Tumor necrosis factor induces apoptosis in hepatoma cells by increasing Ca2+ release from the endoplasmic reticulum and suppressing Bcl-2 expression

Tumor necrosis factor (TNF) plays an import role in the control of apoptosis. The most well known apoptotic pathway regulated by TNF involves the TNFR1-associated death domain protein, Fas-associated death domain protein, and caspase-8. This study examines the mechanism of TNF-induced apoptosis in FaO rat hepatoma cells. TNF treatment significantly increased the percentage of apoptotic cells. TNF did not activate caspase-8 but activated caspase-3, -10, and -12. The effect of TNF on the expression of different members of the Bcl-2 family in these cells was studied. We observed no detectable changes in the steady-state levels of Bcl-X-L, Bax, and Bid, although TNF suppresses Bcl-2 expression. Dantrolene suppressed the inhibitory effect of TNF on Bcl-2 expression. TNF induced release of Ca2+ from the endoplasmic reticulum. (ER) that was blocked by dantrolene. Importantly, the expression of BcI-2 blocked TNF-induced apoptosis and decreased TNF-induced Ca2+ release. These results suggest that TNF induces apoptosis by a mechanism that involves increasing Ca2+ release from the ER and suppression of Bcl-2 expression.