Ke. Friend et al., ESTROGEN REGULATES THE EXPRESSION OF SEVERAL DIFFERENT ESTROGEN-RECEPTOR MESSENGER-RNA ISOFORMS IN RAT PITUITARY, Proceedings of the National Academy of Sciences of the United Statesof America, 92(10), 1995, pp. 4367-4371
A 5.2-kb mRNA band that contains estrogen receptor (ER) sequence and e
xhibits sex- and tissue-specific expression has been identified in rat
pituitary via Northern analysis; this band is composed of at least tw
o distinctive ER mRNA isoforms, This mRNA is expressed in high levels
in female pituitary but is absent in male pituitary and uterus, wherea
s the mRNA encoding the full-length receptor (6.2 kb) is expressed in
all the aforementioned tissues. Estradiol treatment potently induces t
he expression of the 5.2-kb band in the male pituitary. Oligonucleotid
e hybridization and ribonuclease-protection experiments indicate that
the pituitary ER variant is missing exons 1-4. Two corresponding cDNA
clones, truncated estrogen receptor product 1 and 2 (TERP-1 and TERP-2
), were isolated by using the anchored PCR Both sequences contain a 31
-bp segment of specific sequence upstream of exon 5; TERP-2, however,
contains an additional 66 bp of specific sequence between the 31-bp se
gment and exon 5, On Northern analysis, probes complementary to the 31
-bp segment of specific sequence hybridize only to the 5.2-kb band. Im
munoblotting identified several proteins in rat pituitary that could r
epresent the translation products of these or related transcripts. In
summary, several ER isoforms have been identified that exhibit both ti
ssue-specific expression and marked estrogen regulation and differ fro
m full-length receptor by virtue of sequence upstream of the exon 4/5
boundary, Physiologically, the putative proteins encoded by these or s
imilar isoforms might be important modulators of the tissue- and promo
ter-specific effects of estradiol.