2,3,7,8-Tetrachlorodibenzo-p-dioxin and kynurenine induce Parkin expression in neuroblastoma cells through different signaling pathways mediated by the aryl hydrocarbon receptor.

Parkin regulates protein degradation and mitophagy in dopaminergic neurons. Deficiencies in Parkin expression or function lead to cellular stress, cell degeneration, and the death of dopaminergic neurons, which promotes Parkinson's disease. In contrast, Parkin overexpression promotes neuronal survival. Therefore, the mechanisms of Parkin upregulation are crucial to understand. We describe here the molecular mechanism of AHR-mediated Parkin regulation in human SH-SY5Y neuroblastoma cells. Specifically, we report that the human Parkin gene (PRKN) is transcriptionally upregulated by the aryl hydrocarbon receptor (AHR) through two different selective ligand-dependent pathways. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a stress-inducing AHR ligand, indirectly promotes PRKN transcription by inducing ATF4 expression via TCDD-mediated endoplasmic reticulum (ER) stress. In contrast, kynurenine, a nontoxic AHR agonist, induces PRKN transcription by promoting AHR binding to the PRKN promoter without activating ER stress. Our results demonstrate that AHR activation may be a potential pharmacological pathway to induce human Parkin, but such a strategy must carefully consider the choice of AHR ligand to avoid neurotoxic side effects.

The Aryl Hydrocarbon Receptor Ligand 6-Formylindolo(3,2-b)carbazole Promotes Estrogen Receptor Alpha and c-Fos Protein Degradation and Inhibits MCF-7 Cell Proliferation and Migration.

INTRODUCTION: Worldwide, breast cancer is the most common cancer in women and is the main cause of death among all neoplasia in this group. Luminal A breast cancer represents approximately 70% of all breast cancers and is treated with hormone therapies targeting estrogen receptor alpha (ERα). Unfortunately, patients develop drug resistance leading to recurrence of neoplasia due to estrogen-independent ERα reactivation. Therefore, it is crucial to identify new molecular targets downstream ERα signaling pathway that allows the implementation of better treatments to improve the outcome of breast cancer patients. Overexpression of c-Fos, an ERα gene target, has been associated with increased cell motility, malignancy, metastasis, and invasion while its neutralization results in decreased breast cancer tumorigenesis. The aryl hydrocarbon receptor (AHR) ligands halogenated and polycyclic aromatic hydrocarbons, highly toxic compounds, down regulate c-Fos and ERα levels. The present study aimed to evaluate whether 6-formylindolo(3,2-b)carbazole (FICZ), a no toxic AHR agonist, modifies c-Fos levels in MCF-7 mammary carcinoma cells as well as to determine its effects on cell proliferation and migration. In addition, the possible mechanism through which FICZ mediates c-Fos levels in MCF-7 cells was investigated. METHODS: Initially, the effect of FICZ on c-Fos mRNA and protein levels in MCF-7 cells, untreated or treated with estradiol, was evaluated by qPCR and Western blot. 2,3,7,8-Tetrachloro-dibenzo-p-dioxin, an AHR prototype agonist, was used as a positive control. Next, we examined the effect of FICZ on MCF-7 cell proliferation and migration by cell counting, MTT, 3H-thymidine incorporation, and scratch-wound assays. Finally, the involvement of proteasome 26S on ERα and c-Fos protein degradation was investigated by the use of MG132 and Western blot. RESULTS: The data show that FICZ treatment downregulates c-Fos mRNA and protein levels, most likely by promoting ERα proteasome degradation, blocking MCF-7 cell proliferation and migration. The results also demonstrate that liganded ERα was required for FICZ-mediated ERα degradation. CONCLUSIONS: Activation of AHR results in a decreased MCF-7 cell proliferation and migration by ERα and c-Fos down regulation. Targeting AHR might be a promising therapy for breast cancer treatment, particularly when estrogen-independent ERα reactivation presents.

Parkin is transcriptionally regulated by the aryl hydrocarbon receptor: Impact on α-synuclein protein levels.

Parkin (PRKN) is a ubiquitin E3 ligase that catalyzes the ubiquitination of several proteins. Mutations in the human Parkin gene, PRKN, leads to degeneration of dopaminergic (DA) neurons, resulting in autosomal recessive early-onset parkinsonism and the loss of PRKN function is linked to sporadic Parkinson's disease (PD). Additionally, several in vitro studies have shown that overexpression of exogenous PRKN protects against the neurotoxic effects induced by a wide range of cellular stressors, emphasizing the need to study the mechanism(s) governing PRKN expression and induction. Here, Prkn was identified as a novel target gene of the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor and member of the bHLH/PAS (basic helix-loop-helix/Per-Arnt-Sim) superfamily. AhR binds and transactivates the Prkn gene promoter. We also demonstrated that AhR is expressed in DA neurons and that its activation upregulates Prkn mRNA and protein levels in the mouse ventral midbrain. Additionally, the AhR-dependent increase in PRKN levels is associated with a decrease in the protein levels of its target substrate, α-synuclein, in an AhR-dependent manner, because this effect is not observed in Ahr-null mice. These results suggest that treatments designed to induce PRKN expression through the use of nontoxic AhR agonist ligands may be novel strategies to prevent and delay PD.

