An effect of K-ras gene mutation on epidermal growth factor receptor signal transduction in PANC-1 pancreatic carcinoma cells

Abstract

The Ras protein is involved in tyrosine kinase signal transduction pathway steps such as EGFR signalling. Most human pancreatic carcinomas harbor a point mutation of K-ras oncogene and overexpress transforming TGF- α. We studied how K-ras gene mutation could influence the EGFR signal transduction mechanism and the autonomous proliferation of pancreatic carcinoma cells, using PANC-1 human pancreatic carcinoma line and WI-38 normal human fibroblast cell line as a control. PANC-1 cells responded to neither EGF nor exogenous TGF-α, although anti-TGF-α MAb suppressed their growth. Expression of TGF-α mRNA was detected only in PANC-1 cells, which confirmed EGFR being within an autocrine loop. Ras protein and MAP kinase were constitutively activated in PANC-1 cells so that the cells did not respond to treatment with staurosporine or herbimycin A, and exhibited slight response to EGF stimulation. PANC-1 cells harbored K-ras gene mutation in codon 12. In contrast, EGF stimulation induced an elevation of GTP-bound ratio to Ras protein and an activation of MAP kinase with accelerated growth in WI-38 cells. From these findings, we concluded that K- ras gene mutation possibly plays an important role in the autonomous proliferation of PANC-1 pancreatic carcinoma cells, and that an autocrine loop represented by TGF-α and EGFR may further accelerate the growth of PANC-1 cells.