A SAF binding site in the promoter region of human gamma-fibrinogen gene functions as an IL-6 response element

Incidence and risk factors of deep vein thrombosis in patients with spinal cord injury: a systematic review with meta-analysis

Background

Spinal cord injury (SCI) is a highly disabling disease with huge public health burden. The complications associated with it, especially deep vein thrombosis (DVT), further aggravate the disability.

Objective

To explore the incidence and risk factors of DVT after SCI, in order to provide guidance for disease prevention in the future.

Methods

A search was performed on PubMed, Web of Science, Embase, and Cochrane database up to November 9, 2022. Literature screening, information extraction and quality evaluation were performed by two researchers. The data was later combined by metaprop and metan commands in STATA 16.0.

Results

A total of 101 articles were included, including 223,221 patients. Meta-analysis showed that the overall incidence of DVT was 9.3% (95% CI: 8.2%-10.6%), and the incidence of DVT in patients with acute and chronic SCI was 10.9% (95% CI: 8.7%-13.2%) and 5.3% (95% CI: 2.2%-9.7%), respectively. The incidence of DVT decreased gradually with the accumulation of publication years and sample size. However, the annual incidence of DVT has increased since 2017. There are 24 kinds of risk factors that may contribute to the formation of DVT, involving multiple aspects of the baseline characteristics of the patient, biochemical indicators, severity of SCI, and comorbidities.

Conclusions

The incidence of DVT after SCI is high and has been gradually increasing in recent years. Moreover, there are numerous risk factors associated with DVT. Comprehensive preventive measures need to be taken as early as possible in the future.

Systematic Review Registration

www.crd.york.ac.uk/prospero, identifier CRD42022377466.

Hyponatremia in horses with septic pneumopathy

Background

Hyponatremia is common in horses with bacterial pleuropneumonia, but no further characterization of this abnormality has been reported.

Objectives

Describe admission plasma sodium concentration ([Na]) in horses with septic pneumopathy and evaluate any association of plasma [Na] with markers of systemic inflammation.

Animals

Medical records of horses >1 month of age that between 2008 and 2021 had a transtracheal aspirate (TTA) performed, abnormal TTA cytology, positive TTA culture, pulmonary disease on ultrasonography, radiography or both, and plasma [Na] assessed by direct ion‐selective‐electrode (dISE). Horses with concurrent diarrhea or azotemia were excluded.

Methods

Clinical and clinicopathological variables of interest between hypo‐ and normonatremic horses were compared. Spearman correlation and Fisher exact tests were used to identify significant associations (P < .05).

Results

Twenty of 35 horses had hyponatremia (median, 132 mmol/L; 25‐75th interquartile range [IQR], 129.7‐133.1 mmol/L; reference range, 134.2‐138.4 mmol/L). A higher proportion of horses with systemic inflammatory response syndrome (SIRS) had hyponatremia (P = .01). Hyponatremic patients had higher mean plasma fibrinogen concentration (461 ± 160.5 mg/dL; P = .01) and higher rectal temperature (38.8 ± 0.7°C; P = .02) than normonatremic horses. Negative correlations were found between plasma [Na] and fibrinogen (P = .001; ρ = −0.57) concentrations and between plasma [Na] and rectal temperature (P = .001; ρ = −0.51). Presence or absence of pleural effusion did not influence severity of hyponatremia. Mean duration of hospitalization was longer (P = .04) in hyponatremic horses (9.8 ± 6.6 days).

Conclusions and Clinical Importance

Hyponatremia at admission is associated with the presence of inflammation, SIRS, and with longer duration of hospitalization.

