The upstream regulatory regions of the hepatocyte growth factor gene promoter are essential for its expression in transgenic mice

Genomic instability causes HGF gene activation in colon cancer cells, promoting their resistance to necroptosis

BACKGROUND & AIMS

Genomic instability promotes colon carcinogenesis by inducing genetic mutations, but not all genes affected by this process have been identified. We investigated whether genomic instability in human colorectal cancer (CRC) cells produces mutations in the hepatocyte growth factor (HGF) gene.

METHODS

We genotyped human colon tumor tissues and adjacent nontumor tissues collected from 78 patients University of Pittsburgh Health Sciences and Veterans Hospital, along with 40 human CRC and adjacent nontumor tissues in a commercial microarray. We used cellular, biochemical, and molecular biological techniques to investigate the factors that alter HGF signaling in colon cancer cells and its effects on cell proliferation and survival.

RESULTS

All tested human CRC tissues and cell lines that had microsatellite instability contained truncations in the regulatory deoxyadenosine tract element (DATE) of the HGF gene promoter. The DATE was unstable in 14% (11 of 78) of CRC samples; DATE truncation was also polymorphic and detected in 18% (13 of 78) of CRC tissues without microsatellite instability. In CRC cell lines, truncation of DATE activated expression of HGF, resulting in its autocrine signaling via MET. This promoted cell proliferation and resistance to necroptosis. HGF signaling via MET reduced levels of the receptor-interacting serine-threonine kinase 1, a mediator of necroptosis, in CRC cells. High levels of HGF protein in tumor tissues correlated with lower levels of receptor-interacting serine-threonine kinase 1 and shorter survival times of patients.

CONCLUSIONS

Thirty-one percent of CRC samples contain alterations in the DATE of the HGF promoter. Disruption of the DATE increased HGF signaling via MET and reduced levels of receptor-interacting serine-threonine kinase 1 and CRC cell necroptosis. DATE alteration might be used as a prognostic factor or to select patients for therapies that target HGF-MET signaling.

Hepatocyte Growth Factor Isoforms in Tissue Repair, Cancer, and Fibrotic Remodeling

Hepatocyte growth factor (HGF), also known as scatter factor (SF), is a pleotropic factor required for normal organ development during embryogenesis. In the adult, basal expression of HGF maintains tissue homeostasis and is up-regulated in response to tissue injury. HGF expression is necessary for the proliferation, migration, and survival of epithelial and endothelial cells involved in tissue repair in a variety of organs, including heart, lung, kidney, liver, brain, and skin. The administration of full length HGF, either as a protein or using exogenous expression methodologies, increases tissue repair in animal models of tissue injury and increases angiogenesis. Full length HGF is comprised of an N-terminal hairpin turn, four kringle domains, and a serine protease-like domain. Several naturally occurring alternatively spliced isoforms of HGF were also identified. The NK1 variant contains the N-terminal hairpin and the first kringle domain, and the NK2 variant extends through the second kringle domain. These alternatively spliced forms of HGF activate the same receptor, MET, but they differ from the full length protein in their cellular activities and their biological functions. Here, we review the species-specific expression of the HGF isoforms, their regulation, the signal transduction pathways they activate, and their biological activities.

Regulation of hepatocyte growth factor expression by NF-κB and PPARγ in adipose tissue

Hepatocyte growth factor (HGF) is expressed as an angiogenic factor in adipose tissue. However, the molecular mechanism of Hgf expression remains largely unknown in the tissue. We addressed the issue by studying Hgf expression in adipocytes and macrophages. Hgf was expressed more in the stromal-vascular fraction than the adipocyte fraction. The expression was fivefold more in macrophages than the stromal-vascular faction and was reduced by 50% after macrophage deletion in adipose tissue. The expression was reduced by differentiation in adipocytes and by tumor necrosis factor-α or lipopolysaccharide treatment in macrophages. The expression was suppressed by nuclear factor (NF)-κB in C57BL/6 mice with NF-κB p65 overexpression under the aP2 gene promoter (aP2-p65 mice) but enhanced by inactivation of NF-κB p65 in mouse embryonic fibroblasts. The Hgf gene promoter was suppressed by p65 overexpression, which blocked peroxisome proliferator-activated receptor-γ (PPARγ) interaction with RNA polymerase II. The p65 activity was abolished by knockdown of histone deacetylase 3. Hgf expression was upregulated by hypoxia in vitro and in vivo. Compared with vascular endothelial growth factor (Vegf), which was predominately expressed in mature adipocytes, Hgf was mainly expressed in nonadipocytes, suggesting that Hgf and Vegf may have different cell sources in adipose tissue. In mechanism, Hgf expression is inhibited by NF-κB through suppression of PPARγ function in the Hgf gene promoter. Both Hgf and Vegf are induced by hypoxia. The study provides a molecular mechanism for the difference of inflammation and hypoxia in the regulation of angiogenic factors.

