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Martyn K White

Publications and source records attributed to Martyn K White.

At least 19 recordsLinked to original sources
PubMed2006

Regulation of the Pur-alpha promoter by E2F-1.

Puralpha is a ubiquitously expressed multifunctional nucleic acid-binding protein that is involved in many cellular processes including transcriptional regulation, the cell cycle, oncogenic transformation, and post-natal brain development. Previously, Puralpha protein was found to bind to E2F-1, inhibit E2F-1 transcriptional activity, and reverse the effects of ectopic E2F-1 expression on cell growth. Also Puralpha binds to a GC/GA-rich sequence within its own promoter and inhibits gene expression, that is, Puralpha is autoregulated. We now report that the Puralpha promoter (pPuralpha) is induced by E2F-1 and that this activity maps to a consensus E2F-1 binding motif that is juxtaposed to the Puralpha binding site. Deletion mutants of the E2F-1 protein showed that the region between amino acid residues 88-241 is important for this activity. E2F-1-associated activation of the pPuralpha was inhibited by co-expression of Puralpha, pRb, and an RNA species with specific binding to E2F-1. Chromatin immunoprecipitation (ChIP) assay using primers that flanked the juxtaposed Puralpha and E2F-1 binding sites verified the presence of Puralpha and E2F-1 on the pPuralpha in vivo. In a Tet-inducible cell line, Puralpha delayed cell cycle progression. Thus, E2F-1 and Puralpha interplay appears to be involved in the regulation of Puralpha expression and the cell cycle.

5' Untranslated Regions↗
PubMed2006

Reciprocal transactivation between HIV-1 and other human viruses.

A variety of rare clinical syndromes are seen with strikingly increased prevalence in HIV-1-infected individuals, many with underlying viral etiologies. The emergence of these diseases in AIDS reflects a reduction in the ability of the immune system to mount an adequate defense against viruses in general due to the damage inflicted to the immune system by HIV-1 infection. However, in many cases, it has been found that HIV-1 can enhance the level of expression and hence the life cycle of other viruses independently of immunosuppression through specific interactions with the viruses. This can occur either directly by HIV-1 proteins such as Tat enhancing the activity of heterologous viral promoters, and/or indirectly by HIV-1 inducing the expression of cytokines and activation of their downstream signaling that eventually promotes the multiplication of the other virus. In a reciprocal manner, the effects of other viruses can enhance the pathogenicity of HIV-1 infection in individuals with AIDS through stimulation of the HIV-1 promoter activity and genome expression. The purpose of this review is to examine the cross-interactions between these viruses and HIV-1.

Gene Expression Regulation, Viral↗
PubMed2006

Glioblastoma multiforme with small cell neuronal-like component: association with human neurotropic JC virus.

The human polyomavirus JCV, the etiological agent of progressive multifocal leukoencephalopathy, has been associated with primitive neuroectodermal tumors and various glial-derived tumors, including glioblastoma multiforme (GBM). Here we describe the unique clinical case of a 54-year-old man who presented with headaches, hemiparesis and drowsiness. T1 and T2 magnetic resonance images revealed a large solid tumor with a cystic component located in the right temporal lobe, with extension into the parietal lobe. Histologically, the tumor was composed of two areas, a main area of large neoplastic cells with pleomorphic atypical nuclei and abundant cytoplasm, which by immunohistochemistry was reactive for glial fibrillary acidic protein, mixed with several foci of poorly differentiated tumoral cells with elongated nuclei and scant cytoplasm, negative for GFAP, but robustly immunoreactive for synaptophysin and phosphoneurofilaments. Results from PCR in laser capture microdissected cells from both areas of the tumor revealed the presence of DNA sequences corresponding to the early, late and control regions (CR) of the JCV genome and expression of JCV proteins T-antigen and Agnoprotein in both phenotypes. No evidence for capsid protein was observed, excluding productive viral infection. Sequencing demonstrated the presence of the JCV Mad-1 strain with distinct point mutations in the CR of isolates from both, GBM and small cell architectural areas. The presence of JCV DNA sequences and expression of viral proteins further reinforces the role of the widely spread human neurotropic virus in early transformation and in the development of brain tumors.

Brain Neoplasms↗
PubMed2006

Human polyomavirus JCV late leader peptide region contains important regulatory elements.

