Mutant KRAS-induced Macrophage Migration Inhibitory Factor (MIF) secretion promotes resistance to cetuximab in colorectal cancer

Abstract

The tumor microenvironment is recognized as a developing crosstalk between different cells by secretion of growth factors and cytokines thus providing oncogenic signals enhancing tumor progression and drug resistance. Here, I hypothesized that tumor cells carrying KRAS mutation-induced cytokines may have critical roles in intercellular communication between microenvironment and tumor cells. I first investigated biological evidence of secreted cytokines in KRAS mutant-type (KRASMT) cell lines. I explored the roles of cytokine that cell morphology, proliferation, colony formation, wound healing, and invasion ability were enhanced when KRAS wild-type (KRASWT) cells were exposed to conditioned media (CM) from KRASMT cells and I found macrophage migration inhibitory factor (MIF) was highly expressed in KRASMT cells by analysis of proteomics. I also observed secreted MIF level between KRASWT and KRASMT cells, and it was highly secreted in KRASMT cells. In addition, compared with colorectal cancer patients whose KRAS mutation was not harbored, MIF expression was higher in patients who have KRAS mutation. The predictive marker of KRAS mutation in colorectal cancer patients is associated with resistance to anti-epidermal growth factor receptor (EGFR) antibodies cetuximab (CTX). Following the hypothesis, I investigated that secreted cytokines from KRASMT cells have an effect on the cetuximab resistance to the surrounding cells including KRASWT cells. Treatment of CM led to cetuximab resistance in KRASWT cells and MIF blockade prevented cetuximab resistance. Moreover, CM from MIF knocked out KRASMT cells by using CRISPR/Cas9 system resulted in sensitizing to cetuximab resistance compared with treatment of CM from KRASMT cells. <br/> In conclusion, I demonstrated for the first time that MIF promoted the cetuximab resistance of KRASWT colorectal cancer cells, and this effect was mediated by paracrine and autocrine signaling-induced activation of the intracellular AKT signaling pathways and regulated by NF-kB transcription factor through oncogenic KRAS mutation. These findings suggest that MIF may be a promising predictive biomarker for the cetuximab resistance of KRAS wild-type colorectal cancer patients.<br/>