PCTAIRE-2, A CDC2-RELATED SERINE THREONINE KINASE, IS PREDOMINANTLY EXPRESSED IN TERMINALLY DIFFERENTIATED NEURONS/

PCTAIRE are members of a subfamily of Cdc2-related kinases that have b een shown to be preferentially expressed in post-mitotic cells. To exa mine the neural functions of PCTAIRE, rat cDNA clones encoding PCTAIRE 1, 2 and 3 were isolated, and their expression patterns in the brain were analyzed. Among the three rat PCTAIREs, only PCTAIRE 2 was found to be specifically expressed in the brain. Furthermore, its expression was transiently increased during brain development, peaking 7-15 days after birth. Within the brain, PCTAIRE 2 was concentrated in the neur onal layers of the hippocampus and olfactory bulb, which mostly consis t of post-mitotic neurons. In an immunocytochemical experiment, immuno reactivity for PCTAIRE 2 was detected in the cell bodies and extended neurites of neurons, bur not in astrocytes. The PCTAIRE 2 protein was recovered in the particulate fraction and resistant to solubilization with non-ionic detergent, suggesting thar PCTAIRE 2 might be present a s a component of a lame protein complex. An immunoprecipitation assay. revealed that the PCTAIRE 2 was associated with Ser/Thr-phosphorylati ng activity for histone H1, and that its activity depended on associat ion with a regulatory partner that can be released under high-salt con ditions. These findings suggest that PCTAIRE 2 is a Ser/Thr kinase tha t might play a unique role in terminally differentiated neurons.