Constitutive expression of HGF modulates renal epithelial cell phenotype and induces c-met and fibronectin expression

Hepatocyte growth factor (HGF) is a potent renotropic factor that has been shown to play important roles in kidney development and recovery from acute renal injury. To examine the effects of HGF on renal tubular epithelium, we generated HGF-producing renal epithelial cells by stably transfecting mIMCD-3 and OK cells with an expression plasmid containing human HGF cDNA. Expression of HGF in the transfected cells was confirmed by detection of HGF mRNA by Northern blot analysis and detection of HGF secretion into the conditioned medium by ELISA. HGF-transfected cells exhibited fibroblast-like scattered morphology and increased cell motility. They formed branching tubules when grown in 3-D collagen gel. In addition, HGF-producing cells grew faster than their parental cells, but failed to form colonies in soft agar. These phenotypic changes were inhibited by a specific, neutralizing anti-HGF antibody. Interestingly, both c-met transcript and c-met protein were increased in HGF-transfected cells, suggesting that HGF amplifies its own action via stimulation of c-met expression. Autocrine expression of HGF and c-met in renal epithelial cells also stimulated fibronectin gene expression, which was totally blocked by incubation with a neutralizing anti-HGF but not a pan-specific anti-TGF-beta antibody, suggesting that it is independent of TGF-beta production. Our data demonstrate that HGF as a single factor stimulates renal epithelial cell proliferation, migration, differentiation, and extracellular matrix remodeling, making it uniquely suited to promote renal tubulogenesis during development, as well as to reconstitute tubular integrity following acute injury.

Hepatocyte growth factor protects renal epithelial cells from apoptotic cell death

Hepatocyte growth factor (HGF) is a pleiotropic factor that plays an essential role in renal tubular repair and regeneration following injury. Studies indicate that administration of exogenous HGF to animals stimulates renal epithelial cell DNA synthesis and accelerates recovery from acute renal failure (ARF). However, whether increased cell proliferation accounts for all of the beneficial effects of HGF in ARF is unknown. In this study, we demonstrate that HGF protects renal epithelial cells from undergoing apoptotic cell death. Treatment of renal epithelial mIMCD-3 cells with 25 microM cisplatin in the serum-free medium induced significant apoptosis, as assessed by fluorescent Dye H-33342 staining, TUNEL staining, light and electron microscopy, and DNA laddering analysis. However, constitutive expression of HGF by transfection in mIMCD-3 cells resulted in resistance to cisplatin-induced apoptotic death. The survival rate of HGF-producing C1 cells was more than 2-fold greater as compared to control, mIMCD-3 cells following treatment with 25 microM cisplatin for 2 days. These results suggest that HGF may not only activate tubular repair processes but also ameliorate the initial injury by protecting renal epithelial cells from undergoing apoptosis.

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

To understand the molecular mechanisms of hepatocyte growth factor (HGF) gene transcription in vivo, we report the generation and characterization of transgenic mice harboring various lengths of the mouse HGF promoter linked to the chloramphenicol acetyltransferase reporter gene. Analysis of different tissues of the transgenic mouse lines having the 2.7-kilobase (kb) promoter construct revealed a pattern of reporter gene expression in embryonic and adult tissues that paralleled that of endogenous HGF gene expression. A similar expression pattern was observed in the 0.7-kb transgenic lines. However, in contrast to in vitro data, no promoter activity was detected in four independent transgenic lines harboring the 0.1-kb construct. Akin to the activity of the endogenous HGF gene, which is induced in the liver, lung, and spleen in response to 70% partial hepatectomy, the reporter gene driven by the 2.7-kb promoter construct was strongly induced, whereas that driven by the 0.7-kb promoter construct was modestly induced in these organs after partial hepatectomy. Together, these data suggest that the region between -0.1 and -0.7 kb of the HGF gene promoter is essential to drive its expression in vivo and that additional upstream sequences located between -0.7 and -2.7 kb are also necessary for its maximum inducibility in response to cues that stimulate tissue growth and regeneration.

