Transcriptional regulation of RACK1 and modulation of its expression: Role of steroid hormones and significance in health and aging

Unveiling RACK1: a key regulator of the PI3K/AKT pathway in prostate cancer development

The dysregulated PI3K/AKT pathway is pivotal in the onset and progression of various cancers, including prostate cancer. However, targeting this pathway directly poses challenges due to compensatory upregulation of alternative oncogenic pathways. This study focuses on the novel regulatory activity of the Receptor for Activated Protein Kinase (RACK1), a scaffolding/adaptor protein, in governing the PI3K/AKT pathway within prostate cancer. Through a genetic mouse model, our research unveils RACK1's pivotal role in orchestrating AKT activation and the genesis of prostate cancer. RACK1 deficiency hampers AKT activation, effectively impeding prostate tumor formation induced by PTEN and p53 deficiency. Mechanistically, RACK1 facilitates AKT membrane translocation and fosters its interaction with mTORC2, thereby promoting AKT activation and subsequent tumor cell proliferation and tumor formation. Notably, inhibiting AKT activation via RACK1 deficiency does not trigger feedback upregulation of HER3 and androgen receptor (AR) expression and activation, distinguishing it from direct PI3K or AKT targeting. These findings position RACK1 as a critical regulator of the PI3K/AKT pathway and a promising target for curtailing prostate cancer development arising from pathway aberrations.

Endocrine Disrupting Toxicity of Bisphenol A and Its Analogs: Implications in the Neuro-Immune Milieu

Endocrine-disrupting chemicals (EDCs) are natural or synthetic substances that are able to interfere with hormonal systems and alter their physiological signaling. EDCs have been recognized as a public health issue due to their widespread use, environmental persistence and the potential levels of long-term exposure with implications in multiple pathological conditions. Their reported adverse effects pose critical concerns about their use, warranting their strict regulation. This is the case of bisphenol A (BPA), a well-known EDC whose tolerable daily intake (TDI) was re-evaluated in 2023 by the European Food Safety Authority (EFSA), and the immune system has been identified as the most sensitive to BPA exposure. Increasing scientific evidence indicates that EDCs can interfere with several hormone receptors, pathways and interacting proteins, resulting in a complex, cell context-dependent response that may differ among tissues. In this regard, the neuronal and immune systems are important targets of hormonal signaling and are now emerging as critical players in endocrine disruption. Here, we use BPA and its analogs as proof-of-concept EDCs to address their detrimental effects on the immune and nervous systems and to highlight complex interrelationships within the immune-neuroendocrine network (INEN). Finally, we propose that Receptor for Activated C Kinase 1 (RACK1), an important target for EDCs and a valuable screening tool, could serve as a central hub in our toxicology model to explain bisphenol-mediated adverse effects on the INEN.

Disruption of Epithelial Barrier Integrity via Altered GILZ/c-Rel/RACK1 Signaling in Inflammatory Bowel Disease

BACKGROUND AND AIMS

Given the role of Receptor for Activated C Kinase 1 (RACK1) in both immune cell activation and in the maintenance of the intestinal epithelial barrier integrity, we investigated whether it was involved in inflammatory bowel disease (IBD).

METHODS

RACK1 expression was analyzed in intestinal mucosal samples of healthy and IBD patients, in mice with chemically induced colitis, and in diseased in vitro 2D and 3D coculture models by luciferase assay, reverse transcription-quantitative PCR, Western blotting, immunofluorescence, and immunohistochemistry. Based on our finding that glucocorticoid-induced leucine zipper (GILZ or tsc22d3) positively correlates with RACK1 expression in IBD patients, GILZ knockout mice and cell silencing experiments were performed.

RESULTS

RACK1 was significantly decreased in IBD, especially in ulcerative colitis. This was associated with an NF-κB/c-Rel-related mechanism, correlating with decreased GILZ protein expression. GILZ depletion confirmed a decrease in RACK1 expression, which favored SRC activation and led to a significant reduction in E-cadherin, resulting in impaired epithelial barrier integrity. Finally, our data highlighted that this novel mechanism could be considered to develop new therapies since dexamethasone, the first line of treatment in IBD, restored RACK1 expression through the glucocorticoid receptor in a c-Rel/GILZ-independent manner.

