Organelle motility regulated by the cell's environment: dissection of signaling pathways regulating movements of peroxisomes

Chloroplasts and pigment granules are known to be intracellularly transloca ted upon discrete extracellular stimuli. The machineries transducing these signals inside cells are yet not understood. In studies investigating the m otility of peroxisomes, we were able to identify both extracellular and int racellular signaling steps regulating movements of these organelles. Follow ing simultaneous stimulation of CHO cells with both extracellular ATP and l ysophosphatidic acid, an arrest of peroxisomes was observed. This block of motility was shown to be dependent on signaling cascades involving heterotr imeric G proteins of the class G(i)/G(o), phospholipase C, calcium influx, and activation of protein kinase C as well as of mitogen-activated protein kinase. Cytosolic phospholipase A(2) is a point of convergence for these pa thways, resulting in the release of arachidonic acid. This signaling pathwa y is specific for peroxisomes and does not influence motility of mitochondr ia, lysosomes, or endosomes. However, since the cytoskeleton and its associ ated proteins including the motor proteins play an important role in mediat ing motility of all cell organelles, it may well be that variant signaling cascades exist ensuring specific regulation of each distinct compartment.