Transcriptional regulation of the hepatocyte growth factor gene by the nuclear receptors chicken ovalbumin upstream promoter transcription factor and estrogen receptor

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.

In vivo and in vitro evidence for increased expression of HGF receptor in kidney of diabetic rat

Renal hypertrophy develops early in the course of diabetes and has been linked to progressive renal disease. Although the mechanism of renal hypertrophy is unknown, evidence suggests that local alterations in the production of one or more growth factors and/or their receptors are crucial to this process. In this study, we demonstrate that the c-met protooncogene product, a tyrosine kinase receptor for hepatocyte growth factor (HGF), is increased in the kidney of the diabetic rat. Northern blot analysis showed that renal expression of the c-met gene was substantially increased in rats made diabetic by administration of streptozotocin. Immunohistochemical studies revealed that the protein for c-met was concordantly elevated in cortical and medullar tubular epithelium following the onset of diabetes. Moreover, in vitro studies demonstrated that short-term exposure to high glucose concentration markedly stimulated c-met expression in cultured proximal tubular (opossum kidney) and inner medulla collecting duct cells (mIMCD-3). The results of enhanced renal expression of c-met together with elevated HGF indicate that the HGF/c-met system is markedly activated in the diabetic rat. These findings suggest that the HGF/c-met system may play a role in the diabetic renal hypertrophy.

Primary structure of rat HGF receptor and induced expression in glomerular mesangial cells

The c-met protooncogene encodes a transmembrane tyrosine kinase receptor for hepatocyte growth factor (HGF). It has been widely suggested that HGF and its receptor constitute a paracrine signaling system, in which mesenchymally derived cells produce ligand that binds to the receptor predominantly expressed on cells of epithelial origin. In this study, we have isolated and completely sequenced the entire coding region of c-met cDNA from the rat kidney. The nucleotide sequence of the rat c-met cDNA revealed that the HGF receptor is encoded within single open-reading frame as 190 kDa of a transmembrane glycoprotein consisting of 1,382 amino acids. Determination of c-met mRNA levels in various tissues revealed a widespread expression of c-met with the highest levels in kidney, lung, and liver. We found simultaneous induction of both HGF and its receptor gene expression by interleukin-6 (IL-6) in primary cultured rat glomerular mesangial cells. The expression of HGF and c-met was remarkably stimulated following incubation of rat mesangial cells with IL-6, in a time- and dose-dependent manner Our data suggest that autocrine action of HGF may be achieved in vivo through simultaneous induction of both HGF and its receptor expression in renal mesenchymal cells.

Identification of a cell-type-specific transcriptional repressor in the promoter region of the mouse hepatocyte growth factor gene

Hepatocyte growth factor (HGF), a cytokine with multiple functions, exhibits cell-type-specific as well as cytokine- and steroid hormone-regulated expression. The HGF gene is known to be expressed predominately in mesenchymal but not in epithelial cells. In this study, we report the identification of a cell-type-specific transcriptional repressor in the promoter region of the mouse HGF gene, which is evidently responsible for the suppression of HGF expression in epithelial cells. Gel mobility shift assays and DNase I footprinting studies revealed that a 27-bp element (-16 to +11) around the transcription initiation site is responsible for the binding of a nuclear protein which is present in epithelial but not in mesenchymally derived cells. Further analysis of the binding activity of the DNA region with nuclear protein revealed that an approximately 19-bp sequence containing a unique palindromic structure (5'-AACCGACCGGTT-3') overlapped by a CAP box is essential for binding. Substitution of a single base (the contact site) within this region by site-directed mutagenesis resulted in total abrogation of the binding of the nuclear protein and a concomitant increase in the transcriptional activity of various lengths of HGF-chloramphenicol acetyltransferase fused genes when transfected into the epithelial cell line RL95-2 but not the mesenchymal cell line NIH 3T3. Southwestern (DNA-protein) analyses revealed that the nuclear protein which binds to this repressor element is a single polypeptide of approximately 70 kDa. Analysis of the nuclear extract prepared from regenerating mouse liver at various times after two-thirds partial hepatectomy by gel mobility shift assay revealed a substantial reduction (more than 75% within 3 h) in the binding of the repressor to its cognate binding site. Our results suggest that a cis-acting transcriptional repressor in the promoter region of the mouse HGF gene is involved in cell-type-specific regulation through binding to its cognate trans-acting protein which exists in epithelial cells but is absent in fibroblast cells.

