RESUMEN
We previously demonstrated that type 2C protein phosphatases (PP2C) Ptc2 and Ptc3 are required for DNA checkpoint inactivation after DNA double-strand break repair or adaptation in Saccharomyces cerevisiae. Here, we show the conservation of this pathway in mammalian cells. In response to DNA damage, ataxia telangiectasia mutated (ATM) phosphorylates the Chk2 tumour suppressor kinase at threonine 68 (Thr68), allowing Chk2 kinase dimerization and activation by autophosphorylations in the T-loop. The oncogenic protein Wip1, a PP2C phosphatase, binds Chk2 and dephosphorylates phospho-Thr68. Consequently, Wip1 opposes Chk2 activation by ATM after ionizing irradiation of cells. In HCT15 colorectal cancer cells corrected for functional Chk2 activity, Wip1 overexpression suppressed the contribution of Chk2 to the G2/M DNA damage checkpoint. These results indicate that Wip1 is one of the phosphatases regulating the activity of Chk2 in response to DNA damage.
Asunto(s)
Fosfoproteínas Fosfatasas/farmacología , Proteínas Serina-Treonina Quinasas/biosíntesis , Proteínas Supresoras de Tumor/biosíntesis , Proteínas de la Ataxia Telangiectasia Mutada , Ciclo Celular/efectos de los fármacos , Proteínas de Ciclo Celular/farmacología , Proteínas de Ciclo Celular/efectos de la radiación , Quinasa de Punto de Control 2 , Neoplasias Colorrectales/metabolismo , Daño del ADN , Proteínas de Unión al ADN/farmacología , Proteínas de Unión al ADN/efectos de la radiación , Activación Enzimática , Humanos , Fosforilación , Proteína Fosfatasa 2C , Proteínas Serina-Treonina Quinasas/farmacología , Proteínas Serina-Treonina Quinasas/efectos de la radiación , Proteínas de Saccharomyces cerevisiae , Treonina/metabolismo , Células Tumorales Cultivadas , Proteínas Supresoras de Tumor/farmacología , Proteínas Supresoras de Tumor/efectos de la radiaciónRESUMEN
Triiodothyronine (T3) increases mitochondrial respiration and promotes the uncoupling between oxygen consumption and ATP synthesis. T3 effect is mediated partly through transcriptional control of genes encoding mitochondrial proteins. We determined the effect of T3 on mRNA levels of uncoupling proteins (UCP) and proteins involved in the biogenesis of the respiratory chain in human skeletal muscle and on UCP2 mRNA expression in adipose tissue. Ten young, healthy males received 75 to 100 5g of T3 per day for 14 days. The increase in plasma-free T3 levels was associated with an increase of resting metabolic rate and a decrease of respiratory quotient. In skeletal muscle, treatment with T3 induced a twofold increase of both UCP2 and UCP3 mRNA levels (p c oxidase subunits 2 and 4, nuclear respiratory factor 1, mitochondrial transcription factor A, and the co-activator PGC1 did not change during the treatment. In adipose tissue, UCP2 mRNA levels increased threefold. The direct effect of T3 on skeletal muscle an d adipose tissue UCP2 and UCP3 mRNA expression was demonstrated in vitro in human primary cultures. Our data show that T3 induces UCP2 and UCP3 mRNA expression in humans. In skeletal muscle, UCP regulation by T3 is not associated with the transcriptional regulation of respiratory chain proteins.