Growth hormone receptor and growth hormone-binding protein messages in mouse placenta contain the exon analogous to human exon 3

Rising maternal circulating GH during murine pregnancy suggests placental regulation

Placenta-derived hormones including growth hormone (GH) in humans contribute to maternal adaptation to pregnancy, and intermittent maternal GH administration increases foetal growth in several species. Both patterns and abundance of circulating GH are important for its activity, but their changes during pregnancy have only been reported in humans and rats. The aim of the present study was to characterise circulating profiles and secretory characteristics of GH in non-pregnant female mice and throughout murine pregnancy. Circulating GH concentrations were measured in whole blood (2 μL) collected every 10 min for 6 h in non-pregnant diestrus female C57Bl/6J mice (n = 9), and pregnant females at day 8.5-9.5 (early pregnancy, n = 8), day 12.5-13.5 (mid-pregnancy, n = 7) and day 17.5 after mating (late pregnancy, n = 7). Kinetics and secretory patterns of GH secretion were determined by deconvolution analysis, while orderliness and regularity of serial GH concentrations were calculated by approximate entropy analysis. Circulating GH was pulsatile in all groups. Mean circulating GH and total and basal GH secretion rates increased markedly from early to mid-pregnancy, and then remained elevated. Pulse frequency and pulsatile GH secretion rate were similar between groups. The irregularity of GH pulses was higher in all pregnant groups than that in non-pregnant mice. Increased circulating GH in murine pregnancy is consistent with an important role for this hormone in maternal adaptation to pregnancy and placental development. The timing of increased basal secretion from mid-pregnancy, concurrent with the formation of the chorioallantoic placenta and initiation of maternal blood flow through it, suggests regulation of pituitary secretion by placenta-derived factors.

Polymorphisms in the growth hormone receptor: A case-control study in breast cancer

The human growth hormone receptor (GHR) mediates the effects of growth hormone (GH1), starting a signalling cascade that is involved in the regulation of proliferation, differentiation and apoptosis. Recently, an isoform of the GHR gene lacking exon 3 (GHRd3) was associated with accelerated responsiveness to growth hormone. In this study, we investigated the association of the GHRd3 polymorphism with breast cancer risk and performed a haplotype analysis with 3 additional single nucleotide polymorphisms (SNPs) (Gly186Gly, Cys440Phe and Ile544Leu) in the GHR coding region in a Polish cohort. We did not observe any effect of the 4 polymorphisms on breast cancer risk. Neither did the 3 most common haplotypes influence breast cancer risk. However, a rare haplotype (dGGC), containing the GHRd3 allele, was associated with a decreased breast cancer risk (OR 0.30, 95% CI 0.11-0.80).

Growth hormone binding protein in normal and aneuploid pregnancy: a paradoxical decrease in trisomy 18

OBJECTIVE

To explore whether abnormalities in growth hormone binding protein (GHBP) may underlie the growth restriction associated with fetal aneuploidy.

DESIGN

A retrospective casecontrol study.

SETTING

Monash Medical Centre. Clayton, Victoria, Australia.

POPULATION

Twenty-one trisomy 18, and 30 trisomy 21 pregnancies, and 170 chromosomally normal pregnancies at 15-18 weeks of gestation representing three to five controls per case matched for source, gestation and duration of storage.

METHODS

GHBP was measured using a ligand immunofunctional assay

RESULTS

In the chromosomally normal pregnancies GHBP levels decreased slightly but significantly across the narrow gestational window studied. Compared with controls, levels of GHBP, expressed as median (95% CI) multiples of the median (MoM). in the trisomy 21 pregnancies were similar, 1.0 (0.92-1.39) MoM and 1.27 (1.04-1.50) MoM, respectively; P = 0.061 (Mann-Whitney U test) but were significantly reduced in the trisomy 18 pregnancies, 0.68 (0.5 1-0.84) MoM: P = 0.0014 (Mann-Whitney U test).