Modulation of hepatocyte growth factor gene expression by estrogen in mouse ovary

Hepatocyte growth factor (HGF) is expressed in a variety of tissues and cell types under normal conditions and in response to various stimuli such as tissue injury. In the present study, we demonstrate that the transcription of the HGF gene is stimulated by estrogen in mouse ovary. A single injection of 17 beta-estradiol results in a dramatic and transient elevation of the levels of mouse HGF mRNA. Sequence analysis has found that two putative estrogen responsive elements (ERE) reside at -872 in the 5'-flanking region and at +511 in the first intron, respectively, of the mouse HGF gene. To test whether these ERE elements are responsible for estrogen induction of HGF gene expression, chimeric plasmids containing variable regions of the 5'-flanking sequence of HGF gene and the coding region for chloramphenicol acetyltransferase (CAT) gene were transiently transfected into both human endometrial carcinoma RL 95-2 cells and mouse fibroblast NIH 3T3 cells to assess hormone responsiveness. Transfection results indicate that the ERE elements of the mouse HGF gene can confer estrogen action to either homologous or heterologous promoters. Nuclear protein extracts either from RL95-2 cells transfected with the estrogen receptor expression vector or from mouse liver bound in vitro to ERE elements specifically, as shown by band shift assay. Therefore, our results demonstrate that the HGF gene is transcriptionally regulated by estrogen in mouse ovary; and such regulation is mediated via a direct interaction of the estrogen receptor complex with cis-acting ERE elements identified in the mouse HGF gene.

The mouse hepatocyte growth factor-encoding gene: structural organization and evolutionary conservation

A mouse genomic phage library was screened by using a cDNA probe coding for mouse hepatocyte growth factor (HGF). Five overlapping genomic clones which contained the entire mouse HGF gene were isolated and characterized by restriction mapping, Southern hybridization and DNA sequencing. HGF spans about 65 kb and consists of 18 exons separated by 17 introns, similar to its human counterpart. The nucleotide (nt) sequences of the introns at the exon-intron junctions are GT-AG, analogous to those found in other eukaryotic genes. The exon-intron gene organization of HGF is highly homologous to that of several other genes encoding kringle-containing proteins, especially HGF-like protein and plasminogen. This result suggests that HGF probably evolved through gene duplication and/or exon shuffling events from an ancestral gene. Southern hybridization of genomic DNA from different species revealed that a high degree of homology exists among a variety of vertebrates, including chicken, when a mouse HGF cDNA was used as a probe. This evolutionary conservation of HGF strongly suggests that the protein may play an important role in normal cell physiology. Our current results on mouse HGF structure provide basic and detailed information to carry out further manipulation, such as gene targeting.

Modulation of c-MET proto-oncogene (HGF receptor) mRNA abundance by cytokines and hormones: evidence for rapid decay of the 8 kb c-MET transcript

The c-MET proto-oncogene product is a transmembrane tyrosine kinase receptor which was recently shown to transmit an array of important cellular responses induced by Hepatocyte Growth Factor (HGF). These biological effects include induction of mitogenesis, motogenesis, morphogenesis, metastogenesis and anti-tumor activity on a variety of epithelial cells. All of these processes are known to be associated with normal and abnormal tissue growth and development. The 190 kDa c-MET protein is encoded by a major transcript of 8 kilobases (kb), which is reported to be expressed predominantly in epithelial tissues. The expression pattern of c-MET mRNA and protein are drastically modified in many tumor tissues and cell lines. Currently, no information is available on the molecular mechanisms that regulate c-MET mRNA level. In the present communication, we report for the first time that the inflammatory cytokines such as IL-1 alpha, IL-6 and TNF-alpha, as well as TGF-beta 1, EGF, HGF and the steroidal hormones (estrogen, progesterone, tamoxifen and dexamethasone) markedly influence the steady-state levels of the 8 kb c-MET mRNA in human carcinoma cell lines derived from human tissues such as ovary, breast and endometrium. We demonstrate that c-MET receptor protein is present at high levels in primary tumors of human ovaries (clear cell carcinomas). We present evidence that the 8 kb c-MET mRNA undergoes rapid degradation with a half-life of less than 30 min and that this decay can be quickly inhibited by cycloheximide. Our results suggest that the expression of the c-met proto-oncogene resembles that of an immediate early response gene.

