Induction of Src-suppressed C kinase substrate (SSeCKS) in vascular endothelial cells by bacterial lipopolysaccharide

AKAP12 deficiency impairs VEGF-induced endothelial cell migration and sprouting

Aim

Protein kinase (PK) A anchoring protein (AKAP) 12 is a scaffolding protein that anchors PKA to compartmentalize cyclic AMP signalling. This study assessed the consequences of the downregulation or deletion of AKAP12 on endothelial cell migration and angiogenesis.

Methods

The consequences of siRNA‐mediated downregulation AKAP12 were studied in primary cultures of human endothelial cells as well as in endothelial cells and retinas from wild‐type versus AKAP12^−/− mice. Molecular interactions were investigated using a combination of immunoprecipitation and mass spectrometry.

Results

AKAP12 was expressed at low levels in confluent endothelial cells but its expression was increased in actively migrating cells, where it localized to lamellipodia. In the postnatal retina, AKAP12 was expressed by actively migrating tip cells at the angiogenic front, and its deletion resulted in defective extension of the vascular plexus. In migrating endothelial cells, AKAP12 was co‐localized with the PKA type II‐α regulatory subunit as well as multiple key regulators of actin dynamics and actin filament‐based movement; including components of the Arp2/3 complex and the vasodilator‐stimulated phosphoprotein (VASP). Fitting with the evidence of a physical VASP/AKAP12/PKA complex, it was possible to demonstrate that the VEGF‐stimulated and PKA‐dependent phosphorylation of VASP was dependent on AKAP12. Indeed, AKAP12 colocalized with phospho‐Ser157 VASP at the leading edge of migrating endothelial cells.

Conclusion

The results suggest that compartmentalized AKAP12/PKA signalling mediates VASP phosphorylation at the leading edge of migrating endothelial cells to translate angiogenic stimuli into altered actin dynamics and cell movement.

SSeCKS/AKAP12 scaffolding functions suppress B16F10-induced peritoneal metastasis by attenuating CXCL9/10 secretion by resident fibroblasts

SSeCKS/Gravin/AKAP12 (SSeCKS) is a kinase scaffolding protein known to suppress metastasis by attenuating tumor-intrinsic PKC- and Src-mediated signaling pathways [1]. In addition to downregulation in metastatic cells, in silico analyses identified SSeCKS downregulation in prostate or breast cancer-derived stroma, suggesting a microenvironmental cell role in controlling malignancy. Although orthotopic B16F10 and SM1WT1[Braf^V600E] mouse melanoma tumors grew similarly in syngeneic WT or SSeCKS-null (KO) mice, KO hosts exhibited 5- to 10-fold higher levels of peritoneal metastasis, and this enhancement could be adoptively transferred by pre-injecting naïve WT mice with peritoneal fluid (PF), but not non-adherent peritoneal cells (PC), from naïve KO mice. B16F10 and SM1WT1 cells showed increased chemotaxis to KO-PF compared to WT-PF, corresponding to increased PF levels of multiple inflammatory mediators, including the Cxcr3 ligands, Cxcl9 and 10. Cxcr3 knockdown abrogated enhanced chemotaxis to KO-PF and peritoneal metastasis in KO hosts. Conditioned media from KO peritoneal membrane fibroblasts (PMF), but not from KO-PC, induced increased B16F10 chemotaxis over controls, which could be blocked with Cxcl10 neutralizing antibody. KO-PMF exhibited increased levels of the senescence markers, SA-β-galactosidase, p21^waf1 and p16^ink4a, and enhanced Cxcl10 secretion induced by inflammatory mediators, lipopolysaccharide, TNFα, IFNα and IFNγ. SSeCKS scaffolding-site mutants and small molecule kinase inhibitors were used to show that the loss of SSeCKS-regulated PKC, PKA and PI3K/Akt pathways are responsible for the enhanced Cxcl10 secretion. These data mark the first description of a role for stromal SSeCKS/AKAP12 in suppressing metastasis, specifically by attenuating signaling pathways that promote secretion of tumor chemoattractants in the peritoneum.

