NAC1, A POZ/BTB protein interacts with Parkin and may contribute to Parkinson's disease

Loss-of-function in the Parkin protein is thought to play a part in causing neuronal cell death in patients with Parkinson's disease. This study explores the effect of Parkin degradation, via the overexpression of nucleus accumbens 1 (NAC1), on cell viability. It was found that NAC1 and Parkin are co-localized within the cell and interact with one another, leading to a decrease in Parkin levels. Moreover, NAC1 down-regulates Parkin by presenting it for ubiquitin-dependent proteasome degradation, which causes a decrease in proteasomal activity in neuronal cells. Consequently, this decrease in proteasomal activity leads to an increase in the cells' susceptibility to proteasome inhibition-induced toxicity. It was also found that Parkin and NAC1 are key proteins found to be present mainly in the cytoplasm and are co-localized in neurons of Parkinson's disease patients. Interestingly, mutation in the POZ/BTB domain (Q23L) of NAC1 disrupts the co-localization and interaction of NAC1 with Parkin and it further abrogates the proteasome inhibition-induced toxicity. We further observed that co-transfection of the mutant form of NAC1 with Parkin reversed the proteasome activity and 20S proteasome protein levels. These results indicate a novel interaction between NAC1 and Parkin that leads to neuronal cell death, a main characteristic in Parkinson's disease.

Nucleus Accumbens 1, a Pox virus and Zinc finger/Bric-a-brac Tramtrack Broad protein binds to TAR DNA-binding protein 43 and has a potential role in Amyotrophic Lateral Sclerosis

Protein degradation is a critical component of cellular maintenance. The intracellular translocation and targeting of the Ubiquitin Proteasome System (UPS) differentially coordinates a protein's half-life and thereby its function. Nucleus Accumbens 1 (NAC1), a member of the Pox virus and Zinc finger/Bric-a-brac Tramtrack Broad complex (POZ/BTB) family of proteins, participates in the coordinated proteolysis of synaptic proteins by mediating recruitment of the UPS to dendritic spines. Here we report a novel interaction between NAC1 and TAR DNA-binding protein 43 (TDP-43), a protein identified as the primary component of ubiquitinated protein aggregates found in patients with Amyotrophic Lateral Sclerosis (ALS). In vitro translated full-length TDP-43 associated with both the POZ/BTB domain and the non-POZ/BTB domain of NAC1 in GST pulldown assays. Other POZ/BTB proteins (including zinc finger POZ/BTB proteins and atypical POZ/BTB proteins) showed weak interactions with TDP-43. In addition, NAC1 and TDP-43 were present in the same immunocomplexes in different regions of mouse brain and spinal cord. In primary spinal cord cultures, TDP-43 expression was mainly nuclear, whereas NAC1 was both nuclear and cytoplasmic. In order to mimic ALS-like toxicity in the spinal cord culture system, we elevated extracellular glutamate levels resulting in the selective loss of motor neurons. Using this model, it was found that glutamate toxicity elicited a dose-dependent translocation of TDP-43 out of the nucleus of cholinergic neurons and increased the co-localization of NAC1 and TDP-43. These findings suggest that NAC1 may function to link TDP-43 to the proteasome; thereby, facilitating the post-translational modifications of TDP-43 that lead to the development of ALS.

The POZ/BTB protein NAC1 interacts with two different histone deacetylases in neuronal-like cultures

