High expression of Met/hepatocyte growth factor receptor suppresses tumorigenicity in NCI-H1264 lung carcinoma cells

A functional screen identifies miR-34a as a candidate neuroblastoma tumor suppressor gene

MicroRNAs are small noncoding RNAs that have critical roles in regulating a number of cellular functions through transcriptional silencing. They have been implicated as oncogenes and tumor suppressor genes (oncomirs) in several human neoplasms. We used an integrated genomics and functional screening strategy to identify potential oncomirs in the pediatric neoplasm neuroblastoma. We first identified microRNAs that map within chromosomal regions that we and others have defined as frequently deleted (1p36, 3p22, and 11q23-24) or gained (17q23) in high-risk neuroblastoma. We then transiently transfected microRNA precursor mimics or inhibitors into a panel of six neuroblastoma cell lines that we characterized for these genomic aberrations. The majority of transfections showed no phenotypic effect, but the miR-34a (1p36) and miR-34c (11q23) mimics showed dramatic growth inhibition in cell lines with 1p36 hemizygous deletion. In contrast, there was no growth inhibition by these mimics in cell lines without 1p36 deletions. Quantitative reverse transcription-PCR showed a perfect correlation of absent miR-34a expression in cell lines with a 1p36 aberration and phenotypic effect after mimetic add-back. Expression of miR-34a was also decreased in primary tumors (n = 54) with 1p36 deletion (P = 0.009), but no mutations were discovered in resequencing of the miR-34a locus in 30 neuroblastoma cell lines. Flow cytometric time series analyses showed that the likely mechanism of miR-34a growth inhibition is through cell cycle arrest followed by apoptosis. BCL2 and MYCN were identified as miR-34a targets and likely mediators of the tumor suppressor phenotypic effect. These data support miR-34a as a tumor suppressor gene in human neuroblastoma.

MET gene copy number in non-small cell lung cancer: molecular analysis in a targeted tyrosine kinase inhibitor naïve cohort

INTRODUCTION

Recent clinical success of epidermal growth factor (EGFR)-tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer (NSCLC) have raised hopes that targeting other deregulated growth factor signaling, such as the hepatocyte growth factor/MET pathway, will lead to new therapeutic options for NSCLC. Furthermore, NSCLC present secondary EGFR-TKIs resistance related to exons 20 and 19 EGFR mutations or more recently to MET amplification. The aim of this study was to determine MET copy number related to EGFR copy number and K-Ras mutations in a targeted TKI naive NSCLC cohort.

METHODS

We investigated 106 frozen tumors from surgically resected NSCLC patients. Genes copy number of MET and EGFR were assessed by quantitative relative real-time polymerase chain reaction and K-Ras mutations by sequencing.

RESULTS

MET is amplified in 22 cases (21%) and deleted in nine cases (8.5%). EGFR is amplified in 31 cases (29%). K-Ras is mutated in 11 cases (10.5%). As observed for EGFR amplification, MET amplification is never associated with K-Ras mutation. MET amplification could be associated with EGFR amplification. MET amplification is not related to clinical and pathologic features. MET amplification and EGFR amplification showed a trend toward poor prognosis in adenocarcinomas.

CONCLUSION

In EGFR-TKIs naive NSCLC patients, MET amplification is a frequent event, which could be associated with EGFR amplification, but not with K-Ras mutation. MET amplification may identify a subset of NSCLC for new targeted therapy. It will also be important to evaluate MET copy number to properly interpret future clinical trials.

Gab1 but not Grb2 mediates tumor progression in Met overexpressing colorectal cancer cells

Hepatocyte growth factor receptor (Met) plays an important role in the progression of multiple cancer types. The overexpression of Met in DLD-1 colon carcinoma cells with kirsten rat sarcoma oncogene homolog (KRAS) oncogene activation resulted in enhanced subcutaneous and orthotopic tumor growth rate and increased metastatic potential. To elucidate the mechanism of this effect, we stably expressed kinase-inactive Met(K1110A), Src homology 2 (SH2)-binding domain-inactive Met(Y1349/1356F), growth factor receptor-bound protein 2 (Grb2) non-binding Met(N1358H) and mutant receptors with ability to selectively recruit signaling proteins Grb2, src homology domain c-terminal adaptor homolog (Shc), phospholipase c-gamma (PLCgamma) and p85 phosphatidyl inositol 3 kinase. As subcutaneous implants, DLD-1 cells that expressed the majority of these receptor constructs failed to recapitulate the tumor growth-enhancing effect of the wild-type Met receptor. The Grb2- and Shc-recruiting Met mutants demonstrated slight but consistent tumor-suppressive activity, whereas the expression of N1358H mutant stimulated tumor growth rate comparable with the wild-type receptor. This suggests that direct Grb2/Shc binding does not contribute to the tumor progression activity of Met receptor. The tumors expressing Grb2- and Shc-recruiting Met receptors demonstrated a marked loss in Grb2-associated adaptor protein 1 (Gab1) protein levels, which was not observed in the cell lines, consistent with a post-translationally regulated process. Moreover, a moderate level of Gab1 overexpression stimulated tumor growth. The findings suggest a delicate balance for intact Y1349/1356 SH2-binding domain to mediate the tumor progression activity of the coactivated Met-rat sarcoma oncogene homolog (RAS) pathways. Selectivity for specific adaptor protein involvement may be the key that determines the tissue- and cell-type specificity of Met-mediated tumorigenicity in human cancers.

