Transcriptional Regulatory Functions of Heterogeneous Nuclear Ribonucleoprotein-U and -A/B in Endotoxin-Mediated Macrophage Expression of Osteopontin

RNA Binding Proteins that Mediate LPS-induced Alternative Splicing of the MyD88 Innate Immune Regulator

Inflammation driven by Toll-like receptor (TLR) signaling pathways is required to combat infection. However, inflammation can damage host tissues; thus it is essential that TLR signaling ultimately is terminated to prevent chronic inflammatory disorders. One mechanism that terminates persistent TLR signaling is alternative splicing of the MyD88 signaling adaptor, which functions in multiple TLR signaling pathways. While the canonical long isoform of MyD88 (MyD88-L) mediates TLR signaling and promotes inflammation, an alternatively-spliced shorter isoform of MyD88 (MyD88-S) produces a dominant negative inhibitor of TLR signaling. MyD88-S production is induced by inflammatory agonists including lipopolysaccharide (LPS), and thus MyD88-S induction is thought to act as a negative feedback loop that prevents chronic inflammation. Despite the potential role that MyD88-S production plays in inflammatory disorders, the mechanisms controlling MyD88 alternative splicing remain unclear. Here, we identify two RNA binding proteins, SRSF1 and HNRNPU, that regulate LPS-induced alternative splicing of MyD88.

Osteopontin: A Bone-Derived Protein Involved in Rheumatoid Arthritis and Osteoarthritis Immunopathology

Osteopontin (OPN) is a bone-derived phosphoglycoprotein related to physiological and pathological mechanisms that nowadays has gained relevance due to its role in the immune system response to chronic degenerative diseases, including rheumatoid arthritis (RA) and osteoarthritis (OA). OPN is an extracellular matrix (ECM) glycoprotein that plays a critical role in bone remodeling. Therefore, it is an effector molecule that promotes joint and cartilage destruction observed in clinical studies, in vitro assays, and animal models of RA and OA. Since OPN undergoes multiple modifications, including posttranslational changes, proteolytic cleavage, and binding to a wide range of receptors, the mechanisms by which it produces its effects, in some cases, remain unclear. Although there is strong evidence that OPN contributes significantly to the immunopathology of RA and OA when considering it as a common denominator molecule, some experimental trial results argue for its protective role in rheumatic diseases. Elucidating in detail OPN involvement in bone and cartilage degeneration is of interest to the field of rheumatology. This review aims to provide evidence of the OPN’s multifaceted role in promoting joint and cartilage destruction and propose it as a common denominator of AR and OA immunopathology.

Angiotensin II-Induced Long Non-Coding RNA Alivec Regulates Chondrogenesis in Vascular Smooth Muscle Cells

Long non-coding RNAs (lncRNAs) play key roles in Angiotensin II (AngII) signaling but their role in chondrogenic transformation of vascular smooth muscle cells (VSMCs) is unknown. We describe a novel AngII-induced lncRNA Alivec (Angiotensin II-induced lncRNA in VSMCs eliciting chondrogenic phenotype) implicated in VSMC chondrogenesis. In rat VSMCs, Alivec and the nearby gene Acan, a chondrogenic marker, were induced by growth factors AngII and PDGF and the inflammatory cytokine TNF-α. AngII co-regulated Alivec and Acan through the activation of AngII type1 receptor signaling and Sox9, a master transcriptional regulator of chondrogenesis. Alivec knockdown with GapmeR antisense-oligonucleotides attenuated the expression of AngII-induced chondrogenic marker genes, including Acan, and inhibited the chondrogenic phenotype of VSMCs. Conversely, Alivec overexpression upregulated these genes and promoted chondrogenic transformation. RNA-pulldown coupled to mass-spectrometry identified Tropomyosin-3-alpha and hnRNPA2B1 proteins as Alivec-binding proteins in VSMCs. Furthermore, male rats with AngII-driven hypertension showed increased aortic expression of Alivec and Acan. A putative human ortholog ALIVEC, was induced by AngII in human VSMCs, and this locus was found to harbor the quantitative trait loci affecting blood pressure. Together, these findings suggest that AngII-regulated lncRNA Alivec functions, at least in part, to mediate the AngII-induced chondrogenic transformation of VSMCs implicated in vascular dysfunction and hypertension.