CONCLUSIONS

We provide the first evidence that an alteration of RACK1/SRC/E-cadherin regulatory mechanism, correlating with decreased GILZ protein expression, is involved in epithelial barrier disruption. The clinical relevance is based on the fact that this mechanism involving GILZ/c-Rel-related RACK1 expression could be considered to improve IBD therapies, particularly in patients with low or no response to glucocorticoid treatment.

VEGFB promotes adipose tissue thermogenesis by inhibiting norepinephrine clearance in macrophages

Adipokines play key roles in adaptive thermogenesis of beige adipocytes, though its detailed regulatory mechanisms are not fully understood. In the present study, we identify a critical function of vascular endothelial growth factor B (VEGFB)/vascular endothelial growth factor receptor 1 (VEGFR1) signaling in improving thermogenesis in white adipose tissue (WAT). In mouse subcutaneous WAT (scWAT), thermogenesis activation leads to the up-regulation of VEGFB in adipocytes and its receptor VEGFR1 in macrophages. Ablation of adipocyte VEGFB results in deficiency in murine WAT browning. Meanwhile, supplementation of VEGFB promotes WAT thermogenesis, but this effect is blocked by knockout of macrophage VEGFR1. Mechanistic studies show that the VEGFB-activated VEGFR1 inhibits p38 MAPK signaling through its dissociation with receptor for activated C kinase 1, thereby preventing norepinephrine transporter (solute carrier family 6 member 2) and norepinephrine-degrative monoamine oxidase a mediated norepinephrine clearance in macrophages. Our findings demonstrate that VEGFB/VEGFR1 circuit contributes to the WAT thermogenesis.

RACK1 contributes to the upregulation of embryonic genes in a model of cardiac hypertrophy

Receptors for activated C kinases (RACKs) have been shown to coordinate PKC-mediated hypertrophic signalling in mice. However, little information is available on its participation in embryonic gene expression. This study investigated the involvement of RACK1 in the expression of embryonic genes in a zebrafish (ZF) ex vivo heart culture model by using phenylephrine (PE) or a growth factors cocktail (GFs) as a prohypertrophic/regeneration stimulus. Blebbistatin (BL) inhibition has also been studied for its ability to block the signal transduction actions of some PEs. qRT‒PCR and immunoblot analyses confirmed the upregulation of RACK1 in the PE- and GFs-treated groups. BL administration counteracted PE-induced hypertrophy and downregulated RACK1 expression. Immunohistochemical analyses of the heart revealed the colocalization of RACK1 and embryonic genes, namely, Gata4, Wt1, and Nfat2, under stimulation, whereas these genes were expressed at lower levels in the BL treatment group. Culturing ZF heart cells activated via GFs treatment increased the expression of RACK1. The overexpression of RACK1 induced by the transfection of recombinant RACK1 cDNA in ZF heart cells increased the expression of embryonic genes, especially after one week of GFs treatment. In summary, these results support the involvement of RACK1 in the induction of embryonic genes during cardiac hypertrophy/GFs stimulation in a fish heart model, which can be used as an alternative study model for mammals.

RNA sequencing of exosomes secreted by fibroblast and Schwann cells elucidates mechanisms underlying peripheral nerve regeneration

JOURNAL/nrgr/04.03/01300535-202408000-00035/figure1/v/2023-12-16T180322Z/r/image-tiff Exosomes exhibit complex biological functions and mediate a variety of biological processes, such as promoting axonal regeneration and functional recovery after injury. Long non-coding RNAs (lncRNAs) have been reported to play a crucial role in axonal regeneration. However, the role of the lncRNA-microRNA-messenger RNA (mRNA)-competitive endogenous RNA (ceRNA) network in exosome-mediated axonal regeneration remains unclear. In this study, we performed RNA transcriptome sequencing analysis to assess mRNA expression patterns in exosomes produced by cultured fibroblasts (FC-EXOs) and Schwann cells (SC-EXOs). Differential gene expression analysis, Gene Ontology analysis, Kyoto Encyclopedia of Genes and Genomes analysis, and protein-protein interaction network analysis were used to explore the functions and related pathways of RNAs isolated from FC-EXOs and SC-EXOs. We found that the ribosome-related central gene Rps5 was enriched in FC-EXOs and SC-EXOs, which suggests that it may promote axonal regeneration. In addition, using the miRWalk and Starbase prediction databases, we constructed a regulatory network of ceRNAs targeting Rps5, including 27 microRNAs and five lncRNAs. The ceRNA regulatory network, which included Ftx and Miat, revealed that exsosome-derived Rps5 inhibits scar formation and promotes axonal regeneration and functional recovery after nerve injury. Our findings suggest that exosomes derived from fibroblast and Schwann cells could be used to treat injuries of peripheral nervous system.