The selective distribution of LYVE-1-expressing endothelial cells and reticular cells in the reticulo-endothelial system (RES)

LYVE-1, a receptor molecule for hyaluronan, is expressed in the lymphatic endothelium, blood sinus endothelium, and certain macrophage lineages. The present immunohistochemical study revealed a broader distribution of LYVE-1 in vascular endothelial cells of the murine lung, adrenal gland, and heart as well as the liver and spleen. In addition, sinus reticular cells-including sinuslining cells-in the medulla of the lymph node also intensely expressed LYVE-1. Ultrastructurally, immuno-gold particles for LYVE-1 were localized on the entire length of plasma membrane in all cell types. Most of these LYVE-1-expressing cells had previously been classified as the reticuloendothelial system (RES) specialized for eliminating foreign particles. An LPS stimulation decreased the LYVE-1 expression in macrophages but elevated the expression at mRNA and protein levels in the liver and lung, major organs for the elimination of blood-born waste substances. LYVE-1-expressing endothelial cells in these organs participated in the endocytosis of exogenous particles, and the uptake ability was conspicuously enhanced by the LPS challenge. Although the expression of the degrading enzyme, hyaluronidase, was generally low in the LYVE-1-expressing cells, they were topographically associated with a dense distribution of macrophages possessing hyaluronidase activities in each tissue. These findings suggest that the LYVE-1-expressing cells might be involved in the uptake of hyaluronan and other waste products as well as foreign particles circulating in the blood and lymph while participating in the subsequent degradation in relay with adjacent macrophage populations.

Thermoresponsive Polymer Micropatterns Fabricated by Dip-Pen Nanolithography for a Highly Controllable Substrate with Potential Cellular Applications

We report a novel approach for patterning thermoresponsive hydrogels based on N,N-diethylacrylamide (DEAAm) and bifunctional Jeffamine ED-600 by dip-pen nanolithography (DPN). The direct writing of micron-sized thermoresponsive polymer spots was achieved with efficient control over feature size. A Jeffamine-based ink prepared through the combination of organic polymers, such as DEAAm, in an inorganic silica network was used to print thermosensitive arrays on a thiol-silanized silicon oxide substrate. The use of a Jeffamine hydrogel, acting as a carrier matrix, allowed a reduction in the evaporation of ink molecules with high volatility, such as DEAAm, and facilitated the transfer of ink from tip to substrate. The thermoresponsive behavior of polymer arrays which swell/deswell in aqueous solution in response to a change in temperature was successfully characterized by atomic force microscopy (AFM) and Raman spectroscopy: a thermally induced change in height and hydration state was observed, respectively. Finally, we demonstrate that cells can adhere to and interact with these dynamic features and exhibit a change in behavior when cultured on the substrates above and below the transition temperature of the Jeffamine/DEAAm thermoresponsive hydrogels. This demonstrates the potential of these micropatterned hydrogels to act as a controllable surface for cell growth.

HSPA12B regulates SSeCKS-mediated astrocyte inflammatory activation in neuroinflammation

Reactive astrocytosis has been considered either beneficial or detrimental effection in neuroinflammatory disease. HSPA12B, a new member belongs to the 70-kDa family of heat shock proteins (HSP70) which could modulate inflammatory response, also shows an connection with the astrocyte activation. Recently, it was reported that Src-Suppressed-C Kinase Substrate (SSeCKS) was detected in heat shock protein A12B (HSPA12B) interacting proteins using a yeast 2-hybrid system. SSeCKS, a major Lipopolysaccharide (LPS) response protein, has been involved in regulating astrocyte activation via production of proinflammatory factor in CNS inflammation. In this study, we found HSPA12B might regulate the expression and activity of SSeCKS to promote astrocyte inflammatory activation and release of inflammatory mediators, such as TNF-α and IL-1β in spinal cord primary astroglial cultures exposed to LPS treatment. The promoting mechanism of interaction between HSPA12B and SSeCKS on LPS-induced astrocyte activation was mediated via the activation of JNK and p38 signaling pathways but not ERK1/2 MAPK signaling pathway. HSPA12B binded to SSeCKS via its both N terminus consisted of amino acids 1-330 and C terminus consisted of amino acids 1278-1596. And, in vivo, we confirmed the interaction between HSPA12B and SSeCKS of astrocyte activation in the pathogenesis of EAE. The regulatory mechanisms of HSPA12B-SSeCKS interaction may possibly be the key therapeutic strategy of neuroinflammatory disease.