The Relevance of Noncoding DNA Variations of Paraoxonase Gene Cluster in Atherosclerosis-Related Diseases

The human paraoxonase (PON) gene cluster is comprised of three contiguous genes (PON1, PON2 and PON3) of presumably common origin coding three lactonases of highly similar structure and substrate specificity. The catalytic activity of PON proteins is directed toward artificial organophosphates and in physiological conditions toward thiolactones and oxidized phospholipids. Consequently, PON enzymes are regarded as an effective defense against oxidative stress and, as a result, against atherosclerosis development. Additionally, both PON's serum activity and its concentration are influenced by several polymorphic variations in coding and noncoding DNA regions of the PON gene cluster remaining in linkage disequilibrium. Hence, the genetic polymorphism of the PON gene cluster may contribute to atherosclerotic process progression or deceleration. In this review the authors analyzed the relevance of noncoding DNA polymorphic variations of PON genes in atherosclerosis-related diseases involving coronary and peripheral artery disease, stroke, diabetes mellitus, dementia and renal disease and concluded that the effect of PON gene cluster' polymorphism has a considerable impact on the course and outcome in these conditions. The following PON genetic variations may serve as additional predictors of the risk of atherosclerosis in selected populations and individuals.

Acute phase response to exertional heat stroke in mice

NEW FINDINGS

What is the central question of this study? Exertional heat stroke is accompanied by a marked inflammatory response. In this study, we explored the time course of acute phase proteins during recovery from severe heat stress in mice and the potential role of skeletal muscles as their source. What is the main finding and its importance? Exertional heat stroke transiently increased expression of acute phase proteins in mouse liver and plasma and depleted liver and plasma fibrinogen, a typical response to severe trauma. In contrast, skeletal muscle fibrinogen production was stimulated by heat stroke, which can provide an additional reservoir for fibrinogen supply to maintain the clotting potential throughout the body and locally within the muscle.

ABSTRACT

Exertional heat stroke (EHS), the most severe manifestation of heat illness, is accompanied by a marked inflammatory response. The release of acute phase proteins (APPs) is an important component of inflammation, which can assist in tissue survival/repair. The time course of APPs in recovery from EHS is unknown. Furthermore, skeletal muscles produce APPs during infection, but it is unknown whether they can produce APPs after EHS. Our objective was to determine the time course of representative APPs in liver, plasma and skeletal muscle during recovery from EHS. Male C57BL6/J mice ran in a forced running wheel at 37.5°C, 40% relative humidity until symptom limitation. Exercise control (EXC) mice ran for the same duration and intensity at 22.5°C. Samples were collected (n = 6-12 per group) over 14 days of recovery. Protein abundance was quantified using immunoblots. Total and phosphorylated STAT3 (pSTAT3) at Tyr705, responsible for APP activation, increased in liver at 0.5 h after EHS compared with EXC, (P < 0.05 and P < 0.001, respectively). In contrast, in tibialis anterior (TA) muscle, total STAT3 increased at 3 h (P < 0.05) but pSTAT3 (Tyr705) did not. Liver serum amyloid A1 (SAA1) increased at 3 and 24 h after EHS (P < 0.05), whereas plasma SAA1 increased only at 3 h (P < 0.05). SAA1 was not detected in TA muscle. In liver and plasma, fibrinogen decreased at 3 h (P < 0.01) and increased in TA muscle (P < 0.05). Lipocalin-2 was undetectable in liver or TA muscle. Recovery from EHS is characterized by a transient acute phase response in both liver and skeletal muscle. However, APP expression profiles and subtypes differ between skeletal muscle and liver.

Tigecycline Interferes with Fibrinogen Polymerization Independent of Peripheral Interactions with the Coagulation System

Tigecycline offers broad anti-bacterial coverage for critically ill patients with complicated infections. A described but less researched side effect is coagulopathy. The aim of this study was to test whether tigecycline interferes with fibrinogen polymerization by peripheral interactions. To study the effect of unmetabolized tigecycline, plasma of healthy volunteers were spiked with increasing concentrations of tigecycline. In a second experimental leg, immortalized human liver cells (HepG2) were treated with the same concentrations to test an inhibitory effect of hepatic tigecycline metabolites. Using standard coagulation tests, only the activated thromboplastin time in humane plasma was prolonged with increasing concentrations of tigecycline. Visualization of the fibrin network using confocal live microscopy demonstrated a qualitative difference in tigecycline treated experiments. Thrombelastometry and standard coagulation tests did not indicate an impairment of coagulation. Although the discrepancy between functional and immunologic fibrinogen levels increased in cell culture assays with tigecycline concentration, fibrinogen levels in spiked plasma samples did not show significant differences determined by functional versus immunologic methods. In our in vitro study, we excluded a direct effect of tigecycline in increasing concentrations on blood coagulation in healthy adults. Furthermore, we demonstrated a rapid loss of mitochondrial activity in hepatic cells with supra-therapeutic tigecycline dosages.