Hepatocyte-specific deletion of farnesoid X receptor delays but does not inhibit liver regeneration after partial hepatectomy in mice

Farnesoid X receptor (FXR), the primary bile acid-sensing nuclear receptor, also plays a role in the stimulation of liver regeneration. Whole body deletion of FXR results in significant inhibition of liver regeneration after partial hepatectomy (PHX). FXR is expressed in the liver and intestines, and recent reports indicate that FXR regulates a distinct set of genes in a tissue-specific manner. These data raise a question about the relative contribution of hepatic and intestinal FXR in the regulation of liver regeneration. We studied liver regeneration after PHX in hepatocyte-specific FXR knockout (hepFXR-KO) mice over a time course of 0-14 days. Whereas the overall kinetics of liver regrowth in hepFXR-KO mice was unaffected, a delay in peak hepatocyte proliferation from day 2 to day 3 after PHX was observed in hepFXR-KO mice compared with Cre(-) control mice. Real-time polymerase chain reaction, western blot and co-immunoprecipitation studies revealed decreased cyclin D1 expression and decreased association of cyclin D1 with CDK4 in hepFXR-KO mice after PHX, correlating with decreased phosphorylation of the Rb protein and delayed cell proliferation in the hepFXR-KO livers. The hepFXR-KO mice also exhibited delay in acute hepatic fat accumulation following PHX, which is associated with regulation of cell cycle. Further, a significant delay in hepatocyte growth factor-initiated signaling, including the AKT, c-myc, and extracellular signal-regulated kinase 1/2 pathways, was observed in hepFXR-KO mice. Ultraperformance liquid chromatography/mass spectroscopy analysis of hepatic bile acids indicated no difference in levels of bile acids in hepFXR-KO and control mice.

CONCLUSION

Deletion of hepatic FXR did not completely inhibit but delays liver regeneration after PHX secondary to delayed cyclin D1 activation.

Somatic mutation and functional polymorphism of a novel regulatory element in the HGF gene promoter causes its aberrant expression in human breast cancer

The HGF gene is transcriptionally silenced in normal differentiated breast epithelial cells, but its repression fails to occur in mammary carcinoma tissues and cell lines. The molecular mechanisms underpinning aberrant HGF expression in breast cancer cells are unknown. Here we report the discovery of a DNA element located 750 bp upstream from the transcription start site in the human HGF promoter that acts as a transcriptional repressor and is a target of deletion mutagenesis in human breast cancer cells and tissues. This HGF promoter element consists of a mononucleotide repeat of 30 deoxyadenosines (30As), which we have termed "deoxyadenosine tract element" (DATE). Functional studies revealed that truncation mutations within DATE have profound local and global effects on the HGF promoter region by modulating chromatin structure and DNA-protein interactions, leading to constitutive activation of the HGF promoter in human breast carcinoma cell lines. We found that 51% of African Americans and 15% of individuals of mixed European descent with breast cancer harbor a truncated DATE variant (25As or fewer) in their breast tumors and that the truncated allele is associated with cancer incidence and aberrant HGF expression. Notably, breast cancer patients with the truncated DATE variant are substantially younger than those with a wild-type genotype. We also suggest that DATE may be used as a potential genetic marker to identify individuals with a higher risk of developing breast cancer.

A novel activating function of c-Src and Stat3 on HGF transcription in mammary carcinoma cells

In the normal breast, hepatocyte growth factor (HGF) is primarily expressed by stromal cells, and stimulates in a paracrine manner epithelial cells expressing the HGF receptor (Met). In invasive human breast carcinomas, HGF and Met are frequently overexpressed, possibly establishing an autocrine HGF/Met loop that promotes tumour cell invasion. However, the mechanisms leading to autocrine HGF expression in carcinoma cells are not known. We previously demonstrated a cooperative effect between c-Src and Stat3 in the activation of HGF transcription in mammary carcinoma cells. The present report defines a novel Stat3 consensus site at nt -95 in the HGF promoter that is highly conserved in human and mouse, and is required for c-Src and Stat3 to activate HGF transcription in breast epithelial cells. DNA-protein binding studies demonstrated high affinity binding of a Stat3-containing complex to the nt -95 site. Endogenous Stat3 binding to this region of the HGF promoter in carcinoma cells expressing HGF was demonstrated using a chromatin immunoprecipitation assay. In addition, coexpression of Stat3 and activated c-Src caused increased expression of endogenous HGF mRNA and protein and marked cell scattering in breast epithelial cells. Our results delineate a novel c-Src/Stat3-dependent mechanism that regulates HGF promoter activity, and is linked to transformation of mammary epithelial cells.

