Modulation of EGF receptor by tumor necrosis factor-alpha in human hepatocellular carcinoma HepG2 cells.

TNF alpha is known to exert multi-regulatory effects on normal and malignant cell functions by binding to the corresponding cell surface receptor. However, the existence of cross interaction between TNF alpha and EGF receptor has been proposed. In this study, we investigated the modulatory effect of TNF alpha on EGF receptor of a human hepatocellular carcinoma cell line-HepG2. The results suggested that TNF alpha was able to modulate the EGF receptor of HepG2 cells. The modulatory effect of TNF alpha on the EGF receptor of HepG2 cells exhibited its unique characteristics in comparison with the previous reports on other tumor cells. TNF alpha could also enhance the tyrosine phosphorylation of the EGF receptor of HepG2 cells. However, the effect appeared only if EGF was present, and was not mediated by TNF alpha alone. Therefore, the effect of TNF alpha on EGF receptor tyrosine phosphorylation in HepG2 cells was due to enhancing the receptor's response to EGF. TNF alpha was also able to reduce the affinity of the high-affinity receptor for EGF. However, there was no significant alteration in terms of the expression of EGF receptor, EGF internalization, or EGF degradation when HepG2 cells were treated with TNF alpha. Since TNF alpha is an inhibitory agent for HepG2 cell growth, this cross interaction between TNF alpha and EGF receptor may play a role in the inhibition of cell growth.