HUMAN LARYNX EXPRESSES ISOFORMS OF THE ESTROGEN-RECEPTOR

Commercially available enzyme immunoassays (EIAs) were used for oestro gen (ER) and progesterone (PR) receptor determination in the cytosol f raction of 118 human larynx cancer specimens and in the corresponding histologically proven non-malignant tissues. Fifty-one ER positive can cerous samples had corresponding non-cancerous tissues also expressing the receptor. A high resolution isoelectric focusing (IEF) technique followed by immunoblotting with the H222 anti-ER monoclonal antibody w as used to evaluate the presence of ER isoforms in the 51 ER positive human larynx cancer specimens and in their corresponding non-malignant tissues. In both tissues, four ER isoforms were detected, with isoele ctric points (pl) similar to those obtained in breast and endometrium carcinomas (6.1, 6.3, 6.6 and 6.8). A significant difference in the ex pression of ER isoforms between cancerous and non-cancerous tissues wa s found; precisely, the 94.1% of the ER positive nonmalignant specimen s co-expressed the four,isoforms, while they were detected in only the 35.3% of the malignant specimens (P < 0.0001 by Fisher's exact test). In larynx cancer, the concentration values of ER and PR did not corre late, nevertheless tumours co-expressing the four ER isoforms had PR l evels significantly higher than those which did not (P = 0.02 by Mann- Whitney-Wilcoxon sum rank test). To investigate the possibility that t he isoforms of the monomeric 4S form of the ER (those with pl 6.3, 6.6 and 6.8) could dimerise, a cold agarose gel electrophoresis technique was used on IEF-separated ER isoforms. In summary, the evidence shows that all the isoforms are able to form homodimers and that the isofor ms at pi 6.3 and 6.8 are able to dimerise with that at pl 6.6 but, und er the same experimental conditions, they do not form the 6.3/6.8 hete rodimer. It was concluded that: (1) the four isoforms of the ER are co -expressed by the non-malignant human larynx and the cancer loses the capacity to express some of them; (2) the complete complement of ER is oforms (all four) is needed for PR expression; (3) the monomeric 4S is oform with pi 6.6 has the capacity to form homo- and heterodimers, whi le the remaining two are only able to homodimerise.