Down regulation of the octamer binding protein Oct-1 during growth arrest and differentiation of a neuronal cell line

Bovine Transcription Factor POU Class 2 Homeobox 1 (POU2F1/Oct1) Protein Promotes BoHV-1 Replication in MDBK Cells

Bovine herpesvirus type 1 (BoHV-1) causes severe diseases in bovine species and great economic burden to the cattle industry worldwide. Due to its complex life cycle, many host factors that affect BoHV-1 replication remain to be explored. To understand the possible roles that the Oct1 cellular protein could play in this process, we first created Oct1-deficient MDBK cells using CRISPR/Cas9-mediated genome editing. Upon infection, the absence of Oct1 in MDBK cells significantly impacted BoHV-1 replication, a phenotype rescued by over-expressing the wild-type Oct1 protein in the deficient cells. We further found that the expression of all three classes of temporal genes, including essential and non-essential viral genes, were significantly reduced in Oct1 knockout MDBK cells, following both high and low multiplicity of infection. In summary, our findings confirm that the bovine Oct1 protein acts as a pro-viral factor for BoHV-1 replication by promoting its viral gene transcription in MDBK cells.

Models of Herpes Simplex Virus Latency

Our current understanding of HSV latency is based on a variety of clinical observations, and in vivo, ex vivo, and in vitro model systems, each with unique advantages and drawbacks. The criteria for authentically modeling HSV latency include the ability to easily manipulate host genetics and biological pathways, as well as mimicking the immune response and viral pathogenesis in human infections. Although realistically modeling HSV latency is necessary when choosing a model, the cost, time requirement, ethical constraints, and reagent availability are also equally important. Presently, there remains a pressing need for in vivo models that more closely recapitulate human HSV infection. While the current in vivo, ex vivo, and in vitro models used to study HSV latency have limitations, they provide further insights that add to our understanding of latency. In vivo models have shed light on natural infection routes and the interplay between the host immune response and the virus during latency, while in vitro models have been invaluable in elucidating molecular pathways involved in latency. Below, we review the relative advantages and disadvantages of current HSV models and highlight insights gained through each.

Herpes Simplex Virus Establishment, Maintenance, and Reactivation: In Vitro Modeling of Latency

All herpes viruses establish lifelong infections (latency) in their host, and herpes simplex viruses (HSVs) are highly prevalent worldwide. Recurrence of HSV infections contributes to significant disease burden in people and on rare occasion can be fatal. Cell culture models that recapitulate latent infection provide valuable insight on the host processes regulating viral establishment and maintenance of latency. More robust and rapid than infections in live animal studies, advancements in neuronal culture techniques have made the systematic analysis of viral reactivation mechanisms feasible. Only recently have human neuronal cell lines been available, but models in the natural host cell are a critical addition to the currently available models.

[Herpes simplex virus type 1 latency and reactivation: an update]

Following primary infections HSV-1 replicates productively in epithelial cells and enters sensory neurons via nerve termini. After retrograde transport the virus genome is delivered into the cell nucleus, where it establishes lifelong latent infections. During latency, the virus genome remains as a chromatinized episome expressing only a set of latency-associated transcripts (LAT) and a group of microRNAs that inhibit expression of key lytic viral functions. Periodically the virus can reactivate to reinitiate lytic, secondary infections at peripheral tissues. The ability to establish both lytic and latent infections relies on the coexistence in the virus genome of two alternative gene expression programs, under the control of epigenetic mechanisms. Latency is an adaptive phenotype that allows the virus to escape immune host responses and to reactivate and disseminate to other hosts upon recognizing danger signals such as stress, neurologic trauma or growth factor deprivation.