Transcription is a complex process that relies on the cooperative interaction between sequence-specific factors and the basal transcription machinery. The strength of a promoter depends on upstream or downstream cis-acting DNA elements, which bind transcription factors. In this study, we investigated whether DNA elements located downstream of the JCV late promoter, encompassing the late leader peptide region, which encodes agnoprotein, play regulatory roles in the JCV lytic cycle. For this purpose, the entire coding region of the leader peptide was deleted and the functional consequences of this deletion were analyzed. We found that viral gene expression and replication were drastically reduced. Gene expression also decreased from a leader peptide point mutant but to a lesser extent. This suggested that the leader peptide region of JCV might contain critical cis-acting DNA elements to which transcription factors bind and regulate viral gene expression and replication. We analyzed the entire coding region of the late leader peptide by a footprinting assay and identified three major regions (region I, II and III) that were protected by nuclear proteins. Further investigation of the first two protected regions by band shift assays revealed a new band that appeared in new infection cycles, suggesting that viral infection induces new factors that interact with the late leader peptide region of JCV. Analysis of the effect of the leader peptide region on the promoter activity of JCV by transfection assays demonstrated that this region has a positive and negative effect on the large T antigen (LT-Ag)-mediated activation of the viral early and late promoters, respectively. Furthermore, a partial deletion analysis of the leader peptide region encompassing the protected regions I and II demonstrated a significant down-regulation of viral gene expression and replication. More importantly, these results were similar to that obtained from a complete deletion of the late leader peptide region, indicating the critical importance of these two protected regions in JCV regulation. Altogether, these findings suggest that the late leader peptide region contains important regulatory elements to which transcription factors bind and contribute to the JCV gene regulation and replication.

Blotting, Northern↗
PubMed2006

Cdk9 phosphorylates p53 on serine 392 independently of CKII.

The tumor suppressor p53 is an important cellular protein, which controls cell cycle progression. Phosphorylation is one of the mechanisms by which p53 is regulated. Here we report the interaction of p53 with another key regulator, cdk9, which together with cyclin T1 forms the positive transcription elongation complex, p-TEFb. This complex cooperates with the HIV-1 Tat protein to cause the phosphorylation of the carboxyl terminal domain (CTD) of RNA polymerase II and this facilitates the elongation of HIV-1 transcription. We demonstrate that cdk9 phosphorylates p53 on serine 392 through their direct physical interaction. Results from protein-protein interaction assays revealed that cdk9 interacts with the C-terminal domain (aa 361-393) of p53, while p53 interacts with the N-terminal domain of cdk9. Transfection and protein binding assays (EMSA and ChIP) demonstrated the ability of p53 to bind and activate the cdk9 promoter. Interestingly, cdk9 phosphorylates serine 392 of p53, which could be also phosphorylated by casein kinase II. Kinase assays demonstrated that cdk9 phosphorylates p53 independently of CKII. These studies demonstrate the existence of a feedback-loop between p53 and cdk9, pinpointing a novel mechanism by which p53 regulates the basal transcriptional machinery.

Brain Neoplasms↗
PubMed2006

The polyomavirus, JCV and its involvement in human disease.

The human neurotropic polyomavirus, JC virus (JCV), is the etiologic agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the central nervous system that occurs mainly in immunosuppressed patients. JCV has also been found to be associated with human tumors of the brain and other organs. In this chapter, we describe JC virus and its role in human diseases.

Central Nervous System Diseases↗
PubMed2006

Activation of early gene transcription in polyomavirus BK by human immunodeficiency virus type 1 Tat.

Polyomavirus BK (BKV) is a serious problem for immunocompromised patients, where latent virus can enter into the lytic cycle causing cytolytic destruction of host cells. BKV infects >80% of the population worldwide during childhood and then remains in a latent state in the kidney. In the context of immunosuppression in kidney transplant patients, reactivation of the viral early promoter (BKV(E)) results in production of T antigen, enabling virus replication and transition from latency to the lytic phase, causing polyomavirus-associated nephropathy. Reactivation of BKV can also cause complications such as nephritis, atypical retinitis and haemorrhagic cystitis in AIDS patients. Here, the effects of human immunodeficiency virus type 1 (HIV-1) proteins Tat and Vpr on BKV transcription were investigated and it was demonstrated that Tat dramatically stimulated BKV(E). Site-directed mutagenesis analysis of potential Tat-responsive transcriptional motifs complemented by an electrophoretic mobility shift assay (EMSA) showed that Tat activated BKV(E) by inducing binding of the NF-kappaB p65 subunit to a kappaB motif near the 3' end of BKV(E). In addition, a sequence within the 5' UTR of BKV(E) transcripts (BKV(E)-TAR) was identified that is identical to the HIV-1 transactivation response (TAR) element. The BKV(E)-TAR sequence bound TAT in RNA EMSA assays and deletion of the BKV(E)-TAR sequence eliminated Tat transactivation of BKV(E) transcription. Thus, Tat positively affected BKV(E) transcription by a dual mechanism and this may be important in diseases involving BKV reactivation in AIDS patients.