Revealing the alternative promoter usage of SAF/MAZ gene by bichromatic fluorescent reporter construct

The large-scale identification of putative alternative promoters study shows more than 52% of human genes are regulated by alternative promoters. The human myc-associated zinc finger protein (SAF/MAZ) gene have SAF-1 and SAF-3 variants transcripted from two transcription start sites (TSSs). By using SAF/MAZ promoter as a model, we set up an approach to probe how the alternative promoters are regulated in real time. We have constructed the bichromatic fluorescent reporter driven by SAF/MAZ 5'-proximal promoter plasmids from which transactivation status of SAF-1 and SAF-3 alternative promoter could be monitored by EGFP and DsRed expression respectively. The results showed that the SAF-3 expression is regulated by alternative promoters. When the bichromatic fluorescent reporter was driven by -1692/+277 or -1401/+277 SAF/MAZ promoter the dominant expression of SAF-3 would be observed in comparison with SAF-1 expression. We also identified that Elk-1 is an inhibitory transcription factor for SAF-3 expression. The temporal diversity of SAF-1 and SAF-3 expressions can be observed via bichromatic fluorescent reporters. These imply that the bichromatic fluorescent reporter driven by alternative promoter construct might be a useful tool for decoding the temporal regulatory repertoire of alternative promoter in human genes.

An increase in the cerebral infarction area during fatigue is mediated by il-6 through an induction of fibrinogen synthesis

OBJECTIVES

Our study aimed to investigate the impact of fatigue on the severity of stroke and to explore the underlying mechanisms.

METHODS

Fatigued male rats underwent middle cerebral artery occlusion and the infarcted brain area was determined. Then, coagulation parameters were assessed in the fatigued group and a control group. In addition, the level of fibrinogen was determined in rats deprived of sleep for various numbers of days. To study whether interleukin-6 was involved in fibrinogen synthesis during fatigue, we also measured levels of interleukin-6 in rats deprived of sleep for various numbers of days. Furthermore, brain injury by middle cerebral artery occlusion was measured in wild-type mice, interleukin-6-/- mice and wild-type mice treated with bezafibrate.

RESULTS

More severe cerebral infarction was observed in the fatigued rats, resulting in an infarct ratio of 23.4%. The infarct ratio was significantly increased in the fatigued rats compared with that in the control group (8%, p<0.05). The level of fibrinogen was increased significantly in the fatigued rats compared with that in the control group. In addition, a marked reduction in fibrinogen level was observed in the fatigued interleukin-6-/- mice compared to their wild-type counterparts, whereas no difference was observed between fatigued wild-type mice and interleukin-6-/- rats treated with recombinant human interleukin-6. The reduction in brain injury due to middle cerebral artery occlusion during fatigue was observed in interleukin-6-/- mice and wild-type mice treated with bezafibrate.

CONCLUSION

Fatigue could increase stroke severity and was associated with the interleukin-6-induced expression of fibrinogen.

