Involvement of NP95 in G2/M Arrest and Its Colocalization with H2AX afterX-irradiation

Abstract

H2AX is rapidly phosphorylated in response to ionizing radiation (IR)and is considered to be critical for recognition and repair of DNA doublestrand breaks (DSB). Moreover, the inhibition of DNA replication byhydroxyurea (HU) or UV-light has also been known to induce thephosphorylation and the foci formation of H2AX. We have recently shown that homozygouly Np95-inactivated embryonic stem(ES) cells are more sensitive to X-rays, UV-light, MNNG, and HU than ES wildtype or Np95+/-ES cells, suggesting that NP95 functions as a component inthe multiple DNA damage response pathways. In this study, we found that aconsiderable proportion of Np95-/- cells failed to stop at G2 phase andproceeded into mitosis after 8 Gy X-irradiation. We also observed thecolocalization of NP95 with H2AX following X-irradiation of m5S cells,suggesting that NP95 interacts with H2AX in the recognition and repair ofDSB. [J Radiat Res 44:404 (2003)]