NAC1 is a cocaine-regulated POZ/BTB (Pox virus and Zinc finger/Bric-a-brac Tramtrack Broad complex) protein. NAC1 is increased by cocaine selectively in the nucleus accumbens, a CNS region important for drug addiction. NAC1's role in the cell, however, is not known. Each of the two NAC1 isoforms, sNAC1 (short NAC1) and lNAC1 (long NAC1), may serve as corepressors for other POZ/BTB proteins. This study investigated whether sNAC1 and lNAC1 demonstrated protein-protein interactions with other corepressors. Histone deacetylase (HDAC) inhibition reversed sNAC1 and lNAC1 repression of Gal4 luciferase, but only in neuronal-like cultures. Because these inhibitors do not distinguish among histone deacetylases, two histone deacetylases were selected for further study. HDAC 3 and 4 both demonstrated protein-protein interactions with sNAC1 and lNAC1. This was shown using coimmunoprecipitations, glutathione-S-transferase (GST) pulldowns and mammalian two-hybrids. Importantly, either the POZ domain or NAC1 without the POZ domain can bind these two HDACs. Other corepressors, specifically NCoR (nuclear receptor corepressor), SMRT (silencing mediator for retinoid and thyroid hormone receptor) and mSin3a, do not exhibit protein-protein interactions with sNAC1 and lNAC1. None showed protein-protein interactions in GST pulldowns or mammalian two-hybrids. Taken together, the results of these experiments indicate sNAC1 and lNAC1 recruit histone deacetylases for transcriptional repression, further enhancing POZ/BTB protein mediated repression.

The mouse nac1 gene, encoding a cocaine-regulated bric-a-brac tramtrac broad complex/pox virus and zinc finger protein, is regulated by ap1

NAC1 cDNA was identified as a novel transcript induced in the nucleus accumbens from rats chronically treated with cocaine. NAC1 is a member of the Bric-a-brac Tramtrac Broad complex/Pox virus and Zinc finger family of transcription factors and has been shown by overexpression studies to prevent the development of behavioral sensitization resulting from repeated cocaine treatment. This paper reports the cloning and characterization of the corresponding gene. The mouse Nac1 gene consist of six exons, with exon 2 containing an alternative splice donor, providing a molecular explanation of the splice variants observed in mouse and rat. Transcripts of Nac1 were ubiquitously detected in different mouse tissues with prominent expression in the brain. The mouse Nac1 gene was localized to chromosome 8, suggesting a highly plausible candidate gene to explain differences in cocaine-induced behaviors between C57BL6/J and DBA/2J mice that had previously been mapped to the area. In addition, a functional AP1 binding site has been identified in an intron 1 enhancer of the Nac1 gene that plays an essential role in the activation of the gene in differentiation of neuroblastoma cells. Co-transfection with c-jun and c-fos expression plasmids, which encode the two subunits of AP1, activated the wild type Nac1 intron 1 enhancer two-fold over basal, nearly at the level of NAC1 enhancer activity seen in differentiated N2A cells. Mutation of the AP1 site completely abrogated all activation of the NAC1 enhancer in differentiated N2A cells. Activation of immediate early genes such as c-fos and c-jun following chronic drug treatments has been well characterized. The present data describe one potential regulatory cascade involving these transcription factors and activation of NAC1. Identification of drug induced alterations in gene expression is key to understanding the types of molecular adaptations underlying addiction.

Differences in expression, actions and cocaine regulation of two isoforms for the brain transcriptional regulator NAC1

BTB/POZ proteins can influence the cell cycle and contribute to oncogenesis. Many family members are present in the mammalian CNS. Previous work demonstrated elevated NAC1 mRNA levels in the rat nucleus accumbens in response to cocaine. NAC1 acts like other BTB/POZ proteins that regulate transcription but is unusual because of the absence of identifiable DNA binding domains. cDNAs were isolated encoding two NAC1 isoforms differing by only 27 amino acids (the longer isoform contains 514 amino acids). The mRNAs for both isoforms were simultaneously expressed throughout the rat brain and peripheral tissues. Semi-quantitative reverse transcription-polymerase chain reaction analysis revealed that the mRNA of the longer isoform was more abundant than the mRNA of the shorter isoform. Western blot analysis demonstrated a similar unequal distribution between the isoforms in the CNS. The longer isoform was the more abundant of the two NAC1 proteins and the ratio between them differed throughout the rat brain. The shorter isoform was not detected in most of the examined peripheral tissues, suggesting differences from the CNS in post-transcriptional processing. Both isoforms repressed transcription in H293T cells using a Gal4-luciferase reporter system. However, the shorter isoform did not repress transcription as effectively as the longer isoform. Transfection of different ratios for both isoforms, in order to replicate the relative amounts observed throughout the CNS, supported an interaction between the isoforms. The net effect on transcriptional repression was determined by the ratio of the two NAC1 isoforms. Each isoform exhibited the subnuclear localization that is characteristic of many BTB/POZ proteins. A rapid and transient increase in the level of the shorter isoform occurred in the nucleus accumbens 2 h following a single i.p. cocaine injection. We conclude that the two isoforms of NAC1 may differentially affect neuronal functions, including the regulation of cocaine-induced locomotion.

