Amplification and overexpression of the hepatocyte growth factor receptor (HGFR/MET) in rat DMBA sarcomas

Tumorigenic effects of TLX overexpression in HEK 293T cells

BACKGROUND

The human orphan receptor TLX (NR2E1) is a key regulator of neurogenesis, adult stem cell maintenance, and tumorigenesis. However, little is known about the genetic and transcriptomic events that occur following TLX overexpression in human cell lines.

AIMS

Here, we used cytogenetics and RNA sequencing to investigate the effect of TLX overexpression with an inducible vector system in the HEK 293T cell line.

METHODS AND RESULTS

Conventional spectral karyotyping was used to identify chromosomal abnormalities, followed by fluorescence in situ hybridization (FISH) analysis on chromosome spreads to assess TLX DNA copy number. Illumina paired-end whole transcriptome sequencing was then performed to characterize recurrent genetic variants (single nucleotide polymorphisms (SNPs) and indels), expressed gene fusions, and gene expression profiles. Lastly, flow cytometry was used to analyze cell cycle distribution. Intriguingly, we show that upon transfection with a vector containing the human TLX gene (eGFP-hTLX), an isochromosome forms on the long arm of chromosome 6, thereby resulting in DNA gain of the TLX locus (6q21) and upregulation of TLX. Induction of the eGFP-hTLX vector further increased TLX expression levels, leading to G0-G1 cell cycle arrest, genetic aberrations, modulation of gene expression patterns, and crosstalk with other nuclear receptors (AR, ESR1, ESR2, NR1H4, and NR3C2). We identified a 49-gene signature associated with central nervous system (CNS) development and carcinogenesis, in addition to potentially cancer-driving gene fusions (LARP1-CNOT8 and NSL1-ZDBF2) and deleterious genetic variants (frameshift insertions in the CTSH, DBF4, POSTN, and WDR78 genes).

CONCLUSION

Taken together, these findings illustrate that TLX may play a pivotal role in tumorigenesis via genomic instability and perturbation of cancer-related processes.

Retracted Article: RNA-sequencing identified miR-3681 as a negative regulator in the proliferation and migration of cervical cancer cells via the posttranscriptional suppression of HGFR

In this study, RNA-sequencing was used to investigate the differentially expressed miRNAs between cervical cancer tissues and matched adjacent non-tumor tissues. Five miRNAs were sharply downregulated in the cancer tissue, including miR-199a, miR-22, miR-615, miR-3681-3p (miR-3681), and miR-1193. Among them, miR-3681 was uncharacterized. The results from qPCR analysis showed that miR-3681 expression was decreased in patients with cervical cancer compared with the control, and decreased in the human cervical cancer cell lines SiHa, HeLa, C4-1, C-33A and Caski, compared with the normal human cervical epithelial cell line HCerEpic. Then, different concentrations of miR-3681 mimic and miR-3681 inhibitor were respectively transfected into the human cervical cancer cell line C-33A, and the expression of miR-3681, cell proliferation, cell apoptosis and cell migration were measured after 48 h. The results showed that the miR-3681 mimic increased the miR-3681 level, suppressed cell proliferation and migration, and induced cell apoptosis in a dose-dependent manner. In contrast, the miR-3681 inhibitor decreased the miR-3681 level, promoted cell proliferation and migration, and inhibited cell apoptosis in a dose-dependent manner. Moreover, bioinformatics analysis showed that there was a miR-3681 binding site in the mRNA 3'UTR of HGFR, which was robustly upregulated in cervical cancer cell lines compared with HCerEpic cells. In addition, luciferase activity analysis demonstrated that miR-3681 could directly target HGFR, which promoted the proliferation and migration of C-33A cells via activation of the PI3K/Akt pathway in a dose-dependent manner. Furthermore, our results showed that knockdown of HGFR could antagonize the promotion of anti-miR-3681 on the activation of the PI3K/Akt pathway and cell proliferation and migration. In conclusion, MiR-3681 was identified as a negative regulator in the proliferation and migration of cervical cancer cells. This function is associated with the posttranscriptional suppression of HGFR and the deactivation of the PI3K/Akt pathway.

