Estrogen receptor variants ERdelta5 and ERdelta7 down-regulate wild-type estrogen receptor activity

Estrogen receptor alpha isoform ERdelta7 in myometrium modulates uterine quiescence during pregnancy

BACKGROUND

Circulating estrogen (E2) levels are high throughout pregnancy and increase towards term, however its local tissue specific actions vary across gestation. For example, myometrial E2 regulated uterotonic action is disabled until term, whereas it's proliferative function is maintained in the breast. We have identified gestationally regulated splicing events, mediated by hnRNPG and modulated by E2 that generate alternatively spliced estrogen receptor alpha (ERα) variants (ERΔ7 and ERα46) in the myometrium. These variants allow for differential, gestationally regulated, modulation of the uterotonic action of E2.

METHODS

Human myometrium isolated from preterm and term non-laboring and laboring pregnant women were analyzed for ERα isoforms and splice factor levels. Lentiviral mediated shRNA knockdown of hnRNPG and overexpression of ERΔ7 were performed in human myometrial (hTERT-HM) cells. Functional 3D collagen contraction assays were executed.

FINDINGS

ERΔ7 acts as a dominant negative repressor of the uterotonic action of ERα66 and ERα46 isoforms through the regulation of the myometrial gap junction protein GJA1. Elimination of hnRNPG inhibits the generation of ERΔ7 while overexpression of ERΔ7 inhibited GJA1 expression. Moreover in vivo human myometrial hnRNPG levels decline at term in an E2 dependent manner resulting in a withdrawal of ERΔ7 levels and its tocolytic action at term.

INTERPRETATION

Our findings implicate the unique role of ERΔ7 as a modulator of myometrial quiescence and define the mechanism of ERΔ7 generation, through hormonally regulated splicing events. FUND: This study was supported by NIH OPRU U01 supplement (HD047905), University of Pittsburgh and Wayne State University Perinatal Research Initiative (USA).

Transcriptional interaction of an estrogen receptor splice variant and ErbB4 suggests convergence in gene susceptibility pathways in schizophrenia

Mounting evidence from clinical and basic research suggests that estrogen signaling may be altered in the brains of people with schizophrenia. Previously, we found that DNA sequence variation in the estrogen receptor (ER) alpha gene, lower ERalpha mRNA levels, and/or blunted ERalpha signaling is associated with schizophrenia. In this study, we asked whether the naturally occurring truncated ERalpha isoform, Delta7, which acts as a dominant negative, can attenuate gene expression induced by the wild-type (WT) receptor in an estrogen-dependent manner in neuronal (SHSY5Y) and non-neuronal (CHOK1 and HeLa) cells. In addition, we determined the extent to which ERalpha interacts with NRG1-ErbB4, a leading schizophrenia susceptibility pathway. Reductions in the transcriptionally active form of ErbB4 comprising the intracytoplasmic domain (ErbB4-ICD) have been found in schizophrenia, and we hypothesized that ERalpha and ErbB4 may converge to control gene expression. In the present study, we show that truncated Delta7-ERalpha attenuates WT-ERalpha-driven gene expression across a wide range of estrogen concentrations in cells that express functional ERalpha at base line or upon co-transfection of full-length ERalpha. Furthermore, we find that ErbB4-ICD can potentiate the transcriptional activity of WT-ERalpha at EREs in two cell lines and that this potentiation effect is abolished by the presence of Delta7-ERalpha. Immunofluorescence microscopy revealed nuclear co-localization of WT-ERalpha, Delta7-ERalpha, and ErbB4-ICD, whereas immunoprecipitation assays showed direct interaction. Our findings demonstrate convergence between ERalpha and ErbB4-ICD in the transcriptional control of ERalpha-target gene expression and suggest that this may represent a convergent pathway that may be disrupted in schizophrenia.

