Acylglycerol kinase augments JAK2/STAT3 signaling in esophageal squamous cells
Xiuting Chen, … , Mengfeng Li, Libing Song
Xiuting Chen, … , Mengfeng Li, Libing Song
Published May 8, 2013
Citation Information: J Clin Invest. 2013;123(6):2576-2589. https://doi.org/10.1172/JCI68143.
View: Text | PDF
Research Article Oncology Article has an altmetric score of 10

Acylglycerol kinase augments JAK2/STAT3 signaling in esophageal squamous cells

Abstract

JAK2 activity is tightly controlled through a self-inhibitory effect via its JAK homology domain 2 (JH2), which restricts the strength and duration of JAK2/STAT3 signaling under physiological conditions. Although multiple mutations within JAK2, which abrogate the function of JH2 and sustain JAK2 activation, are widely observed in hematological malignancies, comparable mutations have not been detected in solid tumors. How solid tumor cells override the autoinhibitory effect of the JH2 domain to maintain constitutive activation of JAK2/STAT3 signaling remains puzzling. Herein, we demonstrate that AGK directly interacted with the JH2 domain to relieve inhibition of JAK2 and activate JAK2/STAT3 signaling. Overexpression of AGK sustained constitutive JAK2/STAT3 activation, consequently promoting the cancer stem cell population and augmenting the tumorigenicity of esophageal squamous cell carcinoma (ESCC) cells both in vivo and in vitro. Furthermore, AGK levels significantly correlated with increased STAT3 phosphorylation, poorer disease-free survival, and shorter overall survival in primary ESCC. More importantly, AGK expression was significantly correlated with JAK2/STAT3 hyperactivation in ESCC, as well as in lung and breast cancer. These findings uncover a mechanism for constitutive activation of JAK2/STAT3 signaling in solid tumors and may represent a prognostic biomarker and therapeutic target.

Authors

Xiuting Chen, Zhe Ying, Xi Lin, Huanxin Lin, Jueheng Wu, Mengfeng Li, Libing Song

×

Figure 2

AGK enhances JAK2 activity by blocking JH2-mediated autoinhibition of JAK2.

Options: View larger image (or click on image) Download as PowerPoint
AGK enhances JAK2 activity by blocking JH2-mediated autoinhibition of JA...
(A) Depletion of AGK did not affect the interaction between JAK2 and STAT3 (left panel). Depletion of STAT3 did not alter the interaction between JAK2 and AGK (middle panel). Depletion of JAK2 impaired the interaction between AGK and STAT3 (right panel). (B) Schematic illustration of wild-type JAK2 and the truncated JAK2. (C) Coimmunoprecipitation assay showing that AGK specifically interacted with the JH2 domain of JAK2. (D) Immunoprecipitated HA-tagged JAK2 and the JH2 domain were gel purified, transferred to a membrane, and incubated with His-tagged recombinant AGK, then detected using an antibody specific to 6 × His or the HA tag. Recombinant His-tagged AGK was used as a control. (E) Expression of p-JAK2 (Tyr1007-1008) in whole-cell lysates (WCL) from HEK293T cells transfected with vector or AGK (left panel). Total JAK2 was used as a control. Tyrosine phosphorylation status of the immunoprecipitated JH2 domain from HEK293T cells cotransfected with JH2 and vector or AGK (right panel). (F) In vitro kinase assay of immunoprecipitated JAK2 incubated with or without recombinant AGK. Recombinant STAT3 was used as the substrate. (G) The expression of p-STAT3 (Tyr705) and p-JAK2 (Tyr1007-1008) in the indicated cells infected with wild-type AGK or a kinase-dead AGK mutant (AGK G126E). (H) Immunoprecipitation assay indicating that the mutated AGK (AGK G126E) interacted with JAK2 in the indicated cells.