Association of JC virus large T antigen with myelin basic protein transcription factor (MEF-1/Puralpha) in hypomyelinated brains of mice transgenically expressing T antigen

Effects of In Utero EtOH Exposure on 18S Ribosomal RNA Processing: Contribution to Fetal Alcohol Spectrum Disorder

Fetal alcohol spectrum disorders (FASD) are leading causes of neurodevelopmental disability. The mechanisms by which alcohol (EtOH) disrupts fetal brain development are incompletely understood, as are the genetic factors that modify individual vulnerability. Because the phenotype abnormalities of FASD are so varied and widespread, we investigated whether fetal exposure to EtOH disrupts ribosome biogenesis and the processing of pre-ribosomal RNAs and ribosome assembly, by determining the effect of exposure to EtOH on the developmental expression of 18S rRNA and its cleaved forms, members of a novel class of short non-coding RNAs (srRNAs). In vitro neuronal cultures and fetal brains (11-22 weeks) were collected according to an IRB-approved protocol. Twenty EtOH-exposed brains from the first and second trimester were compared with ten unexposed controls matched for gestational age and fetal gender. Twenty fetal-brain-derived exosomes (FB-Es) were isolated from matching maternal blood. RNA was isolated using Qiagen RNA isolation kits. Fetal brain srRNA expression was quantified by ddPCR. srRNAs were expressed in the human brain and FB-Es during fetal development. EtOH exposure slightly decreased srRNA expression (1.1-fold; p = 0.03). Addition of srRNAs to in vitro neuronal cultures inhibited EtOH-induced caspase-3 activation (1.6-fold, p = 0.002) and increased cell survival (4.7%, p = 0.034). The addition of exogenous srRNAs reversed the EtOH-mediated downregulation of srRNAs (2-fold, p = 0.002). EtOH exposure suppressed expression of srRNAs in the developing brain, increased activity of caspase-3, and inhibited neuronal survival. Exogenous srRNAs reversed this effect, possibly by stabilizing endogenous srRNAs, or by increasing the association of cellular proteins with srRNAs, modifying gene transcription. Finally, the reduction in 18S rRNA levels correlated closely with the reduction in fetal eye diameter, an anatomical hallmark of FASD. The findings suggest a potential mechanism for EtOH-mediated neurotoxicity via alterations in 18S rRNA processing and the use of FB-Es for early diagnosis of FASD. Ribosome biogenesis may be a novel target to ameliorate FASD in utero or after birth. These findings are consistent with observations that gene-environment interactions contribute to FASD vulnerability.

Animal Models for Progressive Multifocal Leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a severe demyelinating disease of the CNS caused by the human polyomavirus JC (JCV). JCV replication occurs only in human cells and investigation of PML has been severely hampered by the lack of an animal model. The common feature of PML is impairment of the immune system. The key to understanding PML is working out the complex mechanisms that underlie viral entry and replication within the CNS and the immunosurveillance that suppresses the virus or allows it to reactivate. Early models involved the simple inoculation of JCV into animals such as monkeys, hamsters, and mice. More recently, mouse models transgenic for the gene encoding the JCV early protein, T-antigen, a protein thought to be involved in the disruption of myelin seen in PML, have been employed. These animal models resulted in tumorigenesis rather than demyelination. Another approach is to use animal polyomaviruses that are closely related to JCV but able to replicate in the animal such as mouse polyomavirus and SV40. More recently, novel models have been developed that involve the engraftment of human cells into the animal. Here, we review progress that has been made to establish an animal model for PML, the advances and limitations of different models and weigh future prospects.

5-HT1B receptors play a prominent role in the proliferation of T-lymphocytes

Serotonin plays a role in T cell activation, but there is no clear consensus of which of the 14 serotonergic receptors control this activations pathway. We have used a broad range of serotonergic receptor antagonists to define the functional involvement of these receptors governing the proliferation of primary T cells as well as in T cell lines. Our data shows that antagonism of the 5-HT(1B) receptor inhibits the proliferation of both human and murine primary helper T cells and of human helper T cell lines. As a whole, our data suggest that other serotonergic receptors may contribute to the proliferative signals, but the 5-HT(1B) receptor plays the most dominant role.

