The involvement of mitochondria in the cell death process: communication from mitochondria to the nucleus

Abstract

A thorough understanding of the mechanisms of cell death could open the door to numerous opportunities for therapeutic modulation. In addition to disease state treatment options, cell death modulation may also have benefit in toxicological research of xenobiotics. The studies described here focus on two extensively studied compounds: acetaminophen (APAP) and S-(1,1,2,2-tetrafluoroethyl)- L-cysteine (TFEC). Investigations into the toxicity of these compounds have suggested a critical role for the mitochondria in cell death related to direct effects on this organelle. The function that the mitochondria play in the cellular-mediated, as well as the xenobiotic-induced process, is generating wide interest. In particular, different pathways that hinge on the mitochondria in cell death processes have been identified, especially during apoptosis. Additionally, specific changes in HSP60, a nuclear encoded, mitochondrial protein, have been identified after TFEC dosing, indicating a communication pathway from the site of damage, in mitochondria, to the nucleus. The general background for this type of communication, called retrograde regulation in yeast is described in Chapter 1. Chapter 2 details our search for a mammalian system similar to the yeast retrograde regulation system through the use of Southern blots and degenerate primer RT-PCR. This search identified mitochondrial cytochrome b, an integral part of the mitochondrial electron transport chain complex III, as a possible reporter protein. The effects of TFEC and APAP on complex III activity in mammalian cells, as a means to characterize a role for cytochrome b in the cell death process, are described in Chapter 3. Complex III activities in mice that overexpress the anti-apoptotic BCL-2 after dosing with APAP were evaluated in Chapter 4. Although our data suggest a potential role for cytochrome b in a cell death process, the exact role remains elusive.