NAC-1 is a brain POZ/BTB protein that can prevent cocaine-induced sensitization in the rat

Levels of the mRNA NAC-1 are increased in the rat forebrain weeks after cocaine exposure. This long-term neuroadaptation occurs during the expression of behavioral sensitization, a model of psychostimulant-induced paranoia. NAC-1, the protein encoded by this cocaine-regulated mRNA, contains a Pox virus and zinc finger/bric-a-brac tramtrack broad complex (POZ/BTB) motif, which mediates interactions among several transcriptional regulators. The present studies demonstrate that NAC-1 acts as a transcription factor. NAC-1 was localized to the nucleus of neurons in the brain. Transfection of NAC-1 in cell culture repressed transcription of a reporter gene. NAC-1 was also able to affect the actions of other POZ/BTB proteins in mammalian two-hybrid studies; these interactions required the presence of the POZ/BTB domain. However, NAC-1 appears to be a unique POZ/BTB transcriptional regulator because it does not contain any zinc finger regions found in these other DNA-binding proteins. Adenoviral-mediated overexpression of NAC-1 protein in the rat nucleus accumbens prevented the development but not the expression of behavioral sensitization produced by repeated administration of cocaine. Thus, NAC-1 may modify the long-term behaviors of psychostimulant abuse by regulating gene transcription in the mammalian brain.

Activation of surfactant protein-B transcription: signaling through the SP-A receptor utilizing the PI3 kinase pathway

This study describes receptor-activated signaling initiated by surfactant protein-A (SP-A), and the means by which it activates transcription of surfactant protein-B. Pulmonary surfactant is a mixture of lipids and associated proteins produced by type II pneumocytes. Interaction of SP-A with its cognate receptor (SPAR) on type II cells is involved in regulating surfactant secretion. This interaction also increases transcription of surfactant proteins and several other genes. To study SP-A cytokine activity, we used as a model surfactant-protein (SP-B) transcription, the activators of which have been characterized. HNF-3 and TTF-1 transcription factors are known to stimulate SP-B transcription. SP-A caused increased phosphorylation and nuclear localization of both. Corresponding increases in protein binding to the SP-B promoter were demonstrated by gel shift analysis. SP-A increased protein binding to HNF-3 and TTF-1 consensus recognition elements. Footprinting analysis indicated that SP-A-induced protein binding to SP-B promoter was greater in amount, but not different in location, from that seen in control cells, which normally transcribe SP-B. SP-A caused transient increases in PI3 kinase localization at the plasma membrane, and SP-A signaling to elicit increased SP-B transcription was blocked by LY294002, an inhibitor of PI3 kinase. Therefore, SP-A signals through PI3 kinase to increase SP-B transcription in type II pneumocytes by enhancing TTF-1 and HNF-3 activation of the SP-B promoter. SP-A activation of this signaling pathway, which affects many cellular functions and has not previously been implicated in type II cell transcriptional activity, has profound import for understanding type II cell biology.