The functional role of an interleukin 6-inducible CDK9.STAT3 complex in human gamma-fibrinogen gene expression

The signal transducer and activator of transcription 3 (STAT3) is an IL-6-inducible transcription factor that mediates the hepatic acute phase response (APR). Using gamma-fibrinogen (FBG) as a model of the APR, we investigated the requirement of an IL-6-inducible complex of STAT3 with cyclin-dependent kinase 9 (CDK9) on gamma-FBG expression in HepG2 hepatocarcinoma cells. IL-6 induces rapid nuclear translocation of Tyr-phosphorylated STAT3 that forms a nuclear complex with CDK9 in nondenaturing co-immunoprecipitation and confocal colocalization assays. To further understand this interaction, we found that CDK9-STAT3 binding is mediated via both STAT NH2-terminal modulatory and COOH-terminal transactivation domains. Both IL-6-inducible gamma-FBG reporter gene and endogenous mRNA expression are significantly decreased after CDK9 inhibition using the potent CDK inhibitor, flavopiridol (FP), or specific CDK9 siRNA. Moreover, chromatin immunoprecipitation (ChIP) experiments revealed an IL-6-inducible STAT3 and CDK9 binding to the proximal gamma-FBG promoter as well as increased loading of RNA Pol II and phospho-Ser2 CTD Pol II on the TATA box and coding regions. Finally, FP specifically and efficiently inhibits association of phospho-Ser2 CTD RNA Pol II on the gamma-FBG promoter, indicating that CDK9 kinase activity mediates IL-6-inducible CTD phosphorylation. Our data indicate that IL-6 induces a STAT3.CDK9 complex mediated by bivalent STAT3 domains and CDK9 kinase activity is necessary for licensing Pol II to enter a transcriptional elongation mode. Therefore, disruption of IL-6 signaling by CDK9 inhibitors could be a potential therapeutic strategy for inflammatory disease.

Markers of inflammation are inversely associated with V̇o2 max in asymptomatic men

We investigated whether markers of inflammation, including a cytokine (IL-6), acute-phase reactants [C-reactive protein (CRP) and fibrinogen], and white blood cell (WBC) count are associated with maximal O2 consumption (V̇o2 max) in men without coronary heart disease (CHD). In asymptomatic men ( n = 172, 51 ± 9.3 yr old), V̇o2 max was measured during a symptom-limited graded treadmill exercise test. Physical activity level was assessed by a standardized questionnaire. IL-6 and CRP were measured by immunoassays, fibrinogen by the Clauss method, and WBC count with a Coulter counter. IL-6 and CRP were logarithmically transformed to reduce skewness. Multivariable regression was used to assess whether markers of inflammation were associated with V̇o2 max after adjustment for age, body mass index, CHD risk factors, and lifestyle variables (physical activity level, percent body fat, and alcohol intake). V̇o2 max was 34.5 ml·kg−1·min−1 (SD 6.1). Log IL-6 ( r = −0.38, P < 0.001), log CRP ( r = −0.40, P < 0.001), fibrinogen ( r = −0.42, P < 0.001), and WBC count ( r = −0.22, P = 0.004) were each correlated with V̇o2 max. In separate multivariable linear regression models that adjusted for age, body mass index, CHD risk factors, and lifestyle variables, log IL-6 [β-coeff = −1.66 ± 0.63 (SE), P = 0.010], log CRP [β-coeff = −0.99 ± 0.33 (SE), P = 0.003], fibrinogen [β-coeff = −1.51 ± 0.44 (SE), P = 0.001], and WBC count [β-coeff = −0.52 ± 0.30 (SE), P = 0.088] were each inversely associated with V̇o2 max. In conclusion, higher circulating levels of IL-6, CRP, and fibrinogen are independently associated with lower V̇o2 max in asymptomatic men.

Analysis of the role of the PAC1 receptor in neutrophil recruitment, acute-phase response, and nitric oxide production in septic shock

