Abstract A42: Interleukin-6 induces secretion of SPINK1 and trypsin in colorectal cancer
Authors: Räsänen Kati , Lehtinen Elina , Nokelainen Kristiina , Hautala Laura , Itkonen Outi , Stenman Ulf-Håkan , Koistinen Hannu 
Published: October 2016

Abstract
Inflammation is known to promote colorectal cancer (CRC) tumorigenesis, but the underlying molecular mechanisms are still being uncovered. Proinflammatory cytokine interleukin-6 (IL-6) is primarily secreted by the cells of the tumor microenvironment (TME), mainly by inflammatory cells but also by activated fibroblasts. IL-6 stimulates growth and survival signaling in CRC. Inflammatory signals regulate also the production and activity of proteases and their inhibitors. Serine protease inhibitor Kazal type1 (SPINK1, aka tumor-associated trypsin inhibitor, TATI) is expressed in several tissues and over-expression of SPINK1 predicts an unfavorable outcome in many cancers, including colon cancer. The SPINK1 gene contains an IL-6 responsive element and in addition to being a protease inhibitor, it also acts as an acute phase reactant and a growth factor. Expression of serine proteases trypsin-1 and -2, the main targets of SPINK1, also correlate with malignancy and metastatic potential. The aim of this study was to assess the paracrine signaling between fibroblast-derived IL-6 and cancer cell-derived SPINK1, trypsin-1 and -2. The following expression analyses were used: quantitative PCR, immunohistochemistry, immunofluorometric assays and Western blotting. The results show that CRC cells Colo205 and HT-29 express SPINK1 and secrete it into the culture medium. IL-6 dose-dependently increased the mRNA expression and protein levels of SPINK1. Conditioned media from fibroblasts had the same effect, and conversely CRC media increased IL-6 secretion in the fibroblasts, indicating paracrine signaling between these cell types. In CRC tissues cancer cells were positive for SPINK1, while IL-6 was found in fibroblasts surrounding the cancer cells, confirming the in vitro results. In Colo205 cells the baseline levels of trypsin-1 and -2 and the respective genes PRSS1 and PRSS2 were much higher compared to HT-29 cells. In Colo205 cells IL-6 led to concomitant increase in the secretion of trypsin-1 and -2, whereas in HT-29 cells these remained constantly low. Mechanistically, addition of IL-6 led to activation of the canonical Stat3 pathway, as indicated by Stat3 phosphorylation. Stat3 inhibitor reduced both SPINK1 and trypsin-1 and -2 levels, demonstrating that Stat3 is the transcription factor driving their expression. Taken together, our results show a connection between TME-derived inflammatory response and increased SPINK1 and trypsin-1 and -2 levels. Elevated serum SPINK1 has been shown to be an independent prognostic factor in colon cancer. As SPINK1 acts as a growth factor in some cancers, it has also been suggested as a therapeutic target. Therefore assessment of SPINK1 expression and function has several potentially important clinical applications in colorectal and other cancers. The study also strengthens the role of tumor microenvironment in tumor progression and emphasizes the importance of studying tumor-stroma crosstalk of proteolytic processing.
Citation Format: Kati Räsänen, Elina Lehtinen, Kristiina Nokelainen, Laura Hautala, Outi Itkonen, Ulf-Håkan Stenman, Hannu Koistinen. Interleukin-6 induces secretion of SPINK1 and trypsin in colorectal cancer. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr A42.