Controlling TIME: How MNK Kinases Function to Shape Tumor Immunity

A number of studies have clearly established the oncogenic role for MAPK-interacting protein kinases (MNK) in human malignancies. Modulation of MNK activity affects translation of mRNAs involved in cancer development, progression, and resistance to therapies. As a result, there are ongoing efforts to develop and evaluate MNK inhibitors for cancer treatment. However, it is important to recognize that MNK activity also plays an important role in regulating the innate and adaptive immune systems. A better understanding of the role of MNK kinases and MNK-mediated signals in regulating the immune system could help mitigate undesired side effects while maximizing therapeutic efficacy of MNK inhibitors. Here, we provide a systematic review on the function of MNK kinases and their substrates in immune cells.

HnRNPA1 interacts with G-quadruplex in the TRA2B promoter and stimulates its transcription in human colon cancer cells

The human TRA2B gene consists of 10 exons and 9 introns and produces 5 splice isoforms (TRA2β1 to TRA2β5). TRA2B exon 2 encodes multiple premature termination codons. TRA2β1 lacks exon 2 and is translated into a functional transformer 2β (Tra2β) protein, whereas TRA2β4 contains 10 exons and works as a functional RNA. Overexpressed Tra2β and ectopic expression of TRA2β4 may be oncogenic. We found that heterogeneous nuclear ribonucleoprotein (hnRNP)A1 and hnRNPU interacted with TRA2β4 exon 2. Minigene assays revealed that hnRNPA1 facilitated inclusion of exon 2, whereas hnRNPU promoted its skipping. However, knockdown of hnRNPA1 or hnRNPU reduced both TRA2β1 and TRA2β4 levels, and overexpression of these hnRNPs increased levels of both isoforms, suggesting that hnRNPA1 and hnRNPU mainly regulate the transcription of TRA2B. In fact, hnRNPA1 and hnRNPU positively regulated the promoter activity of TRA2B. Circular dichroism analyses, electrophoretic mobility shift assays and chromatin immunoprecipitation assays demonstrated the presence of G-quadruplex (G4) formation in the promoter of TRA2B. Formation of G4 suppressed TRA2B transcription, whereas hnRNPA1, but not hnRNPU, interacted with the G4 to facilitate transcription. Our results suggest that hnRNPA1 may modulate TRA2B transcription through its regulation of G4 formation in its promoter in colon cancer cells.

Regulatory Roles of Osteopontin in Production of Monocyte-Origin MCP-1

Osteopontin (OPN), expressed by various immune cells, plays a critical role in leukocyte migration. Although OPN was found to selectively induce the expression of proinflammatory chemokines, the molecular mechanisms that control OPN gene expression and its underlying mechanism for migration and recruitment of inflammatory cells remain largely unknown. In this study, real-time polymerase chain reaction and enzyme-linked immunosorbent assay were used to determine OPN and monocyte chemoattractant protein 1 (MCP-1) expression. Signaling and molecular events between OPN and MCP-1 were analyzed by Western blot. Leukocyte migration in the presence of OPN was measured by chemotaxis assay. Our data indicated that phosphoinositide 3-kinase (PI3K), c-Jun NH2-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) that are activated upon stimulation with lipopolysaccharide were shown to upregulate OPN expression. Endogenous production of OPN was attributable to increased production of MCP-1, and this effect could be blocked by an anti-β1 integrin antibody and JNK and p38 kinase inhibitors. Furthermore, we found that the effect of OPN on inflammatory cell migration was mediated through inducing the expression of MCP-1 in monocytes. These results support a role of OPN in monocyte migration via MCP-1, which may represent an additional mechanism for innate and adaptive immune responses.

Growth arrest-specific protein 7 regulates the murine M1 alveolar macrophage polarization

Growth arrest-specific gene 7 (Gas7) is preferentially expressed in terminally differentiated brain cells and plays a crucial role during neuronal development and neurite outgrowth. Apart from that, Gas7 was found to be abundantly expressed in immune cells like murine macrophage without knowing the actual roles in immune reaction. By using the Illumina microarray analysis, we observed a clear induction of Gas7 but no other Gas family members in murine M1-polarized alveolar macrophage, which was further confirmed by RT-qPCR, Western blotting, and immunostaining analysis, suggesting a likelihood that Gas7 may participate in murine alveolar macrophage polarization. Moreover, we found that the upregulation of Gas7 in M1-polarized alveolar macrophage was almost fully blocked by IKK selective inhibitor BMS, which links Gas7 induction to nuclear factor kappa beta (NF-κB) signaling activation. Interestingly, we found that Gas7 knockdown by small interfering RNA transfection did not affect the pro-inflammatory cytokine gene Tnf and Ilb expression, whereas the expressions of canonic M1 marker gene Nos2 and other M1-dependent genes Il12b, Il6, Cxcl1, Cxcl2, and Cxcl9 were found to be reduced. Furthermore, Gas7-related M1 gene expression in alveolar macrophage was not dependent on NF-κB and STAT1 pathway. Our results demonstrate that Gas7 is potentially involved in regulation of murine M1 alveolar macrophage polarization.