Downregulation of sorting nexin 10 is associated with overexpression of miR-30d during liver cancer progression in rats.

As of 2012, liver cancer was the second leading cause of death worldwide, and hepatocellular carcinoma is the most common primary cancer of the liver. The identification of molecules that might be molecular markers or therapeutic targets is urgently needed to improve clinical management. Based on a microarray analysis performed in our laboratory, we selected six genes-namely, ANXA2, DYNLT1, PFKP, PLA2G7, KRT19, and SNX10-as candidates for validation as tumor markers of liver cancer in a rat model. Their patterns of overexpression in preneoplastic lesions and established tumors at 10 different time points between 24 h and 18 months were analyzed to identify putative tumor markers for further studies. We validated the microarray results by quantitative reverse transcription polymerase chain reaction, which revealed high transcriptional expression for five of the genes, consistent with their high protein expression during cancer progression reported in the literature. However, studies of the association of sorting nexin 10 with different types of cancer are limited, prompting further study. The characterization of sorting nexin 10 in preneoplastic lesions and established tumors revealed messenger RNA overexpression and a simultaneous decrease in sorting nexin 10 protein expression. A group of microRNAs related to sorting nexin 10 messenger RNA were selected based on a data analysis conducted using miRDB and microrna.org . An analysis of the expression of these microRNAs revealed an increase in the transcription of microRNA-30d whenever the sorting nexin 10 protein was downregulated. These results suggest that sorting nexin 10 is a potential liver cancer marker exhibiting characteristics of a putative suppressor protein that is likely regulated by microRNA-30d.

Aryl hydrocarbon receptor influences nitric oxide and arginine production and alters M1/M2 macrophage polarization.

AIMS: The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the toxicity of environmental pollutants. It is also implicated in the regulation of the immune system. Ahr-null macrophages overproduce several proinflammatory cytokines following LPS-mediated stimulation, suggesting that AHR affects the balance between the inflammatory M1 and anti-inflammatory M2 phenotypes. Therefore, the present study aimed to examine whether the loss of AHR modifies macrophage polarization. MATERIALS AND METHODS: Peritoneal macrophages from wild-type and Ahr-null mice were differentiated into M1 or M2 phenotype by treatment with LPS/IFNγ or IL-4, and several M1 and M2 markers were determined by qPCR and ELISA assays. Macrophage phagocytic capacity was determined through phagocytosis of yeast and Leishmania major infection assays. Nitric oxide (NO) and urea production, and arginase activity were also determined. KEY FINDINGS: When macrophages were polarized to the M1 phenotype, Ahr-null cells presented a mixed response; higher levels of IL-1ß, IL-6, IL-12, and TNFα were observed after IFNγ- and LPS-mediated activation. However, Ahr-null cells also exhibited decreased NO production and phagocytic capacity. When macrophage was polarized to the M2 phenotype, Ahr-null cells exhibited lower levels of Fizz1, Ym1, and IL-10. In contrast, arginase activity was increased when compared to wild-type macrophages. In addition, macrophages from Ahr-null mice were more susceptible to L. major infection. SIGNIFICANCE: Disruption of the Ahr gene alters macrophage polarization when compared to WT macrophage. These changes may affect the development and resolution of several diseases such as bacterial or parasitic infections.

Toxoplasma gondii: effect of maternal infection in the development of lymphoid organs of BALB/c neonates.

Toxoplasmosis is one of the worldwide parasitic zoonoses. Alterations in the lymphopoietic system are still poorly studied. We analyzed lymphoid organs of BALB/c mice neonates from Toxoplasma gondii-intraperitoneally-infected mothers on 19th day of gestation, with 30 tachyzoites of strain RH. Normal non-infected pregnant females were used as controls. At 7 days after birth, animals were classified as neonates from infected (NIM) and neonates from non-infected mothers (NNIM). Weight of the thymus and number of thymic cells in NIM were decreased, percentage of apoptosis was significantly increased. Decrease in lymphocytes and monocytes and an increase of plasma cells were observed in bone marrow of NIM. Peripheral blood of NIM showed an increase of monocytes and neutrophils and a decrease in lymphocytes. Infection of the mother during the last day of gestation provokes in the neonates changes in the lymphoid organs that could explain survival of 75% of them.