Roles of p21, p53, cyclin D1, CDK-4, estrogen receptor in aflatoxin B1-induced cytotoxicity in testicular tissue of mice

This study was done in order to investigate time-dependent effect of AFB1 on expression of genes involving in cell cycle check point machinery at G, S, and M phases. For this purpose, 24 mature male Swiss albino mice were randomly divided into control and test groups. The animals in test group subdivided into three groups, which received the AFB1 at a daily dose of 20 mu g/kg body weight, through intraperitoneal (i.p.) route, for 7, 14, and 21 days. The p21, p53, cyclin D1, CDK4, and ER expressions at both mRNA and protein level were analyzed by using reverse transcription PCR (RT-PCR) and immunohistochemistry, respectively. Moreover, the tubular differentiation (TDI) and spermiogenesis (SPI) indices were analyzed. Finally, the testicular DNA fragmentation was assessed by using DNA Ladder test. Observations revealed that the AFB1 remarkably (P<.05) reduced cyclin D1, Cdk4, and ER expression at both mRNA and protein levels. Up-regulated p21 and p53 expression was revealed in AFB1-received animals, which developed time dependently. Histological examinations exhibited a significant reduction in TDI and SPI indices. Finally, the AFB1 resulted in severe DNA fragmentation. Our data showed that the AFB1 by down-regulating the cyclin D1, Cdk4, and ER expression adversely affects cyclin D1/Cdk4 and cyclin D1/ER interactions. Moreover, the AFB1-induced overexpression of p21 (as a kinase inhibitor), in turn results in cell cycle arrest via inhibiting the Cdk4 interaction with cyclin D1. Finally, the AFB1-induced DNA damage triggers the p53-dependent apoptosis pathway independent to p21 overexpression.