Interferon-α regulates glutaminase 1 promoter through STAT1 phosphorylation: relevance to HIV-1 associated neurocognitive disorders.

HIV-1 associated neurocognitive disorders (HAND) develop during progressive HIV-1 infection and affect up to 50% of infected individuals. Activated microglia and macrophages are critical cell populations that are involved in the pathogenesis of HAND, which is specifically related to the production and release of various soluble neurotoxic factors including glutamate. In the central nervous system (CNS), glutamate is typically derived from glutamine by mitochondrial enzyme glutaminase. Our previous study has shown that glutaminase is upregulated in HIV-1 infected monocyte-derived-macrophages (MDM) and microglia. However, how HIV-1 leads to glutaminase upregulation, or how glutaminase expression is regulated in general, remains unclear. In this study, using a dual-luciferase reporter assay system, we demonstrated that interferon (IFN) α specifically activated the glutaminase 1 (GLS1) promoter. Furthermore, IFN-α treatment increased signal transducer and activator of transcription 1 (STAT1) phosphorylation and glutaminase mRNA and protein levels. IFN-α stimulation of GLS1 promoter activity correlated to STAT1 phosphorylation and was reduced by fludarabine, a chemical that inhibits STAT1 phosphorylation. Interestingly, STAT1 was found to directly bind to the GLS1 promoter in MDM, an effect that was dependent on STAT1 phosphorylation and significantly enhanced by IFN-α treatment. More importantly, HIV-1 infection increased STAT1 phosphorylation and STAT1 binding to the GLS1 promoter, which was associated with increased glutamate levels. The clinical relevance of these findings was further corroborated with investigation of post-mortem brain tissues. The glutaminase C (GAC, one isoform of GLS1) mRNA levels in HIV associated-dementia (HAD) individuals correlate with STAT1 (

Interferon-α Regulates Glutaminase 1 Promoter through STAT1 Phosphorylation: Relevance to HIV-1 Associated Neurocognitive Disorders

HIV-1 associated neurocognitive disorders (HAND) develop during progressive HIV-1 infection and affect up to 50% of infected individuals. Activated microglia and macrophages are critical cell populations that are involved in the pathogenesis of HAND, which is specifically related to the production and release of various soluble neurotoxic factors including glutamate. In the central nervous system (CNS), glutamate is typically derived from glutamine by mitochondrial enzyme glutaminase. Our previous study has shown that glutaminase is upregulated in HIV-1 infected monocyte-derived-macrophages (MDM) and microglia. However, how HIV-1 leads to glutaminase upregulation, or how glutaminase expression is regulated in general, remains unclear. In this study, using a dual-luciferase reporter assay system, we demonstrated that interferon (IFN) α specifically activated the glutaminase 1 (GLS1) promoter. Furthermore, IFN-α treatment increased signal transducer and activator of transcription 1 (STAT1) phosphorylation and glutaminase mRNA and protein levels. IFN-α stimulation of GLS1 promoter activity correlated to STAT1 phosphorylation and was reduced by fludarabine, a chemical that inhibits STAT1 phosphorylation. Interestingly, STAT1 was found to directly bind to the GLS1 promoter in MDM, an effect that was dependent on STAT1 phosphorylation and significantly enhanced by IFN-α treatment. More importantly, HIV-1 infection increased STAT1 phosphorylation and STAT1 binding to the GLS1 promoter, which was associated with increased glutamate levels. The clinical relevance of these findings was further corroborated with investigation of post-mortem brain tissues. The glutaminase C (GAC, one isoform of GLS1) mRNA levels in HIV associated-dementia (HAD) individuals correlate with STAT1 (p<0.01), IFN-α (p<0.05) and IFN-β (p<0.01). Together, these data indicate that both HIV-1 infection and IFN-α treatment increase glutaminase expression through STAT1 phosphorylation and by binding to the GLS1 promoter. Since glutaminase is a potential component of elevated glutamate production during the pathogenesis of HAND, our data will help to identify additional therapeutic targets for the treatment of HAND

Effect of dominant negative forms of MKK3 and MKK6 on pH-responsive induction of PEPCK mRNA

Acid-base homeostasis is essential for survival. When metabolic acidosis is induced by factors such as prolonged starvation, severe shock, high protein diet, or uncontrolled type I diabetes, the kidneys act to compensate for the decreasing pH. Renal catabolism of glutamine, which is sustained through increased expression of phosphoenolpyruvate carboxykinase (PEPCK) and glutaminase (GA), is activated during metabolic acidosis. Mitogen activated protein kinase kinases three and six (MKK3 and MKK6) are thought to play roles in the signal transduction pathway that lead to enhanced PEPCK and glutaminase activity. To examine the potential roles of MKK3 and MKK6, LLC-PK1-FBPase+ cells were stably transfected with dominant negative (dn) forms of either or both kinases. Expression of the transgenes was controlled by a Tetracycline-responsive promoter element (TRE). Doxycycline (dox) is used to inhibit transcription by preventing the tTA transcription factor from binding to the TRE. The absence of dox then enables transcription and turns on expression of the mutated kinase. Western blots were performed on extracts of clonal cell lines to determine the levels of the MKK isoforms as well as the levels of p38 and phosphorylated p38 in LLC-PK1-FBPase+ cells grown in both the absence and presence of dox. Northern blots were also performed to determine the effect of dnMKK expression on levels of PEPCK mRNA. Expression of both dominant negative kinases, but not the expression of either dnMKK3 or dnMKK6 alone, blocked the acid-induced increases in the levels of PEPCK mRNA and the Anisomycin stimulated increases in levels of phosphorylated p38.Highest Honors

Effect of over-expression of zeta-crystallin on glutaminase mRNA stability, The

During metabolic acidosis, increased renal catabolism of glutaminegenerates ammonium and bicarbonate ions to partially restore normal acid-basebalance. The remaining carbons derived from glutamine are then used to synthesizeglucose. This adaptive response is sustained in part by a pH-responsive increase inglutaminase (GA) that results from selective stabilization of the GA mRNA.Previous studies have shown that the 3’-UTR of the GA mRNA contains a pHresponseelement that consists of a direct repeat of an eight-base AU sequence andthat this element binds ζ-crystallin with high affinity and specificity. Increasedbinding of this protein during metabolic acidosis may initiate the pH-responsivestabilization of the GA mRNA. A tetracycline-responsive expression system (tet-off) was developed to test the effect of over-expression of ζ-crystallin on the expression and the stability of the GA mRNA. Two constructs, pcDNA 3.1-βG-GA–Hygro and pTRE2-ζ-crystallin, were created. The pcDNA 3.1/Hygro vector is designed for high-level,constitutive expression in mammalian cell lines and contains the selectable marker,hygromycin. A chimeric βG-GA cDNA segment that encodes β-globin and the 3’-UTR of the GA mRNA was inserted into the pcDNA 3.1/Hygro vector. Theconstruct, pTRE2-ζ-crystallin contains the tet-responsive element (TRE) that drivesthe expression of ζ-crystallin. The two plasmids were co-transfected into 8C cellsthat express high levels of the tTA protein that binds to and activates transcriptionfrom the TRE only in the absence of doxycycline (Dox). Clonal cell lines wereselected with hygromycin. These cells were grown in the presence and absence ofDox and screened with ζ-crystallin specific antibodies to identify clonal lines thatexhibit a large induction of ζ-crystallin when grown in the absence of Dox. RNAisolated from the selected line was quantified using Real-Time RT-PCR. Theresulting data demonstrate that over-expression of ζ-crystallin does not increase GAmRNA levels.Highest Honors