HIGHLIGHTS

Gas7 was induced in LPS/IFNγ mediated M1 polarization. Gas7 are induced during time course of M1 polarization. Gas7 upregulation was dependent on NF-κB pathway in M1 polarized AMs. Gas7 knockdown reduced the M1 markers gene expression in M1 polarized AMs.

Viral DNA Replication Orientation and hnRNPs Regulate Transcription of the Human Papillomavirus 18 Late Promoter

The life cycle of human papillomaviruses (HPVs) is tightly linked to keratinocyte differentiation. Although expression of viral early genes is initiated immediately upon virus infection of undifferentiated basal cells, viral DNA amplification and late gene expression occur only in the mid to upper strata of the keratinocytes undergoing terminal differentiation. In this report, we show that the relative activity of HPV18 TATA-less late promoter P₈₁₁ depends on its orientation relative to that of the origin (Ori) of viral DNA replication and is sensitive to the eukaryotic DNA polymerase inhibitor aphidicolin. Additionally, transfected 70-nucleotide (nt)-long single-strand DNA oligonucleotides that are homologous to the region near Ori induce late promoter activity. We also found that promoter activation in raft cultures leads to production of the late promoter-associated, sense-strand transcription initiation RNAs (tiRNAs) and splice-site small RNAs (spliRNAs). Finally, a cis-acting AAGTATGCA core element that functions as a repressor to the promoter was identified. This element interacts with hnRNP D0B and hnRNP A/B factors. Point mutations in the core prevented binding of hnRNPs and increased the promoter activity. Confirming this result, knocking down the expression of both hnRNPs in keratinocytes led to increased promoter activity. Taking the data together, our study revealed the mechanism of how the HPV18 late promoter is regulated by DNA replication and host factors.

It has been known for decades that the activity of viral late promoters is associated with viral DNA replication among almost all DNA viruses. However, the mechanism of how DNA replication activates the viral late promoter and what components of the replication machinery are involved remain largely unknown. In this study, we characterized the P₈₁₁ promoter region of HPV18 and demonstrated that its activation depends on the orientation of DNA replication. Using single-stranded oligonucleotides targeting the replication fork on either leading or lagging strands, we showed that viral lagging-strand replication activates the promoter. We also identified a transcriptional repressor element located upstream of the promoter transcription start site which interacts with cellular proteins hnRNP D0B and hnRNP A/B and modulates the late promoter activity. This is the first report on how DNA replication activates a viral late promoter.

Osteopontin: A novel regulator at the cross roads of inflammation, obesity and diabetes

Since its first description more than 20 years ago osteopontin has emerged as an active player in many physiological and pathological processes, including biomineralization, tissue remodeling and inflammation. As an extracellular matrix protein and proinflammatory cytokine osteopontin is thought to facilitate the recruitment of monocytes/macrophages and to mediate cytokine secretion in leukocytes. Modulation of immune cell response by osteopontin has been associated with various inflammatory diseases and may play a pivotal role in the development of adipose tissue inflammation and insulin resistance. Here we summarize recent findings on the role of osteopontin in metabolic disorders, particularly focusing on diabetes and obesity.

A long noncoding RNA mediates both activation and repression of immune response genes

An inducible program of inflammatory gene expression is central to antimicrobial defenses. This response is controlled by a collaboration involving signal-dependent activation of transcription factors, transcriptional co-regulators, and chromatin-modifying factors. We have identified a long noncoding RNA (lncRNA) that acts as a key regulator of this inflammatory response. Pattern recognition receptors such as the Toll-like receptors induce the expression of numerous lncRNAs. One of these, lincRNA-Cox2, mediates both the activation and repression of distinct classes of immune genes. Transcriptional repression of target genes is dependent on interactions of lincRNA-Cox2 with heterogeneous nuclear ribonucleoprotein A/B and A2/B1. Collectively, these studies unveil a central role of lincRNA-Cox2 as a broad-acting regulatory component of the circuit that controls the inflammatory response.

