Non-Cell-Autonomous Regulation of Retrograde Motoneuronal Axonal Transport in an SBMA Mouse Model.

Defects in axonal transport are seen in motoneuronal diseases, but how that impairment comes about is not well understood. In spinal bulbar muscular atrophy (SBMA), a disorder linked to a CAG/polyglutamine repeat expansion in the androgen receptor (AR) gene, the disease-causing AR disrupts axonal transport by acting in both a cell-autonomous fashion in the motoneurons themselves, and in a non-cell-autonomous fashion in muscle. The non-cell-autonomous mechanism is suggested by data from a unique "myogenic" transgenic (TG) mouse model in which an AR transgene expressed exclusively in skeletal muscle fibers triggers an androgen-dependent SBMA phenotype, including defects in retrograde transport. However, motoneurons in this TG model retain the endogenous AR gene, leaving open the possibility that impairments in transport in this model also depend on ARs in the motoneurons themselves. To test whether non-cell-autonomous mechanisms alone can perturb retrograde transport, we generated male TG mice in which the endogenous AR allele has the testicular feminization mutation (Tfm) and, consequently, is nonfunctional. Males carrying the Tfm allele alone show no deficits in motor function or axonal transport, with or without testosterone treatment. However, when Tfm males carrying the myogenic transgene (Tfm/TG) are treated with testosterone, they develop impaired motor function and defects in retrograde transport, having fewer retrogradely labeled motoneurons and deficits in endosomal flux based on time-lapse video microscopy of living axons. These findings demonstrate that non-cell-autonomous disease mechanisms originating in muscle are sufficient to induce defects in retrograde transport in motoneurons.

Survival and Diversity of Human Homologous Dietary MicroRNAs in Conventionally Cooked Top Sirloin and Dried Bovine Tissue Extracts.

Dietary microRNAs (miRNAs), notably those found in milk, are currently being investigated for their potential to elicit biological effects via canonical binding to human messenger RNA targets once ingested. Besides milk, beef and other bovine tissue-derived ingredients could also be a relevant source of potentially bioactive dietary miRNAs. In this study, we characterized the human homologous miRNA profiles in food-grade, bovine-sourced sirloin, heart and adrenal tissue (raw, cooked, and pasteurized, freeze-dried extracts) via deep-sequencing and quantitative reverse transcription PCR (RT-qPCR). A total of 198 human homologous miRNAs were detected at 10 or more normalized reads in all replicates (n = 3) of at least one preparation method. Tissue origin rather than preparation method was the major differentiating factor of miRNA profiles, and adrenal-based miRNA profiles were the most distinct. The ten most prevalent miRNAs in each tissue represented 71-93% of the total normalized counts for all annotated miRNAs. In cooked sirloin, the most abundant miRNAs were miR-10b-5p, (48.8% of total annotated miRNA reads) along with the muscle-specific miR-1 (24.1%) and miR-206 (4.8%). In dried heart extracts, miR-1 (17.0%), miR-100-5p (16.1%) and miR-99a-5p (11.0%) gave the highest normalized read counts. In dried adrenal extracts, miR-10b-5p (71.2%) was the most prominent followed by miR-143-3p (7.1%) and 146b-5p (3.7%). Sequencing results for five detected and two undetected miRNAs were successfully validated by RT-qPCR. We conclude that edible, bovine tissues contain unique profiles of human homologous dietary miRNAs that survive heat-based preparation methods.

Spanish black radish (Raphanus sativus L. Var. niger) diet enhances clearance of DMBA and diminishes toxic effects on bone marrow progenitor cells.

Vegetables of the Cruciferae family contain high levels of glucosinolates, metabolites of which are believed to enhance detoxification. Spanish black radishes (SBR) contain 4× more glucosinolates than other crucifers. This study examined whether feeding mice a diet containing 20% SBR for 2 wk could enhance metabolism of 7,12-dimethylbenz(a)anthracene (DMBA) and inhibit DMBA-mediated bone marrow toxicity. Expression of Phase I and II detoxification enzymes was significantly greater for mice fed SBR than control diet. Six hours after DMBA administration, the blood levels of DMBA in mice fed the SBR diet were significantly lower than mice fed a control diet. DMBA reduced bone marrow cells in mice fed control diet to a significantly greater extent than mice fed the SBR diet. Colony forming assays demonstrated that mice on the SBR diet had 1) less reduction in lymphoid CFU-preB progenitor cells, 2) greater recovery of CFU-preB progenitor cells at 168 h, and 3) less reduction of CFU-GM progenitor cells at 6 h. Therefore, mice fed a 20% SBR diet for 2 wk had greater expression of detoxification enzymes, faster metabolism of DMBA, and a reduction in DMBA-induced bone marrow toxicity. Overall, these results support the hypothesis that glucosinolates in SBR are protective against acute toxicity.

