C-RAF activation promotes BAD poly-ubiquitylation and turn-over by the proteasome.

BAD, a member of the BCL2 family, exhibits an original mode of regulation by phosphorylation. In the present report, we examine the role of the kinase C-RAF in this process. We show that the inducible activation of C-RAF promotes the rapid phosphorylation of BAD on Serine-112 (Ser-75 in the human protein), through a cascade involving the kinases MEK and RSK.

Isoform-specific interaction of C-RAF with mitochondria.

The proteins of the RAF family (A-RAF, B-RAF, and C-RAF) are serine/threonine kinases that play important roles in development, mature cell regulation, and cancer. Although it is widely held that their localization on membranes is an important aspect of their function, there are few data that address this aspect of their mode of action. Here, we report that each member of the RAF family exhibits a specific distribution at the level of cellular membranes and that C-RAF is the only isoform that directly targets mitochondria.

RAF kinases and mitochondria.

Over the past decade, several investigators reported that a fraction of the RAF kinases are recruited to the mitochondria. Although we are still far from a global understanding of the molecular consequences of RAF translocation on mitochondrial physiology and metabolism, the recent description of some molecular interactions that are established by C-RAF in this organelle, principally with the proteins Bcl-2 and Bag-1, provides some clues. Here, we discuss the possible contribution of RAF targeting to mitochondria to their modulation of apoptosis signaling, as well as to this organelle's physiology.

Reversible membrane interaction of BAD requires two C-terminal lipid binding domains in conjunction with 14-3-3 protein binding.

BAD is a Bcl-2 homology domain 3 (BH3)-only proapoptotic member of the Bcl-2 protein family that is regulated by phosphorylation in response to survival factors. Binding of BAD to mitochondria is thought to be exclusively mediated by its BH3 domain. We show here that BAD binds to lipids with high affinities, predominantly to negatively charged phospholipids, such as phosphatidylserine, phosphatidic acid, and cardiolipin, as well as to cholesterol-rich liposomes.

B-Raf and C-Raf signaling investigated in a simplified model of the mitogenic kinase cascade.

Signaling pathways based on the reversible phosphorylation of proteins control most aspects of cellular life in higher organisms. Extracellular stimuli can induce growth, differentiation, survival and the stress response through a number of highly conserved signaling pathways. We discuss how the intensity and duration of signals may have dramatic consequences on the way cells respond to stimuli.