Hepatocyte growth factor receptor c-MET is associated with FAS and when activated enhances drug-induced apoptosis in pediatric B acute lymphoblastic leukemia with TEL-AML1 translocation

Expression of c-MET, the HGF (hepatocyte growth factor) tyrosine kinase receptor, was investigated in pediatric B-acute lymphoblastic leukemia (ALL) patients. c-MET was found to be expressed in normal B cells and in B-ALL patients with the t(12;21) TEL-AML1 translocation, but it is not expressed in the most part of B-ALL without the t(12;21). We also found that c-MET, related to proliferation and protection from apoptosis, is associated with the pro-apoptotic protein FAS in TEL-AML1 B-ALL cells and in normal B lymphocytes. The possible role of this protein complex in drug-induced apoptosis was thus investigated in REH TEL-AML1 B-ALL cell line. REH cells prestimulated with HGF and treated with doxorubicin had shown a higher apoptotic rate than non-HGF-prestimulated ones (p = 0.03). REH cells stimulated with IL-3 and treated with doxorubicin did not undergo apoptosis more than nonstimulated cells, demonstrating that increased proliferation in itself is not directly related to the higher apoptotic sensitivity observed with HGF stimulation. These results indicate that c-MET activation enhances specifically FAS-mediated apoptosis in TEL-AML1 ALL cells and, considering that the c-MET/FAS complex is present only in normal B lymphocytes and in TEL-AML1 leukemias, this implies that it may have an important contribution in cellular homeostasis and in high sensitivity of TEL-AML1 ALL to chemotherapeutic regimens.

Involvement of HGF/SF-Met signaling in prostate adenocarcinoma cells: evidence for alternative mechanisms leading to a metastatic phenotype in Pr-14c

BACKGROUND

Hepatocyte growth factor/scatter factor (HGF/SF) facilitates intercellular communication between the epithelial carcinoma and its surrounding stromal tissue during metastatic invasion through interaction with its proto-oncogenic receptor, Met, found on carcinoma cells. This study utilizes the C31/Tag transgenic mouse prostate cancer cell line model in an attempt to characterize the interaction between HGF/SF and Met on the metastatic potential of prostate cancer.

METHODS

Exogenous HGF was supplied to the prostate adenocarcinoma cell line (Pr-14) and metastatic cell line (Pr-14c) to evaluate mitogenicity by proliferation assays, morphological characteristics on an extracellular matrix substrate, and motogenic properties using the scatter assay, invasion chambers, and zymogram studies to analyze secretory enzymes produced by the cell lines.

RESULTS

RNA and protein analyses show that the cell lines express similar amounts of Met. Pr-14 cells have an increased growth rate following HGF/SF treatment, whereas the metastatic Pr-14c cells show little change. Morphological studies of Pr-14c cells on extracellular matrix demonstrate negligible changes when compared to the tubular formation of Pr-14 cells after HGF/SF stimulation. Motility studies of the metastatic cells following HGF/SF treatment reveal a potentially faulty signaling pathway downstream of Met activation in the metastatic prostate cells.

CONCLUSIONS

Our studies suggest that proliferation, invasion, and cell morphological characteristics may be induced independently from the HGF/SF-Met pathway in C31/Tag metastatic prostate cancer cells.

Allelic imbalance at loci containing FGFR, FGF, c-Met and HGF candidate genes in non-small cell lung cancer sub-types, implication for progression

Fibroblast growth factors (FGF), hepatocyte growth factor (HGF) and their receptors, FGFR and c-Met, are essential components of the regulatory networks between the epithelium and mesenchyme in embryonic lung, but their respective roles in tumour growth are not clear. We performed allelotyping at loci containing the candidate genes FGFR-1-2-3-4, FGF-1-2-7-10, c-Met and HGF in 36 non-small cell lung cancer (NSCLC) (20 squamous-cell carcinomas (SQC) and 16 adenocarcinomas (ADC)), by surrounding each locus with two microsatellites (MS), as close as possible to the genes of interest. Unexpectedly, SQC and ADC were frequently altered at all of these loci, and SQC showed more simultaneously altered loci. In ADC, alterations at the 15q13-22 locus (FGF7 candidate gene) were significantly more frequent. Thus, these loci showed different patterns of molecular alterations between SQC and ADC. Finally, alterations at loci containing FGFR and HGF candidate genes were inversely correlated to the lymph node status in SQC and ADC, respectively.