Frequent MYC coamplification and DNA hypomethylation of multiple genes on 8q in 8p11-p12-amplified breast carcinomas

Genetic and epigenetic (DNA methylation, histone modifications, microRNA expression) crosstalk promotes inactivation of tumor suppressor genes or activation of oncogenes by gene loss/hypermethylation or duplications/hypomethylation, respectively. The 8p11-p12 chromosomal region is a hotspot for genomic aberrations (chromosomal rearrangements, amplifications and deletions) in several cancer forms, including breast carcinoma where amplification has been associated with increased proliferation rates and reduced patient survival. Here, an integrative genomics screen (DNA copy number, transcriptional and DNA methylation profiling) performed in 229 primary invasive breast carcinomas identified substantial coamplification of the 8p11-p12 genomic region and the MYC oncogene (8q24.21), as well as aberrant methylation and transcriptional patterns for several genes spanning the 8q12.1-q24.22 genomic region (ENPP2, FABP5, IMPAD1, NDRG1, PLEKHF2, RRM2B, SQLE, TAF2, TATDN1, TRPS1, VPS13B). Taken together, our findings suggest that MYC activity and aberrant DNA methylation may also have a pivotal role in the aggressive tumor phenotype frequently observed in breast carcinomas harboring 8p11-p12 regional amplification.

Inversion upstream of FOXF1 in a case of lethal alveolar capillary dysplasia with misalignment of pulmonary veins

Alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV) is a congenital malformation that leads to severe pulmonary hypertension and respiratory failure. It has been associated with deletion of, or mutation in, FOXF1 on 16q24.1, a gene encoding a forkhead transcription factor expressed in the mesenchyme of the developing lung. Here we report on the identification of a pericentric inversion on chromosome 16 (p11.2q24.1) in a case of lethal ACDMPV with atrioventricular septal defect and duodenal atresia. Array-CGH indicated that the inversion is balanced, and FISH showed that the q-arm breakpoint occurs 134 ± 10 kb upstream (5'; centromeric) of FOXF1. This is suggestive of cis-regulatory elements located more than 130 kb 5' of FOXF1, and analysis of genome-wide data sets of chromatin modifications in two different cell types suggested that the FOXF1 regulatory domain covers more than 300 kb, and perhaps up to 433 kb, upstream of the gene, but only 3 kb downstream. The 588 kb gene-free region between FOXF1 and the next gene in the centromeric direction, IRF8, is highly conserved between species and divided into two distinct regulatory domains by an insulator element. Another putative insulator occurs just downstream of FOXF1. Our results further strengthen the association between FOXF1 and a spectrum of malformations that include ACDMPV, atrioventricular septal defects, and gastrointestinal atresia. Furthermore, the presented analysis aids in defining the critical genomic region for this syndrome.

High levels of γ-glutamyl hydrolase (GGH) are associated with poor prognosis and unfavorable clinical outcomes in invasive breast cancer

Background

Previously, we performed analysis of gene expression in 46 axillary lymph node negative tumors and identified molecular gene signatures that resulted in different clinical outcomes. The aim of this study was to determine the correlation of γ-glutamyl hydrolase (GGH), fatty acid amide hydrolase (FAAH), Pirin (PIR) and TAF5-like RNA polymerase II, p300/CBP-associated factor (PCAF)-associated factor, 65 kDa (TAF5L), selected from identified gene signatures, with clinical outcomes as well as classical clinicopathological characteristics in primary invasive breast cancer patients.

Methods

The protein levels of GGH, FAAH, PIR and TAF5L were assessed by immunohistochemistry (IHC) on a panel of 80 primary invasive breast tumors. Quantitative real-time PCR (qRT-PCR) and western blot analysis were performed to verify the expression levels of the candidate biomarkers. Patient disease-specific survival (DSS) and recurrence-free survival (RFS) were evaluated using the Kaplan-Meier method. The prognostic biomarkers were identified by univariate analysis with a log-rank test and by multivariate analysis with Cox proportional hazards regression models.