Increased SSeCKS expression in rat hepatic stellate cells upon activation in vitro and in vivo

Recent reports suggest that src suppressed c kinase substrates (SSeCKS) are early inflammatory response protein. However, there is only scarce knowledge on the functional role of SSeCKS in liver under conditions of acute inflammation. In the present study, we investigated SSeCKS expression in liver after administration of carbon tetrachloride (CCl4) in rats and in isolated primary hepatic stellate cells (HSCs) upon activation on a plastic dish. We found that SSeCKS mRNA was hardly detectable in healthy liver tissue and further increased in carbon tetrachloride-mediated acute liver failure. SSeCKS protein expression was mainly found in hepatic stellate cells. In vitro, SSeCKS expression in activated rat HSCs was dramatically increased. The upregulation of SSeCKS protein expression in rat HSCs during activation in vitro and in vivo suggested the possibility of SSeCKS, an important part of function of the activated HSCs, perhaps through modulation of liver regeneration or formation of liver fibrosis after various injuries.

Vagal efferent fiber stimulation ameliorates pulmonary microvascular endothelial cell injury by downregulating inflammatory responses

Electrical stimulation of the vagus nerve may have positive effects on many inflammatory diseases. This study determined the beneficial effects of vagus nerve stimulation and the mechanisms by which it attenuates lipopolysaccharide (LPS)-induced acute lung injury (ALI). Rats were intraperitoneally injected with 10 mg/kg LPS to induce ALI. The results showed that vagus nerve stimulation could improve lung injury, as evidenced by remarkable reductions in lung edema (wet-to-dry weight ratio), neutrophil infiltration (myeloperoxidase activity), and pulmonary permeability [total number of cells and protein concentrations in bronchoalveolar lavage fluid (BALF)]. In addition, vagus nerve stimulation not only decreased the expressions of Src-suppressed C kinase substrate and E-selectin proteins in lung tissue but also effectively attenuated the concentrations of the proinflammatory cytokines tumor necrosis factor-α, interleukin-1β, and interleukin-6 in BALF. These suggest that vagus nerve stimulation is a suitable treatment for LPS-induced ALI and indicate that it helps ameliorate pulmonary microvascular endothelial cell injury by downregulating inflammatory responses.

Expression of SRC suppressed C kinase substrate in rat neural tissues during inflammation

Src-suppressed C kinase substrate (SSeCKS), an in vivo and in vitro protein kinase C substrate, is a major lipopolysaccharide (LPS) response protein which markedly upregulated in several organs, including brain, lung, heart, kidney etc., indicating a possible role of SSeCKS in inflammatory process. However, the expression and biological function of SSeCKS during neuronal inflammation remains to be elucidated, so we established an inflammatory model injected with LPS to investigate the gene expression patterns of SSeCKS in neural tissues by using TaqMan quantitative real-time PCR and immunohistochemistry in rat. Real-time PCR showed that LPS stimulated the expression of SSeCKS mRNA in a dose- and time-dependent manner in sciatic nerves, spinal cords and dorsal root ganglions. Immunohistochemistry showed that SSeCKS colocalized with nerve fibers in sciatic nerve after LPS administration, but there was no colocalization between SSeCKS and Schwann cells. In addition, SSeCKS colocalized with neurons which existed in dorsal root ganglions and spinal cords. These findings indicated that SSeCKS might play some important roles in sciatic nerve fibers and neurons in spinal cords and dorsal root ganglions after LPS injection.

Ubiquitin-specific protease 2-69 in macrophages potentially modulates metainflammation

Macrophages play a critical role in chronic inflammation and metabolic diseases. We identified a longer splice variant of ubiquitin specific protease (USP) 2-69 as a novel molecule that modulates pathways implicated in metabolic disorders. Expression levels of aP2/FABP4 and PAI-1/SERPINE1 genes were increased by 4- and 1.8-fold, respectively, after short hairpin RNA-mediated knockdown (KD) of the USP2 gene, and such expression was alleviated by overexpression of USP2-69 in human myeloid cell lines. Supernatants derived from USP2-KD cells induced IL6 (∼6-fold) and SAA3 (∼15-fold) in 3T3-L1 adipocytes to suggest the anti-inflammatory properties of USP2. In addition, we observed a 30% decrease in the number of macrophages in mesenteric adipose tissue derived from USP2-69 transgenic mice fed a high-fat diet for 14 wk compared with that in their C57BL/6 littermates (P<0.01), which was consistent with a ∼40% decrease in transcription of aP2 and PAI-1. The aP2 locus exhibited elevated chromatin accessibility (>2.1-fold), methylation of histone H3 lysine 4 (>4.5-fold), and acetylation of histone H4 (>2.5-fold) in USP2-KD cells. Transfection of isopeptidase-mutated USP2-69 did not alter chromatin conformation on the aP2 locus in USP2-KD cells. Our results suggest that USP2-69 suppresses meta-inflammatory molecules involved in the development of type-2 diabetes.