Pathology of borderline HER-2/neu breast carcinoma: a biologically distinct phenotype

PURPOSE

The significance of HER-2/neu results obtained by immunohistochemical analyses (IHC) which are neither negative nor strongly positive is controversial. The incidence of fluorescence in situ hybridization (FISH) positivity in these tumors is small and the implication is that these borderline results represent laboratory misclassification. We analyzed the tumor characteristics of these HER-2/neu borderline tumors to determine if they represent a unique tumor type.

METHODS

HER-2/neu status was determined by image analysis (IA) of IHC sections in 669 cases of invasive breast cancer. Borderline cases were reflexed to FISH to determine gene status. HER-2/neu results were compared to tumor morphology and other tumor markers.

RESULTS

HER-2/neu was negative, borderline and positive in 69.5, 15.8, and 14.6% of cases, respectively. HER-2/neu amplification was present in 17.3% of borderline cases. The borderline group is significantly different from the HER-2/neu positive group for all parameters studied except Ki-67. Compared to the HER-2/neu negative group, the borderline group showed a significantly higher HER-2/neu gene copy number and a trend towards lower progesterone receptor expression (p=0.058). Compared to the HER-2/neu negative group, the HER-2/neu borderline/FISH-negative group showed significantly lower PR expression. Compared to the HER-2/neu positive group, the HER-2/neu borderline/FISH positive group showed significant differences with multiple parameters.

CONCLUSION

Borderline HER-2/neu tumors are a unique tumor type and do not represent laboratory imprecision. Hormone receptor alterations are associated with early changes in HER-2/neu expression. While IA is capable of detecting these changes, current FISH methodology is not.

Clinical significance of the quantitative assessment of the cytosolic concentration of HER-2/neu protein in breast cancer by immunoenzymatic assay (ELISA)

PURPOSE

Retrospective analysis to assess the prognostic and predictive value of HER-2/ neu expression in breast tumors, quantified by enzyme immunoassay (ELISA).

METHODS

Quantification of HER-2/neu was performed on cytosolic extracts from 914 cases of primary invasive breast carcinomas. Relapse-free and overall survival data were available from 889 patients. The prognostic value of HER-2/neu levels was assessed considering them as a continuous, dichotomic or quartile variable.

RESULTS

Cytosolic HER-2/neu levels ranged widely in breast carcinomas (median: 746.5 NHU/mg; range: 2.8-80,000 NHU/mg protein). HER-2/neu protein levels were significantly higher in either moderately or poorly differentiated tumors, as well as in those showing a ductal histological type, aneuploidy or a high S-phase fraction. There was a significant and positive association between cytosolic and membranous HER-2/neu levels (n=162, r sub S=0.53; P<0.0001). In addition, cytosolic HER-2/neu level correlated weakly with progesterone receptors but not with estrogen receptors. Elevated cytosolic HER-2/neu levels (> or =1,400 NHU/mg protein) were associated with a high probability of both shortened relapse-free survival and overall survival. This same cut-off value was obtained when we divided the overall group of patients in a training set. However, this HER-2/neu value did not achieve any statistical significance in a validation set used to make sure that the cut-off was correct. Nevertheless, when we divided the obtained data into three different groups with respect to the quartile values (Q) of the intratumoral oncoprotein levels (< or = Q1 vs Q1-Q2 vs > Q3), we observed that patients with either low HER-2/ neu levels (< or = Q1) or high HER-2/neu levels (> Q3) had shorter both relapse-free survival and overall survival curves than those patients with intermediate HER-2/neu levels. On the other hand, high HER-2/neu levels predicted a poor response to adjuvant chemotherapy but not to adjuvant hormonal therapy with tamoxifen.

CONCLUSIONS

The results of the present investigation indicate that by quantitatively determining the content of HER-2/neu oncoprotein, groups of high-risk breast cancer patients could be identified, for a more effective clinical management.