Nuclear to cytoplasmic translocation of heterogeneous nuclear ribonucleoprotein U enhances TLR-induced proinflammatory cytokine production by stabilizing mRNAs in macrophages

TLR signaling is associated with the transcription of various proinflammatory cytokines, including TNF-α, IL-6, and IL-1β. After transcription, the mRNA of these proinflammatory cytokines needs to be tightly controlled at the posttranscriptional level to achieve an optimal expression. However, the precise mechanism of posttranscriptional regulation is not fully understood. In the current study, we found the expression of heterogeneous nuclear ribonucleoprotein U (hnRNP U), also termed scaffold attachment factor A, was greatly induced by TLR stimulation in macrophages. Knockdown of hnRNP U expression greatly attenuated TLR-induced expression of TNF-α, IL-6, and IL-1β, but not IL-12, whereas hnRNP U overexpression greatly increased TLR-induced expression of TNF-α, IL-6, and IL-1β. Furthermore, hnRNP U knockdown accelerated the turnover and decreased the t(1/2) of TNF-α, IL-6, and IL-1β mRNA. RNA immunoprecipitation demonstrated that hnRNP U bound to the mRNA of these proinflammatory cytokines through the RGG motif. Importantly, we showed that TLR stimulation provided a stimulus for hnRNP U nuclear to cytoplasmic translocation. Therefore, we propose that hnRNP U induced by TLR signaling binds to the mRNA of a subset of proinflammatory cytokines and positively regulates the expression of these cytokines by stabilizing mRNA.

S-nitrosylation in the regulation of gene transcription

BACKGROUND

Post-translational modification of proteins by S-nitrosylation serves as a major mode of signaling in mammalian cells and a growing body of evidence has shown that transcription factors and their activating pathways are primary targets. S-nitrosylation directly modifies a number of transcription factors, including NF-κB, HIF-1, and AP-1. In addition, S-nitrosylation can indirectly regulate gene transcription by modulating other cell signaling pathways, in particular JNK kinase and ras.

SCOPE OF REVIEW

The evolution of S-nitrosylation as a signaling mechanism in the regulation of gene transcription, physiological advantages of protein S-nitrosylation in the control of gene transcription, and discussion of the many transcriptional proteins modulated by S-nitrosylation is summarized.

MAJOR CONCLUSIONS

S-nitrosylation plays a crucial role in the control of mammalian gene transcription with numerous transcription factors regulated by this modification. Many of these proteins serve as immunomodulators, and inducible nitric oxide synthase (iNOS) is regarded as a principal mediatiator of NO-dependent S-nitrosylation. However, additional targets within the nucleus (e.g. histone deacetylases) and alternative mechanisms of S-nitrosylation (e.g. GAPDH-mediated trans-nitrosylation) are thought to play a role in NOS-dependent transcriptional regulation.

GENERAL SIGNIFICANCE

Derangement of SNO-regulated gene transcription is an important factor in a variety of pathological conditions including neoplasia and sepsis. A better understanding of protein S-nitrosylation as it relates to gene transcription and the physiological mechanisms behind this process is likely to lead to novel therapies for these disorders. This article is part of a Special Issue entitled Regulation of Cellular Processes by S-nitrosylation.

Osteopontin in macrophage function

The secreted phosphorylated protein osteopontin (OPN) is expressed in a variety of tissues and bodily fluids, and is associated with pathologies including tissue injury, infection, autoimmune disease and cancer. Macrophages are ubiquitous, heterogeneous cells that mediate aspects of cell and tissue damage in all these pathologies. Here, the role of OPN in macrophage function is reviewed. OPN is expressed in macrophage cells in multiple pathologies, and the regulation of its expression in these cells has been described in vitro. The protein has been implicated in multiple functions of macrophages, including cytokine expression, expression of inducible nitric oxide synthase, phagocytosis and migration. Indeed, the role of OPN in cells of the macrophage lineage might underlie its physiological role in many pathologies. However, there are numerous instances where the published literature is inconsistent, especially in terms of OPN function in vitro. Although the heterogeneity of OPN and its receptors, or of macrophages themselves, might underlie some of these inconsistencies, it is important to understand the role of OPN in macrophage biology in order to exploit its function therapeutically.