SP-A as a cytokine: surfactant protein-A-regulated transcription of surfactant proteins and other genes

Pulmonary surfactant is a mixture of phospholipids and surfactant-associated proteins made by alveolar type II cells that is necessary for normal lung function. Surfactant secretion and reuptake by type II cells are regulated in part by interaction of surfactant protein-A (SP-A) with a specific receptor (SPAR) on type 11 cells. Several chemicals and hormones affect both surfactant secretion and also surfactant gene expression, but consequences of SP-A-SPAR interaction beyond regulating surfactant secretion and reuptake are unknown. Accordingly, we studied the effects of SP-A on surfactant protein gene transcription, mRNA levels, and transcript stability. SP-A elicited new transcription of surfactant proteins SP-A, SP-B, and SP-C and SPAR and c-Jun but had no effect on beta-actin or c-fos transcription. Antibody against SP-A receptor blocked SP-A-induced transcription, confirming that these actions of SP-A were receptor-mediated. SP-A effects on overall transcript levels were more complex. However, SP-A, SP-B, and SP-C mRNA levels doubled in SP-A-treated cells compared to controls. SP-A is known to stabilize surfactant, control its secretion and reuptake by type II cells, and augment host antimicrobial defenses. These data indicate that SP-A also acts as an autocrine cytokine: it binds its receptor and specifically regulates transcription of surfactant proteins and other genes.

Surfactant protein-A receptor-mediated inhibition of calcium signaling in alveolar type II cells

Receptor-mediated inhibition of cellular activating signals is not well understood. Type II alveolar cells secrete surfactant in response to such secretagogs as terbutaline, calcium (Ca) ionophores (e.g., ionomycin [Io]), and adenosine triphosphate (ATP). A cell membrane receptor for SP-A, one of the surfactant proteins, regulates secretion by negative feedback. We used quantitative fluorescence microscopy to study the effects of SP-A on alterations in cytosolic Ca2+ ([Ca2+]i) elicited by surfactant secretagogs. Freshly isolated type II cells were loaded with Fura-2, then treated with secretagog, in the presence or absence of SP-A. Io and ATP produced biphasic increases in cytosol [Ca2+]i, reflecting first Ca2+ release from intracellular stores, and then influx through the cell membrane. Thapsigargin (TG) and Io directly initiate Ca2+ release; ATP elicits Ca2+ release via receptor-mediated mechanisms. Ca2+ release causes cell membrane Ca channels to open by as yet poorly understood mechanisms. Io itself acts as an additional Ca2+ channel. SP-A blocks much of the Ca2+ release and some of the Ca2+ influx elicited by these secretagogs. Antibody against SP-A receptor restores secretagog-induced Ca2+ fluxes from inhibition by SP-A, confirming that the inhibitory activity of SP-A is mediated through its receptor. Type II cells incubated in Ca2+-free medium plus SP-A show diminished Ca2+ release responses to TG or ATP, suggesting that the action of SP-A to prevent secretagog initiated increases in [Ca2+]i may reflect its ability to block Ca2+ release from cytoplasmic Ca stores. The feedback inhibition of surfactant secretion by SP-A may, correspondingly, be a manifestation of this effect. Because recent work suggests that TGF-beta also inhibits Ca2+ fluxes, SP-A and TGF-beta could be representative of a group of physiologic regulators that act by modulating intracellular Ca signaling.

Mechanism of interferon action: in vivo activation of 91 kDa transcription factor

Interferons are a family of secreted polypeptides with distinct biological effects. These effects include the regulation of expression of specific cellular genes, antiviral properties, and inhibition of cell growth and proliferation. We investigated the effect of sodium orthovanadate (vanadate), an inhibitor of protein-phosphotyrosine phosphatases, on early biochemical events associated with the stimulation of transcription factor p91 activation by interferon-alpha (IFN alpha) in live human cells. We report that the treatment of cells with vanadate selectively potentiated (2-3 fold) the levels of IFN-stimulated tyrosine phosphorylation of p91 (and not of p113) as compared to the levels of p91 activated by IFN alone and that this was associated with the increased accumulation of phosphorylated p91 in the nucleus, and the activation of protein tyrosine kinases that phosphorylate p91. These results suggest the possible involvement of a vanadate sensitive protein-tyrosine phosphatase(s) in the deactivation of phosphorylated p91 in live human cells.

