World Health Organization defines endocrine disrupting chemicals (EDCs) as »exogenous substances or mixtures that alter function(s) of the endocrine system and consequently cause adverse effects in an intact organism, or its progeny, or (sub)populations«. They have been linked to numerous disorders, such as obesity, diabetes, infertility, impaired thyroid and neuroendocrine system functions, impaired development, altered function of the immune system, and cancer development and progression due to their effect on increased cell invasiveness and metastasis. However, their effects on integrinmediated cell adhesion are not yet well researched. Similarly, a very heterogenous body of data on their effect on the immune system function was produced. EDCs have various modes of action, while exerting nonmonotonic effects and effects at low doses. Tests for identification of EDCs are based on well-known mechanisms of action but have disadvantages. In this doctoral dissertation we will investigate the effect of EDCs on the immune system function through the receptor for activated kinase C 1 (RACK1), and on cell adhesion processes through the vitronectin receptor (VTNR, also known as integrin αVβ3). We will try to develop in-vitro tests for the identification of EDCs with such actions. RACK1 has an important role in immune activation and is regulated through a balance between glucocorticoid and androgen levels. In this study, we investigated the effects of three bisphenols (BPA, BPAF, BPS) on RACK1 expression and on the innate immune responses in the THP-1 human promyelocytic cell line. BPA and BPAF reduced RACK1 promoter transcriptional activity, mRNA expression, and protein levels; however, BPS had the opposite effects. As expected, these data for RACK1 expression were paralleled by lipopolysaccharide-induced interleukin-8 and tumor necrosis factor-α production. We demonstrated the involvement of nuclear factor NF-κB, glucocorticoid receptor (GR), and androgen receptor (AR) in the regulation of RACK1 expression upon exposure to bisphenols. Thus, RACK1 represents an important target of EDCs, and serves as a screening tool for immunotoxic potential. Furthermore, RACK1 can be exploited to unmask multiple molecular interactions of hormone-active substances, to better dissect out their mechanisms of action. The actions of MES on VTNR are implicated by binding sites for hormones on this receptor, which is involved in tumor angiogenesis and metastasis. VTNR-expressing human umbilical vein endothelial cells (HUVECs) were used to determine the effects of EDCs and endogenous hormones on cell adhesion to vitronectin-coated surfaces, and on VTNR activation. Cell adhesion was significantly increased for BPA, triclocarban, and triclosan (10, 100 nM; p <0.05), with similar trends for BPAF and BPS (10, 100 nM; p >0.05). These EDCs did not induce the activated conformation of VTNR, and showed nonmonotonic inverted U-shaped dose-response curves for cell adhesion. No changes in cell adhesion were seen for the endogenous hormones 5α-dihydrotestosterone, 17β-estradiol, and triiodothyronine, and for imatinib and paroxetine. These data indicate that EDC-mediated increases in HUVEC adhesion to vitronectin are not mediated through androgenic, estrogenic, or thyroid activities, nor through activation of VTNR. Although these effects of EDCs on HUVEC adhesion require further investigation of the underlying mechanism(s) of action to define
their biological relevance, the low-dose effects and nonmonotonic responses revealed here define the urgent need for further risk assessment of these EDCs.
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