The human estrogen receptor-alpha isoform hERalpha46 antagonizes the proliferative influence of hERalpha66 in MCF7 breast cancer cells.

The expression of two human estrogen receptor-alpha (hERalpha) isoforms has been characterized within estrogen receptor-alpha-positive breast cancer cell lines such as MCF7: the full-length hERalpha66 and the N terminally deleted hERalpha46, which is devoid of activation function (AF)-1. Although hERalpha66 is known to mediate the mitogenic effects that estrogens have on MCF7 cells, the exact function of hERalpha46 in these cells remains undefined. Here we show that, during MCF7 cell growth, hERalpha46 is mainly expressed in the nucleus at relatively low levels, whereas hERalpha66 accumulates in the nucleus.

Evidence for two distinct functional glucocorticoid receptors in teleost fish.

Using RT-PCR with degenerated primers followed by screening of a rainbow trout (Oncorhynchus mykiss) intestinal cDNA library, we have isolated from the rainbow trout a new corticosteroid receptor which shows high sequence homology with other glucocorticoid receptors (GRs), but is clearly different from the previous trout GR (named rtGR1). Phylogenetic analysis of these two sequences and other GRs known in mammals, amphibians and fishes indicate that the GR duplication is probably common to most teleost fish. The open reading frame of this new trout GR (named rtGR2) encodes a protein of 669 amino acids and in vitro translation produces a protein of 80 kDa that appears clearly different from rtGR1 protein (88 kDa).

Peptide insertion in the DNA-binding domain of fish glucocorticoid receptor is encoded by an additional exon and confers particular functional properties.

The trout glucocorticoid receptor (rtGR) contains an additional sequence of nine amino acids located between the two zinc fingers of the DNA-binding domain (DBD) (Endocrinology 136 (1995) 3774). Polymerase chain reaction on trout genomic DNA and sequencing were performed in the DBD region, demonstrating that this peptide is encoded by an additional exon of 27 nucleotides between the two exons encoding the two zinc fingers of other nuclear receptors. This additional sequence in the rtGR confers a better binding affinity of the receptor to a single GRE, as shown by gel shift experiments with GST-DBDrtGR fusion proteins, deleted or not of the nine amino acids (Delta9).

The glucocorticoid receptor represses the positive autoregulation of the trout estrogen receptor gene by preventing the enhancer effect of a C/EBPbeta-like protein.

Stress and cortisol are known to have negative effects on vitellogenesis in oviparous species. This provides a physiological context in which to explore in more detail the molecular mechanisms involved in transcriptional interferences between two steroids receptors, the estradiol receptor (ER) and the glucocorticoid receptor (GR). We have previously shown that the cortisol inhibitory effect on rainbow trout (rt) vitellogenesis is the result of a repression of the estradiol-induced ER-positive autoregulation by activated GR.

Glucocorticoid-induced glucose release is abolished in trout hepatocytes with elevated hsp70 content.

The metabolic potential of cells with elevated heat shock protein 70 (hsp70) content was examined by measuring unstimulated and glucocorticoid-stimulated glucose release in trout hepatocytes maintained in primary culture. Exposure of hepatocytes to either heat shock (HS;+15 degrees C) or sodium arsenite (50 microM) did not affect cell viability, but resulted in significantly higher hsp70 levels over a 24 h recovery period. Hsp70 accumulation had no significant impact on unstimulated glucose release, but completely abolished cortisol-induced glucose release in trout hepatocytes.