Identification of the estrogen sensitive marker in human endometrial carcinoma RL95-2 cells

Estrogen exerts a variety of biological effects on human reproductive tissues. However, little is understood about the estrogenic effect on human endometrial cells in vitro. This study was designed to investigate estrogen action on c-myc and c-fos oncogenes and lactoferrin gene expression in human endometrial carcinoma RL95-2 cells. The results indicate that estrogen can induce c-myc oncogene expression in 4 h. Neither c-fos nor the lactoferrin messenger was detectable, nor could they be induced by estrogen. Transfection with human estrogen receptor expression vector to the RL95-2 cells does not restore the estrogen responsiveness. In addition to estrogen, epidermal growth factor (EGF) and tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) can also induce c-myc expression with no effect on c-fos or lactoferrin expression. Our data suggest that the c-myc oncogene in human endometrial carcinoma RL95-2 cells is the sensitive target gene for steroid hormone and growth factor action.

Structural and functional characterization of the mouse hepatocyte growth factor gene promoter

To understand the molecular mechanisms underlying the regulation of hepatocyte growth factor (HGF) gene expression and to define the DNA sequences essential for its cell-type specific and inducible expression, we have isolated and characterized the 5'-flanking region of the HGF gene. A genomic clone containing 2.8 kilobases of the 5'-flanking region of the HGF gene has been isolated from a mouse liver genomic library. Sequence analysis showed that the promoter region of the mouse HGF gene contains a noncanonical TATA box (ATAAA). Further analysis of the 5'-flanking region revealed a number of putative regulatory elements, such as four interleukin-6 response elements (IL-6 RE), two potential binding sites for NF-IL6, a TGF-beta inhibitory element (TIE), a cAMP response element (CRE), two estrogen response elements (ERE) including one located in the first intron, a potential vitamin D response element (VDRE) which overlaps a chicken ovalbumin upstream promoter (COUP) transcription factor binding element, two liver-specific transcription factor (C/EBP) binding sites, and a B cell- and macrophage-specific transcriptional factor binding site (PU.1/ETS). To determine the location of sites that may be critical for the function of the HGF promoter, we constructed a series of chimeric genes containing variable regions of the 5'-flanking sequence of HGF gene and the coding region for chloramphenicol acetyltransferase (CAT). Transient transfection of chimeric plasmids demonstrated that the mouse HGF gene promoter containing 70 base pairs of the 5'-flanking sequences were active in mouse fibroblast NIH 3T3 cells and in human endometrial carcinoma RL95-2 cells. This basal transcription activity of the HGF promoter was modulated in NIH 3T3 and RL95-2 cells by multiple upstream elements. Three positive elements were identified at positions -2848 to -2674, -1386 to -1231, and -699 to -274, and three negative candidate elements were mapped to positions -1652 to -1386, -964 to -699, and -274 to -70, respectively. By the combination of a series of 5'-end deletion and internal deletion, a cell type-specific negative regulatory element in RL95-2 cells was localized to the nucleotide position -964 to -699. Moreover, the reporter plasmid containing interleukin 6 (IL-6) response element was responsive to IL-6 stimulation in stably transfected NIH 3T3 cells. Our findings revealed a complex pattern of transcriptional regulation of the mouse HGF gene expression.