The roles of RACK1 in the pathogenesis of Alzheimer's disease

The receptor for activated C kinase 1 (RACK1) is a protein that plays a crucial role in various signaling pathways and is involved in the pathogenesis of Alzheimer's disease (AD), a prevalent neurodegenerative disease. RACK1 is highly expressed in neuronal cells of the central nervous system and regulates the pathogenesis of AD. Specifically, RACK1 is involved in regulation of the amyloid-β precursor protein processing through α- or β-secretase by binding to different protein kinase C isoforms. Additionally, RACK1 promotes synaptogenesis and synaptic plasticity by inhibiting N-methyl-D-aspartate receptors and activating gamma-aminobutyric acid A receptors, thereby preventing neuronal excitotoxicity. RACK1 also assembles inflammasomes that are involved in various neuroinflammatory pathways, such as nuclear factor-kappa B, tumor necrosis factor-alpha, and NOD-like receptor family pyrin domain-containing 3 pathways. The potential to design therapeutics that block amyloid-β accumulation and inflammation or precisely regulate synaptic plasticity represents an attractive therapeutic strategy, in which RACK1 is a potential target. In this review, we summarize the contribution of RACK1 to the pathogenesis of AD and its potential as a therapeutic target.

In Vitro Effects of Bisphenol Analogs on Immune Cells Activation and Th Differentiation

AIMS

Investigate the immunomodulatory effects of bisphenols in the THP-1 cell line and peripheral blood mononuclear cells in response to lipopolysaccharide (LPS) activation or to phorbol 12-myristate 13-acetate (PMA) and ionomycin.

BACKGROUND

We have previously demonstrated the usefulness of the evaluation of RACK1 expression as a link between endocrine disrupting activity and the immunotoxic effect of xenobiotics. We demonstrated that while BPA and BPAF reduced RACK1 expression, BPS was able to increase it.

OBJECTIVE

Bisphenol A (BPA) is one of the most commonly used chemicals in the manufacturing of polycarbonate plastics and plastic consumer products. Its endocrine disrupting (ED) potential and changes in European regulations have led to replacing BPA in many uses with structurally similar chemicals, like bisphenol AF (BPAF) and bisphenol S (BPS). However, emerging data indicated that bisphenol analogues may not be safer than BPA both in toxic effects and ED potential.

METHODS

THP-1 cell line and peripheral blood mononuclear cells were activated with lipopolysaccharide (LPS) or with phorbol 12-myristate 13-acetate (PMA) and ionomycin.

RESULTS

BPA and BPAF decreased LPS-induced expression of surface markers and the release of pro-inflammatory cytokines, while BPS increased LPS-induced expression of CD86 and cytokines. BPA, BPAF, and BPS affected PMA/ionomycin-induced T helper differentiation and cytokine release with gender-related alterations in some parameters investigated.

CONCLUSION

Data confirm that bisphenols can modulate immune cell differentiation and activation, further supporting their immunotoxic effects.

Effects of endocrine active contaminating pesticides on RACK1 expression and immunological consequences in THP-1 cells

We have previously demonstrated that RACK1, which expression is under steroid hormone control, plays an important role in the activation of immune cells and its expression can be useful to evaluate the immunotoxic profile of endocrine disrupting chemicals (EDCs). Hence, we investigated the effects of three contaminating and persistent pesticides: the fungicide vinclozolin (VIN), the herbicide atrazine (ATR) and the insecticide cypermethrin (CYP) on RACK1 expression and on innate immune response. VIN resulted in modest alteration of RACK1 while ATR and CYP reduced in a dose dependent manner RACK1 expression, ultimately leading to the decrease in lipopolysaccharide-induced IL-8 and TNF-α release and CD86 and CD54 surface marker expression. Moreover, our data indicate that, after exposure to EDCs, alterations of RACK1 expression can also occur with mechanisms not directly mediated by an interaction with a nuclear or membrane steroid receptors. Therefore, RACK1 could represent a useful EDCs screening tool to evaluate their immunotoxic potential and to dissect their mechanisms of action.

