Cell cycle regulation of c-Jun N-terminal kinase activity at the centrosomes

The c-Jun N-terminal kinase (JNK), a subgroup of the mitogen-activated prot ein kinase (MAPK) family of serine/threonine kinases, has established funct ions in cell growth and apoptosis. While the mechanisms are unclear, JNK ha s also been also implicated in signaling pathways that initiate cell cycle checkpoints and cell cycle progression. By following the localization of ac tive and inactive JNK during the cell cycle, we have found that the majorit y of cellular JNK is soluble and present in the cytoplasm and the nucleus. Interestingly, insoluble fractions of JNK are also localized in nuclear and cytoplasmic speckles, and to the centrosomes. While JNK is associated with the centrosome throughout the cell cycle, it is only active at the centros ome from S phase through anaphase. This novel localization of centrosomal J NK is a possible link between JNK-activating stimuli and centrosome or cell cycle events. (C) 2001 Academic Press.