Endocrine disrupting chemicals (EDCs), such as xenoestrogens (XEs), have been shown to mimic or antagonize the effects of physiological estrogens via novel cellular signaling mechanisms, increasing the likelihood of reproductive and developmental abnormalities. Previous studies from our lab in pituitary cells demonstrated that these steroid-mimicking compounds potently and rapidly exert their effects via activation of non-genomic signaling pathways [e.g. mitogen-activated protein kinases (MAPKs), G proteins, Ca2+] leading to alterations of specific cellular functional endpoints (cell proliferation, apoptoss and differentiated functions such as secretion of peptides). Alkylphenols (APs;nonylphenol (NP) and the structurally related bisphenol-A (BPA)) are known XEs that have been detected in significant amounts in human serum and urine (nM range). Individual APs activate extracellular-regulated kinases (ERKs) as well as potently disrupt physiologic estrogen signaling at low, environmentally relevant concentrations with pronounced non-monotonic concentration- dependence. These XEs, however, do not exist in an environmental setting as individual compounds, but rather as mixtures. Few studies have examined the combinatorial effects to alter non-genomic signaling pathways and functional responses induced by estradiol (E2). The overall hypothesis underlying this study is that mixtures of XEs such as BPA and APs can cause compounded inappropriate regulation of signaling via membrane estrogen receptor (mER) subtypes in a pituitary cell line (GH3/B6/F10). To test this hypothesis the following Specific Aims are proposed:
Aim I : Determine the combined effect of XEs with the physiologic estrogen E2, on signaling pathways;
Aim II : Identify the membrane-bound estrogen receptor (mER) subtype by which XE mixtures initiate non-genomic signaling pathways;
AIM III : Examine correlations between the signaling pathway effects of combined XE exposure to disruption of cellular functional responses.
This study will evaluate the ability of endocrine disrupting chemicals (i.e. bisphenol-A, bisphenol-S and nonylphenol), as chemical mixtures, to alter estradiol-induced non-genomic signaling pathways (Mitogen Activated Protein Kinases: ERK &JNK) in a dose- and time-dependant manner. The multidisciplinary approach of the project will encompass aspects of endocrinology, biochemistry, and toxicology in order to obtain new information on the combinatorial effects of these chemicals on functional endpoints of the rat pituitary cell line GH3/B6/F10 (i.e. cell proliferation/death). With little or no knowledge about te toxicological risk of these compounds when found as mixtures, this study therefore aims to address a significant public health concern.