Molecular cloning and characterization of cDNA encoding mouse hepatocyte growth factor

A cDNA encoding mouse hepatocyte growth factor (HGF) has been cloned and completely sequenced by use of reverse transcriptase-polymerase chain reaction (RT-PCR) and subsequent cloning. Sequence analysis reveals that mouse HGF, similar to its human and rat counterparts, consists of 728 amino acids, and both the alpha- and beta-chains are encoded in a single open reading frame. Strong homology exists in the primary structure of HGF among the three species of mouse, rat and human (more than 90%), especially in Kringle 1 of the alpha chain which is assumed to be an essential domain for binding of HGF to its receptor, c-MET, a proto-oncogene product. Our results suggest the existence of evolutionary pressure to conserve the distinct structure, and presumably the biological functions, of HGF.

COUP-TF acts as a competitive repressor for estrogen receptor-mediated activation of the mouse lactoferrin gene

We previously demonstrated that the estrogen response module (mERM) of the mouse lactoferrin gene, which contains an overlapping chicken ovalbumin upstream promoter transcription factor (COUP-TF)- and estrogen receptor-binding element, is responsible for estrogen induction. In this report we show that COUP-TF represses the mERM response to estrogen stimulation. Mutation and deletion of the COUP-TF-binding element or reduction of the endogenous COUP-TF increases mERM estrogen responsiveness. Likewise, overexpression of the COUP-TF expression vector blocked the estrogen-stimulated response of mERM in transfected cells. The molecular mechanism of this repression is due to the competition between COUP-TF and the estrogen receptor for binding at identical contact sites in the overlapping region of the mERM. Our results indicate that two members of the steroid-thyroid receptor superfamily work in concert to modulate lactoferrin gene expression.

Differential molecular mechanism of the estrogen action that regulates lactoferrin gene in human and mouse

The 5'-flanking region of the human lactoferrin gene was isolated from a human placental genomic library. This genomic clone contains a 16-kilobase pair (kbp) insert and produces seven fragments when digested with the SacI restriction enzyme. We sequenced one of the fragments that comprises 1294 bp of the 5'-flanking sequence, 79 bp of the first exon, and 690 bp of the first intron. A major transcription start site was mapped by primer extension. The region immediately upstream from the transcription initiation site following the first exon is abundant in G and C nucleotides. In the promoter and 5'-flanking region within a 300-bp stretch (-465 to -165) of the DNA, we found a noncanonical TATA box (ATAAA), CAAT-like sequence (CAAC) and sequences homologous to the consensus SP1 binding site, Pu.1/Sp.1 binding element (PU box), two half-palindromic estrogen response elements (EREs; GGTCA), an imperfect ERE (GGTCAAGGCGATC), and a sequence resembling the chicken ovalbumin upstream promoter transcription factor (COUP-TF) binding site (GTCTCACAGGTCA). The COUP-TF binding site and the imperfect ERE shared five nucleotides (GGTCA). With the exception of the two half-palindromic EREs, the elements with very well matched sequences were also found in the corresponding positions in the mouse lactoferrin gene. The synthetic oligonucleotide, including the 26 bp of COUP/ERE sequence, was cloned before the SV40 promoter in a chloramphenicol acetyltransferase reporter construct. These chimeric plasmids were transiently transfected into human endometrium carcinoma RL95-2 cells to assess hormone responsiveness. We found that the COUP/ERE element acted as an enhancer in response to estrogen stimulation. In vitro DNase I footprinting analysis showed binding of the estrogen receptor on the imperfect ERE. In contrast to the mouse lactoferrin COUP/ERE element, COUP-TF does not interact with this element, as demonstrated by band shift assay and site-directed mutagenesis. Therefore, the molecular mechanisms of the estrogen action that govern the lactoferrin gene expression differ between mouse and human.

