This study identifies a novel crosstalk paradigm between the IGF1R and EGFR in colon cancer cells. IGF1R activation by ligand exposure in growth factor deprived cells induces Akt activation in the FET, CBS and GEO colon cancer cell lines. Investigation of IGF1R mediated signaling pathways using siRNA approaches indicated that, as expected, PI3K was activated by IGF1R. MAPK activity as reflected by phospho-Erk induction was not significantly activated until later times following release of these cells from growth factor deprivation stress. The appearance of phospho-Erk was proximal to EGFR activation. Treatment of cells with the PI3K inhibitor LY294002 prior to release from stress resulted in a concentration dependent loss of EGFR activation while treatment with the MAPK inhibitor PD98059 did not block EGFR activation indicating that EGFR activation was downstream of the IGF1R/PI3K pathway. PD98059 inhibition of MAPK was associated with a concentration dependent reduction in EGFR-mediated phospho-Erk. EGFR inhibitor blocked induction of phospho-Erk showing that MAPK activity was a consequence of EGFR mediated signaling. On the other hand, a small molecule IGF1R inhibitor, PQIP, blocked Akt phosphorylation. The divergent signaling functions of IGF1R and EGFR suggested the potential for synergism by a combination of therapy directed at the 2 receptors. Combination treatment with PQIP and EGFR inhibitor Tarceva resulted in synergistic effects as indicated by combination index analysis in all 3 cell lines tested.

Chronic inflammatory periodontal disease develops in part from the infiltration of a large number of classically activated inflammatory macrophages that release inflammatory cytokines important for disease progression, including inflammasome-dependent IL-1β. Streptococcus gordonii is a normally commensal oral microorganism; while not causative, recent evidence indicates that commensal oral microbes are required for the full development of periodontal disease. We have recently reported that inflammatory macrophages counterintuitively allow for the increased survival of phagocytosed S. gordonii over non-activated or alternatively activated macrophages. This survival is dependent on increased ROS production within the phagosome of the inflammatory macrophages and resistance by the bacterium and can result in S. gordonii damaging the phagolysosomes. Here we show that activated macrophages infected with live S. gordonii release more IL-1β than macrophages infected with other oral microbes, both classical pathogens and commensals. We also find that S. gordonii dependent inflammatory macrophage inflammasome activation requires the cytoplasmic NLRP6. Overall, our results suggest S. gordonii is capable of evading immune destruction, increasing inflammatory mediators, and increasing inflammatory macrophage response; and that this ability is increased under conditions of inflammation. This work reveals additional mechanisms by which normally commensal oral streptococci-macrophage interactions can change, resulting in increased release of mature IL-1β, potentially contributing to an environment that perpetuates inflammation.