Fibronectin supports TNF-α-induced osteopontin expression through β1 integrin and ERK in HN-22 cells

The extracellular matrix (ECM), in collaboration with intracellular signal, plays a critical role in the modulation of cellular behavior and function. Herein, we investigated the influence of fibronectin (FN) and tumor necrosis factor-alpha (TNF-α) on OPN expression in HN-22, a human head and neck squamous cell carcinoma (HNSCC) cell line. The data showed that TNF-α significantly increased OPN expression only in the FN-coated condition. Application of function-blocking antibody directed against β1 integrin abolished this OPN induction. Moreover, TNF-α when added together with activating β1 integrin antibody is sufficient to induced OPN expression. The combination effect of FN and TNF-α was significantly deteriorated by a MEK inhibitor, but not NF-κB inhibitor. We further demonstrated that the phosphorylation of ERK1/2 was strongly enhanced by TNF-α and FN compared to the application of either one alone. Synergistic effect on ERK1/2 phosphorylation was also detected by TNF-α and activating β1 integrin antibody, whereas inhibitory antibody to β1 integrin attenuated FN and TNF-α-induced phosphorylation of ERK1/2. Our results indicate that FN coordinates TNF-α-mediated OPN induction via β1 integrin-dependent signaling mechanism that activates ERK. The results suggest the critical role of tumor micro-environment signaling networks on the regulation of cytokine expression profiles during tumor progression.