The molecular basis of herpes simplex virus latency

Herpes simplex virus type 1 is a neurotropic herpesvirus that establishes latency within sensory neurones. Following primary infection, the virus replicates productively within mucosal epithelial cells and enters sensory neurones via nerve termini. The virus is then transported to neuronal cell bodies where latency can be established. Periodically, the virus can reactivate to resume its normal lytic cycle gene expression programme and result in the generation of new virus progeny that are transported axonally back to the periphery. The ability to establish lifelong latency within the host and to periodically reactivate to facilitate dissemination is central to the survival strategy of this virus. Although incompletely understood, this review will focus on the mechanisms involved in the regulation of latency that centre on the functions of the virus-encoded latency-associated transcripts (LATs), epigenetic regulation of the latent virus genome and the molecular events that precipitate reactivation.

This review considers current knowledge and hypotheses relating to the mechanisms involved in the establishment, maintenance and reactivation herpes simplex virus latency.

POU homeodomain protein OCT1 modulates islet 1 expression during cardiac differentiation of P19CL6 cells

Islet 1 (ISL1), a marker of cardiac progenitors, plays a crucial role in cardiogenesis. However, the precise mechanism underlying the activation of its expression is not fully understood. Using the cardiac differentiation model of P19CL6 cells, we show that POU homeodomain protein, OCT1, modulates Isl1 expression in the process of cardiac differentiation. Oct1 knock-down resulted in reduction of Isl1 expression and downregulated mesodermal, cardiac-specific, and signal pathway gene expression. Additionally, the octamer motif located in the proximal region of Isl1 promoter is essential to Isl1 transcriptional activation. Mutation of this motif remarkably decreased Isl1 transcription. Although both OCT1 and OCT4 bound to this motif, it was OCT1 rather than OCT4 that modulated Isl1 expression. Furthermore, the correlation of OCT1 in regulation of Isl1 was revealed by in situ hybridization in early embryos. Collectively, our data highlight a novel role of OCT1 in the regulation of Isl1 expression.

Effects of perfluoroalkyl compounds on mRNA expression levels of thyroid hormone-responsive genes in primary cultures of avian neuronal cells

There is growing interest in assessing the neurotoxic and endocrine disrupting potential of perfluoroalkyl compounds (PFCs). Several studies have reported in vitro and in vivo effects related to neuronal development, neural cell differentiation, prenatal and postnatal development and behavior. PFC exposure altered hormone levels and the expression of hormone-responsive genes in mammalian and aquatic species. This study is the first to assess the effects of PFCs on messenger RNA (mRNA) expression in primary cultures of neuronal cells in two avian species: the domestic chicken (Gallus domesticus) and herring gull (Larus argentatus). The following thyroid hormone (TH)–responsive genes were examined using real-time reverse transcription-PCR: type II iodothyronine 5′-deiodinase (D2), D3, transthyretin (TTR), neurogranin (RC3), octamer motif–binding factor (Oct-1), and myelin basic protein. Several PFCs altered the mRNA expression levels of genes associated with the TH pathway in avian neuronal cells. Short-chained PFCs (less than eight carbons) altered the expression of TH-responsive genes (D2, D3, TTR, and RC3) in chicken embryonic neuronal cells to a greater extent than long-chained PFCs (more than or equal to eight carbons). Variable transcriptional changes were observed in herring gull embryonic neuronal cells exposed to short-chained PFCs; mRNA levels of Oct-1 and RC3 were upregulated. This is the first study to report that PFC exposure alters mRNA expression in primary cultures of avian neuronal cells and may provide insight into the possible mechanisms of action of PFCs in the avian brain.

Two polymorphisms of presenilin-2 gene (PSEN2) 5' regulatory region are not associated with Alzheimer's disease (AD) in the Polish population

Presenilin 2 gene (PSEN2) is one of the causative genes for familial Alzheimer's disease. A delA polymorphism located in PSEN2 promoter was proposed to be a risk factor for early-onset AD. We examined association between AD and PSEN2 polymorphisms located in two 5'UTR regions in group of 217 late-onset AD patients, 109 mild cognitive impairment patients, and 225 non-demented control subjects. No significant differences for genotype and allele distributions of a delA and a novel insAC polymorphisms in the studied groups as compared to controls were observed. Univariate and multivariate risk estimation shows that neither delA, insAC alleles nor the genotypes are risk factors for AD. No significant interaction between the APOE4 and PSEN2 polymorphisms was found. A bioinformatic analysis showed that delA polymorphism influences binding sites of transcription factors involved in the cellular processes related to AD. The rare variants identified in exon 3 of the PSEN2 could have a potential influence on PSEN2 transcript splicing.

