The role of HGF/c-met signal transduction pathway in non-small cell lung cancer

Objective: HGF and c-Met are often overexpressed in non-small-cell lung cancer (NSCLC). However, their role in tumor progression is not clearly defined. The aim of this study is to investigate the role of HGF/c-Met pathway in NSCLC.Methods: The expression of HGF and c-Met were determined immunohistochemically in parafin-embedded tissue samples of 63 NSCLC patients, which were provided from Dokuz Eylül University School of Medicine pathology archive. DNAs obtained from sections of the same tissues were amplified by polymerase chain reaction (PCR) using exons specific primers that encode tramsmembranal domain (exon 13), juxtamembranal domain (exon 14) and cytoplasmic domain (exons 15-21) ( include tyrosine kinase activity (exons 20-21)) of the c-Met receptor. DNA sequence analysis was conducted in these PCR products. We also investigated the expressions of RhoA and MMPs (MMP-2 and MMP-9) along with their tissue inhibitors (TIMP-1 and TIMP-3) and their association with HGF and c-Met expressions. In addition, the relationship between all the parameters examined by either IHC or PCR and clinical parameters including survival and stage were investigated.Results: Immunohistochemically, strong c-Met and HGF expressions were found in 81 % and 48 % of NSCLC tissues, respectively. c-Met overexpression in squamous cell cancers was significantly higher than in adenocarcinomas. We identified two novel silent mutations, c1254 T-->C transition (D1254D) in exon 20-21 (1) and g1339 A-->G transition (A1339A) in exon 20-21 (2). The positive immunostaining rates for MMP-2, TIMP-1, TIMP-3 and RhoA were 69%, 49%, 32% and 8%, respectively. MMP-9 overexpression was not encountered in any of the cases. We determined that TIMP- 3 and RhoA overexpression was statistically higher in cases, in which HGF overexpression (p=0.002 and p=0.045) or HGF/c-Met coexpression (p=0.010 and p=0.011) were present. In addition, c-Met overexpression/mutations and all the studied immunostaining parameters were not correlated with tumor size, tumor stage, lymph node metastasis and relapse rate. However, the incidence of lymph node involvement was higher in the cases which had HGF/c-Met coexpression. The cases with RhoA overexpression or double mutation in c-Met were found to have significantly lower survival time.Conclusion: Present study shows that HGF/c-Met pathway may play a role in NSCLC development and/or progression. Our data support the opinion that c-Met overexpression may be independent of HGF. Our data suggest that HGF/c-Met overexpression increases invasion and metastasis via RhoA and TIMP-3 in NSCLC, especially in adenocarcinoma. The blockade of the HGF/c-Met pathway with RhoA and/or TIMP-3 inhibitors may be an effective therapeutic target for NSCLC treatment.Keywords: HGF, c-Met, mutation, metastasis, RhoA, TIMP-3, NSCLC