Effects of endocrine disrupting chemicals on the expression of RACK1 and LPS-induced THP-1 cell activation

The existence of a complex hormonal balance among glucocorticoids, androgens and estrogens involved in the regulation of Receptor for Activated C Kinase 1 (RACK1) expression and its related immune cells activation, highlights the possibility to employ this protein as screening tool for the evaluation of the immunotoxic profile of endocrine disrupting chemicals (EDCs), hormone-active substances capable of interfering with the physiologic hormonal signaling. Hence, the aim of this work was to investigate the effect of the exposure of EDCS 17α-ethynylestradiol (EE), diethyl phthalate (DEP) and perfluorooctanesulfonic acid (PFOS) on RACK1 expression and on lipopolysaccharide (LPS)-induced activation of the human monocytic cell line THP-1, a validated model for this investigation. In line with our previous results with estrogen-active compounds, EE treatment significantly induced RACK1 promoter transcriptional activity, mRNA expression, and protein levels, which paralleled an increase in LPS-induced IL-8, TNF-α production and CD86 expression, previously demonstrated to be dependent on RACK1/PKCβ activation. EE mediates its effect on RACK1 expression through G-protein-coupled estrogen receptor (GPER) and androgen receptor (AR) ligand-independent cascade, as also suggested by in silico molecular docking simulation. Conversely, DEP and PFOS induced a dose-dependent downregulation of RACK1 promoter transcriptional activity, mRNA expression, and protein levels, which was mirrored by a reduction of IL-8, TNF-α production and CD86 expression. Mifepristone pre-treatments abolish DEP and PFOS effects, confirming their GR agonist profile, also corroborated by molecular docking. Altogether, our data confirm that RACK1 represents an interesting target of steroid active compounds, which expression offers the opportunity to screen the immunotoxic potential of different hormone-active substances of concerns due to their human exposure and environmental persistence.

Proteostasis Deregulation in Neurodegeneration and Its Link with Stress Granules: Focus on the Scaffold and Ribosomal Protein RACK1

The role of protein misfolding, deposition, and clearance has been the dominant topic in the last decades of investigation in the field of neurodegeneration. The impairment of protein synthesis, along with RNA metabolism and RNA granules, however, are significantly emerging as novel potential targets for the comprehension of the molecular events leading to neuronal deficits. Indeed, defects in ribosome activity, ribosome stalling, and PQC—all ribosome-related processes required for proteostasis regulation—can contribute to triggering stress conditions and promoting the formation of stress granules (SGs) that could evolve in the formation of pathological granules, usually occurring during neurodegenerating effects. In this review, the interplay between proteostasis, mRNA metabolism, and SGs has been explored in a neurodegenerative context with a focus on Alzheimer’s disease (AD), although some defects in these same mechanisms can also be found in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS), which are discussed here. Finally, we highlight the role of the receptor for activated C kinase 1 (RACK1) in these pathologies and note that, besides its well characterized function as a scaffold protein, it has an important role in translation and can associate to stress granules (SGs) determining cell fate in response to diverse stress stimuli.

Analysis of Interaction Network Between Host Protein and M Protein of Swine Acute Diarrhea Syndrome Coronavirus

