It has been shown previously that untransformed
molybdate-stabilized
breast cancer progesterone receptor (PR) complexes can be dissociated by KCl (0.4 to 1M) into eight different intermediate forms, or
isoforms (680-600-361-224-193-119-88-52 kDa), separated by high performance size exclusion chromatography and with the use of computer assisted smoothing and deconvolution procedures (H Cren et al [1993] J Chromatogr 615, 23-36). The purpose of this work was to study the constitution of each
isoform by using different
monoclonal antibodies (mabs) raised against PR-A/B (JZB39 and KD68), against PR-B (PR6 and KC 146), and against hsp90 and
hsp70 heat shock proteins (9D2 and Ab72, respectively). The differential recognition of nontransformed
molybdate-stabilized PR
isoforms by either radioligand (RLA, 3H-Org2058) or by an
enzyme immunoassay (PgR-EIA Abbott) showed the presence of two different PR
isoforms in the non-dissociated PR heteropolymeric peak eluted from a TSK-3000 SW column. After PR dissociation by 0.4 M KCl and interaction of PR
isoforms with the different mabs, the presence of PR-A, PR-B, hsp90 and hsp70 was studied. Results showed that hsp90 was present in
isoforms 1 (680 kDa), 2 (600 kDa) and 3 (361 kDa) exclusively, whereas hsp70 remained strongly bound to
isoforms 4 (224 kDa) and 5 (193 kDa).
Isoforms 6 (119 kDa) reacted with PR6 antibody and represented the PR-B
protein, whereas
isoform 7 (88 kDa) represented PR-A
protein.
Isoform 8 (52 kDa) was not detected by mabs and represented a truncated form of PR. Detection of
isoform 1 either by RLA or by EIA showed ratios EIA/RLA approximately 1 or 2, and these values suggested that this heteropolymeric form may contain a dimeric structure. From these observations, a model is proposed for the composition of each PR
isoform obtained from dissociation of
breast tumor PR.