CONCLUSIONS

These data suggest that decreased levels of maternal growth hormone binding protein, and by implication growth hormone receptor complement, may underlie the early severe growth restriction that is characteristic of trisomy 18.

Species-specific alternative splice mimicry at the growth hormone receptor locus revealed by the lineage of retroelements during primate evolution

In humans, growth hormone receptor (GHR) transcripts exist in two isoforms differing by the retention (GHRfl) or exclusion (GHRd3) of exon 3, whereas in mice GHRfl is solely expressed. This species-specific expression pattern is believed to result from an alternative splice event that, on the basis of conflicting data obtained in humans, has been considered to be tissue-, developmentally, and/or individual-specific. To decipher the molecular basis of this unusual trait, we isolated a 6.8-kilobase fragment spanning exon 3 from individuals expressing GHRfl. Sequence analysis revealed the existence of two 99% identical retroelements flanking this exon. Unexpectedly, individuals expressing GHRd3 displayed a 2.7-kilobase deletion involving exon 3, which most likely results from an ancestral homologous recombination between the two retroelements. The lineage of these retroelements during primate evolution revealed the species specificity of the GHRd3 allele. These findings led us to propose a model underlying the existence of the sole GHRfl allele in most species. Such a retrovirus-mediated alternative splice mimicry, which clears up several as yet unexplained phenomena (i.e. the above-mentioned expression data, the Mendelian inheritance of GHR expression patterns, and the deletion of nonconsecutive exons in growth hormone resistant patients), represents a novel physiological mechanism accounting for protein diversity between and within species.

Rat growth hormone receptor/growth hormone-binding protein mRNAs with divergent 5'-untranslated regions are expressed in a tissue-specific manner

In the rat, the growth hormone receptor (GH-R) gene generates two transcripts, one encoding the transmembrane GH-R, and a shorter one encoding the GH-binding protein (GH-BP). These transcripts exhibit a high degree of heterogeneity in their 5'-untranslated regions (5'-UTRs). Some of the exons encoding these 5'-UTR variants may be flanked by distinct promoter regions whose activity would result in the tissue-specific expression of the GH-R gene. To assess this possibility, we used single-sided polymerase chain reaction (PCR) amplification to characterize 5'-UTR variants in rat GH-R cDNAs, and by using 5'-UTR-specific probes, we determined their pattern of expression in several tissues. Besides two previously described variants (V1 and V2), three new 5'-UTR variants were identified, extending 56 nucleotides (V3), 135 nucleotides (V4), and 209 nucleotides (V5) upstream of the ATG translation initiation codon. The expression of GH-R and GH-BP transcripts was clearly tissue specific. In the liver, GH-BP mRNA was the predominant transcript, whereas in other tissues, there was equivalent expression of both transcripts or predominant expression of GH-R mRNA. With respect to the tissue distribution of the 5'-UTR variants in particular, variants V1 and V5 exhibited a pattern of expression closely resembling that seen with an exon 2 probe, with the overall expression of variant V1 being much higher than that of variant V5. The V2 species was exclusively expressed in liver. Variant V3 was expressed at low levels in liver, muscle, heart, and kidney; in muscle and heart, it was preferentially associated with GH-BP transcripts. Variant V4, although present in liver, was more abundant in extrahepatic tissues and predominantly found in GH-R mRNA transcripts. Southern blot analyses were consistent with exon 2 and the exons encoding the V1 and V2 sequences being in proximity, with the other 5'-UTR sequences being encoded by exons located further upstream of exon 2. These findings support the concept that different 5'-UTR variants are the result of the different promoters acting in a tissue-specific manner. The association of specific 5'-UTR variants with either GH-R or GH-BP transcripts raises the possibility that the alternative splicing process that generates GH-BP mRNA in the rat might be controlled by the 5'-flanking region regulating the expression of specific leader exons.