Results

The GGH and FAAH protein levels were significantly up-regulated in invasive breast cancer tumors compared with adjacent non-cancerous tissues. Furthermore, the protein levels of GGH and FAAH were significantly correlated in tumor tissues. Tumoral GGH protein expression was significantly correlated with shorter DSS and RFS. Furthermore, the protein expression of GGH was positively correlated with undifferentiated tumors (BRE grade III) and ER/PR expressing tumors. Multivariate regression analysis showed that only GGH protein expression independently predicts DSS. No such correlations were found for FAAH, PIR and TAF5L protein expression. However, elevated protein levels of FAAH were positively associated with high number of lymph node involvement and upregulated levels of PIR were positively related with lymph node metastasis. The TAF5L was pronouncedly down-regulated in primary invasive breast cancer tissues compared to matched adjacent non-cancerous tissues.

Conclusion

These data show for the first time that cytoplasmic GGH might play a relevant role in the development and progression of invasive breast cancer, warranting further investigations. Our findings suggest that GGH serve as a potential biomarker of unfavorable clinical outcomes over short-term follow-up in breast cancer. The GGH may be a very attractive targeted therapy for selected patients.

Elevated cyclin B2 expression in invasive breast carcinoma is associated with unfavorable clinical outcome

BACKGROUND

Breast cancer is a potentially fatal malignancy in females despite the improvement in therapeutic techniques. The identification of novel molecular signatures is needed for earlier detection, monitoring effects of treatment, and predicting prognosis. We have previously used microarray analysis to identify differentially expressed genes in aggressive breast tumors. The purpose of the present study was to investigate the prognostic value of the candidate biomarkers CCNB2, ASPM, CDCA7, KIAA0101, and SLC27A2 in breast cancer.

METHODS

The expression levels and subcellular localization of the CCNB2, ASPM, CDCA7, KIAA0101, and SLC27A2 proteins were measured using immunohistochemistry (IHC) on a panel of 80 primary invasive breast tumors. Furthermore, the mRNA levels of CCNB2, KIAA0101, and SLC27A2 were subsequently examined by qRT-PCR to validate IHC results. Patient disease-specific survival (DSS) was evaluated in correlation to protein levels using the Kaplan-Meier method. Multivariate Cox regression analysis was used to determine the impact of aberrant protein expression of the candidate biomarkers on patient DSS and to estimate the hazard ratio at 8-year follow-up.

RESULTS

Elevated cytoplasmic CCNB2 protein levels were strongly associated with short-term disease-specific survival of breast cancer patients (≤ 8 years; P<0.001) and with histological tumor type (P= 0.04). However, no association with other clinicopathological parameters was observed. Multivariate Cox regression analysis specified that CCNB2 protein expression is an independent prognostic marker of DSS in breast cancer. The predictive ability of several classical clinicopathological parameters was improved when used in conjunction with CCNB2 protein expression (C-index = 0.795) in comparison with a model without CCNB2 expression (C-index = 0.698). The protein levels of ASPM, CDCA7, KIAA0101, and SLC27A2 did not correlate with any clinicopathological parameter and had no influence on DSS. However, a significant correlation between the expression of the CCNB2 and ASPM proteins was detected (P = 0.03).

CONCLUSION

These findings suggest that cytoplasmic CCNB2 may function as an oncogene and could serve as a potential biomarker of unfavorable prognosis over short-term follow-up in breast cancer.

Fluorescence in situ hybridization (FISH) for genomic investigations in rat

This chapter concentrates on the use of fluorescence in situ hybridization (FISH) for genomic investigations in the laboratory rat (Rattus norvegicus). The selection of protocols included in the chapter has been inspired by a comprehensive range of previously published molecular cytogenetic studies on this model organism, reporting examples of how FISH can be applied for diverse investigative purposes, varying from comparative gene mapping to studies of chromosome structure and genome evolution, to characterization of chromosomes aberrations as well as transgenic insertions. The protocols, which include techniques for the preparation of mitotic chromosomes and DNA fibers from short-term cell cultures, have been gathered through the years and repeatedly tested in our laboratory, and all together aim at providing sufficient experimental versatility to cover a broad range of cytogenetic and cytogenomic applications.

