NOS2 enhances KRAS-induced lung carcinogenesis, inflammation and microRNA-21 expression

Abstract

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. KRASG12D;NOS2KO mice exhibited delayed lung tumorigenesis and a longer overall survival time compared to that of KRASG12D;NOS2WT (wild-type) controls. Correspondingly, tumors in KRASG12D;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 KRASG12D;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 KRASG12D;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. Deficiency of inducible nitric oxide synthase (NOS2) was found to inhibit tumorigenesis in mice with lung cancers associated with activating mutations in the KRAS protooncogene. NOS2 deficiency further suppressed KRAS-induced lung inflammation and decreased expression of microRNA-21, a non-coding RNA involved in oncogenic Ras signaling. The frequent over-expression of NOS2 in human lung cancer and NOS2 nitric oxide production in mice suggest that the synthase could be a potential target for KRAS-induced lung cancers. Copyright © 2012 UICC.