Bisphenol S Disrupts Estradiol-Induced Nongenomic Signaling in a Rat Pituitary Cell Line: Effects on Cell Functions

René Viñas and Cheryl S. Watson

Department of Biochemistry and Molecular Biology, University of Texas Medical Branch Galveston, Texas, USA

Abstract

Background: Bisphenol A (BPA) is a well-known endocrine disruptor that imperfectly mimics the effects of physiologic estrogens via membrane-bound estrogen receptors (mERα, mERβ, and GPER/GPR30), thereby initiating nongenomic signaling. Bisphenol S (BPS) is an alternative to BPA in plastic consumer products and thermal paper.

Objective: To characterize the nongenomic activities of BPS, we examined signaling pathways it evoked in GH₃/B₆/F₁₀ rat pituitary cells alone and together with the physiologic estrogen estradiol (E₂). Extracellular signal-regulated kinase (ERK)– and c-Jun-N-terminal kinase (JNK)–specific phosphorylations were examined for their correlation to three functional responses: proliferation, caspase activation, and prolactin (PRL) release.

Methods: We detected ERK and JNK phosphorylations by fixed-cell immunoassays, identified the predominant mER initiating the signaling with selective inhibitors, estimated cell numbers by crystal violet assays, measured caspase activity by cleavage of fluorescent caspase substrates, and measured PRL release by radioimmunoassay.

Results: BPS phosphoactivated ERK within 2.5 min in a nonmonotonic dose-dependent manner (10^–15 to 10^–7 M). When combined with 10^–9 M E₂, the physiologic estrogen’s ERK response was attenuated. BPS could not activate JNK, but it greatly enhanced E₂-induced JNK activity. BPS induced cell proliferation at low concentrations (femtomolar to nanomolar), similar to E_2. Combinations of both estrogens reduced cell numbers below those of the vehicle control and also activated caspases. Earlier activation of caspase 8 versus caspase 9 demonstrated that BPS initiates apoptosis via the extrinsic pathway, consistent with activation via a membrane receptor. BPS also inhibited rapid (≤ 1 min) E₂-induced PRL release.

Conclusion: BPS, once considered a safe substitute for BPA, disrupts membrane-initiated E₂-induced cell signaling, leading to altered cell proliferation, cell death, and PRL release.

Key words: bisphenol S, ERα, ERK activation, JNK activation, membrane estrogen receptors, nongenomic effects, prolactinoma cell line, xenoestrogens.

Environ Health Perspect 121:352–358 (2013). http://dx.doi.org/10.1289/ehp.1205826 [Online 17 January 2013]

Address correspondence to C.S. Watson, Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77555-0645 USA. Telephone: (409) 772-2383. E-mail: cswatson@utmb.edu

We thank D. Konkel for critically editing the manuscript.

This research was supported by the Passport Foundation and an F31 Ruth L. Kirschstein National Research Service Award from the National Institutes of Health.

The authors declare they have no actual or potential competing financial interests.

Received 27 July 2012; Accepted 13 December 2012; Online 17 January 2013.