Regulation of the Hedgehog Signaling by the Mitogen-Activated Protein Kinase Cascade in Gastric Cancer

The hedgehog and mitogen-activated protein kinase (MAPK) signaling pathways regulate growth in many tumors, suggesting cooperation between these two pathways in the regulation of cell proliferation. However, interactions between these pathways have not been extensively studied. We assessed cross-talk between hedgehog and MAPK signaling in the regulation of cell proliferation in gastric cancer. We showed that PTCH expression was significantly correlated with extracellular signal-regulated kinase (ERK) 1/2 phosphorylation (P=0.016) as well as SHH expression (P=0.034) in the 35 gastric cancers assessed by immunohistochemistry. Indeed, MAPK signaling increased the GLI transcriptional activity and induced the expression of hedgehog target genes in gastric cancer cells. The inductive effect of activated KRAS and mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) 1 was blocked by the suppressor of fused (SUFU), indicating that MAPK signaling regulates GLI activity via a SUFU-independent process. Moreover, the deletion of the NH2-terminal domain of GLI1 gene resulted in reduced response to MEK1 stimulation. Our results suggest that the KRAS-MEK-ERK cascade has a positive regulatory role in GLI transcriptional activity in gastric cancer. (C) 2009 Wiley-Liss, Inc.