Expression of transcription factors and matrix genes in response to serum stimulus in vascular smooth muscle cells

During atherogenesis vascular smooth muscle cells are converted from a contractile into a synthetic phenotype characterized by enhanced matrix production. The transcription factors Gax and GATA-6 are considered negative, and Oct-1 positive regulators of the synthetic phenotype. Since the phenotype transition can be induced by culturing the cells with serum, we followed the expression of Gax, GATA-6 and Oct-1, integrins and matrix genes in quiescent porcine vascular smooth muscle cells after serum application. Comparisons were made between enzymatically released primary smooth muscle cells and cells grown out from explants of the medial layer of porcine aorta. The serum-mediated down-regulation of Gax was more intense than that of GATA-6, and stronger in explant-derived than in primary cells. Serum was without influence on the expression of Oct-1. Changes in the expression of the transcription factors preceded the induction of integrin alpha2 and the down-regulation of decorin, while mRNAs for laminin beta1 and osteopontin rose immediately after serum stimulation. Primary cells reacted more rapidly than explant cells with respect to changes in laminin isoforms. Studies with a Gax-expressing adenovirus indicated that among all the gene products tested only the expression of integrin alpha2 responded to Gax induction. Thus, our data show that i) Gax should be considered a transcription factor being directly responsible for only few aspects of the phenotypic conversion of smooth muscle cells and that ii) explant cells may represent a subpopulation of smooth muscle cells, which differ from the total population of smooth muscle cells, as obtained in primary culture, in their response to serum stimuli.

POU domain factors in the neuroendocrine system: lessons from developmental biology provide insights into human disease

POU domain factors are transcriptional regulators characterized by a highly conserved DNA-binding domain referred to as the POU domain. The structure of the POU domain has been solved, facilitating the understanding of how these proteins bind to DNA and regulate transcription via complex protein-protein interactions. Several members of the POU domain family have been implicated in the control of development and function of the neuroendocrine system. Such roles have been most clearly established for Pit-1, which is required for formation of somatotropes, lactotropes, and thyrotropes in the anterior pituitary gland, and for Brn-2, which is critical for formation of magnocellular and parvocellular neurons in the paraventricular and supraoptic nuclei of the hypothalamus. While genetic evidence is lacking, molecular biology experiments have implicated several other POU factors in the regulation of gene expression in the hypothalamus and pituitary gland. Pit-1 mutations in humans cause combined pituitary hormone deficiency similar to that found in mice deleted for the Pit-1 gene, providing a striking example of how basic developmental biology studies have provided important insights into human disease.

Acute changes in maternal thyroid hormone induce rapid and transient changes in gene expression in fetal rat brain

Despite clinical evidence that thyroid hormone is essential for brain development before birth, effects of thyroid hormone on the fetal brain have been largely unexplored. One mechanism of thyroid hormone action is regulation of gene expression, because thyroid hormone receptors (TRs) are ligand-activated transcription factors. We used differential display to identify genes affected by acute T(4) administration to the dam before the onset of fetal thyroid function. Eight of the 11 genes that we identified were selectively expressed in brain areas known to contain TRs, indicating that these genes were directly regulated by thyroid hormone. Using in situ hybridization, we confirmed that the cortical expression of both neuroendocrine-specific protein (NSP) and Oct-1 was affected by changes in maternal thyroid status. Additionally, we demonstrated that both NSP and Oct-1 were expressed in the adult brain and that their responsiveness to thyroid hormone was retained. These data are the first to identify thyroid hormone-responsive genes in the fetal brain.