Expression of estrogen receptor alpha exon-deleted mRNA variants in the human and non-human primate frontal cortex

Although estrogen receptor alpha (ERalpha) mRNA has been detected in the primate frontal cortex, the types of ERalpha transcripts expressed, including exon-deleted variants (Delta), have not been determined in the monkey or human frontal cortex. Because the types of ERalpha mRNA expressed in brain could define neuronal responses to estrogens, we examined the transcript pool of ERalpha mRNAs expressed in normal adult and developing human and macaque frontal cortex. We reverse transcribed total RNA from the postmortem frontal cortex of 29 normal adult humans, 12 rhesus macaques, and 19 people ranging from infants to adults and employed two rounds of nested polymerase chain reaction (PCR) to generate ERalpha products spanning the coding domain. In a third nested PCR, we used primers specific for novel sequences of exon-exon junctions created when whole exons are missing. By sequencing PCR products, we detected 60 instances of 12 distinct DeltaERalpha mRNAs in adult humans and 94 instances of 13 distinct DeltaERalpha mRNAs in monkeys in differing patterns from one individual to another. In adult humans, 83% of individuals expressed at least 1 DeltaERalpha mRNA variant, and 100% of the monkeys expressed at least 1 DeltaERalpha mRNA variant. The single Delta2, Delta5, and Delta7 variants were frequently expressed in both human and monkey frontal cortex, Delta3 variants were rare in both species, and Delta6 variants were more frequently expressed in monkeys. In both species, we detected double, triple and quadruple Deltas, but these were less common than single Deltas. The pattern of human variant expression did not appear to change dramatically as a function of age. These findings imply the potential to produce different ERalpha proteins in frontal cortex, possibly with altered structure and function which may have physiological relevance for gene transcription by virtue of altered functional interactions with each other, other steroid hormone receptors, and genomic DNA.

The naturally occurring variant of estrogen receptor (ER) ERDeltaE7 suppresses estrogen-dependent transcriptional activation by both wild-type ERalpha and ERbeta

We have isolated and functionally characterized the exon 7-skipped variant (ERDeltaE7) of estrogen receptor (ER)alpha, which has emerged as the predominant variant expressed in multiple normal and tumoral tissues. However, to date no function has been established for this variant in mammalian cells. ERDeltaE7 exhibits a negligible ability to bind ligands, insensitivity to allosteric modulation by estrogen and antiestrogens, and loss of estrogen-dependent interaction with p160 coactivators such as SRC-1 and AIB1. ERDeltaE7 is able to form heterodimers with both ERalpha and ERbeta in a ligand-independent manner. Transient expression experiments in HeLa cells show that increasing amounts of ERDeltaE7 result in a progressive inhibition of the estrogen-dependent transcriptional activation by both wild-type ERalpha and ERbeta on estrogen response element-driven promoters. The inhibitory effect of ERDeltaE7 is due to the inhibition of binding of wild-type receptors to their responsive elements. Surprisingly, the activation function (AF)-1-dependent transactivation triggered by epithelial growth factor and phorbol-12-myristate-13-acetate is also abolished in ERDeltaE7 despite AF1 integrity, suggesting a cross-talk between AF1 and AF2 regions of the receptor. These results indicate that the naturally occurring variant ERDeltaE7 is a dominant negative receptor that, when expressed at high levels relative to wild-type ERs, might have profound effects on several estrogen-dependent functions.

Quantitative association between HER-2/neu and steroid hormone receptors in hormone receptor-positive primary breast cancer

BACKGROUND

HER-2/neu, which encodes a receptor tyrosine kinase, is amplified and overexpressed in 20%-25% of human breast cancers. Such tumors are often resistant to hormone therapy. Despite a general inverse association between HER-2/neu amplification/overexpression and estrogen receptor (ER) and/or progesterone receptor (PR) expression, a fraction of patients are both HER-2/neu- and hormone receptor (HR)-positive. The efficacy of hormone therapy in this group is currently a matter of debate. To better understand the relationship between HER-2/neu positivity and HR expression, we analyzed HER-2/neu, ER, and PR as continuous variables in breast cancer cell lines and two cohorts of primary breast cancer patients.

