Chronic inflammation is implicated in the pathophysiology of ovarian cancer. Tumor necrosis factor-alpha (TNF-alpha), a major inflammatory cytokine, is abundant in the ovarian cancer microenvironment. TNF-alpha modulates the expression of CD44 in normal T lymphocytes and CD44 is implicated in ovarian carcinogenesis and metastases. However, little is known about the role of TNF-alpha in CD44 expression of cancer cells. Recent clinical work using TNF-alpha inhibitors for the treatment of ovarian cancer makes the study of TNF-alpha interactions with CD44 crucial to determining treatment a success or a failure. We studied the effect of TNF-alpha on ovarian cancer cells viability, CD44 expression, and in vitro migration/invasion. Our results revealed that TNF-alpha differentially modulates the expression of CD44 in TNF-alpha-resistant ovarian cancer cells, affecting their in vitro migration, invasion, and binding to hyaluronic acid. TNF-alpha up-regulation of CD44 expression was dependent on the activation of c-Jun NH(2)-terminal kinase (JNK) and this activation was accompanied by an increase in their invasive phenotype. On the contrary, if TNF-alpha failed to induce JNK phosphorylation, the end result was down-regulation of both CD44 expression and the invasive phenotype. These results were confirmed by the use of JNK inhibitors and a TNF receptor competitive inhibitor.