Estrogen response module of the mouse lactoferrin gene contains overlapping chicken ovalbumin upstream promoter transcription factor and estrogen receptor-binding elements

Transcription of the lactoferrin gene is stimulated by estrogen in mouse uterus. To study direct estrogen regulation of this gene at the molecular level, we cloned and analyzed the 5'-flanking region of the mouse lactoferrin gene. Sequence analysis revealed a putative estrogen-responsive element (ERE) overlapping with a chicken ovalbumin up-stream promoter (COUP) element located at position -349 to -329 from the transcription initiation site. The ERE element differed from the consensus ERE sequence by one nucleotide at the second position of the 3' half of the element (G to A); the COUP element differed by one nucleotide from the chicken COUP element. Synthetic oligonucleotide containing the mouse lactoferrin COUP/ERE element was inserted into the reporter chloramphenicol acetyltransferase vector, then transiently transfected into human endometrium carcinoma RL95-2 cells to assess hormone responsiveness. We found that the COUP/ERE element confers estrogen action to both homologous and heterologous promoters. Nuclear proteins from diethylstilbestrol-treated mouse uteri and proteins from estrogen receptor expression vector-transfected RL95-2 whole cell extract bound in vitro to COUP/ERE element specifically, as assessed by band-shift assay. By using antibodies specific to the estrogen receptor and the COUP transcription factor, we demonstrated that both proteins were present in mouse uterine tissue and interacted specifically with the COUP/ERE element, as shown by the superband shift. Competition experiments with specific ERE or COUP oligonucleotides also confirmed the interaction between lactoferrin COUP/ERE element with the estrogen receptor and the COUP transcription factor. Therefore, we named this sequence mERM, the mouse lactoferrin estrogen response module.

Characterization of estrogen-responsive mouse lactoferrin promoter

Mouse lactoferrin is expressed in a variety of tissues under different types of control. To understand how molecular mechanisms govern the mode of lactoferrin expression, we isolated and characterized the 5'-flanking region of the lactoferrin gene. Several clones containing lactoferrin gene fragments were isolated from a mouse (129/J) genomic library including clone lambda J14, which contains a 7.5-kilobase pair 5'-flanking sequence. Sequence analysis of the region flanking the transcription initiation site revealed the following: a TATA-like sequence, two CAAT boxes, three GC boxes including one within the first intron, an AP2 site, seven PU boxes, an AC-rich region, a B1 sequence, and an estrogen-responsive element consensus sequence over-lapping with a chicken ovalbumin upstream promoter-binding element. Footprinting analysis demonstrated that several regions, including the putative estrogen-responsive element region, in the 5'-flanking sequence were protected from DNase I digestion. Promoter fragments were cloned into a chloramphenicol acetyltransferase receptor plasmid to study functional activity. The mouse lactoferrin gene promoter was active in human endometrium carcinoma RL 95-2 cells and in rat glioma C6 cells. Multiple upstream elements modulated the basal transcriptional promoter activity. The transcription level directed by this minimal promoter was controlled by both positive (between -1739 and -922) and negative (between -2644 and -1739, and between -589 and -291) regulatory sequences. A tissue-specific regulatory sequence was critical for the establishment of lactoferrin expression in human endometrium carcinoma cells, but not in rat glioma cells located between -1739 and -922. Reporter plasmid 0.6 mL14-CAT, containing the estrogen-responsive element sequence, was estrogen-responsive in the presence of estrogen receptor in human endometrium carcinoma RL 95-2 cells.

Polymorphism and altered methylation of the lactoferrin gene in normal leukocytes, leukemic cells, and breast cancer

Human lactoferrin has been found to be decreased or absent in most breast cancer and leukemia cells. In order to examine the lactoferrin gene for both structural alterations and the degree of methylation, we isolated a 2117-kilobase complementary DNA from human breast tissue. This complementary DNA was used to probe DNA extracted from normal peripheral blood, leukemia cells from patients, leukemia cell lines, and breast cancer cell lines. Immunocytochemical staining of these cells confirmed the decreased production of lactoferrin in malignancy. MspI restriction enzyme fragment patterns demonstrated genetic polymorphism which occurred in DNA from both normal and malignant cells. Polymorphism was also noted with XbaI. In this case, there were two fragment patterns that were only found in DNA from malignant cells. The degree of DNA methylation was also evaluated. The methylation pattern of DNA extracted from malignant cells was highly variable and generally less methylated than DNA extracted from normal WBCs. It is possible that the decrease in lactoferrin associated with cancer is multifactorial and includes gene structural changes as well as altered regulation. Further study is needed to determine whether the changes found in this study are the result of the malignancy or contribute to its onset or maintenance.