◥KRAS is mutated in most pancreatic ductal adenocarcinomas (PDAC) and yet remains undruggable. Here, we report that p38g MAPK, which promotes PDAC tumorigenesis by linking KRAS signaling and aerobic glycolysis (also called the Warburg effect), is a novel therapeutic target. p38g interacted with a glycolytic activator PFKFB3 that was dependent on mutated KRAS. KRAS transformation and overexpression of p38g increased expression of PFKFB3 and glucose transporter GLUT2, conversely, silencing mutant KRAS, and p38g decreased PFKFB3 and GLUT2 expression. p38g phosphorylated PFKFB3 at S467, stabilized PFKFB3, and promoted their interaction with GLUT2. Pancreatic knockout of p38g decreased p-PFKFB3/PFKFB3/GLUT2 protein levels, reduced aerobic glycolysis, and inhibited PDAC tumorigenesis in KPC mice. PFKFB3 and GLUT2 depended on p38g to stimulate glycolysis and PDAC growth and p38g required PFKFB3/S467 to promote these activities. A p38g inhibitor cooperated with a PFKFB3 inhibitor to blunt aerobic glycolysis and PDAC growth, which was dependent on p38g. Moreover, overexpression of p38g, p-PFKFB3, PFKFB3, and GLUT2 in PDAC predicted poor clinical prognosis. These results indicate that p38g links KRAS oncogene signaling and aerobic glycolysis to promote pancreatic tumorigenesis through PFKFB3 and GLUT2, and that p38g and PFKFB3 may be targeted for therapeutic intervention in PDAC.Significance: These findings show that p38g links KRAS oncogene signaling and the Warburg effect through PFKBF3 and Glut2 to promote pancreatic tumorigenesis, which can be disrupted via inhibition of p38g and PFKFB3.

Protein kinases and phosphatases signal by phosphorylation and dephosphorylation to precisely control the activities of their individual and common substrates for a coordinated cellular outcome. In many situations, a kinase/phosphatase complex signals dynamically in time and space through their reciprocal regulations and their cooperative actions on a substrate. This complex may be essential for malignant transformation and progression and can therefore be considered as a target for therapeutic intervention. p38γ is a unique MAPK family member that contains a PDZ motif at its C-terminus and interacts with a PDZ domain-containing protein tyrosine phosphatase PTPH1. This PDZ-coupled binding is required for both PTPH1 dephosphorylation and inactivation of p38γ and for p38γ phosphorylation and activation of PTPH1. Moreover, the p38γ/PTPH1 complex can further regulate their substrates phosphorylation and dephosphorylation, which impacts Ras transformation, malignant growth and progression, and therapeutic response. This review will use the p38γ/PTPH1 signaling network as an example to discuss the potential of targeting the kinase/phosphatase signaling complex for development of novel targeted cancer therapy.

<div>Abstract<p>KRAS is mutated in most pancreatic ductal adenocarcinomas (PDAC) and yet remains undruggable. Here, we report that p38γ MAPK, which promotes PDAC tumorigenesis by linking KRAS signaling and aerobic glycolysis (also called the Warburg effect), is a novel therapeutic target. p38γ interacted with a glycolytic activator PFKFB3 that was dependent on mutated KRAS. KRAS transformation and overexpression of p38γ increased expression of PFKFB3 and glucose transporter GLUT2, conversely, silencing mutant KRAS, and p38γ decreased PFKFB3 and GLUT2 expression. p38γ phosphorylated PFKFB3 at S467, stabilized PFKFB3, and promoted their interaction with GLUT2. Pancreatic knockout of p38γ decreased p-PFKFB3/PFKFB3/GLUT2 protein levels, reduced aerobic glycolysis, and inhibited PDAC tumorigenesis in KPC mice. PFKFB3 and GLUT2 depended on p38γ to stimulate glycolysis and PDAC growth and p38γ required PFKFB3/S467 to promote these activities. A p38γ inhibitor cooperated with a PFKFB3 inhibitor to blunt aerobic glycolysis and PDAC growth, which was dependent on p38γ. Moreover, overexpression of p38γ, p-PFKFB3, PFKFB3, and GLUT2 in PDAC predicted poor clinical prognosis. These results indicate that p38γ links KRAS oncogene signaling and aerobic glycolysis to promote pancreatic tumorigenesis through PFKFB3 and GLUT2, and that p38γ and PFKFB3 may be targeted for therapeutic intervention in PDAC.</p>Significance:<p>These findings show that p38γ links KRAS oncogene signaling and the Warburg effect through PFKBF3 and Glut2 to promote pancreatic tumorigenesis, which can be disrupted via inhibition of p38γ and PFKFB3.</p></div>

<p>Figure S7. PFD collaborates with PFK15 to inhibit glucose uptake, lactate secretion, and Pdac growth and upregulated p-PFKFB3 in Pdac specimens is positively correlated with overexpressed p38ÃŽÃ,³ and Glut2.</p>

<p>Figure S5. PFD decreases p-PFKFB3, PFKFB3 and Glut2 expression in primary KPC tumors and suppresses allograft growth of KPC, but not KPC/p38ÃŽÃ,³ KO tumor, in association with decreased Ki67, p-PFKFB3, PFKFB3 and ÃŽÃ,±-SMA expression in tumor tissues.</p>