Differentiation-related mechanisms which suppress DNA replication

Differentiation of mammalian cells implies cessation of DNA replication and cell proliferation; the potential controls of this coupling are examined here. It is clear that the known or proposed mechanisms of down-regulation of replicative cellular activities vary in different lineages of cell differentiation, and occur in all phases of the cell cycle. In G1 these regulators include p21/Cip1 or p27/Kip1, pRb, and p53; the novel, recently reported mechanisms of their action are summarized. In S phase the availability of nucleotide precursors, the origin recognition complex (ORC), and other replication proteins may be important in differentiation, and in G2 phase the cdc2/cyclin B complex and replication licensing factors determine normal G2 traverse versus an arrest or polyploidisation. Other replication-related mechanisms include transcription factors, e.g., Sp1, telomerase, and nuclear matrix changes. Thus, differentiation alters the activity not only of the various checkpoint proteins, but also of the components of the replicative machinery itself.

Perlecan regulates Oct-1 gene expression in vascular smooth muscle cells

Vascular smooth muscle cells (SMCs) are very quiescent in the mature vessel and exhibit a remarkable phenotype-dependent diversity in gene expression that may reflect the growth responsiveness of these cells under a variety of normal and pathological conditions. In this report, we describe the expression pattern of Oct-1, a member of a family of transcription factors involved in cell growth processes, in cultured and in in vivo SMCs. Oct-1 mRNA was undetectable in the contractile-state in vivo SMCs; was induced upon disruption of in vivo SMC-extracellular matrix interactions; and was constitutively expressed by cultured SMCs. Oct-1 transcripts were repressed when cultured SMCs were plated on Engelbreth-Holm-Swarm tumor-derived basement membranes (EHS-BM) but were rapidly induced after disruption of SMC-EHS-BM contacts; reexpression was regulated at the transcriptional level. To identify the EHS-BM component involved in the active repression of Oct-1 mRNA expression, SMCs were plated on laminin, type IV collagen, fibronectin, or perlecan matrices. Oct-1 mRNA levels were readily detectable when SMCs were cultured on matrices composed of laminin, type IV collagen, or fibronectin but were repressed when SMCs were cultured on perlecan matrices. Finally, the Oct-1-suppressing activity of EHS-BM was sensitive to heparinase digestion but not to chondroitinase ABC or hyaluronidase digestion, suggesting that the heparan sulfate side chains of perlecan play a biologically important role in negatively regulating the expression of Oct-1 transcripts.

Oct-6 (SCIP/Tst-1) is expressed in Schwann cell precursors, embryonic Schwann cells, and postnatal myelinating Schwann cells: comparison with Oct-1, Krox-20, and Pax-3

The POU domain transcription factor Oct-6 (SCIP/Tst-1) is likely to control important stages of Schwann cell development, including the initiation of myelination around birth. Here, we use immunocytochemical and reverse transcriptase-polymerase chain reaction techniques to examine Oct-6 earlier in nerve development, to test the idea that Oct-6 has an additional role in Schwann cell precursors or early embryonic Schwann cells, a possibility raised by previous studies on transgenic mice. Consistent with this, we find low but unambiguous levels of Oct-6 mRNA and protein in Schwann cell precursors of mouse and rat (nerves from 12- and 14-day-old embryos, respectively), with expression levels gradually increasing during early Schwann cell development and towards birth. Unexpectedly, Oct-6 immunoreactivity is clearly present in nuclei of most myelinating cells at least as late as postnatal day 12. Furthermore, many nonmyelinating Schwann cells express Oct-6 in adult life. A comparison of Oct-6 mRNA with other Schwann cell transcription factors-namely, Oct-1, Krox-20, and Pax-3-reveals that each factor exhibits strong developmental regulation and a unique expression pattern in embryonic nerves. Therefore, they are likely to play distinct regulatory roles in early development of the Schwann cell lineage.