Infections caused by Gram-negative bacteria constitute one of the major causes of septic shock, which results from the inability of the immune system to limit bacterial spread during the ongoing infection. In the last decade, it has been demonstrated that vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are two endogenous immunopeptides, which together with three G protein-coupled receptors (VPAC1, VPAC2, and PAC1) exert a significant, therapeutic effect attenuating the deleterious consequences of septic shock by balancing pro- and anti-inflammatory factors. We have recently shown PAC1 receptor involvement in vivo as an anti-inflammatory receptor, at least in part, by attenuating lipopolysaccharide-induced production of proinflammatory interleukin-6. The present study deepens in the protective role of PAC1 receptor in septic shock, elucidating its involvement in the modulation of neutrophil recruitment and in the expression of different molecular sensors such as intercellular adhesion molecule-1, vascular cell adhesion molecule-1, fibrinogen, serum amyloid A, and nitric oxide as important, systemic players of the development of septic shock. Our results, using a mice deficient in PAC1 and a PAC1 antagonist, show that VIP and PACAP as well as the PAC1 receptor are involved in neutrophil recruitment in different target organs, in adhesion molecules expression, and in coagulation-related molecule fibrinogen synthesis. Thus, this study provides some important insights with respect to the involvement of PAC1 into the complexities of sepsis and represents an advantage for the design of more specific drugs complementing standard intensive care therapy in severe sepsis, confirming VIP and PACAP as candidates for multitarget therapy of septic shock.

Transcriptional activity of serum amyloid A-activating factor-1 is regulated by distinct functional modules

Serum amyloid A-activating transcription factor-1 (SAF-1) plays a major role in regulating transcription of several inflammation-responsive genes, including SAA and matrix metalloproteinase-1, that are implicated in the pathogenesis of reactive secondary amyloidosis, atherosclerosis, and arthritis. SAF-1 is a 477-amino acid protein with six zinc fingers. Its activation during inflammatory condition by a phosphorylation event that leads to an altered structure suggested possible structural modification of this protein as a leading cause of higher activity. However, no information is available regarding structural features that might regulate its activity. Here, we have characterized its functional domains, delineating activation and repression modules, DNA binding, and nuclear localization activities. Using GAL4AD chimeras and a DNA-binding assay with proteins prepared from various deletion constructs, the core DNA-binding domain of SAF-1 is mapped between amino acids 282 and 361, which contain second, third, and fourth zinc fingers. Results from several deletion and point mutants using green fluorescent protein reporter show that SAF-1 contains two independent nuclear localization signals; one is composed of a stretch of basic amino acids, and the other is a bipartite signal located within the core DNA-binding domain. SAF-1 contains several negative and positively functioning transactivation modules clustered at the two ends of this protein. Removal of any one of the terminal negative modules renders the SAF-1 protein functionally very active. These findings suggest that the terminal repression modules act in conjunction to regulate the functional activity of this protein.

Overexpression of serum amyloid A-activating factor 1 inhibits cell proliferation by the induction of cyclin-dependent protein kinase inhibitor p21WAF-1/Cip-1/Sdi-1 expression

Inflammation-responsive transcription factor, serum amyloid A-activating factor 1 (SAF-1), has been shown to regulate several genes, including serum amyloid A, gamma-fibrinogen, and matrix metalloproteinase 1, whose abnormal expression is associated with the pathogenesis of arthritis, atherosclerosis, and amyloidosis. Prolonged high level expression of SAF-1 in cultured cells failed to produce any stable cell line that overexpresses SAF-1. To test the fate of SAF-1-overexpressing cells, the cells were monitored for growth and morphological changes over time. The cells that were programmed to overproduce SAF-1 were found to undergo growth arrest and reduce DNA synthesis within 3 days after transfection. These cells undergo marked morphological changes from typical fibroblasts to round morphology and gradually cease to exist. Microarray analysis for cell cycle-specific genes in SAF1-transfected cells identified several candidate genes whose expression levels were altered during SAF-1 overexpression. Cdk inhibitor protein p21 was significantly affected by SAF-1; its expression level was highly induced by cellular conditions where SAF-1 is abundant. The increased level of p21 in the cell drives it to a growth arrest mode, a condition previously found to be controlled by p53. In this study we provide evidence that, similar to p53, SAF-1 is able to activate p21 gene expression by promoting transcription directly via its interaction with the p21 promoter. Together these data indicate that SAF-1 controls cell cycle progression via p21 induction, and pathophysiological conditions that favor overexpression of SAF-1, such as an acute inflammatory condition, can trigger cellular growth arrest.