Impaired motoneuronal retrograde transport in two models of SBMA implicates two sites of androgen action.

Spinal and bulbar muscular atrophy (SBMA) impairs motor function in men and is linked to a CAG repeat mutation in the androgen receptor (AR) gene. Defects in motoneuronal retrograde axonal transport may critically mediate motor dysfunction in SBMA, but the site(s) where AR disrupts transport is unknown. We find deficits in retrograde labeling of spinal motoneurons in both a knock-in (KI) and a myogenic transgenic (TG) mouse model of SBMA. Likewise, live imaging of endosomal trafficking in sciatic nerve axons reveals disease-induced deficits in the flux and run length of retrogradely transported endosomes in both KI and TG males, demonstrating that disease triggered in muscle can impair retrograde transport of cargo in motoneuron axons, possibly via defective retrograde signaling. Supporting the idea of impaired retrograde signaling, we find that vascular endothelial growth factor treatment of diseased muscles reverses the transport/trafficking deficit. Transport velocity is also affected in KI males, suggesting a neurogenic component. These results demonstrate that androgens could act via both cell autonomous and non-cell autonomous mechanisms to disrupt axonal transport in motoneurons affected by SBMA.

Involvement of a specificity proteins-binding element in regulation of basal and estrogen-induced transcription activity of the BRCA1 gene.

INTRODUCTION: Increased estrogen level has been regarded to be a risk factor for breast cancer. However, estrogen has also been shown to induce the expression of the tumor suppressor gene, BRCA1. Upregulation of BRCA1 is thought to be a feedback mechanism for controlling DNA repair in proliferating cells. Estrogens enhance transcription of target genes by stimulating the association of the estrogen receptor (ER) and related coactivators to estrogen response elements or to transcription complexes formed at activator protein (AP)-1 or specificity protein (Sp)-binding sites. Interestingly, the BRCA1 gene lacks a consensus estrogen response element. We previously reported that estrogen stimulated BRCA1 transcription through the recruitment of a p300/ER-alpha complex to an AP-1 site harbored in the proximal BRCA1 promoter. The purpose of the study was to analyze the contribution of cis-acting sites flanking the AP-1 element to basal and estrogen-dependent regulation of BRCA1 transcription. METHODS: Using transfection studies with wild-type and mutated BRCA1 promoter constructs, electromobility binding and shift assays, and DNA-protein interaction and chromatin immunoprecipitation assays, we investigated the role of Sp-binding sites and cAMP response element (CRE)-binding sites harbored in the proximal BRCA1 promoter. RESULTS: We report that in the BRCA1 promoter the AP-1 site is flanked upstream by an element (5'-GGGGCGGAA-3') that recruits Sp1, Sp3, and Sp4 factors, and downstream by a half CRE-binding motif (5'-CGTAA-3') that binds CRE-binding protein. In ER-alpha-positive MCF-7 cells and ER-alpha-negative Hela cells expressing exogenous ER-alpha, mutation of the Sp-binding site interfered with basal and estrogen-induced BRCA1 transcription. Conversely, mutation of the CRE-binding element reduced basal BRCA1 promoter activity but did not prevent estrogen activation. In combination with the AP-1/CRE sites, the Sp-binding domain enhanced the recruitment of nuclear proteins to the BRCA1 promoter. Finally, we report that the MEK1 (mitogen-activated protein kinase kinase-1) inhibitor PD98059 attenuated the recruitment of Sp1 and phosphorylated ER-alpha, respectively, to the Sp and AP-1 binding element. CONCLUSION: These cumulative findings suggest that the proximal BRCA1 promoter segment comprises cis-acting elements that are targeted by Sp-binding and CRE-binding proteins that contribute to regulation of BRCA1 transcription.

Cyclooxygenase-2 promoter activation by the aromatic hydrocarbon receptor in breast cancer mcf-7 cells: repressive effects of conjugated linoleic acid.