NF-κB- and AP-1-mediated DNA looping regulates osteopontin transcription in endotoxin-stimulated murine macrophages

Osteopontin (OPN) is expressed by various immune cells and modulates both innate and adaptive immune responses. However, the molecular mechanisms that control opn gene expression, especially at the chromatin level, remain largely unknown. We have previously demonstrated many specific cis- and trans-regulatory elements that determine the extent of endotoxin (LPS)-mediated induction of OPN synthesis in murine macrophages. In the present study, we confirm that NF-κB also plays an important role in the setting of LPS-stimulated OPN expression through binding to a distal regulatory element. Importantly, we demonstrate that LPS stimulates chromosomal loops in the OPN promoter between NF-κB binding site and AP-1 binding site using chromosome conformation capture technology. The crucial role of NF-κB and AP-1 in LPS-stimulated DNA looping was confirmed, as small interfering RNA knock-down of NF-κB p65 and AP-1 c-Jun exhibited decreased levels of DNA looping. Furthermore, we demonstrate that p300 can form a complex with NF-κB and AP-1 and is involved in DNA looping and LPS-induced OPN expression. Therefore, we have identified an essential mechanism to remodel the local chromatin structures and spatial conformations to regulate LPS-induced OPN expression.

SAF-A has a role in transcriptional regulation of Oct4 in ES cells through promoter binding

Methodologies to reprogram somatic cells into patient-specific pluripotent cells, which could potentially be used in personalized drug discovery and cell replacement therapies, are currently under development. Oct4 activation is essential for successful reprogramming and pluripotency of embryonic stem (ES) cells, albeit molecular details of Oct4 activation are not completely understood. Here we report that endogenous SAF-A is involved in regulation of Oct4 expression, binds the Oct4 proximal promoter in ES cells, and dissociates from the promoter upon early differentiation induced by LIF withdrawal. Depletion of SAF-A decreases Oct4 expression even in the presence of LIF, and results in an increase of the mesodermal marker Brachyury. The overexpression of wild-type human SAF-A rescues the mouse knock-down phenotype and results in increased Oct4 level. We also demonstrate that endogenous SAF-A interacts with the C-terminal domain (CTD) of endogenous RNA polymerase II and that the interaction is independent of CTD phosphorylation and mRNA. Moreover, we show that SAF-A exist in complexes with transcription factors Sox2 and Oct4 as well as STAT3 in ES cells. The number of endogenous SAF-A:Oct4 and SAF-A:Sox2 complexes decreases upon LIF depletion. These discoveries allow us to propose a model for activation of Oct4 transcription.

DNA-protein cross-linking by 1,2,3,4-diepoxybutane

1,2,3,4-diepoxybutane (DEB) is a strongly genotoxic diepoxide hypothesized to be the ultimate carcinogenic metabolite of the common industrial chemical and environmental carcinogen 1,3-butadiene. DEB is a bis-electrophile capable of cross-linking cellular biomolecules to form DNA-DNA and DNA-protein cross-links (DPCs), which are thought to play a central role in its biological activity. Previous studies with recombinant proteins have shown that the biological outcomes of DEB-induced DPCs are strongly influenced by protein identities. The present work combines affinity capture methodology with mass spectrometry-based proteomics and immunological detection to identify the proteins that form DPCs in nuclear extracts from human cervical carcinoma (HeLa) cells. We identified 39 human proteins that form covalent DPCs in the presence of DEB. DNA-protein cross-linking efficiency following treatment with 25 mM DEB was 2-12%, depending on protein identity. High-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI+-MS/MS) analysis of the total proteolytic digests of cross-linked proteins revealed the presence of 1-(S-cysteinyl)-4-(guan-7-yl)-2,3-butanediol conjugates, suggesting that DEB forms DPCs between cysteine thiols within proteins and the N-7 guanine positions within DNA.

S-alkylating labeling strategy for site-specific identification of the s-nitrosoproteome

S-nitrosylation, a post-translational modification of cysteine residues induced by nitric oxide, mediates many physiological functions. Due to the labile nature of S-nitrosylation, detection by mass spectrometry (MS) is challenging. Here, we developed an S-alkylating labeling strategy using the irreversible biotinylation on S-nitrosocysteines for site-specific identification of the S-nitrosoproteome by LC-MS/MS. Using COS-7 cells without endogenous nitric oxide synthase, we demonstrated that the S-alkylating labeling strategy substantially improved the blocking efficiency of free cysteines, minimized the false-positive identification caused by disulfide interchange, and increased the digestion efficiency for improved peptide identification using MS analyses. Using this strategy, we identified total 586 unique S-nitrosylation sites corresponding to 384 proteins in S-nitroso-N-acetylpenicillamine (SNAP)/l-cysteine-treated mouse MS-1 endothelial cells, including 234 previously unreported S-nitrosylated proteins. When the topologies of 84 identified transmembrane proteins were further analyzed, their S-nitrosylation sites were found to mostly face the cytoplasmic side, implying that S-nitrosylation occurs in the cytoplasm. In addition to the previously known acid/basic motifs, the ten deduced consensus motifs suggested that combination of local hydrophobicity and acid/base motifs in the tertiary structure contribute to the specificity of S-nitrosylation. Moreover, the S-nitrosylated cysteines showed preference on beta-strand, having lower relative surface accessibility at the S-nitrosocysteines.

