Mutational activation of the K-Ras oncogene is well established as a key genetic 
step in the development and growth of pancreatic adenocarcinomas. However, the 
mechanism by which aberrant Ras signaling promotes uncontrolled pancreatic tumor 
cell growth remains to be fully elucidated. The recent use of primary human 
cells to study Ras-mediated oncogenesis provides important model cell systems to 
dissect this mechanism. We have used a model of telomerase-immortalized human 
pancreatic duct-derived cells (E6/E7/st) to study mechanisms of Ras growth 
transformation. First, we found that human papillomavirus E6 and E7 oncogenes, 
which block the function of the p53 and Rb tumor suppressors, respectively, and 
SV40 small t antigen were required to allow mutant K-Ras(12D) growth 
transformation. Second, K-Ras(12D) caused growth transformation in vitro, 
including enhanced growth rate and loss of density dependency for growth, 
anchorage independence, and invasion through reconstituted basement membrane 
proteins, and tumorigenic transformation in vivo. Third, we determined that the 
Raf, phosphatidylinositol 3-kinase (PI3K), and Ral guanine nucleotide exchange 
factor effector pathways were activated, although extracellular signal-regulated 
kinase (ERK) activity was not up-regulated persistently. Finally, pharmacologic 
inhibition of Raf/mitogen-activated protein kinase/ERK and PI3K signaling 
impaired K-Ras-induced anchorage-independent growth and invasion. In summary, 
our studies established, characterized, and validated E6/E7/st cells for the 
study of Ras-induced oncogenesis.