Pilot study of the Human Proteome Organisation Brain Proteome Project: Applying different 2-DE techniques to monitor proteomic changes during murine brain development

The Human Proteome Organisation Brain Proteome Project aims at coordinating neuroproteomic activities with respect to analysis of development, aging, and evolution in human and mice and at analysing normal aging processes as well as neurodegenerative diseases. Our group participated in the mouse pilot study of this project using two different 2-DE systems, to find out the optimal conditions for comprehensive gel-based differential proteome analysis. Besides the assessment of the best methodical conditions the question of "How many biological replicate analyses have to be performed to get reliable statistically validated results?" was addressed. In total 420 differences were detected in all analyses. Both 2-DE methods were found to be suitable for comprehensive differential proteome analysis. Nevertheless, each of the methods showed substantial advantages and disadvantages resulting in the fact that modification of both systems is essential. From our results we can draw the conclusions that for the future optimal quantitative differential gel-based brain proteome analyses the sample preparation has to be slightly changed, the resolution of the first as well as the second dimension has to be advanced, the number of experiments has to be increased and that the 2D-DIGE system should be applied.

Investigation on the role of cell transcriptional factor Sp1 and HIV-1 TAT protein in PML onset or development

JC virus (JCV) causes progressive multifocal leukoencephalopathy (PML), characterized by multiple areas of demyelination and attendant loss of brain function. PML is often associated with immunodepression and it is significantly frequent in AIDS patients. The viral genome is divided into early and late genes, between which lies a non-coding control region (NCCR) that regulates JCV replication and presents a great genetic variability. The NCCR of JCV archetype (CY strain) is divided into six regions: A-F containing binding sites for cell factors involved in viral transcription. Deletions and enhancements of these binding sites characterize JCV variants, which could promote viral gene expression and could be more suitable for the onset or development of PML. Therefore, we evaluated by means of polymerase chain reaction (PCR) the presence of JCV genome in cerebrospinal fluid (CSF) of HIV positive and negative subjects both with PML and after sequencing, we analyzed the viral variants found focusing on Sp1 binding sites (box B and D) and up-TAR sequence (box C). It is known that Sp1 activates JCV early promoter and can contribute in maintaining methylation-free CpG islands in active genes, while up-TAR sequence is important for HIV-1 Tat stimulation of JCV late promoter. Our results showed that in HIV-positive subjects all NCCR structures presented enhancements of up-TAR element, whereas in HIV-negative subjects both Sp1 binding sites were always retained. Therefore, we can support the synergism HIV-1/JCV in CNS and we can hypothesize that both Sp1 binding sites could be important to complete JCV replication cycle in absence of HIV-coinfection.

Pur alpha and Sp8 as opposing regulators of neural gata2 expression

Gata2 is an essential hematopoietic transcriptional factor that is also expressed prominently in the nervous system. The early lethality of knockout mice due to severe anemia has largely precluded studies of gata2 neural regulation and function. In this report, we describe the identification of zebrafish Pur alpha and Sp8 orthologs as two factors that function to regulate neuronal expression of gata2. During embryogenesis, Pur alpha is expressed widely, whereas Sp8 has an overlapping pattern of expression with gata2 in the nervous system. Knockdown and ectopic expressions of Pur alpha and Sp8 indicate that these factors function, respectively, as a repressor and an activator of gata2 gene expression in the nervous system. With consideration given to the previously established roles for these factors, we propose a model for how the transcriptional regulation of neural gata2 expression may be involved in controlling cellular proliferation in the nervous system.

Rearrangement patterns of JC virus noncoding control region from different biological samples

The JC virus (JCV) is generally considered the etiological agent of progressive multifocal leukoencephalopathy (PML), a demyelinating brain illness, often associated with immunosuppression and significantly frequent in acquired immunodeficiency syndrome (AIDS) patients. The primary infection by JCV is usually asymptomatic and the virus can remain in a latent status in the kidney. As a consequence of immunological alterations of the host, the virus can show a genetic variability in the noncoding control region (NCCR) due to deletions, duplications, and insertions as compared with the archetype. The NCCR of the archetype strain can be divided into six regions, named boxes A to F. In this study, the authors evaluated the presence of the JCV genome in different biological samples, such as urine, peripheral blood mononuclear cells (PBMCs) and cerebral spinal fluid (CSF) by means of polymerase chain reaction (PCR). After sequencing of the PCR fragments, the NCCR structure of isolated JCV strains was analyzed in order to verify the presence of different viral variants. An analysis of the homology and of the multiple alignment of the obtained sequences in comparison with the archetype strain has been carried out. The results indicated the presence of different rearrangements among the analyzed samples. Whereas in the urine, the NCCR structure always appeared very similar to that of the archetype, in the PBMCs and CSF, the NCCR sequences showed specific and characteristic rearrangements as compared to the archetype. These different rearrangements could be correlated with the emerging of an NCCR organization more suitable for the development of PML.

