Abstract 4506: Elevated expression of IL-1 induces iNOS/NO production and inhibits IL-1Ra synthesis leading to progression of metastatic melanoma

Aberrant expression of proinflammatory IL-1 α and β and the overproduction of nitric oxide (NO) have been shown to promote the progression of some tumors. In previous studies, we had confirmed that inducible nitric oxide synthase (iNOS) was constitutively expressed in most advanced melanomas and highly correlated with poor patient survival. In order to determine whether the imbalance of IL-1 and its natural competitor IL-1 receptor antagonist (IL-1Ra) contributes to the upregulation of iNOS in metastatic melanoma, we initiated an investigation of the expression profile of IL-1 system genes in melanoma and the linkage between IL-1 and iNOS/NO signaling pathways. Immunohistochemistry staining of 38 biopsy samples from metastatic melanoma patients showed that 33 samples highly expressed IL-1α and/or IL-1β. Only 5 samples were negative for both IL-1α and IL-1β expression. RT-PCR confirmed that melanoma cell lines A375, WM793, WM35, and SB2 constitutively expressed high levels of IL-1, IL-1 receptor I (IL-1RI), and iNOS. However, in the same cell lines, there was no detectable IL-1Ra mRNA, which is known to maintain IL-1 balance in normal skin tissues. Our study suggests that the imbalance of IL-1 and IL-Ra is widespread in metastatic melanoma. The engagement of IL-1 and IL-1RI can induce several kinase cascades leading to the activation of SAPK/JNK and NF-κB, and it is well known that transcription of iNOS can be regulated by NF-κB. In our studies, siRNA knockdown of either IL-1α or MyD88 (an important adaptor for IL-1RI signal pathway) in WM375 and A375 led to a dramatic decrease in the phoshorylation of SAPK/JNK and IκB. Furthermore, an 80% decrease of iNOS expression in WM793 was observed after the siRNA knockdown of MyD88. We confirmed that upregulated IL-1 signal pathway can activate NF-κB and the iNOS transcription. Treatment with 200 μM 7-Nitroindazole, a NO synthase inhibitor, not only reduced NO production, but also induced over 50% inhibition of cell growth and a marked increase in IL-1Ra mRNA in WM793 and A375. This indicates that a high level of NO can inhibit the IL-1Ra expression in melanoma cells. Based on our data, we proposed an inflammatory dysfunction model to explain the development of melanoma. It proposes that the constitutive expression of IL-1 can inhibit IL-1Ra expression mediated by the upregulation of iNOS/NO production in melanoma. The constant inhibition of IL-1Ra expression by NO results in a cycle of kinase transduction cascades, which drives NF-κB and its downstream inflammatory genes (including iNOS) constitutively expressed in melanoma. Our studies cast new insight into the mechanism of the pathology of metastatic melanoma. Selective inhibition of iNOS and increasing IL-1Ra levels are promising therapeutic strategies to suppress the aberrant IL-1 inflammation pathway in melanoma. Supported by MDACC SPORE in Melanoma CA093459. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4506.