Hepatocyte growth factor (HGF) is a multifunctional cytokine that controls the growth and differentiation of various tissues. Previously, we described the existence of a negative cis-acting regulatory element(s) within the ؊1-to ؊0.7-kilobase pair (kb) portion of the 5-flanking region of the mouse HGF promoter. In the present study, we show that the repressor element is located at position ؊872 to ؊860 base pairs and comprises an imperfect estrogen-responsive element 5-AGGTCAGAAAGACCA-3. We demonstrate that chicken ovalbumin upstream promoter transcription factor (COUP-TF), a nuclear orphan receptor belonging to the steroid/thyroid hormone receptor superfamily, through binding to this site effectively silences the transcriptional activity of the HGF promoter. We show that estrogen receptor, on the other hand, relieves the repressive action of COUP-TF, resulting in the induction of the HGF promoter. Using mice transgenic for either 2.7 or 0.7 kb of the HGF promoter region linked to the chloramphenicol acetyltransferase reporter gene, we found that injection of estradiol stimulates HGF promoter activity in tissues such as the mammary gland and ovary of mice harboring 2.7 but not 0.7 kb of the mouse HGF promoter region. Potential involvement of the CCAAT/enhancer-binding protein (C/ EBP) family of transcription factors in the regulation of HGF gene expression is also discussed.

No abstract

Hepatocyte growth factor (HGF) is a pleotropic polypeptide that can function as a morphogen, motogen, mitogen, angiogen, carcinogen, and tumor suppressor, depending on the target cell and tissue. Previous studies from our laboratory using transgenic mice have shown that HGF gene expression is tightly regulated at the transcriptional level and that the upstream regulatory elements are crucial for the control of HGF gene transcription. In the present study, we have identified and characterized one of these elements as a peroxisome proliferator-activated receptor ␥ (PPAR␥)-responsive element. This regulatory element was localized at ؊246 to ؊233 base pairs upstream from the transcription start site of the HGF gene promoter having the sequence GGGCCAGGTGACCT. Gel mobility shift and supershift assays demonstrated that this cis-acting element strongly binds to the PPAR␥ isoforms as well as to chicken ovalbumin upstream promoter-transcription factor, a member of the orphan nuclear receptor subfamily. Mutational analysis and gel mobility band shift assays indicated that the binding site is an inverted repeat of the AGGTCA motif with two spacers (inverted repeat 2 configuration) and that the two spacers are important for PPAR␥ binding. This binding site overlaps with functional binding sites for activating protein-2, nuclear factor 1, and upstream stimulatory factor, and together, they constitute a multifunctional composite binding site through which these different transcription factors exert their regulatory effects on HGF promoter activity. Functional assays revealed that PPAR␥, with its ligand, 15-deoxy-prostaglandin J2, strongly stimulates HGF promoter activity. On the other hand, nuclear factor 1, activating protein-2, and chicken ovalbumin upstream promoter-transcription factor transcription factors repress the stimulatory action of PPAR␥ by competing with PPAR␥ for their overlapping binding sites. Furthermore, for the first time, our studies demonstrate that the PPAR␥ ligand, 15-deoxy-prostaglandin J2, induces endogenous HGF mRNA and protein expression in fibroblasts in culture.

In this study, we have localized an enhancer element in the 5'-¯anking region of the HGF gene promoter and have identi®ed its functional transcriptional factors. Through transient transfection of NIH3T3 ®broblast cells and gel mobility shift assays, the functional binding site was localized to a short region (7318 to 7303 bp from the transcription start site) which has a CTCCC sequence. This motif is also conserved in the human HGF promoter and acts as a binding site for the Sp family of transcription factors. In the presence of NIH3T3 nuclear protein extracts, this enhancer region formed speci®c DNA-protein complexes which were totally abrogated by excess amounts of consensus Sp1 oligonucleotide. In gel mobility supershift assays, antiSp1 and anti-Sp3 antibodies speci®cally recognized these complexes as was evident by their slower migration. Sitespeci®c mutation of this binding motif resulted in total loss of Sp1 and Sp3 binding and a concomitant loss of enhancer function within the context of the HGF promoter. Furthermore, in transient cotransfection assays, overexpression of Sp1 and/or Sp3 stimulated HGF promoter activity independently and additively through binding to the Sp1 binding site in the HGF gene promoter region. DNaseI hypersensitive analysis of freshly isolated nuclei from NIH3T3 cells revealed that ®ve hypersensitive sites (HSS) are present within the 2 kb region immediately upstream of the HGF promoter. One of these sites was mapped to position 70.3 kb from the transcription start site. These data show that both Sp1 and Sp3 transcription factors upregulate HGF promoter activity by binding to the Sp1 binding site at position 7318 to 7303 bp in the HGF gene promoter.

No abstract