PKCδ regulates integrin αVβ3 expression and transformed growth of K-ras dependent lung cancer cells

We have previously shown that Protein Kinase C delta (PKC delta) functions as a tumor promoter in non-small cell lung cancer (NSCLC), specifically in the context of K-ras addiction. Here we define a novel PKC delta -> integrin alpha(V)beta(3) -> Extracellular signal-Regulated Kinase (ERK) pathway that regulates the transformed growth of K-ras dependent NSCLC cells. To explore how PKC delta regulates tumorigenesis, we performed mRNA expression analysis in four KRAS mutant NSCLC cell lines that stably express scrambled shRNA or a PKC delta targeted shRNA. Analysis of PKC delta-dependent mRNA expression identified 3183 regulated genes, 210 of which were specifically regulated in K-ras dependent cells. Genes that regulate extracellular matrix and focal adhesion pathways were most highly represented in this later group. In particular, expression of the integrin pair, alpha(V)beta(3), was specifically reduced in K-ras dependent cells with depletion of PKC delta, and correlated with reduced ERK activation and reduced transformed growth as assayed by clonogenic survival. Re-expression of PKC delta restored ITGAV and ITGB3 mRNA expression, ERK activation and transformed growth, and this could be blocked by pretreatment with a alpha(V)beta(3) function-blocking antibody, demonstrating a requirement for integrin alpha(V)beta(3) downstream of PKC delta. Similarly, expression of integrin alpha(V) restored ERK activation and transformed growth in PKC delta depleted cells, and this could also be inhibited by pretreatment with PD98059. Our studies demonstrate an essential role for alpha(V)beta(3) and ERK signaling downstream of PKC delta in regulating the survival of K-ras dependent NSCLC cells, and identify PKC delta as a novel therapeutic target for the subset of NSCLC patients with K-ras dependent tumors.