Puralpha, a single-stranded deoxyribonucleic acid binding protein, augments placental lactogen gene transcription

Analysis of the role of Purα in the pathogenesis of Alzheimer's disease based on RNA-seq and ChIP-seq

Purine rich element binding protein A (Purα), encoded by the Purα gene, is an important transcriptional regulator that binds to DNA and RNA and is involved in processes such as DNA replication and RNA translation. Purα also plays an important role in the nervous system. To identify the function of Pura, we performed RNA sequence (RNA-seq) analysis of Purɑ-KO mouse hippocampal neuron cell line (HT22) to analyze the effect of Purα deletion on neuronal expression profiles. And combined with ChIP-seq analysis to explore the mechanism of Purα on gene regulation. In the end, totaly 656 differentially expressed genes between HT22 and Purα-KO HT22 cells have been found, which include 7 Alzheimer’s disease (AD)-related genes and 5 Aβ clearance related genes. 47 genes were regulated by Purα directly, the evidence based on CHIP-seq, which include Insr, Mapt, Vldlr, Jag1, etc. Our study provides the important informations of Purα in neuro-development. The possible regulative effects of Purα on AD-related genes consist inthe direct and indirect pathways of Purα in the pathogenesis of AD.

The Molecular Function of PURA and Its Implications in Neurological Diseases

In recent years, genome-wide analyses of patients have resulted in the identification of a number of neurodevelopmental disorders. Several of them are caused by mutations in genes that encode for RNA-binding proteins. One of these genes is PURA, for which in 2014 mutations have been shown to cause the neurodevelopmental disorder PURA syndrome. Besides intellectual disability (ID), patients develop a variety of symptoms, including hypotonia, metabolic abnormalities as well as epileptic seizures. This review aims to provide a comprehensive assessment of research of the last 30 years on PURA and its recently discovered involvement in neuropathological abnormalities. Being a DNA- and RNA-binding protein, PURA has been implicated in transcriptional control as well as in cytoplasmic RNA localization. Molecular interactions are described and rated according to their validation state as physiological targets. This information will be put into perspective with available structural and biophysical insights on PURA’s molecular functions. Two different knock-out mouse models have been reported with partially contradicting observations. They are compared and put into context with cell biological observations and patient-derived information. In addition to PURA syndrome, the PURA protein has been found in pathological, RNA-containing foci of patients with the RNA-repeat expansion diseases such as fragile X-associated tremor ataxia syndrome (FXTAS) and amyotrophic lateral sclerosis (ALS)/fronto-temporal dementia (FTD) spectrum disorder. We discuss the potential role of PURA in these neurodegenerative disorders and existing evidence that PURA might act as a neuroprotective factor. In summary, this review aims at informing researchers as well as clinicians on our current knowledge of PURA’s molecular and cellular functions as well as its implications in very different neuronal disorders.

The purine-rich element-binding protein ChPur-α negatively regulates Hsc70 transcription in Crassostrea hongkongensis

ChPur-α, a purine-rich element-binding protein, was discovered showing affinity to the ChHsc70 promoter in Crassostrea hongkongensis by DNA affinity purification and mass spectrometry analysis. Direct interaction between purified ChPur-α and the ChHsc70 promoter region was demonstrated by electrophoretic mobility shift assay in vitro. ChPur-α reduction led to clear enhancements of ChHsc70 transcription in the hemocytes of C. hongkongensis. Consistently, ChPur-α overexpression in heterologous HEK293T cells correlated with repressive phenotype in ChHsc70 promoter expression. ChHsc70 transcription was responsive to heat shock or CdCl2 stress by RT-PCR, signifying an inducible feature of ChHsc70 transcription by physical/chemical stress despite its constitutive nature. ChPur-α transcription was also induced by the two stressors. This indicates a plausible association between ChHsc70 and ChPur-α in the stress-induced genetic regulatory pathway. This study discovered a negatively regulatory role of ChPur-α in controlling ChHsc70 transcription in C. hongkongensis, and contributed to better understanding the regulatory mechanisms in control of Hsc70 transcription.

Bone morphogenetic protein 4 accelerates the establishment of bovine trophoblastic cell lines

Trophoblastic cells play a crucial role in implantation and placentogenesis. A large proportion of the failures of conception in cows occur in the peri-implantation period, which are known as early embryo losses. In exploring this critical phenomenon, trophoblastic cell lines can provide substantial information. Unfortunately, there are few cell lines for this purpose in cattle because of the difficulty of raising successive cell stock in the long term. In this study, 12 new cell lines were established using bone morphogenetic protein 4 (BMP4). BMP4 stimulated embryonic cells to enter the trophoblastic cell lineage but there were no significant differences between intact and BMP4-treated groups. Only one out of 49 embryos developed trophoblastic cells in the intact group. Finally, 12 cell lines were maintained for around 30 passages, and they retained trophoblastic characteristics and expressed bovine trophoblastic genes: placental lactogen, interferon-τ, pregnancy-associated glycoprotein 1, and prolactin-related protein 1. Although the gene expression patterns were different among cell lines and depended on the cells, there was no significant relationship between the expression intensities of genes and the treatment dose of BMP4. All of them expressed bovine POU domain class 5 transcription factor 1 and caudal-type homeobox 2. The expression of these genes was confirmed by quantitative RT-PCR and immunohistochemical detection. These results suggest that BMP4 is involved in the raising of trophoblast cell lines from early embryonic cells and the newly developed cell lines can provide different types of bovine trophoblastic cells with different cell lineages. This may constitute a significant new tool for the examination of trophoblastic differentiation.