Functional analysis of interleukin 6 response elements (IL-6REs) on the human gamma-fibrinogen promoter: binding of hepatic Stat3 correlates negatively with transactivation potential of type II IL-6REs

Several families of transcription factors play important roles in modulating liver-specific gene expression during an acute phase response (APR). Stat3/APR factor is the main transactivator of gene expression by the interleukin (IL)-6 family of cytokines signaling through gp130. During an APR, fibrinogen (FBG) genes are coordinately up-regulated by IL-6 and glucocorticoids. Except for rat gammaFBG, attempts to demonstrate direct binding of IL-6-activated Stat3 to FBG CTGGGAA promoter elements have not been successful. Herein we show the presence of three functional type II IL-6 response elements (IL-6REs) on the human gammaFBG promoter and that the magnitude of Stat3 binding to these elements correlates negatively with their functional activity in reporter gene assays. Stat3-specific binding to gammaFBG IL-6REs was confirmed by cross-competition with alpha2-macroglobulin IL-6RE and specific interactions with anti-Stat3 in electrophoretic mobility shift assays. All type II IL-6REs contributed to full promoter activity; however, transactivation from Site II at -306 to -301 was strongest. In contrast to a previous report, IL-6 failed to induce activation of serum amyloid A-activating factor-1/c-Myc-associated zinc finger protein (SAF-1/MAZ), and mutation of the SAF-1RE had little effect on IL-6 induction of gammaFBG promoter activity. In the absence of a functional glucocorticoid receptor response element, dexamethasone potentiated IL-6-induced gammaFBG promoter activity 2-fold, requiring promoter-proximal Site I and Site II; the promoter-distal Site III had no effect on dexamethasone potentiation of IL-6-induced promoter activity. Notably the propensity for Stat3 binding to human gammaFBG IL-6REs was low compared with Stat3 binding to the alpha2-macroglobulin IL-6RE. Together these data suggest that Stat3 transactivation via IL-6REs on FBG promoters likely involves participation of additional transcription factors and/or coactivators to achieve optimal coordinated up-regulation during an APR.

Protein kinase A signaling pathway regulates transcriptional activity of SAF-1 by unmasking its DNA-binding domains

Serum amyloid A (SAA) activating factor-1 (SAF-1) is an inducible transcription factor that plays a key role in the regulation of several inflammation-responsive genes including SAA and matrix metalloproteinase-1. Increased synthesis of SAA and matrix metalloproteinase-1 is associated with pathogenesis of several diseases including amyloidosis, arthritis, and atherosclerosis. Previously, we showed in vivo interaction of SAF-1 and protein kinase A (PKA) and presented evidence for induction of SAF-1-regulated genes by a PKA signaling pathway. Here we demonstrate a mechanism by which PKA increases functional activities of SAF-1. Site-directed mutagenesis and phosphorylation analyses revealed two sites in the SAF-1 protein, serine 187 and threonine 386, as the target of PKA. Interestingly, mutation of both PKA phosphorylation sites created a highly active SAF-1 protein with high DNA-binding ability. Furthermore, we found that terminal deletion of SAF-1 protein from either end creates SAF-1 isoforms that are highly transcriptionally active. Partial proteolysis experiments indicated that unphosphorylated and phosphorylated SAF-1 proteins are structurally distinct. Together these results suggest that under native condition, N and C termini of SAF-1 are engaged in an inhibitory intramolecular interaction. PKA-mediated phosphorylation increases transcriptional activity of SAF-1 by unmasking the DNA-binding domain.

Extensive association analysis between polymorphisms of PON gene cluster with coronary heart disease in Chinese Han population

OBJECTIVE

An extensive association analysis of PON gene cluster (PONs) with coronary heart disease (CHD) was performed in Chinese Han population.

