Bisphenol A-induced autophagy ameliorates human B cell death through Nrf2-mediated regulation of Atg7 and Beclin1 expression by Syk activation

Abstract

The widely used plasticizer bisphenol A (BPA) is known as an endocrine-disrupting chemical (EDC). Many studies have shown that BPA contributes to diseases involving immune system alterations, but the underlying mechanisms have yet to be elucidated. We previously reported that BPA at concentration of 100 μM caused human B cell death in accordance with an increase in nuclear factor (erythroid-derived 2)-like 2(Nrf2) expression. Autophagy is a cellular process that degraded and recycles cytoplasmic constituents. Here, we investigated whether BPA induces autophagy through Nrf2, which is associated with regulation of B cell death using human WiL2-NS lymphoblast B cells. Then, cell viability was assessed by various assays using trypan blue, MTT or Celltiter glo luminescent substrate and DAPI. When WiL2-NS cells were treated with BPA, cell viability was decreased and LC3 autophagy cargo protein/puncta was increased. BPA-induced autophagy was confirmed by the modification of LC3 puncta formation or autophagy flux turnover with the treatment of hydroxychloroquine(HCQ), NH₄Cl and PI3K inhibitors including 3-methyladenine(3-MA), LY294002 and wortmannin. BPA treatment increased the expression of autophagy-related gene(Atg)7 and Beclin1 as well as Nrf2 induced by the production of reactive oxygen species (ROS). The inhibition of autophagy with siAtg7 or siBeclin1 and Nrf2 depletion aggravated BPA-induced cell death. BPA enhanced the bound of Nrf2 to the specific region on Beclin1 and Atg7 promoter. Spleen tyrosine kinase(Syk) activity was enhanced in response to BPA treatment. Bay61-3606, Syk inhibitor, decreased LC3 and the expression of Atg7 and Beclin1, leading to the increase of BPA-induced B cell death. The results suggest that BPA-induced autophagy ameliorates human B cell death through Nrf2-mediated regulation of Atg7 and Beclin1 expression.

Keywords: Atg7; Autophagy; B cell death; Beclin1; Bisphenol A; Syk.