Investigation of the inflammatory pathways in spontaneously differentiating Caco-2 cells

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2011
Astarcı, Erhan
Intestinal epithelial differentiation entails the formation of highly specialized cells with specific absorptive, secretory, digestive and immune functions. Cell-cell and cell-microenvironment interactions appear to be crucial in determining the outcome of the differentiation process. Using the Caco-2 cell line that can undergo spontaneous differentiation when grown past confluency, we observed a loss of VCAM1 (vascular cell adhesion molecule-1) expression while ICAM1 (intercellular cell adhesion molecule-1) expression was seen to be stable in the course of differentiation. Protein kinase C theta (PKCθ) acted downstream of PKC to inactivate Inhibitor of kappa B (IB) and activate NF-κB in the undifferentiated cells and this axis was inhibited in the differentiated cells. The increase in ICAM1 expression in the differentiated cells was due to a transcriptional upregulation by C/EBP. The protein expressions of both ICAM-1 and VCAM-1, however, were found to decrease in the course of differentiation, with both proteins getting post-translationally degraded in the lysosome. Functionally, a decrease in adhesion to HUVEC cells was observed in the differentiated Caco-2 cells. Thus, the regulation of ICAM-1 and VCAM-1, although both NF-B target genes, appear to be different in the course of epithelial differentiation. microRNAs are known to regulate many cellular pathways. miR-146a, which is known to target NF-κB, was shown to be highly upregulated in differentiated Caco-2 cells. As a predicted target of miR-146a, mRNA and protein expression of MMP16 was inversely correlated with miR-146a during differentiation of Caco-2 cells. miR-146a could bind to the 3’UTR of MMP16 and ectopic expression of miR-146a resulted in a decreased mRNA and protein expression of MMP16 in the undifferentiated Caco-2 and HT-29 cells. Functionally, decreased gelatinase activity determined by gelatin zymography and reduced invasion and migration through Transwells was observed. In the final part of the thesis, the inhibition of NF-κB via PPARγ in 15-Lipoxygenase-1 (15LOX1) expressing cells was investigated. The expression of 15LOX1, a member of the inflammatory arachidonate cascade, could lower phosphorylation of IκBα and NF-κB DNA binding activity which was reversed with a 15LOX1 inhibitor. This inhibition was mediated by phospho-PPARγ, which in turn was phosphorylated by ERK1/2.

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Citation Formats
E. Astarcı, “Investigation of the inflammatory pathways in spontaneously differentiating Caco-2 cells,” Ph.D. - Doctoral Program, Middle East Technical University, 2011.