Apoptosis and growth inhibition by sprouty2 in non-small cell lung cancer

Abstract

Sprouty2 proteins function as inhibitors of receptor tyrosine kinase signalingmainly by interfering with the Ras/Raf/mitogen-activated protein kinasecascade, a pathway frequently deregulated in human non-small cell lungcancer (NSCLC). In this study, it was shown that sprouty2 protein expressionwas consistently downregulated in NSCLC. Analysis of sprouty2 usingONCOMINE data set further indicated that sprouty2 was downregulated inNSCLC tissues compared with normal lung tissues. Ectopic expression ofsprouty2 not only induced cell death in an apoptotic manner but also resultedin cell cycle arrest in various NSCLC cell lines. Furthermore, sprouty2overexpression substantially reduced migratory capacity in H1975 cells.Overexpression of sprouty2 did not interfere with activation of the majordownstream targets of epidermal growth factor receptor (EGFR) includingextracellular signal–regulated kinase, Akt, and signal transducer and activatorof transcription 3/5. Instead, sprouty2 overexpression promoted apoptosis inH1975 cells via activation of c-Jun NH (2)-terminal kinase (JNK). Thetransfection of H358 cells with sprouty2 siRNA decreased phosphorylation ofJNK, which further suggested the specificity of sprouty2 on the activation ofJNK. In addition, sprouty2 expression in combination with gefitinib, a smallmolecule EGFR inhibitor, synergistically induced apoptosis via augmentedactivation of JNK in NSCLC cells. Finally, sprouty2 expression resulted inthe regression of H1975 tumor xenograft in vivo due to the combined effectson tumor cell proliferation, survival and tumor angiogenesis. In conclusion, sprouty2 expression is generally repressed in NSCLC, and overexpression ofsprouty2 contributes to induction of apoptosis, reduced migratory capacity, andgrowth inhibition by enhancing JNK-mediated mitogen-activated proteinkinases pathway. Results of this study implicate that sprouty2 represents atumor suppressor in NSCLC and suggest sprouty2 re-expression as apromising therapeutic target against NSCLC.