The role of the aromatic hydrocarbon receptor (AhR) in transcriptional regulation of the human cyclooxygenase-2 (COX-2) gene remains elusive. We report that the AhR-ligands benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced transcription activity of COX-2 in breast cancer MCF-7 cells. The TCDD-dependent activation of the COX-2 promoter was abrogated by mutation of 2 xenobiotic response elements (XREs) = CGTG). We found that TCDD stimulated the binding of the AhR to COX-2 and cytochrome P4501A1 (CYP1A1) oligonucleotides containing consensus XREs. Conversely, the cotreatment with TCDD plus a mixture of conjugated linoleic acid (CLA) or selected CLA isomers prevented (CLAmix = t10,c12-CLA > c9,t11-CLA) the induction of transcription from the COX-2 promoter. The TCDD-induced binding of the AhR to COX-2 and CYP1A1 oligonucleotides was repressed by cotreatment with CLA (t10,c12-CLA > c9,t11-CLA), and the AhR antagonists, 3-methoxy-4-naphthoflavone, and resveratrol. We conclude that the AhR may be a suitable target for prophylactic strategies that target COX-2 expression.

Induction of the transferrin receptor gene by benzo[a]pyrene in breast cancer MCF-7 cells: potential as a biomarker of PAH exposure.

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental DNA-damaging agents regarded as risk factors for human disease, including lung and breast cancer. The biotransformation of PAHs to carcinogenic metabolites is mediated by the aromatic hydrocarbon receptor (AhR), which activates transcription at xenobiotic responsive elements (XREs = 5'-GCGTG-3') found in the promoter regions of genes encoding for detoxifying enzymes, including CYP1A1 and CYP1B1. In this study, we wished to identify novel biomarkers that may be useful in monitoring critical carcinogenic events of the breast induced by PAHs. Using a GeneMAP CancerArray, we analyzed in breast cancer MCF-7 cells the temporal effects of the AhR agonist benzo[a]pyrene (B[a]P), which is a prototype PAH and known environmental carcinogen. Genes upregulated at least threefold by B[a]P and containing potential XREs within their promoter regions included CYP1A1, CYP1B1, paired box gene 3 (PAX3), cortactin (CTTN/EMS1), beta-2-microglobulin (B2M), and transferrin receptor (TfR). The stimulatory effects of B[a]P on expression of these genes were abrogated by cotreatment with the AhR antagonist flavonoid, alpha-napthoflavone (ANF). The TfR gene was selected for further analysis as its promoter region contains two potential XREs and its expression has been shown to be increased in breast cancer cells. Accumulation of TfR mRNA in B[a]P-treated cells was confirmed by quantitative real time PCR. Transient transfection studies indicated that the transcriptional activity of the TfR promoter was stimulated by B[a]P, whereas ANF counteracted this induction. These results indicate that the TfR gene may be a potential biomarker of PAH exposure.

The ligand status of the aromatic hydrocarbon receptor modulates transcriptional activation of BRCA-1 promoter by estrogen.

In sporadic breast cancers, BRCA-1 expression is down-regulated in the absence of mutations in the BRCA-1 gene. This suggests that disruption of BRCA-1 expression may contribute to the onset of mammary tumors. Environmental contaminants found in industrial pollution, tobacco smoke, and cooked foods include benzo(a)pyrene [B(a)P] and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which have been shown to act as endocrine disruptors and tumor promoters. In previous studies, we documented that estrogen (E2) induced BRCA-1 transcription through the recruitment of an activator protein-1/estrogen receptor-alpha (ER alpha) complex to the proximal BRCA-1 promoter. Here, we report that activation of BRCA-1 transcription by E2 requires occupancy of the BRCA-1 promoter by the unliganded aromatic hydrocarbon receptor (AhR). The stimulatory effects of E2 on BRCA-1 transcription are counteracted by (a) cotreatment with the AhR antagonist 3'-methoxy-4'-nitroflavone; (b) transient expression in ER alpha-negative HeLa cells of ER alpha lacking the protein-binding domain for the AhR; and (c) mutation of two consensus xenobiotic-responsive elements (XRE, 5'-GCGTG-3') located upstream of the ER alpha-binding region. These results suggest that the physical interaction between the unliganded AhR and the liganded ER alpha plays a positive role in E2-dependent activation of BRCA-1 transcription. Conversely, we show that the AhR ligands B(a)P and TCDD abrogate E2-induced BRCA-1 promoter activity. The repressive effects of TCDD are paralleled by increased recruitment of the liganded AhR and HDAC1, reduced occupancy by p300, SRC-1, and diminished acetylation of H4 at the BRCA-1 promoter region flanking the XREs. We propose that the ligand status of the AhR modulates activation of the BRCA-1 promoter by estrogen.

Conjugated linoleic acid attenuates cyclooxygenase-2 transcriptional activity via an anti-AP-1 mechanism in MCF-7 breast cancer cells.