Characterization of nuclear factors modulating the apolipoprotein D promoter during growth arrest: implication of PARP-1, APEX-1 and ERK1/2 catalytic activities

Human Apolipoprotein D (apoD) is upregulated under several stress conditions and pathological situations such as neurodegenerative diseases and cancers. We previously showed that apoD mRNA expression is induced in growth-arrested cells and demonstrated the specific binding of nuclear proteins to the region −514 to −475 of the promoter. Such region contains a pair of Serum Responsive Elements (SRE), an Ets-Binding Site (EBS) and a Glucocorticoid Responsive Element (GRE). In this study, we show that Parp-1, HnRNP-U, CBF-A, BUB-3, Kif4, APEX-1 and Ifi204 bind these regulatory elements of the apoD promoter. Specific binding of HnRNP-U and Parp-1 was confirmed by Electrophoretic Mobility Shift Assay (EMSA). In a biotin pull-down assay, Kif4 and BUB-3 bind preferentially the SRE1 and the EBS-GRE sites, respectively, while APEX-1 seems recruited indirectly to these elements. We found that the mRNA expression of some of these binding factors is upregulated in growth-arrested cells and that these proteins also transactivate the apoD promoter. In agreement with these results, mutants of APEX-1 and of Parp-1 defective for their DNA-binding and catalytic activities could not transactivate the promoter. The knockdown of Parp-1 and HnRNP-U and the use of specific inhibitors of MEK1/2 and of Parp-1 also inhibited the induction of apoD gene expression. Moreover, ERK1/2 was found activated in a biphasic manner post serum-starvation and the inhibition of Parp-1 causes a sustained activation of ERK2 but not ERK1 for up to 2 h. Altogether, these findings demonstrate the importance of Parp-1, APEX-1 and ERK1/2 catalytic activities in the growth arrest-induced apoD gene expression.

Differential expression of intracellular and secreted osteopontin isoforms by murine macrophages in response to toll-like receptor agonists

Osteopontin (OPN), expressed by various immune cells, modulates both innate and adaptive immune responses. Different immune cells have shown differential expression of the two isoforms of OPN: secreted form of OPN (sOPN) and intracellular form of OPN (iOPN). However, the molecular mechanisms that control opn gene expression and the OPN isoforms produced by immune cells remain largely unknown. In this study, we demonstrate that OPN mRNA and protein expression are significantly up-regulated upon stimulation with TLR agonists in macrophages. Interestingly, we find that macrophages constitutively express the secreted form of OPN (sOPN), while the intracellular form of OPN (iOPN) is induced following the stimulation with TLR agonists. Phosphoinositide 3-kinase (PI3K), extracellular signal-regulated kinase (ERK), and c-Jun NH(2)-terminal kinase (JNK) that are activated by LPS stimulation were shown to upregulate OPN expression. In addition, chromatin immunoprecipitation (CHIP) assays showed that AP-1 binds to the proximal AP-1 site in the OPN promoter from LPS-stimulated macrophages. Mutation of the AP-1 site in OPN promoter completely ablates LPS-induced OPN promoter activation. Knockdown of c-Jun and c-Fos expression by small interfering RNA (siRNA) significantly decreases LPS-induced OPN expression. Stable cell lines with iOPN overexpression and knockdown showed that TLR-induced iOPN expression is a negative regulator for interferon-beta (IFN-beta) production. Our findings provide new insight into the transcriptional regulation of opn gene and further clarify the isoforms and functions of OPN produced by macrophages.

Laser capture microdissection and genetic analysis of carbon-labeled Kupffer cells

AIM: To develop a method of labeling and micro-dissecting mouse Kupffer cells within an extraordinarily short period of time using laser capture microdissection (LCM).

METHODS: Tissues are complex structures comprised of a heterogeneous population of interconnected cells. LCM offers a method of isolating a single cell type from specific regions of a tissue section. LCM is an essential approach used in conjunction with molecular analysis to study the functional interaction of cells in their native tissue environment. The process of labeling and acquiring cells by LCM prior to mRNA isolation can be elaborate, thereby subjecting the RNA to considerable degradation. Kupffer cell labeling is achieved by injecting India ink intravenously, thus circumventing the need for in vitro staining. The significance of this novel approach was validated using a cholestatic liver injury model.

