c Impairment of astrocytic glutamate transporter (GLT-1; EAAT2) function is associated with multiple neurodegenerative diseases, including Parkinson's disease (PD) and manganism, the latter being induced by chronic exposure to high levels of manganese (Mn). Mn decreases EAAT2 promoter activity and mRNA and protein levels, but the molecular mechanism of Mn-induced EAAT2 repression at the transcriptional level has yet to be elucidated. We reveal that transcription factor Yin Yang 1 (YY1) is critical in repressing EAAT2 and mediates the effects of negative regulators, such as Mn and tumor necrosis factor alpha (TNF-␣), on EAAT2. YY1 overexpression in astrocytes reduced EAAT2 promoter activity, while YY1 knockdown or mutation of the YY1 consensus site of the EAAT2 promoter increased its promoter activity and attenuated the Mn-induced repression of EAAT2. Mn increased YY1 promoter activity and mRNA and protein levels via NF-B activation. This led to increased YY1 binding to the EAAT2 promoter region. Epigenetically, histone deacetylase (HDAC) classes I and II served as corepressors of YY1, and, accordingly, HDAC inhibitors increased EAAT2 promoter activity and reversed the Mn-induced repression of EAAT2 promoter activity. Taken together, our findings suggest that YY1, with HDACs as corepressors, is a critical negative transcriptional regulator of EAAT2 and mediates Mn-induced EAAT2 repression.

There is an urgent need to develop new strategies to treat ovarian cancer, the most deadly gynecologic malignancy. Histone deacetylase (HDAC) inhibitors are emerging as novel therapeutic drugs in the treatment of a variety of cancers, including those resistant to standard chemotherapy. Since there are multiple HDAC isoforms, determining the precise role of individual HDAC isoenzymes in the growth and progression of ovarian cancer has the potential to influence the use of selective HDAC inhibitors as strategic therapeutic agents that elicit fewer undesirable side effects. Unfortunately, there is limited information about the expression of HDAC isoforms in human ovarian tissues. This report provides evidence for the first time that Class I HDACs are expressed at significantly higher levels in ovarian cancers in comparison to normal ovarian tissues, with no significant difference in Class II HDAC expression between the two groups. Furthermore, ovarian cancer cells are far more sensitive than normal ovarian cells to the potent HDAC inhibitor romidepsin (FK228), a drug that displays greater inhibitory selectivity for Class I HDACs over Class II isoforms. Using small interfering RNA (siRNA) methodology, we demonstrate that knocking down the gene expression of HDAC3 and other members of the Class I HDAC family suppresses ovarian cancer cell growth. Taken together, the present studies offer several novel findings that have direct relevance for the strategic use of inhibitors that target Class I HDACs, particularly HDAC3, in the treatment of ovarian cancer.

The G protein-coupled estrogen receptor GPR30 contributes to the neuroprotective effects of 17β-estradiol (E2); however, the mechanisms associated with this protection have yet to be elucidated. Given that E2 increases astrocytic expression of glutamate transporter-1 (GLT-1), which would prevent excitotoxic-induced neuronal death, we proposed that GPR30 mediates E2 action on GLT-1 expression. To investigate this hypothesis, we examined the effects of G1, a selective agonist of GPR30, and GPR30 siRNA on astrocytic GLT-1 expression, as well as glutamate uptake in rat primary astrocytes, and explored potential signaling pathways linking GPR30 to GLT-1. G1 increased GLT-1 protein and mRNA levels, subject to regulation by both MAPK and PI3K signaling. Inhibition of TGF-α receptor suppressed the G1-induced increase in GLT-1 expression. Silencing GPR30 reduced the expression of both GLT-1 and TGF-α and abrogated the G1-induced increase in GLT-1 expression. Moreover, the G1-induced increase in GLT-1 protein expression was abolished by a protein kinase A inhibitor and an NF-κB inhibitor. G1 also enhanced cAMP response element-binding protein (CREB), as well as both NF-κB p50 and NF-κB p65 binding to the GLT-1 promoter. Finally, to model dysfunction of glutamate transporters, manganese was used, and G1 was found to attenuate manganese-induced impairment in GLT-1 protein expression and glutamate uptake. Taken together, the present data demonstrate that activation of GPR30 increases GLT-1 expression via multiple pathways, suggesting that GPR30 is worthwhile as a potential target to be explored for developing therapeutics of excitotoxic neuronal injury.

Background: Tamoxifen (TX), a selective estrogen receptor modulator, enhances glutamate transporter (GLT-1) expression in astrocytes. Results: TX up-regulated GLT-1 expression via the CREB and NF-B pathways. Conclusion: TX enhanced GLT-1 expression at the transcriptional level. Significance: Understanding the mechanisms of TX action on GLT-1 will contribute to the development of neuroprotectants against excitotoxicity.

Glutamate transporter-1 (GLT-1) plays a central role in preventing excitotoxicity by removing excess glutamate from the synaptic clefts. 17β-estradiol (E2) and tamoxifen (TX), a selective estrogen receptor modulator (SERM), afford neuroprotection in a range of experimental models. However, the mechanisms that mediate E2 and TX neuroprotection have yet to be elucidated. We tested the hypothesis that E2 and TX enhance GLT-1 function by increasing transforming growth factor (TGF)-α expression and thus, attenuate manganese (Mn)-induced impairment in astrocytic GLT-1 expression and glutamate uptake in rat neonatal primary astrocytes. The results showed that E2 (10 nM) and TX (1 μM) increased GLT-1 expression and reversed the Mn-induced reduction in GLT-1, both at the mRNA and protein levels. E2/TX also concomitantly reversed the Mn-induced inhibition of astrocytic glutamate uptake. E2/TX activated the GLT-1 promoter and attenuated the Mn-induced repression of the GLT-1 promoter in astrocytes. TGF-α knock-down (siRNA) abolished the E2/TX effect on GLT-1 expression, and inhibition of epidermal growth factor receptor (TGF-α receptor) suppressed the effect of E2/TX on GLT-1 expression and GLT-1 promoter activity. E2/TX also increased TGF-α mRNA and protein levels with a concomitant increase in astrocytic glutamate uptake. All estrogen receptors (ERs: ER-α ER-β and GPR30) were involved in mediating E2 effects on the regulation of TGF-α, GLT-1, and glutamate uptake. These results indicate that E2/TX increase GLT-1 expression in astrocytes via TGF-α signaling, thus offering an important putative target for the development of novel therapeutics for neurological disorders.