SELECTIVE DELETIONS IN THE 90 KDA HEAT-SHOCK PROTEIN (HSP90) IMPEDE HETEROOLIGOMERIC COMPLEX-FORMATION WITH THE GLUCOCORTICOSTEROID RECEPTOR (GR) OR HORMONE-BINDING BY GR

We have developed an in vivo system using coexpression of human glucoc orticosteroid receptor (hGR) and chick hsp90 alpha (chsp90) in recombi nant virus-infected Sf9 cells to study the formation of hetero-oligome ric complexes. We detected, in the cytosol, hGR complexes containing c hsp90 as shown by the displacement of the [H-3]triamcinolone acetonide bound hGR ''8S'' peak on glycerol/ sucrose gradients by specific anti bodies directed against chsp90 (BF4 and D7 alpha). We took advantage o f this system and of the immunoadsorption of hGR containing complexes with anti-hGR antibody to analyze the effect of deletions introduced i nto the hsp90 molecule on the formation of complexes with the hGR. Del etion of the hydrophilic region ''A'', between amino-acids 221 and 290 , abolished the formation of hGR/chsp90 complexes. Deletion of the hyd rophilic region ''B'' (between amino-acids 530 and 581) or deletion of a leucine repeat region ''Z'' in the middle of the molecule (amino-ac ids 392 to 419) still allowed formation of hetero-oligomeric complexes detected by immunoadsorption but the hGR complexes formed with mutate d chsp90s were devoid of steroid binding properties. These results are consistent with (1) the possible involvement of the ''A'' region in t he interaction of hsp90 with steroid receptors and (2) a role of B and Z regions in the hsp90 structure for maintaining the steroid binding property of the hGR.