Inhibition of vesicular stomatitis virus replication by epidermal growth factor in human epidermoid A-431 cells

Here we report that epidermal growth factor (EGF) inhibits the replication of vesicular stomatitis virus (VSV) in human epidermoid carcinoma A-431 cells, as measured by reduction in infectious viral particle production, cell protection assay, and inhibition of viral protein synthesis. The observed antiviral effects of EGF were not apparently due to inhibitory effects on the initial events in VSV infection as postinfection treatment of cells with EGF also resulted in significant inhibition in the levels of viral proteins. The EGF-mediated inhibition of VSV protein synthesis was specific in nature as prior treatment of cells with an excess of anti-EGF receptor monoclonal antibody, which blocks EGF binding, reduced the inhibition of VSV proteins elicited by EGF. In summary, the observed antiviral action of EGF was an early effect of EGF and was mediated via an EGF-responsive cellular pathway(s) that could impair VSV replication.

Inhibition of ligand-induced activation of epidermal growth factor receptor tyrosine phosphorylation by curcumin

We explored the regulation of epidermal growth factor (EGF)-mediated activation of EGF receptor (EGF-R) phosphorylation by curcumin (diferuloyl-methane), a recently identified kinase inhibitor, in cultured NIH 3T3 cells expressing human EGF-R. Treatment of cells with a saturating concentration of EGF for 5-15 min induced increased EGF-R tyrosine phosphorylation by 4- to 11-fold and this was inhibited in a dose- and time-dependent manner by up to 90% by curcumin, which also inhibited the growth of EGF-stimulated cells. There was no effect of curcumin treatment on the amount of surface expression of labeled EGF-R and inhibition of EGF-mediated tyrosine phosphorylation of EGF-R by curcumin was mediated by a reversible mechanism. In addition, curcumin also inhibited EGF-induced, but not bradykinin-induced, calcium release. These findings demonstrate that curcumin is a potent inhibitor of a growth stimulatory pathway, the ligand-induced activation of EGF-R, and may potentially be useful in developing anti-proliferative strategies to control tumor cell growth.

Growth inhibition of human acute promyelocytic leukemia NB-4 cells by interferons and all-trans retinoic acid: trans-modulation of inducible gene expression pathways

Regulation of cell proliferation appears to be a complex process involving the regulated expression and/or interaction of gene regulatory pathways stimulated by binding of specific growth regulators such as inteferons (IFN) and all-trans retinoic acid (RA) to their respective receptors. We investigated the growth regulation of human acute promyelocytic leukemia NB-4 cells by combinations of IFNs and RA, and explored the possible biochemical interactions between IFNs and RA by studying the regulation of expression of IFN- and RA-inducible cellular pathways by RA and IFN respectively. We observed that combinations of IFNs and RA inhibited NB-4 cell growth significantly more than either agent alone. Analysis of cellular inducible pathways demonstrated that RA augmented levels of gene expression: (i) induced by IFN-alpha such as 2'-5'-oligoadenylate synthetase, mRNA 561 and mRNA 6-16; (ii) induced by IFN-gamma such as 2A and P56; and (iii) induced by both IFN-alpha and IFN-gamma such as mRNA 1-8. Furthermore, IFNs also augmented the expression of RAR-alpha mRNA and RAR-alpha. Co-treatment of NB-4 cells by IFN-gamma plus RA induced a sub-set of IFN-induced genes which were not induced by either IFN-gamma or RA alone. These results suggest that gene inducing interactions, the transregulation of IFN-inducible and RA-inducible gene expression pathways by RA and IFNs, respectively, may be closely related to the potentiation of growth inhibition of NB-4 cells by combinations of IFNs and RA. These findings may be useful in establishing a rationale for using IFNs and RA or combinations of IFNs and RA in the treatment of acute promyelocytic leukemia.

