Endoplasmic reticulum protein (ERp) 29 binds as strongly as protein disulfide isomerase (PDI) to bisphenol A

Bisphenol A (BPA), which is used in polycarbonate and epoxy resins, affects the development or function of the central nervous system. Previously, we isolated a BPA-binding protein from rat brain, identified it as protein disulfide isomerase (PDI), and found that BPA binds to the b' domain of PDI and inhibits its activity. There are 20 kinds of PDI family proteins in mammalian endoplasmic reticulum. The member proteins each have a different length and domain arrangement. Here we investigated the binding of BPA and T3 to ERp29, ERp57, and ERp72, which each have the b or b' domain. BPA/T3 binding of ERp57 and that of ERp72 were lower than that of PDI, and BPA did not inhibit the oxidase or reductase activity of these proteins. On the other hand, BPA and T3 bound to ERp29 as strongly as to PDI. The CD spectrum of PDI was changed in the presence of BPA in a dose-dependent manner, while that of ERp29 was not, suggesting that BPA did not affect the conformation of ERp29. We found that PDI suppresses GH expression in rat GH3 cells stimulated by thyroid hormone (T3) overexpression of PDI and that ERp57 reduced the GH level, but overexpression of ERp29 did not change GH expression. These results suggested that affinity to T3 does not involve the reduction of the T3 response. In this study, ERp29 was first identified as a BPA-binding protein but is not involved in the T3 response of GH3 cells.