Evaluation of mRNA expression of estrogen receptor β and its isoforms in human normal and neoplastic endometrium

Abstract

Endometrial cancer is well known to be estrogen-dependent. Two estrogen receptor types, ER␣ and ER␤, are major mediators of a diversity of biologic functions of estrogen and play an important role in estrogen-dependent tissues and cancers. Cloning of ER␤ was followed by the discovery of a variety of its isoforms. Using real-time RT-PCR, the relative expression levels of ER␤1, ER␤2 (ER␤cx), ER␤3, ER␤4 and ER␤5 were studied. We observed coexpression of ER␤ isoforms in the endometrium and upregulation of the ER␤5 transcript in malignant endometrium. We also observed downregulation of ER␤2⌬5 transcript in neoplastic endometrium, using a semiquantitative method. Our results suggest that analyzing the changes in ER␤ and its isoforms may be important in the diagnosis, prognosis and treatment of endometrial cancer. © 2004 Wiley-Liss, Inc. Key words: endometrial cancer; real-time RT-PCR; estrogen receptor; isoformsEstrogens exert very powerful effects on the growth, differentiation and function of many target tissues in female and male reproductive organs. Their best-described mechanism of action is through ER-mediated gene transcription. This ligand-activated transcription factor is known to exist as ␣ and ␤ proteins, products of 2 separate genes and multiple splice variants of both, 1-7 present in varying cellular patterns. The above accounts for the high complexity of ER action, which is cell-and tissue-specific and may modulate a specific response to estrogen.Estrogen has long been known to stimulate cellular proliferation in the uterus. Indeed, hyperestrogenism is strictly connected with a major risk of endometrial cancer, 8 which is the most common female genital track malignancy in Europe. 9 ER␣ and ER␤ have been identified in normal and neoplastic endometrium. 10 -13 Yet, no conclusive data regarding alterations in their expression in tumors were obtained, as was the case with breast and ovarian tumors, where the levels of ER␤ decline in invasive breast cancer 7,14 -16 as well as in ovarian 17-20 and colon 21,22 cancers. With the increasing knowledge of the mechanism of steroid receptors, the analysis of isoforms, products of alternative splicing of ER␣ and ER␤, is steadily gaining acceptance as a marker for tumor prognosis and a guide for best choice of treatment. For example, ER␣, which lacks exon 5, has been associated with breast cancer, 23 as have the ER␤ isoforms ER␤2 (also named ER␤cx) and ER␤2⌬5. 24,25 This suggests that changes in transcript levels of the ER isoforms take place during tumorigenesis and are important both in etiology and in the assessment of cancer invasiveness.We evaluated the mRNA expression of all ER␤ isoforms (referred to as "total ER␤") and of ER␤1, ER␤2, ER␤2⌬5, ER␤3, ER␤4 and ER␤5 in normal and neoplastic endometrium. We refer our findings to histopathologic data (FIGO 1988 criteria 26 ) as well as to menstrual status. We also examined expression of ER␣ and compared the expression of 2 estrogen-dependent genes, AR and PR, between normal and tumor tissues. Our aim was to determine ...

Estrogen receptor β transcript variants associate with oncogene expression in endometrial cancer

“…Our study observing elevated ERβ5 mRNA levels in endometrial cancer, particularly in G3 tumors, is in line with the latter study and with reports from breast and prostate tissue (28,30,40). The demonstrated association of ERβ5 and 5 exonskipped isoforms with the oncogene and cell cycle promoter MYBL2 (B-MYB) suggests that these ERβ variants may be involved in tumor growth.…”

“…However, in other studies, expression of ERβ5 was reported to be unchanged or to be elevated in endometrial cancer tissue (30,39). Our study observing elevated ERβ5 mRNA levels in endometrial cancer, particularly in G3 tumors, is in line with the latter study and with reports from breast and prostate tissue (28,30,40).…”

“…ERβ1 was also previously found not to be associated with the depth of myometrial invasion (31). With regard to ERβ2, some reports demonstrated a decline of this variant in endometrial cancer (31), whereas others found this receptor variant not to be altered in endometroid cancer tissue (30). Our results are in line with the latter report and these findings may be supported by the fact that, in contrast to ERβ5, transcript levels of ERβ2 were not associated with proliferation markers.…”

“…Whereas ERβ1 expression has been described to decline in breast and prostate cancer tissue, this effect seems not to be present in endometrial carcinoma (27)(28)(29). In line with previous studies, we did not observe altered ERβ1 transcript levels in endometrial cancer tissue (30,31). ERβ1 was also previously found not to be associated with the depth of myometrial invasion (31).…”

Molecular Biology of Endometrial Carcinoma

“…In addition to the changed ratio of ER isoforms, incorrectly transcribed proteins derived from ERǏ or ERǐ take part in endometrial carcinogenesis. For example, they include 5 ERǏ, which has been described in endometrial carcinoma but has not been detected in normal endometrium, or ER ǐcx with a dominant negative effect on ERǏ (Skrzypczak et al, 2004). The progesterone receptor (PR), also known as NR3C3 (nuclear receptor subfamily 3, group C, member 3), is an intracellular receptor able to specifically bind progesterone.…”