Mitochondria-Judges and Executioners of Cell Death Sentences

Abstract

Apoptosis is a form of programmed cell death that is critical for basic human development and physiology. One of the more important surprises in cell biology in the last two decades is the extent to which mitochondria represent a physical point of convergence for many apoptosis-inducing signals in mammalian cells. Mitochondria not only adjudicate the decision of whether or not to commit to cell death, but also release toxic proteins culminating in widespread proteolysis, nucleolysis, and cell engulfment. Interactions among BCL-2 family proteins at the mitochondrial outer membrane control the release of these toxic proteins and, by extension, control cellular commitment to apoptosis. This pathway is particularly relevant to cancer treatment, as most cancer chemotherapies trigger mitochondrial-mediated apoptosis. In this Review, we discuss recent advances in the BCL-2 family interactions, their control by upstream factors, and how the mitochondria itself alters these interactions. We also highlight recent clinical insights into mitochondrial-mediated apoptosis and novel cancer therapies that exploit this pathway.

Figure 1

Interactions between the Bcl-2 family of proteins at the mitochondria determines commitment to apoptotic cell death. Physiological or therapeutic apoptotic stimuli alter different classes of Bcl-2 proteins. Activation of effector proteins result in cytochrome c release from mitochondria, and degradation of the cell. (*) Recent evidence indicates that NOXA can also act as an activator BH3 protein.