The NF-κB target genes ICAM-1 and VCAM-1 are differentially regulated during spontaneous differentiation of Caco-2 cells

Abstract

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, which undergoes spontaneous re-differentiation when grown past confluency, we observed a loss of VCAM-1 (vascular cell adhesion molecule 1) mRNA expression, while ICAM-1 (intercellular cell adhesion molecule 1) mRNA expression was seen to increase over the course of differentiation. Protein kinase θ (PKθ) acted downstream of protein kinase Cα (PKCα) to inactivate inhibitor of κB (IκB) and activate nuclear factor κB (NF-κB) in undifferentiated cells, and this pathway was inhibited in the differentiated cells. The increase in ICAM-1 mRNA expression in the differentiated cells was due to increased promoter recruitment of C/EBPβ, which transcriptionally up-regulated ICAM-1 mRNA. However, protein expression of ICAM-1 was found to decrease over the course of differentiation due to degradation in the proteasome and lysosome. Immunohistochemistry using tumor samples from colon cancer patients indicated that non-transformed matched normal cells (well-differentiatied) showed no ICAM-1 expression, but the poorly differentiated tumor cells showed higher expression. Functionally, a decrease in adhesion to human umbilical vein endothelial cells was observed in the differentiated Caco-2 cells. Thus, regulation of ICAM-1 and VCAM-1, although both NF-κB target genes, appears to be different over the course of epithelial differentiation in Caco-2 cells. © 2012 FEBS.