Cell interactions at the nanoscale: piezoelectric stimulation

Nanometric movements of the substrate on which endothelial cells are growing, driven by periodic sinusoidal vibration from 1 Hz to 50 Hz applied by piezo actuators, upregulate endothelin-1 and Kruppel-like factor 2 expression, and increase cell adhesion. These movements are in the z (vertical) axis and ranges from 5 to 50 nm and are similar in vertical extent to protrusions from the cells themselves already reported in the literature. White noise vibrations do not to produce these effects. Vibrational sweeps, if suitably confined within a narrow frequency range, produce similar stimulatory effects but not at wider sweeps. These effects suggest that coherent vibration is crucial for driving these cellular responses. In addition to this, the applied stimulations are observed to be close to or below the random seismic noise of the surroundings, which may suggest stochastic resonance is being employed. The stimulations also interact with the effects of nanometric patterning of the substrates on cell adhesion and Kruppel-like factor 2 and endothelin-1 expression thus linking cell reactions to nanotopographically patterned surfaces with those to mechanical stimulation.

Involvement of SRC-suppressed C kinase substrate in neuronal death caused by the lipopolysaccharide-induced reactive astrogliosis

Src-suppressed C kinase substrate (SSeCKS), a protein kinase C substrate, is a major lipopolysaccharide (LPS) response protein, regulating the inflammatory process. In the process of spinal inflammatory diseases by LPS intraspinal injection, expression of SSeCKS in the spinal cord was increased, mainly in active astrocytes and neurons. Induced SSeCKS was colabeled with terminal deoxynucleotidyl transferase-mediated biotinylated-dUTP nick-end labeling (an apoptosis maker) in the late inflammation processes. These results indicated that SSeCKS might correlate with the inflammatory reaction and late neurodegeneration after LPS injection. A cell type-specific action for SSeCKS was further studied within C6 cells and PC12 cells. Knockdown of SSeCKS by small-interfering RNAs (siRNAs) blocked the LPS-induced inducible nitric oxide synthase (iNOS) expression in C6 cells, while overexpression SSeCKS enhanced iNOS expression. SSeCKS is also participated in regulation of PC12 cell viability. Loss of SSeCKS rescued PC12 cell viability, and excessive SSeCKS exacerbated the cell death upon conditioned medium and tumor necrosis factor-alpha exposure. This study delineates that SSeCKS may be important for host defenses in spinal inflammation and suggests a valuable molecular mechanism by which astrocytes modify neuronal viability during pathological states.

Involvement of Src-suppressed C kinase substrate in experimental autoimmune encephalomyelitis: a link between release of astrocyte proinflammatory factor and oligodendrocyte apoptosis

Src-suppressed C kinase substrate (SSeCKS) is involved in inflammation in the central nervous system (CNS), and plays a role in control of cell signaling and cytoskeletal arrangement. However, the expression and function of SSeCKS and its function in multiple sclerosis (MS) and its common animal model, experimental autoimmune encephalomyelitis (EAE) remained to be elucidated. In the present study, we first reported that SSeCKS was remarkably increased in astrocytes of EAE rats in vivo. TNF-alpha and NO were significantly induced in astrocytes stimulated with LPS/IFN-gamma in vitro, which was blocked in astrocytes transfected with SSeCKS siRNA. These results indicated that SSeCKS played a role in the production of TNF-alpha and NO in astrocytes with inflammatory stimulation. As excessive release of TNF-alpha and NO were major mediators in autoimmune diseases and correlated with oligodendrocyte cell death, we further investigated whether SSeCKS participated in oligodendrocyte apoptosis. Conditioned media (CM) from astrocytes treated with LPS/IFN-gamma decreased oligodendrocyte cell viability, while siRNA targeted to SSeCKS in astrocytes inhibited oligodendrocyte cell death. The results from antibody neutralization and NO inhibition suggested that the oligodendrocyte apoptosis may be due to the production of astrocyte-derived proinflammatory factors (TNF-alpha and NO). These findings revealed that there was a pathogenic interaction between SSeCKS expression in astrocytes and oligodendrocyte apoptosis. Understanding the mechanism of SSeCKS in the pathogenesis of EAE may contribute to the development of new therapeutic strategies against EAE and MS.

