RESUMO
Arsenic in drinking water is of critical concern in West Bengal, India, as it results in several physiological symptoms including dermatological lesions and cancers. Impairment of the DNA repair mechanism has been associated with arsenic-induced genetic damage as well as with several cancers. ERCC2 (Excision Repair Cross-Complementing rodent repair, complementation group 2), mediates DNA-repair by interacting with Cdk-activating kinase (CAK) complex, which helps in DNA proof-reading during transcription. Arsenic metabolism alters epigenetic regulation; we tried to elucidate the regulation of ERCC2 in arsenic-exposed humans. Water, urine, nails, hair and blood samples from one hundred and fifty seven exposed and eighty eight unexposed individuals were collected. Dose dependent validation was done in vitro using HepG2 and HEK-293. Arsenic content in the biological samples was higher in the exposed individuals compared with the content in unexposed individuals (p < 0.001). Bisulfite-modified methylation specific PCR showed a significant (p < 0.0001) hypomethylation of the ERCC2 promoter in the arsenic-exposed individuals. Densitometric analysis of immunoblots showed a nearly two-fold increase in expression of ERCC2 in exposed individuals, but there was an enhanced genotoxic insult as measured by micronuclei frequency. Immuno-precipitation and western blotting revealed an increased (p < 0.001) association of Cdk7 with ERCC2 in highly arsenic exposed individuals. The decrease in CAK activity was determined by observing the intensity of Ser(392) phosphorylation in p53, in vitro, which decreased with an increase in arsenic dose. Thus we infer that arsenic biotransformation leads to promoter hypomethylation of ERCC2, which in turn inhibits the normal functioning of the CAK-complex, thus affecting DNA-repair; this effect was highest among the arsenic exposed individuals with dermatological lesions.
Assuntos
Arsênio/toxicidade , Quinases Ciclina-Dependentes/metabolismo , Exposição Ambiental/efeitos adversos , Poluentes Químicos da Água/toxicidade , Proteína Grupo D do Xeroderma Pigmentoso/metabolismo , Adulto , Arsênio/análise , Metilação de DNA/efeitos dos fármacos , Reparo do DNA/efeitos dos fármacos , Exposição Ambiental/análise , Feminino , Células HEK293 , Células Hep G2 , Humanos , Masculino , Pessoa de Meia-Idade , Regiões Promotoras Genéticas/efeitos dos fármacos , Regulação para Cima/efeitos dos fármacos , Poluentes Químicos da Água/análise , Proteína Grupo D do Xeroderma Pigmentoso/genética , Adulto Jovem , Quinase Ativadora de Quinase Dependente de CiclinaRESUMO
Chronic exposure to arsenic through drinking water affects nearly 26 million individuals in West Bengal, India. Cytogenetic biomarkers like urothelial micronucleus (MN) are extensively used to monitor arsenic exposed population. In 2004-2005, 145 arsenic exposed individuals and 60 unexposed controls were surveyed of which 128 exposed individuals and 54 unexposed controls could be followed up in 2010-2011. In 2004-2005, the extent of arsenic content in the drinking water was 348.23 ± 102.67 µg/L, which was significantly lowered to 5.60 ± 10.83 µg/L in 2010-2011. Comparing the data obtained between 2004-2005 and 2010-2011, there was a significant decline in the MN frequency, when assayed in 2010-2011 compared to 2004-2005. Hence, we infer that urothelial MN can be utilized as a good biomarker in detecting remedial effects from toxicity of the low dose of arsenic through drinking water.
