Detection of breast tumor progesterone receptor isoforms with the PR-enzyme immunoassay kit (Abbott). Effect of heat shock proteins on epitope recognition.

Eighty-nine human breast tumor progesterone receptors were assayed both by a radioligand assay (RLA; 3H-ORG-2058) and by the enzyme immunoassay from Abbott Laboratories (PR-EIA). The correlation obtained between the two methods was EIA = 0.83 RLA + 4.1 fmol/mg protein (r = 0.83). Great discrepancies were observed with EIA/RLA ratios varying from 0.5 to 2. After KCl 0.4 mol/l dissociation and chromatographic separation of 8 PR isoforms [12], the two PR polymeric forms (isoforms 1 and 2) which remained bound to the hsp90 heat shock protein were not or only partially detected by EIA, whereas PR-hsp70 isoforms were highly detected with EIA/RLA ratios increased up to 3.8. Free PR-A and PR-B proteins and the PR-truncated form (52 kDa) were never detected by EIA. Thus, the final result of PR assay using the Abbott method depends directly on the amount of PR-hsp70 isoforms produced through KCl dissociation during the overnight incubation of PR with the KD68 coated beads.