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is an enterovirus that can cause acute diarrhea and death in piglets and cause serious economic losses to the pig industry. SADS-CoV membrane (M) protein mainly plays a key role in biological processes, such as virus assembly, budding, and host innate immune regulation. Understanding the interaction between M protein and host proteins is very important to define the molecular mechanism of cells at the protein level and to understand specific cellular physiological pathways. In this study, 289 host proteins interacting with M protein were identified by glutathione-S-transferase (GST) pull-down combined with liquid chromatography-mass spectrometry (LC-MS/MS), and the protein-protein interaction (PPI) network was established by Gene Ontology (GO) terms and Kyoto Encyclopedia of Gene and Genomes (KEGG) pathways analysis. Results showed that SADS-CoV M protein was mainly associated with the host metabolism, signal transduction, and innate immunity. The Co-Immunoprecipitation (CO-IP) validation results of six randomly selected proteins, namely, Rab11b, voltage-dependent anion-selective channel 1 (VDAC1), Ribosomal Protein L18 (RPL18), RALY, Ras Homolog Family Member A (RHOA), and Annexin A2 (ANXA2), were consistent with LC-MS results. In addition, overexpression of RPL18 and PHOA significantly promoted SADS-CoV replication, while overexpression of RALY antagonized viral replication. This work will help to clarify the function of SADS-CoV M protein in the life cycle of SADS-CoV.

The coupling of RACK1 with the beta isoform of the glucocorticoid receptor promotes resilience to chronic stress exposure

Several intracellular pathways that contribute to the adaptation or maladaptation to environmental challenges mediate the vulnerability and resilience to chronic stress. The activity of the hypothalamic-pituitary-adrenal (HPA) axis is fundamental for the proper maintenance of brain processes, and it is related to the functionality of the isoform alfa and beta of the glucocorticoid receptor (Gr), the primary regulator of HPA axis. Among the downstream effectors of the axis, the scaffolding protein RACK1 covers an important role in regulating synaptic activity and mediates the transcription of the neurotrophin Bdnf. Hence, by employing the chronic mild stress (CMS) paradigm, we studied the role of the Grβ-RACK1-Bdnf signaling in the different susceptibility to chronic stress exposure. We found that resilience to two weeks of CMS is paralleled by the activation of this pathway in the ventral hippocampus, the hippocampal subregion involved in the modulation of stress response. Moreover, the results we obtained in vitro by exposing SH-SY5Y cells to cortisol support the data we found in vivo. The results obtained add novel critical information about the link among Gr, RACK1 and Bdnf and the resilience to chronic stress, suggesting novel targets for the treatment of stress-related disorders, including depression.

Effects of Bisphenols on RACK1 Expression and Their Immunological Implications in THP-1 Cells

Receptor for activated C kinase 1 (RACK1) has an important role in immune activation, and is regulated through a balance between glucocorticoid and androgen levels. We have previously demonstrated that RACK1 expression can serve as a marker for evaluation of immunotoxic profiles of hormone-active substances, such as endocrine-disrupting chemicals (EDCs). 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, a validated model for this investigation. BPA and BPAF reduced RACK1 promoter transcriptional activity, mRNA expression, and protein levels. However, BPS had the opposite effect. As expected, these results on RACK1 were paralleled by lipopolysaccharide (LPS)-induced interleukin-8 (IL-8) and tumor necrosis factor-α (TNFα) production. Since BPA and BPAF induced RACK1 expression in the presence of glucocorticoid receptor (GR) antagonist mifepristone, a role of G-protein-coupled estrogen receptor (GPER) has been considered due to their known estrogenic profile. Therefore, additional molecular effects of BPA and BPAF were unmasked after treatment with different inhibitors of well-known pivotal players of GPER-mediated signaling. BPA exerted its effects on RACK1 via NF-κB, as shown using the NF-κB inhibitor BAY11-7085 and NF-κB-specific luciferase reporter assay. Conversely, BPAF induced RACK1 up-regulation via androgen receptor (AR) activation, as confirmed by treatment with AR antagonist flutamide. Indeed, a biased agonism profile for BPA and BPAF for GPER was suggested based on their different binding modes revealed by our molecular docking. Altogether, our data suggest that RACK1 could represent an important target of EDCs and serves as a screening tool for their immunotoxic potential. Furthermore, RACK1 can be exploited to unmask multiple molecular interactions of hormone-active substances to better dissect out their mechanisms of action.

