CXCL16 is an interferon-inducible chemokine of the CXC-subfamily and functions as an adhesion molecule, when membrane bound, and a chemoattractant when soluble. Upregulation of cell associated CXCL16 (cCXCL16) in colorectal cancer is associated with increased tumor infiltrating lymphocytes and good prognosis. ADAM10 and ADAM17 are metalloproteinases responsible for cleaving CXCL16, releasing soluble CXCL16 (sCXCL16) and contributing to proliferation and migration of mesangial cells, in kidney inflammatory disease. We hypothesize that cCXCL16 is a substrate for ADAM10 and ADAM17 cleavage in colorectal cancer, releasing sCXCL16, which mediates cell proliferation. To this end, we first identified CXCL16 in the human colon carcinoma cell line, RKO, by immunohistochemistry. cCXCL16 was found in the membrane, cytoplasm and nucleus. We treated RKO, in vitro, with an inflammatory cytokine mix containing 1.4 nM rhIFN[gamma], 2.0 nM rhTNF[alpha] and 2.0 nM rhIL1[beta] to increase the cleavage of cCXCL16 to sCXCL16. Overnight incubation with the cytokine mix significantly (P=.004) increased the release of sCXCL16 compared to normal conditions. To confirm that a metalloproteinase is responsible for the cleavage of cCXCL16, we used a broad spectrum metalloproteinase inhibitor, GM6001, in combination with inflammatory stimulation, in cell culture. We assayed the supernatant using ELISA for sCXCL16. GM6001 at 100 [mu]M decreased sCXCL16 to levels indistinguishable from the background. Using siRNA, we knocked down the expression of ADAM10 and ADAM17, independently, to determine if the activity of each on cCXCL16 was mediated by inflammatory stimulation. It was shown that ADAM10 constitutively cleaved cCXCL16, and ADAM17 cleavage activity was induced by inflammatory stimulation. To determine if sCXCL16 increased colorectal cancer cell (CRC) proliferation through ligand-receptor binding, we treated cells with a range of rhCXCL16 from 3.125-100 ng/mL. rhCXCL16 did not increase RKO proliferation at doses up to 100 ng/mL. We used GM6001, to inhibit the cleavage of cCXCL16 into sCXCL16 then performed an ATPase assay and 6 day cell cycle analysis, under inflammatory stimulation. Increased cleavage of cCXCL16 induced by inflammatory stimulation with the cytokine mix containing 1.4 nM rhIFN[gamma], 2.0 nM rhTNF[alpha] and 2.0 nM rhIL1[beta], increased RKO proliferation and reduced apoptosis. We conclude that ADAM10 and ADAM17 cleavage of cCXCL16 to sCXCL16 is increased by ADAM17 activation with inflammatory stimulation. The cleavage of the extracellular portion from cCXCL16 is associated with increased proliferation and decreased apoptosis of colorectal cancer cells.
| Identifer | oai:union.ndltd.org:ucf.edu/oai:stars.library.ucf.edu:etd-7625 |
| Date | 01 January 2011 |
| Creators | Talton, Tamu C. |
| Publisher | STARS |
| Source Sets | University of Central Florida |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Electronic Theses and Dissertations |
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