Puralpha is essential for postnatal brain development and developmentally coupled cellular proliferation as revealed by genetic inactivation in the mouse

The single-stranded DNA- and RNA-binding protein, Puralpha, has been implicated in many biological processes, including control of transcription of multiple genes, initiation of DNA replication, and RNA transport and translation. Deletions of the PURA gene are frequent in acute myeloid leukemia. Mice with targeted disruption of the PURA gene in both alleles appear normal at birth, but at 2 weeks of age, they develop neurological problems manifest by severe tremor and spontaneous seizures and they die by 4 weeks. There are severely lower numbers of neurons in regions of the hippocampus and cerebellum of PURA(-/-) mice versus those of age-matched +/+ littermates, and lamination of these regions is aberrant at time of death. Immunohistochemical analysis of MCM7, a protein marker for DNA replication, reveals a lack of proliferation of precursor cells in these regions in the PURA(-/-) mice. Levels of proliferation were also absent or low in several other tissues of the PURA(-/-) mice, including those of myeloid lineage, whereas those of PURA(+/-) mice were intermediate. Evaluation of brain sections indicates a reduction in myelin and glial fibrillary acidic protein labeling in oligodendrocytes and astrocytes, respectively, indicating pathological development of these cells. At postnatal day 5, a critical time for cerebellar development, Puralpha and Cdk5 were both at peak levels in bodies and dendrites of Purkinje cells of PURA(+/+) mice, but both were absent in dendrites of PURA(-/-) mice. Puralpha and Cdk5 can be coimmunoprecipitated from brain lysates of PURA(+/+) mice. Immunohistochemical studies reveal a dramatic reduction in the level of both phosphorylated and nonphosphorylated neurofilaments in dendrites of the Purkinje cell layer and of synapse formation in the hippocampus. Overall results are consistent with a role for Puralpha in developmentally timed DNA replication in specific cell types and also point to a newly emerging role in compartmentalized RNA transport and translation in neuronal dendrites.

Ras-induced colony formation and anchorage-independent growth inhibited by elevated expression of Puralpha in NIH3T3 cells

Levels of Puralpha, a conserved, sequence-specific single-stranded DNA and RNA binding protein, fluctuate during the cell cycle, declining at the onset of S-phase and peaking at mitosis. In early G1 Puralpha is associated with the hypophosphorylated form of the retinoblastoma protein, Rb. Microinjection of purified Puralpha into NIH3T3 cells arrests the cell cycle at either G1/S or G2/M checkpoints with distinct morphological consequences. Here we ask whether expression of Puralpha can affect colony formation and anchorage-independent growth in ras-transformed NIH3T3 cells. Two to five-fold elevated levels of Puralpha in stably-transfected cell lines retard entry into and progression through S phase in both ras-transformed and non-transformed cells. Puralpha significantly inhibits colony formation by ras-transformed cells but not by non-transformed cells. In addition, cells transfected to express Puralpha formed only about 1/5 the number of large colonies in soft agar as control-transfected cells, demonstrating a marked inhibition of anchorage-independent growth by Puralpha. Biochemical analysis of nuclear and cytoplasmic Puralpha proteins and confocal microscopic analysis of Puralpha location indicate that access of Puralpha to the nucleus is controlled by both protein modification and sequence domains within the protein. Analyses of deletion mutants identify Puralpha domains mediating nuclear exclusion, including several potential destruction motifs and a PEST sequence at aa's 215-231. In the nucleus Puralpha colocalizes with CDK2 and cyclin A. Puralpha and cyclin D1, however, do not colocalize in the nucleus. At mitosis Puralpha is visualized about the condensed chromosomes and in the cytoplasm, where it colocalizes with cyclin B1. The data indicate that the ability of Puralpha to interact with proteins regulating cell proliferation and transformation is controlled by signals that govern its intracellular localization.

