Mutant KRAS in lung cancers induces molecular pathways that regulate cellular proliferation, survival and inflammation, which enhance tumorigenesis. Inducible nitric oxide synthase (NOS2) upregulation and sustained nitric oxide generation are induced during the inflammatory response and correlate positively with lung tumorigenesis. To explore the mechanistic contribution of NOS2 to KRAS-induced lung tumorigenesis and inflammation, we used a genetic strategy of crossing NOS2 knockout (NOS2KO) C57BL6 inbred mice with a KRAS(G12D) -driven mouse lung cancer model. KRAS(G12D);NOS2KO mice exhibited delayed lung tumorigenesis and a longer overall survival time compared to that of KRAS(G12D);NOS2WT (wild-type) controls. Correspondingly, tumors in KRAS(G12D);NOS2KO mice had reduced tumor cell proliferation in adenomas and carcinomas. NOS2 deficiency also led to markedly suppressed inflammatory response by attenuation of macrophage recruitment into alveoli and within tumor foci. In contrast, FOXP3+ regulatory T cells were increased in tumors from KRAS(G12D);NOS2KO mice. We further analyzed the expression of microRNA-21 (miR-21), an oncogenic noncoding RNA involved in oncogenic Ras signaling, by quantitative reverse-transcription polymerase chain reaction and in situ hybridization. Lung carcinomas dissected from KRAS(G12D);NOS2KO mice showed a significantly reduced miR-21 expression along with decreased tumor cell proliferation, suggesting that NOS2 deficiency could attenuate RAS signaling pathways that transactivate miR-21 expression. Therefore, deletion of NOS2 decreases lung tumor growth as well as inflammatory responses initiated by oncogenic KRAS, suggesting that both KRAS and NOS2 cooperate in driving lung tumorigenesis and inflammation. Inhibition of NOS2 may have a therapeutic value in lung cancers with oncogenic KRAS mutations.
|Pine, Sharon R; Mechanic, Leah E; Enewold, Lindsey et al. (2011) Increased levels of circulating interleukin 6, interleukin 8, C-reactive protein, and risk of lung cancer. J Natl Cancer Inst 103:1112-22|
|Schetter, Aaron J; Heegaard, Niels H H; Harris, Curtis C (2010) Inflammation and cancer: interweaving microRNA, free radical, cytokine and p53 pathways. Carcinogenesis 31:37-49|
|Weiss, Jonathan M; Ridnour, Lisa A; Back, Tim et al. (2010) Macrophage-dependent nitric oxide expression regulates tumor cell detachment and metastasis after IL-2/anti-CD40 immunotherapy. J Exp Med 207:2455-67|
|Enewold, Lindsey; Mechanic, Leah E; Bowman, Elise D et al. (2009) Serum concentrations of cytokines and lung cancer survival in African Americans and Caucasians. Cancer Epidemiol Biomarkers Prev 18:215-22|
|Simone, Nicole L; Soule, Benjamin P; Ly, David et al. (2009) Ionizing radiation-induced oxidative stress alters miRNA expression. PLoS One 4:e6377|