BK Virus↗
PubMed2005

Expression of JC virus regulatory proteins in human cancer: potential mechanisms for tumourigenesis.

JC virus (JCV) is a human polyomavirus that is the etiologic agent of the fatal demyelinating disease of the central nervous system known as progressive multifocal leukoencephalopathy (PML). JCV is also linked to some tumours of the brain and other organs as evidenced by the presence of JCV DNA sequences and the expression of viral proteins in clinical samples. Since JCV is highly oncogenic in experimental animals and transforms cells in culture, it is possible that JCV contributes to the malignant phenotype of human tumours with which it is associated. JCV encodes three non-capsid regulatory proteins: large T-antigen, small t-antigen and agnoprotein that interact with a number of cellular target proteins and interfere with certain normal cellular functions. In this review, we discuss how JCV proteins deregulate signalling pathways especially ones pertaining to transcriptional regulation and cell cycle control. These effects may be involved in the progression of JCV-associated tumours and may represent potential therapeutic targets.

Antigens, Viral, Tumor↗
PubMed2005

Human polyomaviruses and brain tumors.

Polyomaviruses are DNA tumor viruses with small circular genomes. Three polyomaviruses have captured attention with regard to their potential role in the development of human brain tumors: JC virus (JCV), BK virus (BKV), and simian vacuolating virus 40 (SV40). JCV is a neurotropic polyomavirus that is the etiologic agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the central nervous system occurring mainly in AIDS patients. BKV is the causative agent of polyomavirus-associated nephropathy (PVN) which occurs after renal transplantation when BKV reactivates from a latent state during immunosuppressive therapy to cause allograft failure. SV40, originating in rhesus monkeys, gained notoriety when it entered the human population via contaminated polio vaccines. All three viruses are highly oncogenic when injected into the brain of experimental animals. Reports indicate that these viruses, especially JCV, are associated with brain tumors and other cancers in humans as evidenced from the analysis of clinical samples for the presence of viral DNA sequences and expression of viral proteins. Human polyomaviruses encode three non-capsid regulatory proteins: large T-antigen, small t-antigen, and agnoprotein. These proteins interact with a number of cellular target proteins to exert effects that dysregulate pathways involved in the control of various host cell functions including the cell cycle, DNA repair, and others. In this review, we describe the three polyomaviruses, their abilities to cause brain and other tumors in experimental animals, the evidence for an association with human brain tumors, and the latest findings on the molecular mechanisms of their actions.

Animals↗
PubMed2005

Detection of JC virus DNA sequences and expression of viral T antigen and agnoprotein in esophageal carcinoma.

BACKGROUND: The human polyomavirus JC virus (JCV) causes progressive multifocal leukoencephalopathy. Subclinical infection with JCV occurs in 85-90% of the population worldwide. The virus usually remains latent but can reactivate under immunosuppressive conditions, resulting in progressive multifocal leukoencephalopathy. JCV is oncogenic in experimental animals and is associated with human brain tumors. JCV is found in normal mucosa of the gastrointestinal tract, and some colon carcinomas express the oncogenic JCV T-antigen protein. The objective of this study was to examine the presence of JCV DNA sequences and JCV protein expression in normal and malignant human esophageal tissues. METHODS: The authors examined the presence of JCV DNA sequences and protein expression in normal and malignant human esophageal tissues. Seventy well characterized biopsy specimens from patients with a spectrum of esophageal disorders were studied by immunohistochemistry, and 18 specimens were analyzed further by polymerase chain reaction amplification. RESULTS: JC viral DNA was isolated from 11 of 13 normal esophageal biopsy specimens (85%) and from 5 of 5 esophageal carcinomas (100%). Using immunohistochemistry, JCV T antigen was detected in 10 of 19 carcinomas (53%), agnoprotein was detected in 8 carcinomas (42%), p53 tumor suppressor was detected in 11 carcinomas (58%), and beta-catenin was detected in 4 carcinomas (21%). Zero of 51 normal, benign, and premalignant esophageal samples expressed viral proteins. Laser-capture microdissection verified the presence and specificity of JCV DNA sequences. beta-Catenin and p53 were colocalized with JCV T-antigen in the nuclei of neoplastic cells. CONCLUSIONS: The results provide evidence for infection of gastrointestinal tract cells by JCV and suggest a potential role of JCV in the development of upper digestive tract carcinomas.