RESULTS: mRNA extracted from the microdissected cell population displayed marked increases in colony-stimulating factor-1 receptor and Kupffer cell receptor message expression, which demonstrated Kupffer cell enrichment. Gene expression by Kupffer cells derived from bile-duct-ligated, versus sham-operated, mice was compared. Microarray analysis revealed a significant (2.5-fold, q value < 10) change in 493 genes. Based on this fold-change and a standardized PubMed search, 10 genes were identified that were relevant to the ability of Kupffer cells to suppress liver injury.

CONCLUSION: The methodology outlined herein provides an approach to isolating high quality RNA from Kupffer cells, without altering the tissue integrity.

DcpS as a therapeutic target for spinal muscular atrophy

Spinal muscular atrophy (SMA) is caused by deletion or mutation of both copies of the SMN1 gene, which produces an essential protein known as SMN. The severity of SMA is modified by variable copy number of a second gene,SMN2, which produces an mRNA that is incorrectly spliced with deletion of the last exon. We described previously the discovery of potent C5-substituted quinazolines that increase SMN2 gene expression by 2-fold. Discovery of potent SMN2 promoter inducers relied on a cellular assay without knowledge of the molecular target. Using protein microarray scanning with a radiolabeled C5-substituted quinazoline probe, we identified the scavenger decapping enzyme, DcpS, as a potential binder. We show that the C5-substituted quinazolines potently inhibit DcpS decapping activity and that the potency of inhibition correlates with potency forSMN2 promoter induction. Binding of C5-substituted quinazolines to DcpS holds the enzyme in an open, catalytically incompetent conformation. DcpS is a nuclear shuttling protein that binds and hydrolyzes the m(7)GpppN mRNA cap structure and a modulator of RNA metabolism. Therefore DcpS represents a novel therapeutic target for modulating gene expression by a small molecule.

Back to the future: a new look at 'old' vitamin D

Our perception of the vitamin D system continues to evolve. Recent studies have re-evaluated the parameters for adequate vitamin D status in humans, revealing a high prevalence of insufficiency in many populations throughout the world. Other reports have highlighted the potential consequences of vitamin D insufficiency beyond established effects on bone homeostasis. Most notably, there is now strong evidence of a role for vitamin D in modulating innate and adaptive immunities, with insufficiency being linked to infectious disease and other immune disorders. To date, signaling pathways for these new responses to vitamin D have been based on established endocrine models for active 1,25-dihydroxyvitamin D, despite present evidence for more localized, intracrine modes of action. In the following review, we provide a fresh perspective on vitamin D signaling in non-classical target cells such as macrophages by highlighting novel factors associated with the transport and action of this pluripotent secosteroid.

RNA stability regulates differential expression of the metastasis protein, osteopontin, in hepatocellular cancer

BACKGROUND

Osteopontin (OPN) is a potential therapeutic target in hepatocellular carcinoma (HCC), because it is a critical mediator of metastatic function. The molecular mechanisms that determine expression of OPN in HCC, however, are unknown. In this study, we examine differential OPN expression in the 2 HCC cell lines: HepG2 and Hep3B.

METHODS

OPN expression, metastatic function, OPN promoter activity, and active transcription of OPN mRNA and its decay were assessed in the 2 HCC cell lines using standard techniques. RNA gel-shift assays were performed to determine binding of cytoplasmic proteins to OPN mRNA.

RESULTS

Expression of OPN cellular/secreted protein and mRNA was greater in HepG2 than Hep3B cells (P < .01). Transient transfection of the OPN promoter construct demonstrated equivalent luciferase activities in the 2 cell lines; the rate of transcription was also equivalent as determined by chromatin immuno-precipitation assay. OPN mRNA half-life was 21 +/- 1 h and 3 +/- 1 h in HepG2 and Hep3B, respectively (P < .02). In HepG2 and Hep3B, the nucleotide sequence of OPN and its 5'-UTR, 3'-UTR, and poly (A) tail lengths were identical. A luciferase construct coupled in line with OPN-5'-UTR and OPN 3'-UTR presented greater expression in HepG2 (P < .01 vs Hep3B). Deletion of nt 10-57 of the OPN 5'-UTR restored luciferase and HA-tagged OPN protein expression in Hep3B but not in Hep G2. RNA gel-shift assays demonstrate different patterns of protein binding to OPN 5'-UTR between the 2 HCC cell lines.