Cloning and analysizing the up-regulated expression of transthyretin-related gene (LR1) in rat liver regeneration following short interval successive partial hepatectomy

AIM: Cloning and analysizing the up-regulated expression of transthyretin-related gene following short interval successive partial hepatectomy (SISPH) to elucidate the mechanism of differentiation, division, dedifferentiation and redifferentiation in rat liver regeneration (LR).

METHODS: Lobus external sinister and lobus centralis sinister, lobus centralis, lobus dexter, lobus candatus were removed one by one from rat liver at four different time points 4, 36, 36 and 36 hr (total time: 4 hr, 40 hr, 76 hr, 112 hr) respectively. Suppression subtractive hybridization (SSH) was carried out by using normal rat liver tissue as driver and the tissue following short interval successive partial hepatectomy (SISPH) as tester to construct a highly efficient forward-subtractive cDNA library. After screening, an interested EST fragment was selected by SSH and primers were designed according to the sequence of the EST to clone the full-length cDNA fragment using RACE (rapid amplification of cDNA end). Homologous detection was performed between the full-lenth cDNA and Genbank.

RESULTS: Forward suppression subtractive hybridization (FSSH) library between 0 h and 112 h following SISPH was constructed and an up-regulated full-length cDNA (named LR1), which was related with the transthyretin gene, was cloned by rapid amplification of cDNA end. It was suggested that the gene is involved in the cellular dedifferentiation in LR following SISPH.

CONCLUSION: Some genes were up-regulated in 112 h following SISPH in rat. LR₁ is one of these up-regulated expression genes which may play an important role in rat LR.

A critical function of USF in HGF gene regulation mediated by a multiconsensus region

Hepatocyte growth factor (HGF) is a multifunctional growth factor implicated in a variety of tissue restructuring processes. Since HGF acts as a highly potent mitogen, HGF expression is suggested to be under a well-defined transcriptional control. The 5' sequence of the HGF gene clusters a set of several binding sites for transcription factors in a so-called multiconsensus region (MCR) located between -230 and 260. Our studies demonstrate that a NF1-like element and the E(1)-box of the MCR form the main complexes with nuclear proteins and that both are involved in transcriptional silencing of the HGF gene in non-HGF expressing cell types. The E(1)-box of two tandemly arranged E-boxes was shown to be a binding site of high affinity interacting with the upstream stimulatory factor (USF). While recombinant expression of a wild-type USF did not affect gene expression, a USF variant lacking the DNA binding domain restored the MCR mediated transcriptional repression. In conclusion, our data provide evidence that USF is a central factor of cell-type specific HGF regulation, acting in cooperation with additional regulatory proteins as a bivalent mediator of transcriptional activation or repression.

The role of hepatocyte growth factor (scatter factor) in epithelial-mesenchymal transition and breast cancer

North American women have a one in eight lifetime risk of developing breast cancer, and approximately one in three women with breast cancer will die of metastases. We, and others, have recently shown that high levels of expression of hepatocyte growth factor (HGF) and its receptor Met are associated with invasive human breast cancer and may be causally linked to metastasis. This high level of HGF and Met expression has been considered as a possible indicator of earlier recurrence and shortened survival in breast cancer patients. In contrast, HGF expression (but not Met) is strongly suppressed in normal breast epithelial cells. HGF and Met are therefore candidate targets for therapeutic intervention in the treatment of breast cancer. We have recently demonstrated that sustained activation or hyper-activation of c-Src and Stat3, which occurs in invasive breast cancer, can stimulate strong expression of HGF in carcinoma cells. In contrast, transient induction of Stat3 occurs in normal epithelium and promotes mammary tubulogenesis. We hypothesize that increased autocrine HGF-Met signaling is a critical downstream function of c-Src-Stat3 activation in mammary tumorigenesis. Future studies will identify novel Stat3 consensus sites that regulate HGF promoter activity and HGF expression preferentially in carcinoma cells and could lead to novel therapeutic drugs that specifically block HGF expression in mammary carcinoma cells, and which could be used in combined treatments to abrogate metastasis.