Activation of HGF/c-Met pathway contributes to the reactive oxygen species generation and motility of small cell lung cancer cells

Small cell lung cancer (SCLC) is a difficult disease to treat and sometimes has overexpression or mutation of c-Met receptor tyrosine kinase. The effects of c-Met/hepatocyte growth factor (c-Met/HGF, ligand for c-Met) on activation of reactive oxygen species (ROS) was determined. HGF stimulation of c-Met-overexpressing H69 SCLC cells (40 ng/ml, 15 min) resulted in an increase of ROS, measured with fluorescent probe 2′-7′-dichlorofluorescein diacetate (DCFH-DA) or dihydroethidine (DHE) but not in c-Met-null H446 cells. ROS was increased in juxtamembrane (JM)-mutated variants (R988C and T1010I) of c-Met compared with wild-type c-Met-expressing cells. ROS was significantly inhibited by preincubation of SCLC cells with pyrrolidine dithiocarbamate (PDTC, 100 μM) and/or SU11274 (small molecule c-Met tyrosine kinase inhibitor, 2 μM) for 3 h. PDTC and SU11274 also abrogated the HGF proliferative signal and cell motility in a cooperative fashion. H2O2 treatment of SCLC cells (over 15 min) led to phosphorylation of c-Met receptor tyrosine kinase and further upregulated downstream phosphorylation of phospho-AKT, ERK1/2, and paxillin in a dose-dependent manner (125 μM to 500 μM). c-Met is an important target in lung cancer, and the pathways responsible for ROS generation together may provide novel therapeutic intervention.

Assessment of allele dosage at polymorphic microsatellite loci displaying allelic imbalance in tumors by means of quantitative competitive-polymerase chain reaction

Analysis of allelic imbalance at polymorphic marker loci is usually employed to identify chromosomal regions affected by recurrent aberrations in tumor genomes. Such regions are likely to harbor genes involved in the onset and/or progression of cancer. Although often used to identify regions of loss of heterozygosity caused by deletions/rearrangements near tumor suppressor gene loci, allelic imbalance can also reflect regional amplification, indicating the presence of oncogenes. It is difficult to tell these two situations apart after ordinary polymerase chain reaction (PCR), but here we describe a method that distinguishes allelic loss from allelic gain. The level of allelic imbalance was determined by quantitative PCR (QPCR) in the presence of an internal control DNA that displayed a third allele at the locus studied. To validate the efficiency of allele quantitation, we analyzed an amplified region in a set of rat fibrosarcomas. In four tumor samples with amplification of the Met oncogene, we could show with QPCR that there was amplification of one of the alleles at a microsatellite marker located close to Met. QPCR may be useful for cancer studies because experiments may be predesigned for using either suitable microsatellite markers or the abundant and polymorphic poly-A tails of rodent identifier sequences.

Impact of c-Met expression on angiogenesis in soft tissue sarcomas: correlation to microvessel-density

PURPOSE AND METHODS

The c-Met protein is significant for oncogenesis and angiogenesis within the c-Met/HGF/SF-mediator system. The aim of this study was the analysis of c-Met immunoexpression/-synthesis and microvessel density as parameters for angiogenesis and prognosis in 115 soft tissue sarcomas.

RESULTS

C-Met could be detected by immunohistochemistry in 87% of sarcomas. In all, 60.9% of cases exhibited absent or faint expression of c-Met protein, and 39.1% high expression of c-Met protein with a correlation between tumor grading and c-Met immunoexpression. Using in situ hybridization with detection of c-met-mRNA-transcripts, c-Met protein synthesis within tumor cells could be demonstrated. A statistically significant correlation between c-Met immunoexpression and tumor microvessel density was found. No prognostic value of c-Met expression and microvessel density could be detected in 56 patients with clinical follow-up ( P=0.8506 and P=0.9329 for disease-free survival).