METHODS

HER-2/neu and ER/PR expression was analyzed by enzyme-linked immunosorbent assay (ELISA) and enzyme immunoassay (EIA), respectively, in 14 human breast cancer cell lines, some of which had been transfected with the HER-2/neu gene. For the clinical study population, HER-2/neu protein levels were assessed by ELISA (cohort A, n = 665), and HER-2/neu gene copy number was determined using fluorescence in situ hybridization (cohort B, n = 894). ER/PR expression was analyzed by EIA (cohort A) or radioligand binding (cohort B). Associations between HER-2/neu and ER/PR expression were analyzed using Spearman's rho correlation and the chi-square test, and absolute levels were compared using the Mann-Whitney U test. All statistical tests were two-sided.

RESULTS

HR-positive human breast cancer cell lines transfected with the HER-2/neu gene expressed statistically significantly lower levels of ER and PR than parental lines. In the clinical cohorts, levels of HER-2/neu overexpression and gene amplification were inversely correlated with ER/PR levels (Cohort A [n = 112]: for ER, r = -0.34, P<.001; for PR, r = -0.24, P =.010. Cohort B [n = 188]: for ER, r = -0.39, P<.001; for PR, r = -0.26, P<.001). Among patients with HR-positive tumors, HER-2/neu-positive tumors had statistically significantly lower ER/PR levels than HER-2/neu-negative ones (Cohort A: for ER, median = 25 fmol/mg [interquartile range [IQR] = 13-78] versus median = 38.5 fmol/mg [IQR = 17-99] and P =.031; for PR, median = 35 fmol/mg [IQR = 12-119] versus median = 88.5 fmol/mg [IQR = 22-236] and P<.001. Cohort B: for ER, median = 44 fmol/mg [IQR = 13-156] versus median = 92 fmol/mg [IQR = 35-235] and P<.001; for PR, median = 36 fmol/mg [IQR = 13-108] versus median = 84 fmol/mg [IQR = 24-250] and P<.001). Patients with higher levels of HER-2/neu overexpression or amplification had statistically significantly lower levels of ER/PR than patients with lower levels of HER-2/neu overexpression or amplification.

CONCLUSION

Because absolute HR levels are strongly related to response to hormone therapy in primary and advanced breast cancer, reduced ER/PR expression may be one mechanism to explain the relative resistance of HER-2/neu-positive:HR-positive tumors to hormone therapy.

Progesterone receptor mRNA variant containing novel exon insertions between exon 4 and exon 5 in human uterine endometrium

The presence of human progesterone receptor (PR) mRNA variants has been demonstrated in uterine endometrium and breast tissues as well as in cancer cells of these tissues. While exon deletions by the alternative splicing in these variants have been reported, there are few reports available on the PR mRNA variants with exon insertion. In the present study, we attempted to detect a PR mRNA variant containing the exon insertions in normal uterine endometrium. Endometrial tissues were subjected to reverse transcription-polymerase chain reaction (RT-PCR) with PCR primers which were located in exons 3 and 8. Analysis of the RT-PCR products revealed the presence of a novel PR mRNA variant which contained a 232 bp inserted nucleotide sequence between exons 4 and 5. We termed this transcript the "i45 PR mRNA variant". Genomic analysis indicated that the inserted sequence was derived from two novel independent exons of 123 bp and 109 bp, termed "exon i45a" and "exon i45b", respectively, which are located between exons 4 and 5 of the human PR gene. The i45 PR mRNA variant was further detected in uterine endometrial cancer tissues as well as in the normal uterine endometrium. These results demonstrate the presence of a novel PR mRNA variant with exon insertions in the human tissue for the first time. The i45 PR variant protein, possibly transcribed from this i45 PR mRNA variant, may play physiological and/or pathological roles in the human uterine endometrium.