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B Turcotte

Publications and source records attributed to B Turcotte.

24 records · Page 2Linked to original sources
PubMed1988

The N-terminal region of the chicken progesterone receptor specifies target gene activation.

Steroid hormone receptors belong to a family of nuclear receptors that trigger transcriptional activation of target genes by specific binding to DNA recognition sequences, usually located in the 5'-flanking region of the target gene. Nuclear receptors appear to be segmented proteins and extensive structure-function analyses have attempted to elucidate the functional significance of individual segments. Two of these regions have been defined as the domains responsible for recognition of responsive elements of target genes (region C) and hormone binding (region E) (refs 2-7). But the functional significance of the N-terminal region (A/B), which diverges extensively even for a given receptor between different species, has remained obscure. We have previously cloned, expressed and analysed the chicken progesterone receptor (cPR) (ref. 8). This receptor and its human homologue from T47D breast cancer cells are unique among the steroid hormone receptors in that two forms, A and B, are present in equal amounts in cytosolic extracts, the latter having the higher molecular weight. For the chicken progesterone receptor, we have presented evidence suggesting that the cPR form A corresponds to an N-terminally truncated form of B (ref. 8). Here we report on the functional difference between the forms A and B in the transcriptional activation of two target genes.

Animals↗
PubMed1987

The chicken progesterone receptor: sequence, expression and functional analysis.

The complete mRNA sequence of the chicken progesterone receptor (cPR) has been determined. Expression of the cloned cDNA both in vivo and in vitro produces a protein that has the same apparent mol. wt on SDS--polyacrylamide gels as the 'natural' cPR form B (109 kd) as determined by immunoblotting and photoaffinity labelling. When expressed in HeLa or in Cos-1 cells the 'cloned' cPR displays hormone binding characteristics indistinguishable from the 'natural' receptor and, in the presence of progestins, exhibits 'tight nuclear binding'. A protein corresponding in size to the cPR form A (79 kd) could be detected by expressing in vivo and in vitro an N-terminally truncated cPR starting at methionine 128. A protein of the same apparent mol. wt results from internal initiation during in vitro translation. In contrast, such a protein was barely detectable after in vivo expression of the cPR cDNA in Cos-1 cells. These results suggest that form A is generated by an oviduct cell specific process involving either internal initiation of translation and/or proteolysis in the vicinity of methionine-128. The cPR contains two highly conserved regions C and E, a characteristic of the steroid/thyroid hormone receptor supergene family. By expression of a series of cPR deletion mutants, region E could be defined as the hormone binding domain whereas region C is indispensable for the tight nuclear association of the progestin-receptor complex. In the presence of progestins, the cloned cPR efficiently trans-activates transcription from the long terminal repeat region (LTR) of the mouse mammary tumor virus (MMTV). Deletion of the entire N-terminal region A/B or of the hormone binding domain E results in a 100-fold reduction of transcriptional activation. No stimulation of transcription can be detected when the C-terminal deletion extends into region C, indicating that this region is involved in the recognition of the hormone responsive element (HRE) of the MMTV LTR.

Amino Acid Sequence↗
PubMed1986

DNase I hypersensitivity and methylation of the 5'-flanking region of the alpha 1-fetoprotein gene during developmental and glucocorticoid-induced repression of its activity in rat liver.

Three major regions of DNase I hypersensitivity (DH) were found in alpha 1-fetoprotein (AFP) chromatin of rat liver. DH site I is located at the transcription initiation site and associated with ongoing AFP transcription. DH site II is located 2.5 kb upstream from the cap site: it is developmental stage-dependent but dissociable from ongoing AFP transcription. DH site III, 3.7 kb upstream from the cap site, behaves as hepatocyte-constitutive. DH sites are present in similar regions of liver albumin chromatin. Dexamethasone-induced AFP gene repression is accompanied by the selective loss of AFP DH site I, a likely result of glucocorticoid receptors binding to a DNA recognition sequence located 5'-adjacent to DH site I. Sl nuclease-hypersensitive sites were found on naked superhelical AFP and albumin DNA, but do not appear to contribute DH sites in liver chromatin. The extent of hypomethylation of HpaII sites at the 5'-end of the AFP gene correlates positively with the level of potential and actual expression of the gene. We conclude that developmental and hormonal regulation of the AFP gene is confined within congruent to 4 kb of 5'-flanking DNA, and we discuss possible hierarchical interactions among DH sites, in relation to DNA methylation and replication.

Aging↗
PubMed1985

Rat alpha 1-fetoprotein messenger RNA: 5'-end sequence and glucocorticoid-suppressed liver transcription in an improved nuclear run-off assay.

Cloned cDNA fragments spanning nearly the entire coding regions of rat AFP and albumin genes were used in liver nuclear run-off assays. Under standard assay conditions, transcription signals detected with 5' probes were systematically stronger than with 3' probes. Heparin eliminated this phenomenon, which suggests that nuclear run-off assays are subject to in vitro reinitiation occurring preferentially in promoter gene regions. Transcription in the presence of heparin indicates that very few polymerases are engaged on the AFP gene in adult rat liver. Dexamethasone treatment of developing rat liver results in the loss of transcribing polymerases from all regions of the AFP gene. Albumin gene transcription is unaffected. Inhibition of liver protein synthesis with cycloheximide does not modify the AFP gene suppressive action of dexamethasone. Glucocorticoid hormone receptors may thus directly interact with the AFP locus, blocking polymerase initiation. We also report the sequence analysis of rat AFP mRNA, which reveals the existence of two potential initiation codons on this molecule.

Albumins↗