Bone marrow stromal cells express two distinct splice variants of ER‐α that are regulated by estrogen

Abstract

Estrogen plays a critical role in bone metabolism in both sexes. While the major action of estrogen is to inhibit bone resorption, it is now clear that early osteoblastic (or stromal) cells are a target for estrogen action, mediating the effects of estrogen on bone formation as well as resorption. However, little is known about the expression or regulation of the estrogen receptor (ER)-alpha in these cells. The expression of ER-alpha is regulated by a complex set of promoters and ER-alpha splice variants are present in different tissues. Thus, we sought to define the ER-alpha splice variants and their regulation by estrogen in the mouse bone marrow stromal cell line, ST-2, which can be induced to differentiate into mature osteoblasts. ST-2 cells expressed the mRNAs and proteins for both the 66 and 46 kDa forms of ER-alpha; the latter lacks the AF-1 domain and can transduce estrogen signaling in some tissues, while serving as a dominant negative receptor in others. Using primers specific for each of the five 5'-untranslated exons of ER-alpha, we found that ST-2 cells utilized only the promoters upstream of exons F and C (in contrast to most reproductive tissues, which utilize promoters upstream of virtually all the five exons). Moreover, 17beta-estradiol (10(-8) M) treatment of ST-2 cells markedly diminished levels of the 66 kDa as well as the 46 kDa ER-alpha proteins, largely through suppression of the transcript arising from the F1 promoter. These data thus indicate that: (1) bone marrow stromal cells express at least two variants of ER-alpha and (2) estrogen down regulates the ER-alpha mRNA and protein in these cells.

Alternative promoter usage and alternative splicing of the rat estrogen receptor α gene generate numerous mRNA variants with distinct 5′-ends

“…The same results were observed in four separately prepared samples. and F1 are spliced to exon 2 via internal exons E2 and F2, respectively [22,25]. We therefore speculated that the alternative splicing from untranslated internal exons onto exon 2 might generate rat ER␣ exon 1 mRNA variants.…”

“…(iv) Human and mouse promoters F and F1 yield exon 1 mRNA variants [22,25,26]. In contrast, truncated rat transcripts originate from promoter C, which is entirely unrelated to promoters F and F1 [27].…”

Identification of C-terminally and N-terminally truncated estrogen receptor α variants in the mouse

“…The ORFs of mouse Wild-type ER␣ (ER␣66), exon 1 ER␣ variant (ER␣46) [17], CTERPs and NTERP were cloned into pcDNA3.1/Hygro(+) (Invitrogen) and confirmed by DNA sequencing.…”

Characterization of the fundamental properties of the N-terminal truncation (Δ exon 1) variant of estrogen receptor α in the rat

“…A P b 0.05 was considered significant. exon F1 and an internal exon F2 to exon 2 were described (Sanyal et al, 2005). These lines of evidence indicate that there are also speciesspecific differences in alternative promoter usage and alternative splicing that generate Δ exon 1 ERα variants.…”