A critical role for Pin2/TRF1 in ATM-dependent regulation. Inhibition of Pin2/TRF1 function complements telomere shortening, radiosensitivity, and the G(2)/M checkpoint defect of ataxia-telangiectasia cells.
Cells derived from patients with the human genetic disorder ataxia-telangiectasia (A-T) display many abnormalities, including telomere shortening, premature senescence, and defects in the activation of S phase and G(2)/M checkpoints in response to double-strand DNA breaks induced by ionizing radiation. We have previously demonstrated that one of the ATM substrates is Pin2/TRF1, a telomeric protein that binds the potent telomerase inhibitor PinX1, negatively regulates telomere elongation, and specifically affects mitotic progression. Following DNA damage, ATM phosphorylates Pin2/TRF1 and suppresses its ability to induce abortive mitosis and apoptosis (Kishi, S., Zhou, X. Z., Nakamura, N., Ziv, Y., Khoo, C., Hill, D. E., Shiloh, Y., and Lu, K. P. (2001) J. Biol. Chem. 276, 29282-29291). However, the functional importance of Pin2/TRF1 in mediating ATM-dependent regulation remains to be established. To address this question, we directly inhibited the function of endogenous Pin2/TRF1 in A-T cells by stable expression of two different dominant-negative Pin2/TRF1 mutants and then examined their effects on telomere length and DNA damage response. Both the Pin2/TRF1 mutants increased telomere length in A-T cells, as shown in other cells. Surprisingly, both the Pin2/TRF1 mutants reduced radiosensitivity and complemented the G(2)/M checkpoint defect without inhibiting Cdc2 activity in A-T cells. In contrast, neither of the Pin2/TRF1 mutants corrected the S phase checkpoint defect in the same cells. These results indicate that inhibition of Pin2/TRF1 in A-T cells is able to bypass the requirement for ATM in specifically restoring telomere shortening, the G(2)/M checkpoint defect, and radiosensitivity and demonstrate a critical role for Pin2/TRF1 in the ATM-dependent regulation of telomeres and DNA damage response.
Kishi
Shuji
S
Cancer Biology Program, Division of Hematology/Oncology, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA.
Lu
Kun Ping
KP
D001260:Ataxia Telangiectasia / Q000235:genetics / Q000378:metabolism; D064007:Ataxia Telangiectasia Mutated Proteins; D001973:Bromodeoxyuridine / Q000378:metabolism; D016203:CDC2 Protein Kinase / Q000378:metabolism; D018797:Cell Cycle Proteins; D002460:Cell Line; D016922:Cellular Senescence; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology*; D016195:G2 Phase / Q000502:physiology; D005799:Genes, Dominant; D006367:HeLa Cells; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008938:Mitosis / Q000502:physiology; D009154:Mutation; D010641:Phenotype; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D016615:Telomere / Q000378:metabolism*; D035321:Telomeric Repeat Binding Protein 1; D013997:Time Factors; D014162:Transfection; D025521:Tumor Suppressor Proteins; D001616:beta-Galactosidase / Q000378:metabolism
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D035321:Telomeric Repeat Binding Protein 1; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D016203:CDC2 Protein Kinase; D001616:beta-Galactosidase; D001973:Bromodeoxyuridine