PCTAIRE-1: Characterization, subcellular distribution, and cell cycle-dependent kinase activity

PCTAIRE-1 is a member of the cyclin-dependent kinase (cdk) family whose fun ction is unknown. We examined the pattern of PCTAIRE-1 protein expression i n a number of normal and transformed cell lines of various origins and foun d that the kinase is ubiquitous. Indirect immunofluorescence indicated that PCTAIRE-1 exhibits cytoplasmic distribution throughout the cell cycle. Con focal microscopy showed that PCTAIRE-1 does not colocalize with components of the cytoskeleton or with the endoplasmic reticulum, We found that endoge nous PCTAIRE-1 and ectopically expressed PCTAIRE-1 display kinase activity when myelin basic protein is used as an acceptor substrate, Similar to othe r members of the cyclin-dependent kinase family, PCTAIRE-1 seems to require binding to a regulatory subunit to display kinase activity. PCTAIRE-1 acti vity is cell cycle dependent and displays a peak, in the S and G(2) phases. We show that the low level of kinase activity observed until the onset of S phase correlates with elevated tyrosine phosphorylation of the molecule.