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Submitted on August 10, 2005
Accepted on February 9, 2006
Department of Pediatrics, Division of Experimental Medicine, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
* To whom correspondence should be addressed. E-mail: cindy.goodyer{at}muhc.mcgill.ca.
Context: hGH exerts profound effects on adiposity through its specific receptor, hGHR. Eight hGHR mRNAs are produced by the hGHR gene due to splicing from alternate 5'UTR first exons into a common acceptor site upstream of the start codon in exon 2. Four transcripts (V2,V3,V5,V9) are ubiquitously expressed, while the other four (V1,V4,V7,V8) are only expressed in normal postnatal liver, suggesting that different promoter usage is a mechanism for developmental- and tissue-specific regulation of the hGHR gene.
Objective: Because it is unknown if this occurs in adipocytes, we screened human adipocyte cDNA for hGHR mRNAs using 5'RACE.
Results: 89% of the clones were V2-like, 3% were V3-like, and 8% were five new mRNA variants (VA-VE). All new 5'UTR sequences mapped within the hGHR 5'flanking region. RT-PCR assays showed expression in multiple fetal and adult tissues and, thus, they are not adipocyte-specific. We compared expression of hGHR mRNAs in adult liver, adult fat and the human preadipocyte SGBS cell line, using duplex RT-PCR. In liver, V1 and V2 are the major hGHR mRNAs while, in adipose, V2 predominates; VA and VC are expressed at similar lower levels in both. In SGBS preadipocytes, 
70% of hGHR mRNA is V2. During differentiation, total hGHR and V2 transcripts are markedly upregulated (hGHR: 2.3 ± 0.2 fold[M±SE], P < 0.01; V2: 3.0 ± 0.8, P < 0.03), while other variants also increased but remained relatively minor transcripts.
Conclusions: We have identified five new hGHR mRNA variants. Because the V2 transcript is predominant in adipocytes at all developmental stages, the mechanisms regulating its expression should be examined.
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