Role of Protein Kinase C in Immune Cell Activation and Its Implication Chemical-Induced Immunotoxicity

Protein kinase C (PKCs) isoforms play a key regulatory role in a variety of cellular functions, including cell growth and differentiation, gene expression, hormone secretion, etc. Patterns of expression for each PKC isoform differ among tissues, and it is also clear that different PKCs are often not functionally redundant, for example specific PKCs mediate specific cellular signals required for activation, proliferation, differentiation and survival of immune cells. In the last 20 years, we have been studying the role of PKCs, mainly PKCβ and its anchoring protein RACK1 (Receptor for Activated C Kinase 1), in immune cell activation, and their implication in immunosenescence and immunotoxicity. We could demonstrate that PKCβ and RACK1 are central in dendritic cell maturation and activation by chemical allergens, and their expressions can be targeted by EDCs and anti-inflammatory drugs. In this chapter, current knowledge on the role of PKC in immune cell activation and possible implication in immunotoxicity will be described.

OXER1 and RACK1-associated pathway: a promising drug target for breast cancer progression

Recent data indicate that receptor for activated C kinase 1 (RACK1) is a putative prognostic marker and drug target in breast cancer (BC). High RACK1 expression is negatively associated with overall survival, as it seems to promote BC progression. In tumors, RACK1 expression is controlled by a complex balance between glucocorticoids and androgens. Given the fact that androgens and androgenic derivatives can inhibit BC cell proliferation and migration, the role of androgen signaling in regulating RACK1 transcription in mammary tumors is of pivotal interest. Here, we provide evidence that nandrolone (19-nortosterone) inhibits BC cell proliferation and migration by antagonizing the PI3K/Akt/NF-κB signaling pathway, which eventually results in RACK1 downregulation. We also show that nandrolone impairs the PI3K/Akt/NF-κB signaling pathway and decreases RACK1 expression via binding to the membrane-bound receptor, oxoeicosanoid receptor 1 (OXER1). High levels of OXER1 are observed in several BC cell lines and correlate with RACK1 expression and poor prognosis. Our data provide evidence on the role played by the OXER1-dependent intracellular pathway in BC progression and shed light on the mechanisms underlying membrane-dependent androgen effects on RACK1 regulation. Besides the mechanistic relevance, the results of the study are of interest from a translational prospective. In fact, they identify a new and actionable pathway to be used for the design of innovative and rational therapeutic strategies in the context of the personalized treatment of BC. In addition, they draw attention on nandrolone-based compounds that lack hormonal activity as potential anti-tumor agents.

Endocrine-Disrupting Chemicals' (EDCs) Effects on Tumour Microenvironment and Cancer Progression: Emerging Contribution of RACK1

Endocrine disruptors (EDCs) can display estrogenic and androgenic effects, and their exposure has been linked to increased cancer risk. EDCs have been shown to directly affect cancer cell regulation and progression, but their influence on tumour microenvironment is still not completely elucidated. In this context, the signalling hub protein RACK1 (Receptor for Activated C Kinase 1) could represent a nexus between cancer and the immune system due to its roles in cancer progression and innate immune activation. Since RACK1 is a relevant EDCs target that responds to steroid-active compounds, it could be considered a molecular bridge between the endocrine-regulated tumour microenvironment and the innate immune system. We provide an analysis of immunomodulatory and cancer-promoting effects of different EDCs in shaping tumour microenvironment, with a final focus on the scaffold protein RACK1 as a pivotal molecular player due to its dual role in immune and cancer contexts.

Ribosomes as a nexus between translation and cancer progression: Focus on ribosomal Receptor for Activated C Kinase 1 (RACK1) in breast cancer

Ribosomes coordinate spatiotemporal control of gene expression, contributing to the acquisition and maintenance of cancer phenotype. The link between ribosomes and cancer is found in the roles of individual ribosomal proteins in tumorigenesis and cancer progression, including the ribosomal protein, receptor for activated C kinase 1 (RACK1). RACK1 regulates cancer cell invasion and is localized in spreading initiation centres, structural adhesion complexes containing RNA binding proteins and poly-adenylated mRNAs that suggest a local translation process. As RACK1 is a ribosomal protein directly involved in translation and in breast cancer progression, we propose a new molecular mechanism for breast cancer cell migration and invasion, which considers the molecular differences between epithelial and mesenchymal cell profiles in order to characterize and provide novel targets for therapeutic strategies. Hence, we provide an analysis on how ribosomes translate cancer progression with a final focus on the ribosomal protein RACK1 in breast cancer.

