Abstract
We previously demonstrated the existence of a balance among steroid hormones, i.e. glucocorticoids and androgens, in RACK1 (receptor for activated C kinase 1) expression and innate immunity activation, which may offer the opportunity to use RACK1 expression as marker to evaluate immunotoxicity of hormone-active substances. Because of the existence of close interconnections between the different steroid hormone receptors with overlapping ligand specificities and signaling pathways, in this study, we wanted to investigate a possible effect of estrogenic active compounds, namely 17β-estradiol, diethylstilbestrol, and zearalenone, on RACK-1 expression and innate immune responses using THP-1 cells as experimental model. All compounds increased RACK1 transcriptional activity as evaluated by reporter luciferase activity, mRNA expression as assessed by real time-PCR and protein expression by western blot analysis, which paralleled an increase in LPS-induced IL-8, TNF-α production, and CD86 expression, which we previously demonstrated to be dependent on RACK1/PKCβ activation. As the induction of RACK1 expression can be blocked by the antagonist G15, induced by the agonist G1 and by the non-cell permeable 17β-estradiol conjugated with BSA, a role of GPER (previously named GPR30) activation in estrogen-induced RACK1 expression could be demonstrated. In addition, a role of androgen receptor (AR) in RACK1 transcription was also demonstrated by the ability of flutamide, a nonsteroidal antiandrogen, to completely prevent diethylstilbestrol-induced RACK1 transcriptional activity and protein expression. Altogether, our data suggest that RACK1 may represent an interesting target of steroid-active compounds, and its evaluation may offer the opportunity to screen the immunotoxic potential of hormone-active substances.
Highlights
After the second world war, industrialized countries have faced a significant increase of diseases, such as cancer, allergy, autoimmunity, and neurological disorders, that can be all linked to neuro–immune–endocrine network alterations
All compounds increased RACK1 transcriptional activity as evaluated by reporter luciferase activity, mRNA expression as assessed by real time-PCR and protein expression by western blot analysis, which paralleled an increase in Lipopolysaccharide from Escherichia coli serotype 0127:B8 (LPS)-induced IL-8, TNF-α production, and CD86 expression, which we previously demonstrated to be dependent on RACK1/PKCβ activation
Increase of RACK1 mRNA expression at 18 h was observed at all concentrations tested (Fig. 1c), with statistical significance at 0.001, 0.1 and 10 μM, while the concentration-related increase in RACK1 protein evaluated at 24 h already appreciable from the concentration of 0.001 μM, reached a statistical significance at concentrations ≥ 0.1 μM (Fig. 1d)
Summary
After the second world war, industrialized countries have faced a significant increase of diseases, such as cancer, allergy, autoimmunity, and neurological disorders, that can be all linked to neuro–immune–endocrine network alterations. Growing evidence clearly indicates that endocrine-disrupting compounds (EDCs) can interfere with the immune system in human and wildlife (Kuo et al 2012). This is a relatively new area of research, because most of the studies on hormonally active substances primarily focused on reproductive and developmental toxicity. To the anthropogenic known endocrine disruptors, we must remember that we are exposed through diet to hormonally active substances of natural origin, including phytoestrogens, such as genistein, daidzein and coumestrol, and mycotoxins such as zearalenone produced by numerous species of Fusarium (UNEP and WHO 2013; Nesic et al 2014)
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