosol prepared from human IM-9 lymphocytes but not with 4S salt-transformed receptors. The human protein recognized by the EC1 antibody is a 56-kDa protein (p56) of moderate abundance located predominantly in the cytoplasm by indirect immunofluorescence. There are at least six isomorphs of p56 by two-dimensional gel analysis. N-Terminal sequencing (20 amino acids) shows that p56 is a unique human protein. When p56 is immunoadsorbed from IM-9 cell cytosol, both the 70- and 90-kDa heat shock proteins are coadsorbed in an immune-specific manner. Neither heat shock protein reacts directly with the EC1 antibody. We conclude that p56 exists in cytosol in a higher order complex containing hsp70 and hsp90, both of which in turn have been found to be associated with untransformed steroid receptors.
Sanchez
E R
ER
Department of Pharmacology, University of Michigan Medical School, Ann Arbor 48109.
Faber
L E
LE
Henzel
W J
WJ
Pratt
W B
WB
D000911:Antibodies, Monoclonal / Q000276:immunology; D002478:Cells, Cultured; D003593:Cytoplasm / Q000032:analysis / Q000276:immunology; D003600:Cytosol / Q000032:analysis; D006360:Heat-Shock Proteins / Q000032:analysis*; D006801:Humans; D008214:Lymphocytes / Q000032:analysis* / Q000276:immunology; D008970:Molecular Weight; D011506:Proteins / Q000032:analysis; D011965:Receptors, Glucocorticoid / Q000032:analysis; D011987:Receptors, Steroid / Q000032:analysis* / Q000276:immunology
D000911:Antibodies, Monoclonal; D006360:Heat-Shock Proteins; D011506:Proteins; D011965:Receptors, Glucocorticoid; D011987:Receptors, Steroid