Bisphenol A and its derivatives induce degradation of HIF-1alpha via the lysosomal pathway in human hepatocarcinoma cell line, Hep3B

Abstract

Bisphenol A (BPA, 2,2-bis(4-hydroxyphenyl)propane), one of the phenolic compounds widely used in the manufacture of plastic and epoxy resins, is known as an endocrine disruptor. In a previous study, we found that BPA induced hypoxia inducible factor-1alpha (HIF-1alpha) degradation by dissociation from heat shock protein 90 (Hsp90). In this study, to investigate the structural requirements for degradation of HIF-1alpha, we estimated the effect of BPA derivatives (BPE, BPF, BPB, Dimethyl butylidene diphenol (DMBDP), Ethyl hexylidene diphenol (EHDP), Bishydroxyphenyl cyclohexane (BHCH), and Methyl benzylidene bisphenol (MBBP)) on HIF-1alpha protein degradation, using human hepatocarcinoma cell line, Hep3B. BPB, DMBDP, BHCH, and MBBP decreased HIF-1alpha protein levels more efficiently than BPA, but BPE, BPF, and EHDP did not affect HIF-1alpha protein levels. BPA degraded HIF-1alpha even in the presence of MG132, a proteasome inhibitor. In this study, we found that ammonium chloride (NH4Cl), a lysosomal enzyme inhibitor, efficiently restored the decrease in HIF-1alpha protein levels by BPA. Recent studies indicated that HIF-1alpha is degraded by the lysosomal pathway as well as the proteasomal pathway. Therefore, we investigated the levels of heat shock cognate 70kDa protein (HSC70) protein after treatment with BPA. We found that BPA induced HSC70 protein and overexpression of HSC70 enhanced HIF-1alpha degradation in Hep3B cells. These results suggested that BPA causes the degradation of HIF-1alpha by induction of HSC70, leading lysosomal degradation of HIF-1alpha.