Objective BACKGROUND & AIMS: Cancer cells rely on aerobic glycolysis to generate ATP for autonomous growth,a phenomenon termed “the Warburg effect”,and how the Warburg effect is turned on and off in cancer,however,is largely unknown.Kras is almost universally mutated in pancreatic ductal adenocarcinoma(Pdac)but is undruggable,and Kras oncogenesis is considered as a process of selective activation of the Warburg effect.We investigated if a Ras effector p38γ MAPK promotes Kras-induced Pdac by activating the Warburg effect with the goal to demonstrate p38γ as a therapeutic target for Pdac.Methods METHODS: We generated mice that were specifically depleted of p38γ(MAPK12)in pancreatic tissues and examined effects on pancreatitis and tumorigenesis.Moreover,a specific p38γ pharmacological inhibitor pirfenidone(PFD)was tested in vitro and in mice for its p38γ-dependent regulatory activities.Mass spectrometry was used to screen for novel p38γ-binding molecules and to identify potential phosphorylation on involved proteins.Further,glycolytic analyses were performed in KPC cells and tumors,with and without p38γ knockout and/or rescue,and clinical pancreatic tumor specimens were analyzed for protein expression and prognostic value.Results RESULTS: Mice with conditional p38γ knockout(KO)had attenuated pancreatitis with reduced pro-inflammatory cytokine expression.Moreover,KPC mice with p38γ KO(KPC/p38γ KO)survived 240 days longer than KPC counterparts.Analyses of three separate KPC and KPC/p38γ KO tumor cell lines(prepared from three respective KPC and KPC/p38γ KO mice)show that p38γ KO leads to decreased glucose uptake,reduced lactate secretion,and suppressed PFK activity.Seahorse-analyses further reveal that there is a decreased extracellular acidification rate(ECAR)(an indicator for glycolysis)but not a decreased oxygen consumption rate(OCR,an indicator of respiration),in KPC/p38γ KO cells as compared to KPC cells.Mechanistically,p38γ binds and phosphorylates the glycolytic activator PFKFB3 at S467 and thereby increases their binding affinity with the glucose transporter Glut2.This conclusion is supported by increased and decreased PFK activity by stably expressing PFKFB3/S467D and PFKFB3/S467A as compared to PFKFB3 in KPC,but not KPC/p38γ KO,cells.Pathway analyses further showed that stable expression of oncogenic Kras(G12V)in HPNE cells increases the levels of p-p38γ,p38γ,PFKFB3 and Glut2,but not Glut1,expression in HPNE cells; p38γ over-expression alone also results in similar increases in PFKFB3 and Glut2.Because Glut2 transfection stimulates protein expression of PFKFB3 but not p38γ,these results together indicate that p38γ may signal downstream of Kras and upstream of Glut2 and PFKFB3 in glycolysis.Of interest,PFKFB3 and Glut2 both depend on p38γ to stimulate glycolysis and/or growth,whereas PFKFB3/S467 phosphorylation is necessary for p38γ-induced glycolysis and Pdac growth and sufficient to promote glycolysis.Depletion of PFKFB3 significantly decreases glucose uptake,lactate secretion,PFK activity,ECAR and colony formation in KPC cells,but not in KPC/p38γ KO cells.The p38γ inhibitor Pirfenidone also suppresses pancreatic tumorigenesis and growth and decreases p-PFKFB3 expression dependent of p38γ in mice and in cells.Furthermore,the p38γ-p-PFKFB3-PFKFB3-Glut2 pathway is overexpressed in clinical specimens and is reversely correlated with patient survival.Conclusions CONCLUSION: Our results demonstrated that p38γ MAPK promotes Pdac tumorigenesis by converting K-Ras oncogenic signaling into PFKFB3/Glut2-dependent glycolysis and targeting p38γ with its inhibitor PFD may be a novel targeted therapy for pancreatic cancer by disrupting metabolic reprogramming.