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

Abstract

Two isoforms of estrogen receptor (ER) have been described: ER␣ and ER␤. The initial gene targeting of ER␣, consisting in the introduction of a Neo cassette in exon 1 [␣ERKO, hereafter called ER␣-Neo KO (knockout)], was reported in 1993. More recently, another mouse deficient in ER␣ because of the deletion of exon 2 (ER␣KO, hereafter called ER␣-⌬2 KO) was generated. In ovariectomized ER␣-wild-type mice, estradiol (E2) increases uterine weight and basal production of endothelial nitric oxide (NO). Both of these effects are abolished in ER␣-⌬2 KO mice. In contrast, we show here that both of these effects of E 2 are partially (uterine weight) or totally (endothelial NO production) preserved in ER␣-Neo KO. We also confirm the presence of two ER␣ mRNA splice variants in uterus and aorta from ER␣-Neo KO mice. One of them encodes a chimeric ER␣ protein (ER␣55), partially deleted in the A͞B domain, that was detected in both uterus and aorta by Western blot analysis. The other ER␣ mRNA splice variant codes for an isoform deleted for the A͞B domain (ER␣46), which was detected in uterus of ER␣-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 E 2 effects in ER␣-Neo KO mice. Furthermore, ER␣-Neo KO mice may help in the elucidation of the specific functions of full-length ER␣ (ER␣66) and ER␣46, both shown to be physiologically generated in vivo.

Truncated Estrogen Receptor α 46-kDa Isoform in Human Endothelial Cells

“…[21][22][23] Specifically, expression of alternatively spliced transcripts lacking the AF-1 domain in ␣ERKO mice seems to mediate estrogen-induced endothelial NO production that is absent in the complete knockout. 24 These insights from mouse models suggest that mouse homologs of ⌬1a-hER␣-46 are sufficient to mediate the acute endothelial effects of estrogen and in principle support our observations of the functional effects of hER␣-46 in human endothelial cells, although the 46-kDa truncated ER␣ protein was not readily detected in mouse aortic lysates. 24 Additional studies are required to investigate possible roles for truncated ERs in mediating acute and transcriptional effects of estrogen in human pathophysiology.…”

Down but not out? A novel protein isoform of the estrogen receptor alpha is expressed in the estrogen receptor alpha knockout mouse

“…While the E2 mRNA encodes only the first 41 amino acids of ER , the E1 mRNA encodes a potential ER isoform with a deletion in the B domain containing the AF-1 function. However, the corresponding E1 ER protein has been detected in ERKO tissues only recently (Pendaries et al 2002). The fact that the H222 antibody was originally used to analyze the presence of ER protein isoforms in ERKO uterine tissue by Western blot techniques (Couse et al 1995) might explain the failure to detect the E1 ER isoform which is expressed in ERKO at lower levels than ER in wild type mice.…”

“…This replacement would affect AF-1 transactivation function but not the DNA or ligand binding domain, which contains the AF-2 transactivation function. Such a protein isoform has recently been observed in mouse tissues (Pendaries et al 2002). The discovery of estrogen receptor (ER ) (Kuiper et al 1996) brought another potential explanation of the observed binding activity.…”

Estradiol Promotes Functional Responses in Inflammatory and Steady-State Dendritic Cells through Differential Requirement for Activation Function-1 of Estrogen Receptor α

“…The IRF family members IRF-4 and IRF-8 play critical roles in the development and function of DCs (19,43,44). Although both factors have been shown to exhibit overlapping activity, they also possess DC subset-specific functions (43 (49). GM-CSF-dependent development of DCs depends not only on IRF-4, but also on other transcription factors, such as IRF-2, RelB, an Nf-kB family member, PU.1, Id2, C/EBP-a, C/EBP-b, IRF-8, and SpiB (20,44).…”