A novel isoform of ERa
lane 1; 5 µg septal endothelial lysate
lane 2; 5 µg basilar endothelial lysate
lane 3; 3 µg uterine homogensate
lane 4; 20 ng recombinant ERa protein
lane 5; 200 ng recombinant ERb protein
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The image shows Western blots of rat septal or basilar endothelial lysate, ovarian homogenate, and recombinant human ER proteins. Blots were probed with: (A) anti-N-term ERa (ER21); (B) anti-hinge ERa (SRA-1000); (C) anti C-term ERa (SRA-1010)
The top band represents the classical 67 kDa receptor and the lower band a novel 55kDa isoform. The lighter band is not a breakdown product of the 67 kDa ERa because epitopes in the N-terminus, C-terminus and hinge regions, were all detected. The Western blots eliminate the possibility that this is a shorter transcript arising from translation initiated at the 6th or 7th ATG since the first 21 amino acids (the epitope for ER21) would be missing. The intact epitope in the hinge eliminates the possibility that this is ERΔ4, which is missing the entire hinge region, leaving a previously unreported isoform as the most likely explanation for the lighter band.
