Oncogenic Ras modulates p38 MAPK-mediated inflammatory cytokine production in glioblastoma cells

Abstract

ABSTRACTInflammation is an important factor promoting the progression of glioblastoma. In the present study we examined the contribution of Ras signaling and TNFα/IL-1β cytokines to the development of the glioblastoma inflammatory microenvironment. Enhanced activation of Ras through de-regulated activation of receptor tyrosine kinases, such as EGFR, PDGFR and cMet, is a hallmark of the majority of glioblastomas. Glioblastoma microenvironment contains high levels of TNFα and IL-1β, which mediate inflammation through induction of a local network of cytokines and chemokines. While many studies have focused on Ras- and TNFα/IL-1β-driven inflammation in isolation, little is known about the co-operation between these oncogenic and microenvironment-derived stimuli. Using constitutively active HRasG12V that mimics enhanced Ras activation, we demonstrate that elevated Ras activity in glioblastoma cells leads to up-regulation of IL-6 and IL-8. Furthermore, Ras synergizes with the microenvironment-derived TNFα and IL-1β resulting in amplified IL-6/IL-8 secretion. IL-8 secretion induced by Ras and TNFα/IL-1β is attenuated by inhibitors targeting Erk, JNK and p38 MAPK pathways. IL-6 secretion significantly decreased upon inhibition of JNK and p38 MAPK pathways. Interestingly, although constitutively active HRasG12V does not increase basal or TNFα/IL-1β stimulated p38 MAPK activity, HRasG12V increased the efficacy of the p38 MAPK inhibitor SB203580 to inhibit IL-1β-induced IL-6 secretion. In summary, oncogenic Ras co-operates with the microenvironment-derived TNFα/IL-1β to sustain inflammatory microenvironment, which was effectively attenuated via inhibition of p38 MAPK signaling.