title: Upregulation of the ATR-CHEK1 pathway in oral squamous cell carcinomas.
abstract: The ATR-CHEK1 pathway is upregulated and overactivated in Ataxia Telangiectasia (AT) cells, which lack functional ATM protein. Loss of ATM in AT confers radiosensitivity, although ATR-CHEK1 pathway overactivation compensates, leads to prolonged G(2) arrest after treatment with ionizing radiation (IR), and partially reverses the radiosensitivity. We observed similar upregulation of the ATR-CHEK1 pathway in a subset of oral squamous cell carcinoma (OSCC) cell lines with ATM loss. In the present study, we report copy number gain, amplification, or translocation of the ATR gene in 8 of 20 OSCC cell lines by FISH; whereas the CHEK1 gene showed copy number loss in 12 of 20 cell lines by FISH. Quantitative PCR showed overexpression of both ATR and CHEK1 in 7 of 11 representative OSCC cell lines. Inhibition of ATR or CHEK1 with their respective siRNAs resulted in increased sensitivity of OSCC cell lines to IR by the colony survival assay. siRNA-mediated ATR or CHEK1 knockdown led to loss of G(2) cell cycle accumulation and an increased sub-G(0) apoptotic cell population by flow cytometric analysis. In conclusion, the ATR-CHEK1 pathway is upregulated in a subset of OSCC with distal 11q loss and loss of the G(1) phase cell cycle checkpoint. The upregulated ATR-CHEK1 pathway appears to protect OSCC cells from mitotic catastrophe by enhancing the G(2) checkpoint. Knockdown of ATR and/or CHEK1 increases the sensitivity of OSCC cells to IR. These findings suggest that inhibition of the upregulated ATR-CHEK1 pathway may enhance the efficacy of ionizing radiation treatment of OSCC.
authors.affiliation: Department of Internal Medicine, Division of Hematology-Oncology, University of Pittsburgh Medical Center, Pittsburgh, PA; University of Pittsburgh Cancer Institute, Pittsburgh, PA.
authors.forename: Rahul A
authors.initials: RA
authors.lastname: Parikh
authors.forename: Leonard J
authors.initials: LJ
authors.lastname: Appleman
authors.forename: Julie E
authors.initials: JE
authors.lastname: Bauman
authors.forename: Madhav
authors.initials: M
authors.lastname: Sankunny
authors.forename: Dale W
authors.initials: DW
authors.lastname: Lewis
authors.forename: Anda
authors.initials: A
authors.lastname: Vlad
authors.forename: Susanne M
authors.initials: SM
authors.lastname: Gollin
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins / Q000235:genetics / Q000378:metabolism; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D000071877:Checkpoint Kinase 1; D002880:Chromosomes, Human, Pair 11 / Q000235:genetics; D002893:Chromosomes, Human, Pair 3 / Q000235:genetics; D004249:DNA Damage / Q000528:radiation effects; D059565:G2 Phase Cell Cycle Checkpoints / Q000528:radiation effects; D018628:Gene Dosage; D055785:Gene Knockdown Techniques; D006801:Humans; D009062:Mouth Neoplasms / Q000235:genetics* / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics* / Q000378:metabolism; D011836:Radiation Tolerance; D015398:Signal Transduction; D014178:Translocation, Genetic; D015854:Up-Regulation
chemical_list: D011494:Protein Kinases; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1