Induction of expression of interferon-stimulated gene factor-3 (ISGF-3) proteins by interferons

Interferon-stimulated gene factor-3 (ISGF-3) is a multiprotein (113, 91, 84, and 48 kDa) transcriptional factor which regulates the expression of a specific set of genes, the interferon (IFN)-stimulated genes. In the studies presented here, we investigated the induction of synthesis of proteins of the ISGF-3 complex by IFNs. We report that both IFN-alpha and IFN-gamma induce a 3- to 5-fold increased expression of p91, p84, and p113 and their phosphotyrosine contents in a dose- and time-dependent manner. The IFN-mediated induction in the levels of p91 correlated well with the increased expression of steady-state levels of p91 mRNA by IFNs. Increased levels of p91 and p84 became detectable after 6 and 4 h treatment with IFN-alpha and IFN-gamma, respectively, and reached a maximum 5.2-fold at 18 h by IFN-alpha and 4-fold at 15 h by IFN-gamma. The levels of p113 were induced up to 3-fold at 15 h by IFN-alpha or IFN-gamma. The induction of ISGF-3 proteins by IFNs was accompanied by an increase in the accumulation of p91, p84, and p113 in the nucleus. The observed induction of increased expression of ISGF-3 proteins does not require continuous presence of IFNs, as removal of IFNs after 6 h of minimal treatment still resulted in a significant increase (2- to 4-fold) in the levels of expression of p91, p84, and p113 over an additional period of 12 h in culture, and induced proteins remained phosphorylated on tyrosine. The IFN-mediated increase in the synthesis of ISGF-3 proteins was blocked by Actinomycin D. Extension of these investigations to other human and mouse responsive cells, Daudi, Hela, and NIH3T3, also demonstrated significant increase in the levels of p91, p84, and p113 by interferons.

Inhibitory effect of curcumin on epidermal growth factor receptor kinase activity in A431 cells

We explored the mechanism of antigrowth action of Curcumin by investigating its effect on epidermal growth factor (EGF) receptor intrinsic kinase activity in the human epidermoid carcinoma A431 cells. The short-term treatment of cells with Curcumin inhibited EGF receptor intrinsic kinase activity up to 90% in a dose- and time-dependent manner, and also inhibited EGF-induced tyrosine phosphorylation of EGF receptors. The observed early effects of Curcumin were mediated via a cellular mechanism(s), and preceded the period when inhibition of cell growth occurred.

Cell cycle-dependent modulation of alpha-interferon-inducible gene expression and activation of signaling components in Daudi cells

To investigate cell cycle-dependent expression of interferon (IFN)-induced genes and signaling pathways, we examined the modulation of IFN-inducible gene expression and p91 activation, and JAK-1 and Tyk-2 kinases' activation in human Burkitt's lymphoma Daudi cells which were synchronized at different points in the cell cycle progression. We observed that each one of 100-, 67-, and 46-kDa 2'-5'-oligoadenylate synthetase (2-5(A)-synthetase) proteins had a unique expression pattern in different phases of the cell cycle which was different from the expression of 2-5(A)-synthetase proteins in exponentially growing Daudi cells. The cell cycle-dependent changes in the overall levels of expression of 2-5(A)-synthetase proteins correlated well with the induction of expression of 2-5(A)-synthetase mRNA as well as the appearance of IFN stimulatory gene factor-3 and expression and activation of p91 in cells released from the G1/S block in the absence of exogenous IFN-alpha. In addition, cells from the G1/S phase exhibited increased tyrosine phosphorylation of JAK-1 and Tyk-2 kinases and p91 by IFN-alpha as compared with asynchronized cells. Enhanced stimulation of activation of JAK-1, Tyk-2, and p91 by IFN-alpha was progressively reduced from G1/S to G2/M to pass G2/M. These findings demonstrate that the levels of constitutive and inducible expression of IFN-alpha-inducible genes, activation of p91, and tyrosine phosphorylation of JAK-1 and Tyk-2 kinases are differentially influenced by the state of the cell cycle.