METHODS AND RESULTS

Thirty polymorphisms of PON1, PON2, and PON3 gene were identified by direct sequencing of genomic DNA derived from 48 randomly selected patients. Twelve polymorphisms were additionally investigated for association with CHD in 474 male patients and 475 controls. Univariate analyses showed the cases had significantly higher frequencies of PON1 192Q allele, 160R allele, -162A allele, and PON2 311C allele than were seen in the controls. Logistic regression analyses revealed only the PON1 R160G and -162G/A polymorphisms remained significantly associated with CHD (P=0.0054 and P=0.0002). Haplotype analyses for various polymorphism combinations additionally confirmed the results of individual polymorphism analyses. Only the frequencies of haplotypes containing -162A allele were significantly higher, whereas only the frequencies of haplotypes containing 160G allele were significantly lower in cases than in controls in various polymorphism combinations.

CONCLUSIONS

This extensive association study has identified the PON1 -162G/A and R160G polymorphisms to be independently associated with CHD in Chinese Han population and warrants additional study to elucidate the biological mechanism.

SAF-2, a splice variant of SAF-1, acts as a negative regulator of transcription

Serum amyloid A-activating factor-1 (SAF-1), a Cys(2)His(2)-type zinc finger transcription factor, regulates inflammation-induced expression of serum amyloid A protein that is linked to the pathogenesis of reactive amyloidosis, rheumatoid arthritis, and atherosclerosis. Here we report the identification of a novel splice variant, SAF-2, of the SAF family bearing strong sequence similarity to SAF-1. The N-terminal 426 amino acids of both SAF-1 and SAF-2 are identical containing two polyalanine tracts, one proline-rich domain, and six zinc fingers. However, the C terminus of SAF-2 containing two additional zinc fingers is different from SAF-1, which indicates the capability of different biochemical function. We show that SAF-2 interacts more avidly with the SAF-binding element, but its transactivation potential is much lower than SAF-1. Furthermore, co-expression of SAF-2 markedly suppresses SAF-1-regulated promoter function. Finally, we show that the level of SAF-2 protein is reduced during many inflammatory conditions, whereas the SAF-1 protein level remains unchanged. Together, these data suggest that the relative abundance of SAF-2 plays a critical role in the fine tuned regulation of inflammation-responsive genes that are controlled by SAF-1.

Cytokine-responsive induction of SAF-1 activity is mediated by a mitogen-activated protein kinase signaling pathway

SAF-1, a zinc finger transcription factor, is activated by a number of inflammatory agents, including interleukin-1 (IL-1) and IL-6. It is involved in the cytokine-mediated transcriptional induction of serum amyloid A, an acute-phase plasma protein that is associated with the pathogenesis of reactive amyloidosis, rheumatoid arthritis, and atherosclerosis. Here, we show that the mitogen-activated protein (MAP) kinase signaling pathway regulates cytokine-mediated induction of the DNA-binding activity and transactivation potential of SAF-1. Phosphorylation of endogenous SAF-1 in response to IL-1 and IL-6 was markedly inhibited by the addition of MAP kinase inhibitors. Consistent with this finding, we show that a consensus MAP kinase phosphorylation site, PPTP, within SAF-1 could be phosphorylated by MAP kinase in vitro. To analyze the contribution of MAP kinase in the activation of SAF-1, we prepared two independent mutant proteins in which the threonine residue of the PPTP motif was altered to either valine or alanine. These mutant proteins lost the ability to be phosphorylated by MAP kinase both in vivo and in vitro and exhibited a significantly reduced ability to promote expression of the SAF-1-regulated promoter. While the DNA-binding activity of wild-type SAF-1 protein was markedly increased upon phosphorylation with MAP kinase, no such increase could be detected with the mutant SAF-1 proteins. Further analysis with the GAL-4 reporter system showed that mutation of the MAP kinase phosphorylation site considerably lowers the transactivation potential of SAF-1. Together, these results show that activation of SAF-1 in response to IL-1 and -6 is mediated via MAP kinase-regulated phosphorylation.

