TNFalpha and IL-8 regulate the expression and function of CD44 variant proteins in human colon carcinoma cells

The mechanisms underlying the inflammatory and metastatic processes share a number of similar pathways, such as those involving adhesion, migration and extravasation. In this article, the effects of pro-inflammatory cytokines on metastatic-related activities of colon cancer cells were tested. The expression and biological activity of the proteoglycan CD44 in low (LS174T) and high metastatic (HM7) cell lines following exposure to TNFalpha and IL-8 were assessed. Treated cells expressed more CD44 splice variants (CD44v), while CD44 standard protein (CD44s) expression remained unchanged. Treatment with TNFalpha induced IL-8 secretion and IL-8 gene transcription in a time-dependent manner. Both cytokines enhanced the ability of the cells to adhere to the CD44-specific ligand hyaluronic acid, an effect that was specifically blocked by an anti-IL-8 antibody. These results suggest that the effect of TNFalpha on IL-8 is responsible for the regulation of the expression of CD44 isoforms. Additional experiments showed that neither of the cytokines tested regulate the expression of CD44 gene regulation via activation of a well-characterized specific 22-bp epidermal growth factor regulatory element present in the CD44 promoter sequence, suggesting that this is not the mechanism of activation. We conclude that immuno-modulatory mediators can modify the expression of cell-to-cell or cell-to-matrix adhesion proteins, implicated in the determination of phenotypes associated with aggressiveness and metastasis of colon cancer cells.