Molecular genetic analysis of a human insulin‐like growth factor 1 promoter P1 variation

Abstract

Insulin-like growth factor 1 (IGF1) exerts important endocrine and paracrine functions in the cardiovascular system. We identified the common variant -1411C>T in the IGF1 upstream promoter P1, located within several overlapping transcription factor binding sites. Using transient transfection assays, we identified this site as a functional enhancer. The T allele-carrying enhancer, compared with the C allelic portion, exerts significantly reduced or even abrogated activity, respectively, in SaOs-2 and HepG2 (all P<0.0001) as well as in differentiated THP-1 macrophages. Electrophoretic mobility shift assay and subsequent supershift experiments in HepG2 identified c-Jun as the binding partner exclusively to the T allele, whereas CCAAT/enhancer-binding protein delta and interferon consensus site-binding protein/interferon-regulating factor 8 interacted only with the C allelic promoter portion. Furthermore, genotyping in a case-control study for essential hypertension (n=745 hypertensive patients; n=769 normotensive control subjects) for this variant revealed an odds ratio for hypertension of 0.73 (95% confidence interval 0.58-0.91, P=0.006) associated with the T allele, and normotensive subjects carrying the protective T allele displayed a significant decrease in diastolic (P=0.036) and systolic (P=0.024) blood pressure levels. We here report detection of a functional enhancer module in the upstream IGF1 promoter region, which might play a key role in local IGF1 bioavailability. Whether -1411C>T is also associated with other IGF1-related disease phenotypes should be evaluated further in population studies.

Dendritic cell-mediated survival signals in Eμ-Myc B-cell lymphoma depend on the transcription factor C/EBPβ

“…We conclude that transcriptional activators other than C/EBPb could contribute to IGF-1 transcriptional regulation, depending on tumour-imposed stress conditions. Indeed, several other transcription factors were shown to activate IGF-1 transcription in diverse cell types, including Stat5 in hepatocytes and putatively in DCs [47][48][49] , C/EBPd in osteoblasts and putatively DCs 50 , and IRF8 in hepatocytes 51 . When IGF-1 and other potentially B-cell growth-promoting cytokines were tested in a DC-independent cell culture, gain of viability between the Em-Myc lymphoma B-cell clones varied substantially.…”

Identification and Functional Analyses of Molecular Haplotypes of the Human Osteoprotegerin Gene Promoter

“…Cis-active elements exert transcriptional activity by interaction with TFs that assemble at the promoter as modules, 25 the composition of an individual module being cell type-and context-specific. For OPG, we propose a hypothetical transcriptional module ( Figure 6B): (I) Sp1, NF-1, and NF-B bind to the MolHap portion, and interact with Egr1 (Ϫ159T allele) to cooperatively stimulate transcription; (II) The Ϫ159C allele leads to a loss of the TFBS for Egr1, the transcriptional module is altered and transcriptional activity is decreased; (III) Truncation leads to a loss of TFBS for Sp1, NF-1, and NFB, whereas Egr1 alone seems to act as a repressor; (IV) Introduction of the Ϫ159C allele into the truncated constructs results in a partial restoration of transcriptional activity.…”

The mechanism of transactivation regulation due to polymorphic short tandem repeats (STRs) using IGF1 promoter as a model

“…It has been reported that a C/EBPD transcription activation complex binds exclusively to the C allele of rs35767 to activate IGF1 promoter activity33. To test whether the C allele is responsible for the promoter activation ability of the 125-bp segment and the length effect of the microsatellite, we mutated haplotype C-T-T to haplotype T-T-T in all of the promoter fragments and examined for their gradational transactivation properties as a function of microsatellite repeat length.…”

“…A transcriptional activator C/EBPD complex binds exclusively to the C allele of this SNP and activates promoter transcriptional activity33. Moreover, genome-wide association studies and epidemiologic studies have consistently demonstrated a significant association between this SNP and circulating IGF1 levels or IGF1-related phenotypes4142434445.…”

“…SNP rs35767 located in the 125-bp segment, is a recognized functional SNP33. A transcriptional activator C/EBPD complex binds exclusively to the C allele of this SNP and activates promoter transcriptional activity33.…”