Proteome changes induced by a short, non-cytotoxic exposure to the mycoestrogen zearalenone in the pig intestine

Intestinal epithelial homeostasis is regulated by a complex network of signaling pathways. Among them is estrogen signaling, important for the proliferation and differentiation of epithelial cells, immune signaling and metabolism. The mycotoxin zearalenone (ZEN) is an estrogen disruptor naturally found in food and feed. The exposure of the intestine to ZEN has toxic effects including alteration of the immune status and is possibly implicated in carcinogenesis, but the molecular mechanisms linked with these effects are not clear. Our objective was to explore the proteome changes induced by a short, non-cytotoxic exposure to ZEN in the intestine using pig jejunal explants. Our results indicated that ZEN promotes little proteome changes, but significantly related with an induction of ERα signaling and a consequent disruption of highly interrelated signaling cascades, such as NF-κB, ERK1/2, CDX2 and HIF1α. The toxicity of ZEN leads also to an altered immune status characterized by the activation of the chemokine CXCR4/SDF-1 axis and an accumulation of MHC-I proteins. Our results connect the estrogen disrupting activity of ZEN with its intestinal toxic effect, associating the exposure to ZEN with cell-signaling disorders similar to those involved in the onset and progression of diseases such as cancer and chronic inflammatory disorders. SIGNIFICANCE: The proteomics results presented in our study indicate that the endocrine disruptor activity of ZEN is able to regulate a cascade of highly inter-connected signaling events essential for the small intestinal crypt-villus cycle and immune status. These molecular mechanisms are also implicated in the onset and progress of intestinal immune disorders and cancer indicating that exposure to ZEN could play an important role in intestinal pathogenesis.

Effect of estrogen-active compounds on the expression of RACK1 and immunological implications

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.

Cortisol-induced SRSF3 expression promotes GR splicing, RACK1 expression and breast cancer cells migration

Recent data have demonstrated that triple negative breast cancer (TNBC) with high glucocorticoid receptor (GR) expression are associated to therapy resistance and increased mortality. Given that GR alternative splicing generates mainly GRα, responsible of glucocorticoids action, we investigated its role in the regulation of RACK1 (Receptor for Activated C Kinase 1), a scaffolding protein with a GRE (Glucocorticoid Response Element) site on its promoter and involved in breast cancer cells migration and invasion. We provide the first evidence that GRα transcriptionally regulates RACK1 by a mechanism connected to SRSF3 splicing factor, which promotes GRα, essential for RACK1 transcriptional regulation and consequently for cells migration. We also establish that this mechanism can be positively regulated by cortisol. Hence, our data elucidate RACK1 transcriptional regulation and demonstrate that SRSF3 involvement in cells migration implies its role in controlling different pathways thus highlighting that new players have to be considered in GR-positive TNBC.

Role of Hormones in the Regulation of RACK1 Expression as a Signaling Checkpoint in Immunosenescence

Immunosenescence defines the decline in immune function that occurs with aging. This has been associated, at least in part, with defective cellular signaling via protein kinase C (PKC) signal transduction pathways. Our data suggest reduced PKC activation and consequently reduced response to lipopolysaccharide (LPS) stimulation and cytokine release. The lack of PKC activation seems to be dependent on the reduced expression of the receptor for activated C kinase 1 (RACK1), a scaffolding protein involved in multiple signal transduction cascades. The defective expression of RACK1 may be dependent on age-related alteration of the balance between the adrenal hormones cortisol and dehydroepiandrosterone (DHEA). DHEA levels reduce with aging, while cortisol levels remain substantially unchanged, resulting in an overall increase in the cortisol:DHEA ratio. These hormonal changes are significant in the context of RACK1 expression and signaling function because DHEA administration in vivo and in vitro can restore the levels of RACK1 and the function of the PKC signaling cascade in aged animals and in human cells. In contrast, there is evidence that cortisol can act as a negative transcriptional regulator of RACK1 expression. The rack1 gene promoter contains a glucocorticoid responsive element that is also involved in androgen signaling. Furthermore DHEA may have an indirect influence on the post-transcriptional regulation of the functions of the glucocorticoid receptor. In this review, we will examine the role of the hormonal regulation of rack1 gene transcriptional regulation and the consequences on signaling and function in immune cells and immunosenescence.