ABSTRACT
TCPTP is an ubiquitously expressed tyrosine phosphatase with a predominant nuclear isoform (TC45) that binds DNA and has a role in G1-S cell cycle progression. Its deregulation by overexpression induces p53-dependent apoptosis, but the physiological role of its DNA-binding function is not known. Using immunocytochemistry and subcellular fractionation, we investigated changes in its localization in response to DNA damage and replication arrest. Rat fibroblasts showed an increase in endogenous TCPTP bound to nuclear components 3 h after exposure to sublethal dose of UV irradiation. Fractionation of nuclei showed an increase in chromatin and nuclear matrix associated component of TC45. After UV treatment, cells showed a concentration of TCPTP in discrete foci and enhanced colocalization with PCNA and p53BP1. Cells arrested at G1-S transition by hydroxyurea showed a loss of the predominant nuclear staining of TCPTP and an increase in cytoplasmic staining. Upon release from replication block, there was a time-dependent increase in number of cells showing prominent nuclear localization. This change in localization coincides with that of PCNA and Cdk2, two other nuclear proteins having functions in DNA replication. These results provide evidence for the regulation of TCPTP in response to DNA damage and replication stress. Dynamic changes in its localization coincident with that of PCNA suggest involvement of TCPTP in DNA repair and replication.