Promoter-binding activity of inflammation-responsive transcription factor SAF is regulated by cyclic AMP signaling pathway

The serum amyloid A activating factor (SAF) was identified as a family of inducible transcription factors that is activated by many mediators of inflammation. Its activation involves a phosphorylation event, whose mechanism is not fully understood. Here, we show that cAMP treatment of several cell types, including mouse liver-derived BNL CL.2, human monocyte-derived THP-1, and a primary culture of vascular smooth muscle cells from porcine aorta, activated cellular SAF's ability to bind DNA. The protein kinase A (PKA) activity in cytoplasmic extracts of cAMP-treated cells was responsible for the potentiation of the DNA-binding activity of the cellular SAF proteins. Furthermore, treatment of nuclear extracts of untreated cells with purified PKA increased the DNA-binding activity of cellular SAF proteins, and specific inhibitors of PKA abrogated the enhanced DNA-binding ability of SAF in the cAMP-treated cells. Consistent with these findings, overexpression of the catalytic subunit of PKA markedly increased expression of the SAF-regulated promoter. These results imply a functional role for the previously detected protein-protein interaction between SAF-1 transcription factor and the catalytic subunit of PKA and further demonstrate the consequences of cAMP-mediated signaling for the expression of SAF-regulated genes.

Catalytic subunit of protein kinase A is an interacting partner of the inflammation-responsive transcription factor serum amyloid A-activating factor-1

Serum amyloid A-activating factor-1 (SAF-1) is a zinc finger transcription factor that is activated by many mediators of inflammation including IL-1, IL-6, and bacterial LPS. However, the mechanism of activation is not fully understood. To identify possible activation partners for SAF-1, we used a yeast two-hybrid system that detected interaction between the catalytic subunit of cyclic AMP-dependent protein kinase (PKA-Calpha) and SAF-1. Immunofluorescence and combined immunoprecipitation-Western blot analyses revealed colocalization and interaction between SAF-1 and PKA-Calpha. In vivo evidence of SAF-1 and PKA-Calpha interaction was further revealed by coimmunoprecipitation of these two proteins in cAMP-activated liver cells. We further show that SAF-1 is phosphorylated in vitro by PKA-Calpha and that addition of cAMP markedly induces in vivo phosphorylation of SAF-1 and transcription of SAF-regulated reporter genes. These results showed that SAF1-PKA-Calpha interaction is involved in functional activation of SAF-1.

Effects of 5' regulatory-region polymorphisms on paraoxonase-gene (PON1) expression

Human HDL-associated paraoxonase (PON1) hydrolyzes a number of toxic organophosphorous compounds and reduces oxidation of LDLs and HDLs. These properties of PON1 account for its ability to protect against pesticide poisonings and atherosclerosis. PON1 also hydrolyzes a number of lactone and cyclic-carbonate drugs. Among individuals in a population, PON1 levels vary widely. We previously identified three polymorphisms in the PON1 regulatory region that affect expression levels in cultured human hepatocytes. In this study, we determined the genotypes of three regulatory-region polymorphisms for 376 white individuals and examined their effect on plasma-PON1 levels, determined by rates of phenylacetate hydrolysis. The -108 polymorphism had a significant effect on PON1-activity level, whereas the -162 polymorphism had a lesser effect. The -909 polymorphism, which is in linkage disequilibrium with the other sites, appears to have little or no independent effect on PON1-activity level in vivo. Other studies have found that the L55M polymorphism in the PON1-coding region is associated with differences in both PON1-mRNA and PON1-activity levels. The results presented here indicate that the L55M effect of lowered activity is not due to the amino acid change but is, rather, largely due to linkage disequilibrium with the -108 regulatory-region polymorphism. The codon 55 polymorphism marginally appeared to account for 15.3% of the variance in PON1 activity, but this dropped to 5% after adjustments for the effects of the -108 and Q192R polymorphisms were made. The -108C/T polymorphism accounted for 22.8% of the observed variability in PON1-expression levels, which was much greater than that attributable to the other PON1 polymorphisms. We also identified four sequence differences in the 3' UTR of the PON1 mRNA.