Abstract
Merkel Cell polyomavirus (MCPyV) is a causal factor in Merkel Cell Carcinoma (MCC). The oncogenic potential is mediated through its viral oncoproteins large T-antigen (LT-ag) and small t-antigen (st-ag). Many cancers arise from sites of infection, chronic irritation and inflammation, and inflammatory signaling pathways are often activated by oncogenic mutations. Chemokines are a family of cytokines that regulate leukocyte trafficking in immunity and inflammation. The aberrant expression of chemokines and chemokine receptors in tumors may regulate the trafficking of leukocytes into the tumor microenvironment. IL33, a member of IL-1 family cytokines, is involved in the response to viral infection and plays important roles in type-2 innate immunity, tumorigenesis and tumor immune evasion.
We assessed IL33/ST2 expression in MCPyV-positive (MKL2) and –negative (MCC13) MCC cell lines in order to examine a possible role of IL33/ST2 pathway in MCC.
Using the human RT2 Profiler PCR Inflammatory Cytokines and Receptors Array, we did a PCR array analysis of 84 different human cytokines and receptor genes. Expression of IL-33 and ST2 was determined by qRT-PCR, immunohistochemistry and western-blot analysis. Luciferase analysis was done to monitor the effect of MCPyV early proteins on IL33 promoter activity and the effect of IL33 on MCPyV early and late promoter activity. Furthermore, mitogen-activated protein kinase (MAPK) and the NF-κB pathways were also assessed after stimulating MCC13 cells with recombinant human (rh) IL33 protein. Finally, proliferation activity after rhIL33 stimulation was assessed by MTT-assay.
PCR array analysis showed higher transcript levels of IL33 in MCC13 cells transfected with st-ag compared to control cells. Western blot analysis confirmed increased IL33 expression by st-ag. Luciferase analysis showed higher IL33 promoter activity in st-ag transfected MCC13 cells. Interestingly, IL33 also increased MCPyV early and late promoter activity. Furthermore, rhIL33 activated both MAPK and the NF-κB pathways and blocking ST2 receptor using polyclonal goat ST2 antibody abolished IL33 activity. Dose-dependent effect of rhIL33 showed higher proliferation activity of MCC13 cells. Immunohistochemical analysis of IL33 and ST2 showed a significant stronger expression in MCC tissues compared to normal skin.
Our study unveiled a novel st-ag dependent IL33 function in MCC. Therefore, neutralizing the IL-33/ST2 axis may thereby represent a therapeutic target in MCPyV-positive MCC patients.
Citation Format: Kashif Rasheed, Silje Fismen, Øystein Grimstad, Baldur Sveinbjørnsson, Ugo Lionel Moens. The MCPyV st-ag and IL33/ST2 axis: critical role in merkel cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2359.
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