Specificity protein-1 and -3 trans-activate the ovine placental lactogen gene promoter

The proximal promoter (-383/+16) of the ovine placental lactogen (oPL) gene provides trophoblast-specific expression in vitro. Footprint 6 (FP6; -319/-349) lies within this region, and transfection of two-base pair mutations across FP6 into BeWo cells identified potential binding sites for CCAAT-enhancer binding protein (CEBP) and specificity proteins (Sp). Transfection of CEBP dominant negative or over-expression constructs did not impact transactivation of the proximal promoter. However, Sp1 and Sp3 over-expression constructs increased (p<or=0.05) transactivation. Additionally, Sp1 and Sp3 short-hairpin RNA constructs reduced (p<or=0.01) transactivation of the proximal promoter. In EMSA supershift assays, Sp1 and Sp3 antibodies were able to inhibit migration of the complexes formed with nuclear extracts from BeWo cells and ovine chorionic binucleate cells (oBNC). Furthermore, Southwestern analysis of oBNC nuclear extracts identified a nuclear protein corresponding with Sp3, identified by Western analysis. In conclusion, these results indicate that Sp1 and Sp3 are capable of interacting with FP6 of the oPL gene proximal promoter and function to enhance its transactivation.

Multiple roles for Puralpha in cellular and viral regulation

Pur-alpha is a ubiquitous multifunctional protein that is strongly conserved throughout evolution, binds to both DNA and RNA and functions in the initiation of DNA replication, control of transcription and mRNA translation. In addition, it binds to several cellular regulatory proteins including the retinoblastoma protein, E2F-1, Sp1, YB-1, cyclin T1/Cdk9 and cyclin A/Cdk2. These observations and functional studies provide evidence that Puralpha is a major player in the regulation of the cell cycle and oncogenic transformation. Puralpha also binds to viral proteins such as the large T-antigen of JC virus (JCV) and the Tat protein of human immunodeficiency virus-1 (HIV-1) and plays a role in the cross-communication of these viruses in the opportunistic polyomavirus JC (JCV) brain infection, progressive multifocal leukoencephalopathy (PML). The creation of transgenic mice with inactivation of the PURA gene that encodes Puralpha has revealed that Puralpha is critical for postnatal brain development and has unraveled an essential role of Puralpha in the transport of specific mRNAs to the dendrites and the establishment of the postsynaptic compartment in the developing neurons. Finally, the availability of cell cultures from the PURA knockout mice has allowed studies that have unraveled a role for Puralpha in DNA repair.

Nucleoprotein interactions governing cell type-dependent repression of the mouse smooth muscle alpha-actin promoter by single-stranded DNA-binding proteins Pur alpha and Pur beta

Pur alpha and Pur beta are structurally related single-stranded DNA/RNA-binding proteins implicated in the control of cell growth and differentiation. The goal of this study was to determine whether Pur alpha and Pur beta function in a redundant, distinct, or collaborative manner to suppress smooth muscle alpha-actin gene expression in cell types relevant to wound repair and vascular remodeling. RNA interference-mediated loss-of-function analyses revealed that, although Pur beta was the dominant repressor, the combined action of endogenous Pur alpha and Pur beta was necessary to fully repress the full-length smooth muscle alpha-actin promoter in cultured fibroblasts but to a lesser extent in vascular smooth muscle cells. The activity of a minimal core enhancer containing a truncated 5' Pur repressor binding site was unaffected by knockdown of Pur alpha and/or Pur beta in fibroblasts. Conversely, gain-of-function studies indicated that Pur alpha or Pur beta could each independently repress core smooth muscle alpha-actin enhancer activity albeit in a cell type-dependent fashion. Biochemical analyses indicated that purified recombinant Pur alpha and Pur beta were essentially identical in terms of their binding affinity and specificity for GGN repeat-containing strands of several cis-elements comprising the core enhancer. However, Pur alpha and Pur beta exhibited more distinctive protein interaction profiles when evaluated for binding to enhancer-associated transcription factors in extracts from fibroblasts and vascular smooth muscle cells. These findings support the hypothesis that Pur alpha and Pur beta repress smooth muscle alpha-actin gene transcription by means of DNA strand-selective cis-element binding and cell type-dependent protein-protein interactions.

Puralpha activates PDGF-A gene transcription via interactions with a G-rich, single-stranded region of the promoter

Transcription of the PDGF-A chain gene is regulated by multiple promoter and silencer elements that are GC-rich and exhibit considerable single-stranded character. In this study, the 42 kDa single-stranded DNA and RNA binding protein, Puralpha, was investigated with respect to its ability to bind and interact functionally with single-stranded DNA elements in the PDGF-A gene. Recombinant GST-Puralpha bound with high affinity and sequence-specificity to the G-rich strands of two such transcriptional control elements, the 5'-S1 nuclease-hypersensitive silencer (5'SHS; -1418 to -1388) and the nuclease-hypersensitive element (NHE; -92 to -48). Ethylation interference footprinting localized binding of Puralpha to a region between nucleotides -91 and -77 within the NHE element, which contains binding sites for the double-stranded DNA-binding transcription factors Sp1, EGR-1 and WT1. Forced expression of Puralpha upregulated transcriptional activity of the PDGF-A promoter but not the 5'SHS silencer in HepG2 cells, demonstrating Puralpha has the potential to activate PDGF-A gene expression. Targeted disruption of the Puralpha gene reduced NHE activity and PDGF-A mRNA expression in mouse embryo fibroblasts, consistent with a physiological role for Puralpha in maintaining optimal transcription of the PDGF-A gene. These results indicate Puralpha enhances transcription of the PDGF-A gene through its interactions with single-stranded, G-rich strands in the promoter, perhaps by stabilizing non-B-form DNA conformations.