Bcl-2 overexpression inhibits tetrachlorohydroquinone-induced apoptosis in NIH3T3 cells: A possible mechanism for tumor promotion

TCHQ is a major carcinogenic metabolite of the widely used wood preservative PCP. Recently, we found that TCHQ was a promoter in a mouse skin carcinogenesis model. However, the mechanism is still not clear. In this study, we showed that overexpression of Bcl-2 effectively suppressed TCHQ-induced apoptosis in NIH3T3 cells, as evidenced by morphological changes and DNA fragmentation. Although production of ROS contributes to TCHQ-induced apoptosis, Bcl-2 failed to attenuate TCHQ-elicited increase of intracellular ROS level. In addition, overexpressed Bcl-2 provides only partial protection against TCHQ-induced cellular DNA damage. We also found that TCHQ induced a change in mitochondrial transmembrane potential, and that caspase-9 and subsequent caspase-3 can be activated during TCHQ-induced acute apoptosis. Interestingly, TCHQ induced a significant upregulation of Bcl-2 expression, and overexpressed Bcl-2 can dramatically inhibit the change of mitochondria membrane potential and activation of both caspase-9 and -3. Thus, our results suggest TCHQ-induced tumor promotion may be through a mechanism of upregulation of Bcl-2 protein and subsequent apoptosis inhibition. (C) 2004 Wiley-Liss, Inc.