The AF-1 activation-function of ERα may be dispensable to mediate the effect of estradiol on endothelial NO production in mice

Two isoforms of estrogen receptor (ER) have been described: ERalpha and ERbeta. The initial gene targeting of ERalpha, consisting in the introduction of a Neo cassette in exon 1 [alphaERKO, hereafter called ERalpha-Neo KO (knockout)], was reported in 1993. More recently, another mouse deficient in ERalpha because of the deletion of exon 2 (ERalphaKO, hereafter called ERalpha-Delta2 KO) was generated. In ovariectomized ERalpha-wild-type mice, estradiol (E-2) increases uterine weight and basal production of endothelial nitric oxide (NO). Both of these effects are abolished in ERalpha-Delta2 KO mice. In contrast, we show here that both of these effects of E2 are partially (uterine weight) or totally (endothelial NO production) preserved in ERalpha-Neo KO. We also confirm the presence of two ERa mRNA splice variants in uterus and aorta from ERalpha-Neo KO mice, One of them encodes a chimeric ERalpha protein (ERalpha55), partially deleted in the A/B domain, that was detected in both uterus and aorta by Western blot analysis. The other ERa mRNA splice variant codes for an isoform deleted for the A/B domain (ERalpha46), which was detected in uterus of ERalpha-Neo KO, and wild-type mice. This protein isoform was not detected in aorta. The identification of these two N-terminal modified isoforms in uterus, and at least one of them in aorta, probably explains the persistence of the E2 effects in ERalphaNeo KO mice. Furthermore, ERa-Neo KO mice may help in the elucidation of the specific functions of full-length ERa (ERalpha66) and ERalpha46, both shown to be physiologically generated in vivo.