Adult↗
PubMed2005

The agnoprotein of polyomaviruses: a multifunctional auxiliary protein.

The late region of the three primate polyomaviruses (JCV, BKV, and SV40) encodes a small, highly basic protein known as agnoprotein. While much attention during the last two decades has focused on the transforming proteins encoded by the early region (small and large T-antigens), it has become increasingly evident that agnoprotein has a critical role in the regulation of viral gene expression and replication, and in the modulation of certain important host cell functions including cell cycle progression and DNA repair. The importance of agnoprotein is underscored by its expression during lytic infection of glial cells by JCV that occurs in progressive multifocal leukoencephalopathy (PML), and also in some JCV-associated human neural tumors particularly medulloblastoma. In this review, we will discuss the structure and function of agnoprotein in the viral life cycle during the course of lytic infection and the consequences of agnoprotein expression for the host cell.

Amino Acid Sequence↗
PubMed2005

p73 Interacts with human immunodeficiency virus type 1 Tat in astrocytic cells and prevents its acetylation on lysine 28.

Human immunodeficiency virus type 1 (HIV-1) Tat is a potent transcriptional activator of the HIV-1 promoter and also has the ability to modulate a number of cellular regulatory circuits including apoptosis. Tat exerts its effects through interaction with viral as well as cellular proteins. Here, we studied the influence of p73, a protein that is implicated in apoptosis and cell cycle control, on Tat functions in the central nervous system. Protein interaction studies using immunoprecipitation followed by Western blot and glutathione S-transferase pull-down assays demonstrated the association of Tat with p73. Tat bound to the N-terminal region of p73 spanning amino acids 1 to 120, and this interaction required the cysteine-rich domain (amino acids 30 to 40) of Tat. Association of p73 with Tat prevented the acetylation of Tat on lysine 28 by PCAF. Functional studies including RNA interference showed that p73 inhibited Tat stimulation of the HIV-1 promoter. Furthermore, p73 prevented the interaction of Tat with cyclin T1 in vitro but not in vivo. These findings suggest possible new therapeutic approaches, using p73, for Tat-mediated AIDS pathogenesis.

Acetylation↗
PubMed2005

What they are, how they work and why they do what they do? The story of SV40-derived gene therapy vectors and what they have to offer.

The natural function of viruses is to deliver their genetic material to cells. Among the most effective of viruses in doing that is Simian Virus-40 (SV40). The properties that make SV40 a successful virus make it an attractive candidate for use as a gene delivery vehicle: high titer replication, infectivity for almost all nucleated cell types whether the cells are dividing or resting, potential for integration into cellular DNA, a peculiar pathway for entering cells that bypasses the cells' antigen processing apparatus, very high stability, and the apparent ability to activate expression of its own capsid genes in trans. Exploiting these and other characteristics of wild type (wt) SV40, increasing numbers of laboratories are studying recombinant (r) SV40-derived vectors. Among the uses to which these vectors have been applied are: delivering therapy to inhibit HIV, hepatitis C virus (HCV) and other viruses; correction of inherited hepatic and other protein deficiencies; immunizing against lentiviral and other antigens; treatment of inherited and acquired diseases of the central nervous system; protecting the lung and other organs from free radical-induced injury; and many others. The effectiveness of these vectors is a reflection of the adaptive evolution that produced their parent virus, wt SV40. This article explores how and why these vectors work, their strengths and their limitations, and provides a functional model for their exploitation for experimental and clinical applications.

Animals↗
PubMed2004

Polyomaviruses and human cancer: molecular mechanisms underlying patterns of tumorigenesis.

Polyomaviruses are DNA tumor viruses with small circular genomes encoding only six proteins including three structural capsid proteins. Despite this simplicity, our understanding of the mechanisms of polyomavirus-mediated tumorigenesis is far from complete. The archetypal primate polyomavirus, SV40, was isolated more than 40 years ago and has been used extensively as a model system for the study of basic eukaryotic cellular processes such as DNA replication and transcription. Two human polyomaviruses have been isolated from clinical samples: JC virus (JCV) and BK virus (BKV). In this review, SV40, JCV, and BKV will be compared based on what is known about their molecular biology from experiments performed in vitro, in cell culture and in laboratory animals. The association of these viruses with clinical tumors is discussed along with the possible roles of these polyomaviruses in the etiology of human malignant disease.

