Oncogenic KRAS sensitizes premalignant, but not malignant cells, to Noxa-dependent apoptosis through the activation of the MEK/ERK pathway

// Annalisa Conti 1 , Maria Teresa Majorini 1 , Richard Elliott 2 , Alan Ashworth 2,8 , Christopher J. Lord 2 , Carlotta Cancelliere 3,4,5 , Alberto Bardelli 3,4,5 , Pierfausto Seneci 6 , Henning Walczak 7 , Domenico Delia 1 and Daniele Lecis 1 1 Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy 2 The Breakthrough Breast Cancer Research Centre and CRUK Gene Function Laboratory, The Institute of Cancer Research, London, UK 3 Department of Oncology, University of Torino, Candiolo, Torino, Italy 4 Candiolo Cancer Institute - FPO, IRCCS, Candiolo, Torino, Italy 5 FIRC Institute of Molecular Oncology (IFOM), Milano, Italy 6 Università Degli Studi di Milano, Dipartimento di Chimica, Milan, Italy 7 Centre for Cell Death, Cancer, and Inflammation, University College London, London, UK 8 Current Address: UCSF Helen Diller Family Comprehensive Cancer Centre, San Francisco, California, USA Correspondence: Daniele Lecis, email: // Keywords : KRAS, Smac mimetics, colorectal cancer, camptothecin Received : January 23, 2015 Accepted : February 21, 2015 Published : March 12, 2015 Abstract KRAS is mutated in about 20-25% of all human cancers and especially in pancreatic, lung and colorectal tumors. Oncogenic KRAS stimulates several pro-survival pathways, but it also triggers the trans-activation of pro-apoptotic genes. In our work, we show that G13D mutations of KRAS activate the MAPK pathway, and ERK2, but not ERK1, up-regulates Noxa basal levels. Accordingly, premalignant epithelial cells are sensitized to various cytotoxic compounds in a Noxa-dependent manner. In contrast to these findings, colorectal cancer cell sensitivity to treatment is independent of KRAS status and Noxa levels are not up-regulated in the presence of mutated KRAS despite the fact that ERK2 still promotes Noxa expression. We therefore speculated that other survival pathways are counteracting the pro-apoptotic effect of mutated KRAS and found that the inhibition of AKT restores sensitivity to treatment, especially in presence of oncogenic KRAS. In conclusion, our work suggests that the pharmacological inhibition of the pathways triggered by mutated KRAS could also switch off its oncogene-activated pro-apoptotic stimulation. On the contrary, the combination of chemotherapy to inhibitors of specific pro-survival pathways, such as the one controlled by AKT, could enhance treatment efficacy by exploiting the pro-death stimulation derived by oncogene activation.