Expression of MET and HGF in bladder cancer tumorigenesis and invasion.

Abstract

4573 Background: The human MET gene encodes the hepatocyte growth factor (HGF) tyrosine kinase receptor. Limited studies in human bladder cancer have demonstrated that expression of MET protein is linked with disease progression and survival. We hypothesized that the expression of both MET and its ligand HGF are altered in bladder cancer. Methods: Expression of MET and HGF in human bladder tissues was explored using Oncomine, an online compendium of cancer transcriptome profiles. The largest relevant dataset was identified and contained 157 samples (Sanchez-Carbayo, et al. 2006). Normalized and log2 transformed mRNA expression values for Affymetrix U133 microarray probe sets corresponding to the genes of interest were compiled and averaged for each gene. Mann-Whitney U testing was used to compare means. Nominal and standard least squares logistic regression was used to evaluate the predictive significance of, and relevance of clinicopathologic variables on, gene expression. Statistical analyses were carried out using JMP 9.0.2. Results: Expression of MET and HGF was compared across subsets of normal bladder tissue (n=48), superficial tumors (n=28), and invasive tumors (n = 81). Relative to normal tissue, MET expression was greater in superficial (p = 0.0008) and invasive tumors (p<0.0001). HGF expression was reduced in both invasive and superficial tumors vs. normal tissue (both p< 0.0001), but was higher in invasive vs. superficial tumors (p= 0.0007). In a logistic regression model of tumor samples, both MET and HGF correlated with tumor invasion (model p=0.0003). Interaction between MET and HGF was not significant (p=0.55). Neither MET nor HGF expression was predicted by regression using age, gender, grade, or nodal stage (p=0.16 and 0.27, respectively). Conclusions: Decreased HGF expression and MET over-expression are strongly associated with tumorigenesis and invasion in bladder cancer. The reduction in HGF expression is blunted in invasive vs. superficial tumors, suggesting a potential loss of negative feedback in more aggressive tumors. Expression of both genes could not be predicted by modeling clinicopathologic variables. MET signaling represents a potential therapeutic target in bladder cancer.