BK Virus↗
PubMed2004

Role of JC virus agnoprotein in DNA repair.

The late region of human neurotropic JC virus encodes a small 71-amino-acid agnoprotein that is also found in the polyomaviruses simian virus 40 and BK virus. Several functions of agnoprotein have been identified, including roles in regulating viral transcription and virion maturation. Earlier studies showed that agnoprotein expressed alone induced p21/WAF-1 expression and caused cells to accumulate in the G(2)/M stage of the cell cycle. Here we report that agnoprotein expression sensitized cells to the cytotoxic effects of the DNA-damaging agent cisplatin. Agnoprotein reduced the viability of cisplatin-treated cells and increased chromosome fragmentation and micronucleus formation. Whereas cisplatin-treated control cells accumulated in S phase, cells expressing agnoprotein did not, instead becoming aneuploid. Agnoprotein expression correlated with impaired double-strand-break repair activity in cellular extracts and reduced expression of the Ku70 and Ku80 DNA repair proteins. After agnoprotein expression, much of the Ku70 protein was located in the perinuclear space, where agnoprotein was also found. Results from binding studies showed an interaction of agnoprotein with Ku70 which was mediated by the N terminus. The ability of agnoprotein to inhibit double-strand break repair activity when it was added to cellular extracts was also mediated by the N terminus. We conclude that agnoprotein inhibits DNA repair after DNA damage and interferes with DNA damage-induced cell cycle regulation. Since Ku70 is a subunit of the DNA-dependent protein kinase that is responsible both for double-strand break repair and for signaling damage-induced cell cycle arrest, the modulation of Ku70 and/or Ku80 by agnoprotein may represent an important event in the polyomavirus life cycle and in cell transformation.

Amino Acid Sequence↗
PubMed2004

Role of raf isoforms in signal transduction pathways relevant to leukemia cell proliferation.

The invited commentary is addressed to the paper of Shelton et al published in this issue of Cell Cycle. The intracellular pathways that control cell growth constitute a complex nexus of signaling interactions that serve to regulate cell proliferation, differentiation and apoptosis. Dysregulation of these processes leads to the loss of control of cell growth that is characteristic of malignancy. Understanding cell signaling is a major challenge for modern biological research. One way to begin to unravel the intricate web of signaling pathways is to investigate the effects of mutant forms of key component proteins. One such protein is the serine/threonine-specific protein kinase, Raf.

Animals↗
PubMed2003

Molecular and biochemical events during differentiation of the HD3 chicken erythroblastic cell line.

The chicken erythroblast cell line HD3 is transformed by a temperature-sensitive mutant of avian erythroleukemia virus. Upon shift to the non-permissive temperature in the presence of inducers (hemin and butyric acid), HD3 cells differentiate to an erythrocyte phenotype and provide a model system for analyzing events associated with this process. Expression of some cell surface proteins undergoes drastic changes as cells mature to the erythrocyte stage with a selective loss of membrane proteins that appears to be species-specific. Specific changes also occur in the expression and activities of cytosolic enzymes reflecting alterations of metabolism. HD3 differentiation is characterized by increased transferrin receptor (TFR) expression and increased hemoglobin (Hb) synthesis, a marker for the erythrocyte. In parallel, there is a decrease in glucose transport and an increase in nucleoside transport signifying a switch from glycolytic hexose metabolism to metabolism of pentose from nucleoside. Likewise the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAD) declines while glucose-6-phosphate dehydrogenase (G6PDH) activity remains constant. Commitment to the erythrocyte lineage alters expression of specific genes: TFR mRNA level increases while expression decreases for GLUT1 and GLUT3 glucose transporter mRNAs and GAD mRNA. However, the relationship between GAD activity and GAD mRNA was complex indicating modulation of GAD mRNA and protein half-lives. Serine/threonine and tyrosine phosphorylation and cAMP levels were shown to regulate the level of these messages. In this review, we describe how HD3 differentiation involves changes in plasma membrane composition, metabolism and gene expression that are orchestrated at different levels of control by multiple signaling modalities.

Animals↗