CONCLUSIONS

We conclude that RNA stability is a new, previously unrecognized mechanism that regulates OPN expression in HCC to convey metastatic function.

Osteopontin: regulation in tumor metastasis

Osteopontin is a secreted phosphoprotein that has been implicated as an important mediator of tumor metastasis and has been investigated for use as a biomarker for advanced disease and as a potential therapeutic target in the regulation of cancer metastasis. The OPN DNA sequence is highly conserved and the protein contains several important functional domains including alpha(v)beta integrin and CD44 binding sites. High levels of OPN expression correlate with tumor invasion, progression or metastasis in multiple cancer. Studies demonstrate that osteopontin mediates the molecular mechanisms which determine metastatic spread, such as prevention of apoptosis, extracellular matrix proteolysis and remodeling, cell migration, evasion of host-immune cells and neovascularization. Transcriptional regulation of OPN is complex and involves multiple pathways, including AP-1, Myc, v-Src, Runx/CBF, TGF-B/BMPs/Smad/Hox, and Wnt/ss-catenin/APC/GSK-3ss/Tcf-4. The current state of knowledge of OPN biology suggests that it is an attractive target for therapeutic modulation of metastatic disease.

Pathophysiological role of osteopontin in hepatic inflammation, toxicity, and cancer

Osteopontin (OPN) is a highly modified integrin-binding extracellular matrix glycophosphoprotein produced by cells of the immune system, epithelial tissue, smooth muscle cells, osteoblasts, and tumor cells. Extensive research has elucidated the pivotal role of OPN in cell signaling that controls inflammation, tumor progression, and metastasis. OPN interaction with the integrin receptors expressed on inflammatory cells through its arginine-glycine-aspartate (RGD) and non-RGD motifs promote migration and adhesion of cells. In the liver, it has been reported that hepatic Kupffer cells secrete OPN facilitating macrophage infiltration into necrotic areas following carbon tetrachloride liver toxicity. Recent work has highlighted the role of OPN in inflammatory liver diseases such as alcoholic and nonalcoholic liver disease and T-cell-mediated hepatitis. The role of OPN in hepatocellular carcinoma (HCC) has also generated significant interest, especially with regards to its role as a prognostic factor. OPN therefore appears to play an important role during liver inflammation and cancer. In this review we will present data to demonstrate the key role played by OPN in mediating hepatic inflammation (neutrophils, monocytes/macrophages, and lymphocytes) and its role in HCC. Greater understanding of the pathophysiologic role of OPN in hepatic inflammation and cancer may enable development of novel inflammation and cancer treatment strategies.

Heterogeneous nuclear ribonucleoprotein A/B and G inhibits the transcription of gonadotropin-releasing-hormone 1

Gonadotropin-releasing hormone 1 (GnRH1) causes the release of gonadotropins from the pituitary to control reproduction. Here we report that two heterogeneous nuclear ribonucleoproteins (hnRNP-A/B and hnRNP-G) bind to the GnRH-I upstream promoter region in a cichlid fish Astatotilapia burtoni. We identified these binding proteins using a newly developed homology based method of mass spectrometric peptide mapping. We show that both hnRNP-A/B and hnRNP-G co-localize with GnRH1 in the pre-optic area of the hypothalamus in the brain. We also demonstrated that these ribonucleoproteins exhibit similar binding capacity in vivo, using immortalized mouse GT1-7 cells where overexpression of either hnRNP-A/B or hnRNP-G significantly down-regulates GnRH1 mRNA levels in GT1-7 cells, suggesting that both act as repressors in GnRH1 transcriptional regulation.

hnRNP proteins and splicing control

Proteins of the heterogeneous nuclear ribonucleoparticles (hnRNP) family form a structurally diverse group of RNA binding proteins implicated in various functions in metazoans. Here we discuss recent advances supporting a role for these proteins in precursor-messenger RNA (pre-mRNA) splicing. Heterogeneous nuclear RNP proteins can repress splicing by directly antagonizing the recognition of splice sites, or can interfere with the binding of proteins bound to enhancers. Recently, hnRNP proteins have been shown to hinder communication between factors bound to different splice sites. Conversely, several reports have described a positive role for some hnRNP proteins in pre-mRNA splicing. Moreover, cooperative interactions between bound hnRNP proteins may encourage splicing between specific pairs of splice sites while simultaneously hampering other combinations. Thus, hnRNP proteins utilize a variety of strategies to control splice site selection in a manner that is important for both alternative and constitutive pre-mRNA splicing.