Peroxisome proliferator-activated receptor gamma-mediated transcriptional up-regulation of the hepatocyte growth factor gene promoter via a novel composite cis-acting element

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 gamma (PPARgamma)-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 PPARgamma 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 PPARgamma 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 PPARgamma, 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 PPARgamma by competing with PPARgamma for their overlapping binding sites. Furthermore, for the first time, our studies demonstrate that the PPARgamma ligand, 15-deoxy-prostaglandin J2, induces endogenous HGF mRNA and protein expression in fibroblasts in culture.

Co-operative effect of c-Src tyrosine kinase and Stat3 in activation of hepatocyte growth factor expression in mammary carcinoma cells

We have previously shown coexpression of hepatocyte growth factor (HGF) and its receptor Met in the invasive tumor front of human breast carcinomas. We have also demonstrated secretion of HGF, constitutive activation of Met, and increased invasion in a murine breast carcinoma cell line, SP1. These observations suggest the presence of an HGF autocrine loop in some breast carcinoma cells, which confers increased survival, growth, and invasiveness during tumor progression and metastasis. c-Src tyrosine kinase, which is critical in regulating the expression of many genes, is activated in SP1 carcinoma cells, as well as in most human breast cancers. We therefore examined the role of c-Src kinase in HGF expression in breast carcinoma cells. Expression of activated c-Src in SP1 cells increased transcription from the HGF promoter and expression of HGF mRNA and protein, while dominant negative c-Src had the opposite effect. Using deletion analysis, we showed that the region between -254 and -70 base pairs was required for c-Src responsiveness of the HGF promoter. This region contains two putative consensus sequences (at -110 and -149 base pairs) for the Stat3 transcription factor, which bind protein complexes containing Stat3 (but not Stat1, -5A, or -5B). Coexpression of activated c-Src and Stat3 synergistically induced strong HGF promoter activity in SP1 cells, as well as in a nonmalignant epithelial cell line, HC11 (HGF negative). c-Src kinase activity correspondingly increased the tyrosine 705 phosphorylation and DNA binding affinity of Stat3 (but not Stat1, -5A, or -5B). Collectively, our data indicate a cooperative effect of c-Src kinase and Stat3 in the activation of HGF transcription and protein expression in breast carcinoma cells. This process may be important in overriding the strong repression of HGF expression in nonmalignant epithelium, and thereby promote tumorigenesis.

Endogenous hepatocyte growth factor ameliorates chronic renal injury by activating matrix degradation pathways

BACKGROUND

Hepatocyte growth factor (HGF) has been shown to promote tubule repair and renal regeneration following acute injury; however, whether HGF also modulates the development and progression of chronic renal diseases that are characterized by progressive tissue fibrosis is uncertain. To examine this question, this study investigated the functional consequence of blocking endogenous HGF signaling in vivo in a model of chronic renal disease. The effects of HGF on the processes of matrix synthesis and degradation in cultured renal epithelial cells were also examined.

METHODS

The level of activity of the HGF/c-met axis was examined in rats following 5/6 nephrectomy at multiple time points. To determine the effects of HGF in modulating chronic renal injury, HGF action was blocked in remnant kidney rats using an anti-HGF antibody. The effects of HGF on extracellular matrix (ECM) synthesis and degradation were examined in renal epithelial cells by (35)S-methionine labeling, Western blotting, and zymographic analysis.

RESULTS

An increase in renal and systemic production of HGF coupled with an increase in renal c-met was observed in rats with remnant kidneys. When HGF action was blocked by the administration of an anti-HGF antibody, rats experienced a rapid decrease in glomerular filtration rate and increased renal fibrosis. Kidney sections from the antibody-treated rats displayed a marked increase in ECM accumulation and in alpha-smooth muscle actin-positive cells in both the interstitium and tubular epithelium. In vitro studies revealed that HGF reduced net ECM accumulation by human proximal tubule cells (HKC), and this effect was abolished by incubating cells with an anti-HGF antibody. HGF did not alter the ECM synthetic rate in HKC cells. Rather, it markedly increased collagenase such as matrix metalloproteinase-9 (MMP-9) protein expression, as evidenced by Western blotting and zymographic analysis. HGF also decreased the expression of tissue inhibitors of matrix metalloproteinase-1 (TIMP-1) and TIMP-2, the endogenous inhibitors of MMPs.

CONCLUSION

These results suggest that HGF is a potent antifibrogenic factor both in vitro and in vivo. Endogenous activation of HGF tends to preserve kidney structure and function in rats with chronic renal disease by activating matrix degradation pathways.