CONCLUSIONS

The results underline a role of c-Met as an oncoprotein in soft tissue sarcomas with correlation between immunoexpression and grading. The statistically significant correlation between c-Met expression and microvessel density (as a parameter of tumor angiogenesis) suggests an angiogenic function of the c-Met/HGF/SF mediator system in malignant mesenchymal tumors.

Recurrent allelic imbalance at the rat Pten locus in DMBA-induced fibrosarcomas

The tumor-suppressor gene PTEN (phosphatase and tensin homolog) is frequently inactivated in different types of human tumors. Less is known about the involvement of the homologous gene Pten in animal model systems of cancer. By sequencing one of the introns of rat Pten, we found an informative intragenic PCR marker suitable for genetic studies. Through use of this marker, the position of Pten in the genetic linkage map was localized to the distal part of rat chromosome 1 (RNO1) by analysis of F2 progeny from an intercross between inbred strains BN and LE. Subsequently, 22 markers from this region (including the intragenic Pten marker) were used to study the occurrence of allelic imbalance in distal RNO1 in fibrosarcomas that had been induced by DMBA in F1(BNxLE) rats. The analysis revealed that allelic imbalance was common in the vicinity of Pten, and there was loss or reduction of one of the Pten alleles in more than 60% of the fibrosarcomas. DNA sequencing was preformed to investigate whether the Pten allele remaining in the tumors was inactivated by mutation. However, no mutations were detected in the genomic sequence of Pten exons 5 to 9 in any of the fibrosarcomas, and normal mRNA transcripts were expressed in all tumors. Thus, based on the targeted selection for loss of Pten observed in some of these tumors and the absence of inactivation of the remaining allele, we suggest that haploinsufficiency of Pten may be an important factor in rat DMBA-induced fibrosarcomas.

Analysis of genetic changes in rat endometrial carcinomas by means of comparative genomic hybridization

Animals of the BDII inbred rat strain are known to be genetically predisposed to endometrial adenocarcinoma (EAC). Using them as models of human EACs, we studied tumors arising in F1 and F2 progeny from BDII animals crossed to animals from two other inbred strains, in which EACs were quite rare. In order to identify chromosomal regions exhibiting DNA copy number changes, comparative genomic hybridization (CGH) was applied in a series corresponding to 27 different solid tumors, most of which were classified as EACs, from these animals. The main findings from the study were that, although many different chromosomes were involved in copy number variation, some of the changes detected were recurrent and quite specific. Among specific changes found were gains in rat chromosome (RNO) regions 4q12 approximately q22, 6q14 approximately q16, and whole chromosome arms in some of the small metacentric chromosomes (e.g., RNO14, 16, and 18). RNO10 was involved in gain in the terminal and proximal regions. Each of these regions contains previously identified cancer-related genes representing possible candidates to be involved in the development of EAC. Furthermore, it was observed that there were clear differences in the pattern of copy number changes between tumors occurring in the two different crosses, and also between solid tumors and cell cultures. Endometrial cancer is the most common human gynecological cancer, but not much is known about specific genetic changes influencing this disease. Two genetic alterations that have been reported from human endometrial cancer are amplification of the ERBB2 gene and mutations in the 12 codon of the KRAS gene. One case of Erbb2 amplification was found but there were no Kras mutations in the rat material studied. We conclude that molecular genetic analysis of the rat BDII model will provide important new information about EAC in mammals.