Regulation of Puralpha gene transcription: evidence for autoregulation of Puralpha promoter

The single-stranded DNA and RNA binding protein, Puralpha, has recently received special attention as this protein, by associating with the specific nucleotide sequence (GGN repeats) and/or several important cellular and viral proteins regulates crucial biological events such as transcription, replication, and cell proliferation. In this study, we focused on the promoter activity of the Puralpha upstream DNA sequence and demonstrated that the sequence spanning 6,000 nucleotides upstream of the Puralpha transcription start site has promoter activity in various cell types. Results from promoter deletion studies revealed that this region encompasses various regulatory motifs which differentially participate in the promoter activity of Puralpha in various cells. The transcription start site of Puralpha is surrounded by the GA/GC-rich sequence which exhibits the ability to interact with Puralpha, suggesting a role for autoregulation of Puralpha transcription. Results from co-transfection studies revealed that ectopic expression of Puralpha reduced transcriptional activity of the Puralpha promoter and the region located between amino acid residues, 1-85 of Puralpha is important for the observed autoregulatory event. The regulatory protein of the human neurotropic virus, JCV, T-antigen, which interacts with Puralpha, decreased transcriptional activity of the Puralpha promoter. Co-expression of JCV T-antigen and Puralpha had no significant effect on the suppression of Puralpha gene transcription by either protein. The importance of this finding in light of earlier results showing down regulation of Puralpha during JCV infection of glial cells is discussed.

The single-stranded DNA- and RNA-binding proteins pur alpha and pur beta link BC1 RNA to microtubules through binding to the dendrite-targeting RNA motifs

Neural BC1 RNA is distributed in neuronal dendrites as RNA-protein complexes (BC1 RNPs) containing Translin. In this study, we demonstrated that the single-stranded DNA- and RNA-binding protein pur alpha and its isoform, pur beta, which have been implicated in control of DNA replication and transcription, linked BC1 RNA to microtubules (MTs). The binding site was within the 5' proximal region of BC1 RNA containing putative dendrite-targeting RNA motifs rich in G and U residues, suggesting that in the cytoplasm of neurons, these nuclear factors are involved in the BC1 RNA transport along dendritic MTs. The pur proteins were not components of BC1 RNP but appeared to associate with MTs in brain cells. Therefore, it is suggested that they may transiently interact with the RNP during transport. In this respect, the interaction of pur proteins with BC1 RNA could be regulated by the Translin present within the RNP, because the binding mode of these two classes of proteins (pur proteins and Translin) to the dendrite-targeting RNA motifs was mutually exclusive. As the motifs are well conserved in microtubule-associated protein 2a/b mRNA as well, the pur proteins may also play a role(s) in the dendritic transport of a subset of mRNAs.

Puralpha: a multifunctional single-stranded DNA- and RNA-binding protein

Puralpha is a ubiquitous, sequence-specific DNA- and RNA-binding protein which is highly conserved in eukaryotic cells. Puralpha has been implicated in diverse cellular functions, including transcriptional activation and repression, translation and cell growth. Moreover, this protein has been shown to be involved in regulating several human viruses which replicate in the central nervous system (CNS), including human immunodeficiency virus type I (HIV-1) and JC virus (JCV). Puralpha exerts part of its activity by interacting with cellular proteins, including pRb, E2F, cyclin A, Sp1 and members of the Y-box family of proteins, including YB-1 and MSY1, as well as viral proteins such as polyomavirus large T-antigen and HIV-1 Tat. The ability of Puralpha to interact with its target DNA sequence and to associate with several viral and cellular proteins is modulated by RNA. Puralpha has also been shown to be involved in cell growth and proliferation. Its association with pRb, E2F and cyclin A coupled with its fluctuating levels throughout the cell cycle, position Puralpha as a crucial factor in the cell cycle. Moreover, microinjection studies demonstrate that Puralpha causes either a G(1) or G(2) arrest depending on the cell cycle time of injection. The gene encoding Puralpha has been localized to a human locus which is frequently deleted in myelogenous leukemias and other cancers and Puralpha gene deletions have been detected in many cases of lymphoid cancers. The following review details the structural characteristics of Puralpha, its family members and the involvement of this protein in regulating various cellular and viral genes, viral replication and cell growth.