Genetic disruption of oncogenic Kras sensitizes lung cancer cells to Fas receptor-mediated apoptosis.

Abstract

Genetic lesions that activate KRAS account for ∼30% of the 1.6 million annual cases of lung cancer. Despite clinical need, KRAS is still undruggable using traditional small-molecule drugs/inhibitors. When oncogenic <i>Kras</i> is suppressed by RNA interference, tumors initially regress but eventually recur and proliferate despite suppression of <i>Kras</i> Here, we show that tumor cells can survive knockout of oncogenic <i>Kras</i>, indicating the existence of <i>Kras</i>-independent survival pathways. Thus, even if clinical KRAS inhibitors were available, resistance would remain an obstacle to treatment. <i>Kras</i>-independent cancer cells exhibit decreased colony formation in vitro but retain the ability to form tumors in mice. Comparing the transcriptomes of oncogenic <i>Kras</i> cells and <i>Kras</i> knockout cells, we identified 603 genes that were specifically up-regulated in <i>Kras</i> knockout cells, including the <i>Fas</i> gene, which encodes a cell surface death receptor involved in physiological regulation of apoptosis. Antibodies recognizing Fas receptor efficiently induced apoptosis of <i>Kras</i> knockout cells but not oncogenic <i>Kras</i>-expressing cells. Increased Fas expression in Kras knockout cells was attributed to decreased association of repressive epigenetic marks at the <i>Fas</i> promoter. Concordant with this observation, treating oncogenic Kras cells with histone deacetylase inhibitor and Fas-activating antibody efficiently induced apoptosis, thus bypassing the need to inhibit Kras. Our results suggest that activation of Fas could be exploited as an Achilles' heel in tumors initiated by oncogenic Kras.