Ras gene mutations in 7,12-dimethylbenz[a]anthracene (DMBA)-induced rat sarcomas

Tumor induction in rats by 7,12-dimethylbenz[a]anthracene (DMBA) will generate malignancies that display reproducible chromosomal abnormalities involving rat chromosome (RNO) 2. Thus, it has been reported that rat DMBA erythroleukemias display RNO2 abnormalities, which in this case were closely correlated to mutations in the Nras oncogene located in RNO2q34. Our cytogenetic analysis in a series of 17 DMBA-induced rat sarcomas showed that 11 (65%) tumors had a significant increase in RNO2 copy number. Furthermore, the incidence of point mutations in codons 12, 13 and 61 of Hras, Kras, and Nras was examined in the same set of sarcomas, and mutations were detected in three (18%) tumors, in codon 61 of Kras (CAA-->CAT) (1 of 17) and Nras (CAA-->CTA) (2 of 17). We conclude that the high frequency of RNO2 gain was in accordance with previous studies of DMBA-induced rat neoplasms, supporting the idea of a significant role of RNO2 in DMBA carcinogenesis. However, there was no clear-cut relationship between activated Nras and gain of RNO2 material, implying that mutational activation of Nras is not the causative factor underlying the gain of RNO2 copy number in rat DMBA sarcomas, in contrast to what has been suggested for DMBA-induced erythroleukemias.

Hgfr/Met oncogene acts as target for gene amplification in DMBA-induced rat sarcomas: free chromatin fluorescence in situ hybridization analysis of amplicon arrays in homogeneously staining regions

Analysis of chromosome rearrangements in tumors is an important means for revealing genetic pathways underlying tumorigenesis and tumor progression. In five of 17 DMBA-induced rat sarcomas, cytogenetic analysis had disclosed homogeneously staining regions (hsrs), which are generally accepted to be cytogenetic signs of gene amplification. Using comparative genomic hybridization (CGH), regional increases in DNA copy number of the proximal part of rat chromosome (RNO) 4 were detected in four of the tumors harboring hsrs. Amplification of the Hgfr/Met oncogene, located at RNO4q21.2, was detected by fluorescence in situ hybridization (FISH) in five tumors. In four of them, a number of flanking genes located in the close vicinity of Hgfr/Met, including Cav1 (q21.1), Wnt2 (q21.2-q21.3), and Cftr (q21.3), also were amplified, though amplification was seen in a lower fraction of the cells than was Hgfr/Met amplification. In the fifth tumor (BL150T), Hgfr/Met was amplified in all cells and was the sole amplified gene of those tested. In addition, the Hgfr/Met FISH signals in BL150T were tightly clustered and formed compact and intense spots compared with the signals seen in the other four tumors. Application of the free chromatin FISH technique to BL150T showed that the genomic Hgfr/Met probe stained the extended chromatin fibers of up to 1.5 Mb with an almost uninterrupted signal, indicating that the BL150T amplicon was build up solely of Hgfr/Met gene sequences. Our results suggest that the Hgfr/Met oncogene is the primary target for amplification in a subset of rat DMBA sarcomas.

Normal pharmacologically-induced, but decreased regenerative liver growth in interleukin-6-deficient (IL-6(-/-)) mice

BACKGROUND/AIMS

In the absence of liver damage, rapid liver growth can be induced pharmacologically by so-called primary liver growth promoters. The importance of the acute-phase cytokines interleukin-6 and tumor necrosis factor-alpha for the actions of these compounds is not clear. This study aimed to investigate the importance of IL-6 and TNF-receptor-1 in pharmacologically-induced liver growth.

METHODS

IL-6 knockout (IL-6(-/-)), TNF-receptor-1 knockout (TNFR1(-/-)) and wild-type mice were treated with the peroxisome proliferator nafenopin and the anti-androgen cyproterone acetate (CPA) in one single injection or for 6 days with daily injections, and examined at 24 or 48 h after treatment. In a control experiment, IL-6(-/-) mice were subjected to two-thirds partial hepatectomy.

RESULTS

Nafenopin treatment increased relative liver weight and DNA synthesis similarly in IL-6(-/-), TNFR1(-/-) and wild-type mice. CPA increased liver weight similarly in all groups, but did not increase DNA synthesis. Expression of peroxisome proliferator activated receptor-alpha mRNA was increased in both IL-6(-/-) and wild-type mice by nafenopin treatment, but not by CPA treatment. After hepatectomy DNA synthesis was suppressed in IL-6(-/-) mice compared to wild-type mice.

