RESUMO
Premature chromatin condensation (PCC) is a hallmark of mammalian cells that begin mitosis before completing DNA replication. This lethal event is prevented by a highly conserved checkpoint involving an unknown, caffeine-sensitive mediator. Here, we have examined the possible involvement of the caffeine-sensitive ATM and ATR protein kinases in this checkpoint. We show that caffeine's ability to inhibit ATR (but not ATM) causes PCC, that ATR (but not ATM) prevents PCC, and that ATR prevents PCC via Chk-1 regulation. Moreover, mimicking cancer cell phenotypes by disrupting normal G(1) checkpoints sensitizes cells to PCC by ATR inhibition plus low-dose DNA damage. Notably, loss of p53 function potently sensitizes cells to PCC caused by ATR inhibition by a small molecule. We present a molecular model for how ATR prevents PCC and suggest that ATR represents an attractive therapeutic target for selectively killing cancer cells by premature chromatin condensation.
Assuntos
Proteínas de Ciclo Celular/antagonistas & inibidores , Cromatina/metabolismo , Fase G1 , Proteínas Serina-Treonina Quinases , Proteínas Mutadas de Ataxia Telangiectasia , Cafeína/farmacologia , Replicação do DNA/efeitos dos fármacos , Humanos , Fase S , Transfecção , Células Tumorais CultivadasRESUMO
An antimicrobial protein from seeds of Pharbitis nil (Pn-AMP) which shows an antifungal activity towards several agriculturally important plant pathogens has been crystallized in the presence of equimolar N-acetylglucosamine with sodium citrate as precipitant. The crystal belongs to the hexagonal space group P6(1)22 (or P6(5)22), with unit-cell parameters a = b = 29.33 (5), c = 133.44 (12) A. Native data were collected using a crystal at 100 K to a resolution of 1.78 A.