Overexpression of cyclooxygenase-2 (COX-2) is regarded as a causative factor in the onset of tumorigenesis of the breast. In this study, we investigated the effects of conjugated linoleic acid (CLA) on COX-2 transcription in MCF-7 breast cancer cells. Results of transient transfection studies revealed that treatment with a CLA mix or selected isomers (c9, t11-CLA; t10, c12-CLA) at concentrations ranging from 20 to 80 micromol/L, attenuated COX-2 transcription induced by the proinflammatory agent 12-O-tetradecanoylphorbol-13-acetate (TPA). In addition, the CLA mix inhibited TPA-induced activity of the collagenase-1 promoter. Using electrophoretic mobility shift assays, we found that the CLA mix reduced TPA-induced recruitment of nuclear proteins to a cAMP response element (CRE) in the COX-2 promoter and a consensus TPA-responsive element (TRE) in the collagenase-1 promoter. Both CRE and TRE are binding sites for activator protein-1 (AP-1). Binding studies revealed that the t10, c12-CLA isomer was more effective than the CLA mix or c9, t11-CLA in reducing binding of cJun to either the COX-2 CRE or collagenase-1 TRE, whereas linoleic acid increased binding to both elements. Overexpression of the AP-1 member, c-Jun, reversed the inhibitory effects of the CLA mix on COX-2 transcription, and restored binding of nuclear proteins to the CRE and TRE. Collectively, these results suggest that CLA represses AP-1-mediated activation of COX-2 transcription.

An estrogen receptor-alpha/p300 complex activates the BRCA-1 promoter at an AP-1 site that binds Jun/Fos transcription factors: repressive effects of p53 on BRCA-1 transcription.

One of the puzzles in cancer predisposition is that women carrying BRCA-1 mutations preferentially develop tumors in epithelial tissues of the breast and ovary. Moreover, sporadic breast tumors contain lower levels of BRCA-1 in the absence of mutations in the BRCA-1 gene. The problem of tissue specificity requires analysis of factors that are unique to tissues of the breast. For example, the expression of estrogen receptor-alpha (ER alpha) is inversely correlated with breast cancer risk, and 90% of BRCA-1 tumors are negative for ER alpha. Here, we show that estrogen stimulates BRCA-1 promoter activity in transfected cells and the recruitment of ER alpha and its cofactor p300 to an AP-1 site that binds Jun/Fos transcription factors. The recruitment of ER alpha/p300 coincides with accumulation in the S-phase of the cell cycle and is antagonized by the antiestrogen tamoxifen. Conversely, we document that overexpression of wild-type p53 prevents the recruitment of ER alpha to the AP-1 site and represses BRCA-1 promoter activity. Taken together, our findings support a model in which an ER alpha/AP-1 complex modulates BRCA-1 transcription under conditions of estrogen stimulation. Conversely, the formation of this transcription complex is abrogated in cells overexpressing p53.

Conjugated linoleic acid inhibits cell proliferation through a p53-dependent mechanism: effects on the expression of G1-restriction points in breast and colon cancer cells.

Previous reports have documented the antiproliferative properties of a mixture of conjugated isomers (CLA) of linoleic acid [LA (18:2)]. In this study, we investigated the mechanisms of CLA action on cell cycle progression in breast and colon cancer cells. Treatment with CLA inhibited cell proliferation in breast cancer MCF-7 cells containing wild-type p53 (p53(+/+)). At cytostatic concentrations, CLA elicited cell cycle arrest in G1 and induced the accumulation of the tumor suppressors p53, p27 and p21 protein. Conversely, CLA reduced the expression of factors required for G1 to S-phase transition including cyclins D1 and E, and hyperphoshorylated retinoblastoma Rb protein. In contrast, the overexpression of mutant p53 (175Arg to His) in MFC-7 cells prevented the CLA-dependent accumulation of p21 and the reduction of cyclin E levels suggesting that the expression of wild-type p53 is required for CLA-mediated activation of the G1 restriction point. To further elucidate the role of p53, the effects of CLA in colon cancer HCT116 cells (p53(+/+)) and p53-deficient (p53(-/-)) HCT116 cells (HCTKO) were examined. The treatment of HCT116 cells with CLA increased the levels of p53, p21, p27 and hypophosphorylated (pRb) protein and reduced the expression of cyclin E, whereas these effects were not seen in p53-deficient HCTKO cells. The t10,c12-CLA isomer was more effective than c9,t11-CLA in inhibiting cell proliferation of MCF-7 breast cancer cells and enhancing the accumulation of p53 and pRb. We conclude that the antiproliferative properties of CLA appear to be a function, at least in part, of the relative content of specific isomers and their ability to elicit a p53 response that leads to the accumulation of pRb and cell growth arrest.