The repressive function of AP2 transcription factor on the hepatocyte growth factor gene promoter

Hepatocyte growth factor is an important multifunctional growth factor whose gene expression is tightly regulated at the transcriptional level. Previous studies from our laboratory have shown that several cis-acting elements are present in the promoter and proximal promoter region of the HGF gene. In this study, we have uncovered that AP2 transcription factor specifically binds to a regulatory site located at -230 to -260 in the upstream region of the HGF gene promoter. Gelshift and supershift assays confirmed that AP2 has high binding affinity to this region. Functional studies which introduced a mutation in the AP2 core binding region as well as cotransfection experiments using an AP2 expression vector revealed that AP2 exerts a repressive role on the HGF gene promoter activity. The AP2 binding site overlaps with those of NF1 and USF/E-box binding sites which we have recently shown to constitute a composite multifunctional docking site for the members of the NF1 and USF transcription factor families. An inverse correlation was noted between AP2 binding activity to this composite site and HGF gene expression in different cell lines. Therefore, AP2-mediated repression of the HGF gene promoter may be part of the molecular mechanism responsible for regulating HGF expression.

The concerted regulatory functions of the transcription factors nuclear factor-1 and upstream stimulatory factor on a composite element in the promoter of the hepatocyte growth factor gene

Hepatocyte growth factor (HGF) is an important multifunctional cytokine whose gene expression is regulated mainly at the transcriptional level. Previous studies using transgenic mice as well as in vitro analyses showed that a potential regulatory element(s) exists between -260 to -230 bp in the upstream region of the HGF gene promoter. In the present study, we have discovered that this region is a composite site through which members of the nuclear factor 1 (NF1) and upstream stimulatory factor (USF) families bind to and regulate HGF gene transcription. Gel mobility shift and supershift assays revealed that USF and NF1 have high binding affinity for this region and that the binding sites of the two different transcription factor families overlap. Functional studies showed that NF1 suppresses HGF gene promoter activity and that USF has an activating function. We found that the NF1/X and NF1/Red1 isoforms strongly suppressed HGF promoter activity while the NF1/L variant had no obvious effects. USF1, but not USF2, of the USF family stimulated HGF gene promoter activity. More interestingly, during liver regeneration after partial hepatectomy, a process which activates the HGF gene, we noted that the binding activity of USF to the HGF promoter element increased while that of NF1 decreased. These data provide insight into the molecular mechanisms that govern HGF gene transcription. Oncogene (2000).

Up-regulation of hepatocyte growth factor receptor: an amplification and targeting mechanism for hepatocyte growth factor action in acute renal failure

BACKGROUND

Hepatocyte growth factor (HGF) and its c-met receptor comprise a signaling system that has been implicated in tissue repair and regeneration. HGF action is specifically targeted to the damaged organ following injury; however, the mechanism underlying this important targeting process remains to be elucidated. We reasoned that induction of c-met expression might be a critical factor in determining the site specificity of this receptor-ligand system. To test this hypothesis, we examined changes in activity of the HGF/c-met system in the folic acid model of acute tubular injury and repair.

METHODS

Tissue HGF and c-met mRNA levels were detected by RNase protection assay and Northern blot analysis following acute renal injury induced by a single injection of folic acid. HGF and c-met proteins were examined by a specific enzyme immunoassay and Western blotting, respectively. C-met expression and trans-activation were investigated by exposing renal epithelial mIMCD-3 cells to various cytokines in vitro.

RESULTS

Extremely rapid induction of renal HGF and c-met mRNA was observed beginning one hour following injection of folic acid. Circulating plasma HGF protein level rose dramatically (approximately 16-fold), peaking first at two hours and again at 24 hours following injection. Despite elevated HGF mRNA in the kidney, total kidney HGF protein actually decreased significantly at 24 hours following injury. On the other hand, both c-met mRNA and c-met protein were markedly increased in the kidney, where active renal tubule repair and regeneration take place. In vitro studies suggested that increased levels of HGF, as well as other cytokines, might account for enhanced c-met expression in renal tubular epithelial cells. Pretreatment of the cells with actinomycin D totally blocked c-met induction, suggesting that induced c-met expression occurs primarily at the transcriptional level. Using a cloned region of the c-met promoter coupled to a reporter gene, we demonstrated that HGF directly stimulated c-met promoter transactivation in renal epithelial cells.

CONCLUSION

These results suggest that local up-regulation of c-met transcription in the kidney is crucial to renal tubule repair and regeneration, not only because it increases overall activity of this receptor-ligand system, but also as a mechanism targeting HGF action specifically to renal epithelia.