Abstract 1899: MKK4/JNK2 down-regulation in NSCLC suppresses tumor growth and metastasis
Authors: Tamer Saad Kaoud, Nancy D. Ebelt, Lili Du, Sabrina Van Ravenstein, Kenneth Y. Tsai, Kevin N. Dalby
Journal: Cancer Research (2017)

Abstract Mitogen-activated protein kinase kinase-4 (MKK4) has been reported to either enhance or suppress oncogenesis. Evidences of its pro-oncogenic activities in breast, pancreatic, lung and skin cancer have been reported. Although the mechanism of its possible tumorigenic role is still unclear. Recent studies in glioblastoma and lung carcinoma have suggested important roles for the constitutive activation of its downstream substrate JNK2. JNKs require phosphorylation by both MKK4 and MKK7 to be fully activated. The JNK2 isoform shows a unique propensity among the JNKs to autophosphorylate in vitro. Here we show that JNK2 autophosphorylation contributes to the proliferation and migration of NSCLC cells under conditions of low serum through an MKK4-dependent mechanism. This suggests a pro-oncogenic role of MKK4 in NSCLC through a JNK2 autophosphorylation-dependent pathway. Evidence in several cell lines, including mouse embryonic stem cells lacking MKK4 or MKK7 suggests that autophosphorylation alone activates JNK2 weakly in cells. However, JNK2 autophosphorylates on Thr-183, to create a pool of JNK2 primed for activation by MKK4, which phosphorylates JNK2 on Tyr-185 to activate it. Under conditions of low serum the down-regulation/overexpression of MKK4 or JNK2 but not MKK7 or JNK1 suppresses/promotes proliferation of multiple NSCLC cell lines, through STAT3. Under the same conditions, A549 cell migration is inhibited upon down regulation of either MKK4 or JNK2. Further supporting the notion that active JNK2 results primarily from autophosphorylation of Thr-183, pan-JNK ATP competitive inhibitors (JNK-IN-8 and SP600125) showed a dose-dependent dephosphorylation of JNK2 in NSCLC cell lines and inhibited their proliferation under conditions of low serum. Moreover, the downregulation of MKK4 or inhibition of JNK2 autophosphorylation by SP600125 inhibited nuclear localization of JNK2 in A549 cells cultured in low serum. To further understand the pro-oncogenic role of MKK4 in the A549 cell line, we investigated tumor growth and lung metastasis in A549 Xenografts in which either JNK2 or MKK4 were stably knocked down. Either JNK2 or MKK4 down regulation showed a similar suppression of tumor growth and lung metastasis if compared to cells expressing an shRNA control. Sequencing of MKK4 in the A549 cells revealed no genomic deletion or somatic mutations. Taken together, the data suggest that MKK4 may exhibit pro-oncogenic properties in NSCLC by activating Thr-183-autophosphorylated JNK2. Targeting this pathway may reduce or block lung tumor progression and/or metastasis. Note: This abstract was not presented at the meeting. Citation Format: Tamer Saad Kaoud, Nancy D. Ebelt, Lili Du, Sabrina Van Ravenstein, Kenneth Y. Tsai, Kevin N. Dalby. MKK4/JNK2 down-regulation in NSCLC suppresses tumor growth and metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1899. doi:10.1158/1538-7445.AM2017-1899