CONCLUSIONS

Liver growth induced by nafenopin and CPA was not dependent on the presence of IL-6 or TNF receptor-1, whereas liver regeneration was decreased in IL-6(-/-) mice.

Genomewide assessment of genetic alterations in DMBA-induced rat sarcomas: cytogenetic, CGH, and allelotype analyses reveal recurrent DNA copy number changes in rat chromosomes 1, 2, 4, and 7

Rat sarcomas, induced by subcutaneous injections of 7,12-dimethylbenz[a]anthracene (DMBA), were studied with the objective of identifying critical chromosome regions associated with tumorigenesis. We employed three genomewide screening techniques-cytogenetics, CGH, and allelotyping-in 19 DMBA-induced sarcomas in F1 (BN/Han x LE/Mol) rats. The most conspicuous finding in the cytogenetic analysis was a high incidence of trisomy for rat chromosome 2 (RNO2). Signs of gene amplification (hsr) were also seen in several tumors. The CGH analysis revealed that gains in copy number were much more common than losses. The gains mostly affected RNO2 (10/19), RNO12q (7/19), and RNO19q (5/19), as well as the proximal part of RNO4 (8/19) and the distal part of RNO7 (7/19). Reduction in copy number was seen in RNO17 (2/19). For the allelotyping, we used 318 polymorphic microsatellite marker loci covering the entire genome. We identified regions of allelic imbalance affecting most of the rat chromosomes. The highest incidences of recurrent allelic imbalance were observed at loci in certain regions in RNO1, 2, 4, and 7 and at lower incidences in parts of RNO12, 16, 18, and 19. The combined results suggested that genetic alterations detected in RNO2 and RNO12 usually corresponded to complete or partial trisomy, whereas those in RNO1 and RNO7 seemed to involve regional deletions and/or gains. Furthermore, we could confirm that copy number gains occur proximally in RNO4, where a previous study showed amplification of the Met oncogene in a subset of these tumors.

Overexpression of the hepatocyte growth factor (HGF) receptor (Met) and presence of a truncated and activated intracellular HGF receptor fragment in locally aggressive/malignant human musculoskeletal tumors

Enhanced hepatocyte growth factor (HGF) receptor (Met) signaling has been suggested to play an important role in the development and progression of various epithelial and nonepithelial tumors. N-terminally truncated forms of the HGF receptor have been shown to be constitutively activated and tumorigenic in animal experiments. In the present study, 102 benign and malignant human musculoskeletal tumors were examined for expression of the HGF receptor by Western blotting and/or immunohistochemistry. A clear predominance of HGF receptor expression was seen in malignant as compared to benign tumors (Western blotting, P < 0.001; immunohistochemistry, P < 0.02). For the first time we show HGF receptor expression in the following four tumor types: dermatofibrosarcoma protuberans, clear cell sarcoma of tendons, malignant primitive neuroectodermal tumor, and benign fibrous histiocytoma. In three cases of sarcoma with high HGF receptor expression by Western blotting, we found indications of a short 85-kd N-terminally truncated HGF receptor that was tyrosine phosphorylated and located in the cytoplasm. Although fragments of this length were seen in 18 of 65 tumors, most were not tyrosine-phosphorylated. Northern blotting revealed only the 7.5-kb full-length HGF receptor transcript, suggesting that the 85-kd fragment is generated by an alternative initiation of translation or by proteolytic cleavage. Southern blotting detected no amplification of the Hgfr/Met gene in the 35 tumors examined, in contrast to our recent report of Hgfr/Met gene amplification in 7, 12-dimethylbenz(a)anthracene (DMBA)-induced rat sarcomas. The present data suggest that the locally aggressive and malignant properties of human mesenchymal tumors maybe related, in part, to high levels of full-length HGF receptors, and in some cases to the occurrence of N-terminally truncated HGF receptors, activated independently of HGF.