Structure and Function of a Human Insulin-like Growth Factor-I Gene Promoter

Abstract

We have identified and characterized a promoter regulatory region for the human insulin-like growth factor-I (IGF-I) gene. The 5'-ends of IGF-I mRNAs were first mapped to a series of sites within a 158-nucleotide portion of exon 1 that was found to be structurally similar to the recently delineated transcription start region of the chicken IGF-I gene. In both species multiple initiation sites are probably a reflection of the absence of typical transcriptional regulatory signals, such as a TATA or CCAAT box, in the proximal promoter, although neither gene sequence resembles a GC-rich housekeeping promoter, which also controls a dispersed initiation region. To test promoter function, hybrid genes were constructed linking human IGF-I DNA to a promoterless reporter plasmid. Fusion genes containing from 385-4300 nucleotides of the IGF-I 5'-flanking region enhanced luciferase activity after transfection into the IGF-I-producing SK-N-MC cell line. A plasmid with 1630 nucleotides of 5'-DNA gave maximal activity and directed accurate initiation of the hybrid gene while the same promoter fragment inserted in the reverse orientation was inert. Although cognate recognition sequences were identified for several transcription factors in the 1630 nucleotides 5' to the transcription start region, no sites were found that resembled the putative GH response element recently mapped to the proximal promoter of the rat Spi2.1 gene.(ABSTRACT TRUNCATED AT 250 WORDS)

AP-1-Like Motif as a Key to Understanding the Insulin-Like Growth Factor I (IGF-I) Gene Regulation.

“…These data suggested that this 5' flanking region of chicken IGF-I functions as a functional gene promoter in vivo. Interestingly, the region surrounding the transcription initiation sites was very highly conserved ('99%) in all species, and the gene promoters were also identified in rat and human IGF-I counterparts afterwards [11,12]. In the regulatory region of the chicken IGF-I gene, we identified several putative cis-active elements as can also be assumed from the literature (Fig.…”

Association between <i>IGF1/Tas</i>I polymorphism and milk traits of Polish Holstein Friesian cows

“…Mature IGF-I is encoded only by parts of exons 3 and 4. Transcripts derived from the exons 1 and 2 are alternately spliced onto exon 3 to generate two mRNA species (class 1 and class 2) and are regulated by distinct promoters (Adamo et al 1991, Kim et al 1991. There is extremely high conservation of both the nucleotide (93 %) and amino acid (96 %) sequences between bovine and human IGF-lA class.…”

An E box in the exon 1 promoter regulates insulin-like growth factor-I expression in differentiating muscle cells

“…The IGF-I630/Luc construct, containing nucleotides Ϫ1630 to ϩ322 of the human IGF-I exon 1 sequence cloned upstream of a luciferase (Luc) reporter gene, was a kind gift from Peter Rotwein (Oregon Health Sciences University, Portland, OR) (18). The IGF-I promoter was subcloned as a PstI fragment into the pGL3-Basic reporter vector (Promega; Southampton, UK), which lacks promoter and enhancer elements, to create pGL1630.…”

“…In particular, core promoter elements responsible for gene expression in a variety of cell types appear to cluster around TSS3 (42). Interestingly, a potential MyoD1-like E box sequence lies ϳ76 nt downstream of the first TSS (TSS1, numbered according to the human sequence) and ϳ62 nt upstream of TSS3, which is also the major TSS used in skeletal muscle (11,18,36). Furthermore, this element and its flanking nucleotides are highly conserved through evolutionary time; thus we hypothesized that this element may have a role in the regulation of IGF-I expression in skeletal muscle.…”