Role of src-suppressed C kinase substrate in rat pulmonary microvascular endothelial hyperpermeability stimulated by inflammatory cytokines

OBJECTIVE

The aim of the study was to investigate the role of src-suppressed C kinase substrate (SSeCKS) in the modulation of rat pulmonary microvascular endothelial cells (RPMVEC) permeability elicited by interleukin (IL)-1β and tumor necrosis factor (TNF)-α.

METHODS

The gene expression of SSeCKS was analyzed by reverse transcription-polymerase chain reaction. Immunoblotting was used to determine the SSeCKS protein expression and the activation of the protein kinase C (PKC) signaling pathway. A RPMVEC monolayer was constructed to determine changes of transendothelial electrical resistance (TER) and FITC-dextran flux (P (d)) across the monolayer. SSeCKS-specific small interfering RNA was transfected into RPMVEC.

RESULTS

IL-1β and TNF-α activated the PKC signaling pathway in RPMVEC, and up-regulated the gene and protein expression of SSeCKS. Depletion of endogenous SSeCKS in RPMVEC significantly attenuated cytokine-induced decrease in TER and increase in P (d), but not to the basal levels. PKC inhibitors also significantly decreased cytokine-induced hyperpermeability and SSeCKS expression.

CONCLUSIONS

SSeCKS is involved in the endothelial hyperpermeability induced by IL-1β and TNF-α in inflammatory process.

Interleukin-17F-induced pulmonary microvascular endothelial monolayer hyperpermeability via the protein kinase C pathway

BACKGROUND

Interleukin (IL)-17F is involved in lung inflammation, but the effect of IL-17F on endothelial permeability and its signaling pathway remain ill-defined. The current study sought to investigate the effect of IL-17F on endothelium and assess the role of protein kinase C (PKC) and src-suppressed C kinase substrate (SSeCKS) in this process.

METHODS

Rat pulmonary microvascular endothelial monolayers were constructed to determine changes of permeability as measured by means of FITC-dextran and Hank's solution flux across monolayers and transendothelial electrical resistance with or without IL-17F and PKC inhibitors. Additional monolayers were stained using FITC-phalloidin for filamentous actin (F-actin). The gene expression of SSeCKS was analyzed by the reverse transcription-polymerase chains. Alterations of SSeCKS protein were investigated by immunoblotting and immunoprecipitation.

RESULTS

IL-17F increased endothelial monolayer permeability in a dose- and time-dependent manner. F-actin staining revealed that permeability changes were accompanied by reorganization of cytoskeleton. In the presence of PKC inhibitors, the IL-17F-induced hyperpermeability and reorganization of F-actin were attenuated. The gene and protein expression of SSeCKS were conspicuously elevated after IL-17F challenge. The process of SSeCKS phosphorylation followed a time course that mirrored the time course of hyperpermeability induced by IL-17F. IL-17F-induced SSeCKS phosphorylation was abrogated after PKC inhibitors pretreatment. The translocation of SSeCKS from the cytosol to the membrane and a significant increase in the SSeCKS association with the cytoskeleton were found after IL-17F treatment.

CONCLUSIONS

IL-17F is an important mediator of increased endothelial permeability. PKC and SSeCKS are integral signaling components essential for IL-17F-induced hyperpermeability.

The role of beta-1,4-galactosyltransferase-I in the skin wound-healing process

Cell-surface carbohydrate chains are known to contribute to cell migration, interaction, and proliferation. beta-1,4-galactosyltransferase-I (beta-1,4-GalT-I), which is one of the best-studied glycosyltransferases, plays a key role in the synthesis of type 2 chains in N-glycans and the core 2 branch in O-glycans. Recently, it has been reported that skin wound healing is significantly delayed in beta-1,4-GalT-I mice. However, the expression of beta-1,4-GalT-I and its biological function in the skin wound-healing process remain to be elucidated. We used real-time polymerase chain reaction to demonstrate that the expression of beta-1,4-GalT-I mRNA reached plateau values at 12 hours after skin was injured and remained elevated until 11 days after the injury. Furthermore, lectin blotting showed that beta-1,4-galactosylated carbohydrate chains were also increased after skin injury. A double-staining method combining lectin-fluorescent staining with RCA-I and immunofluorescence was first used to determine the cellular localization of beta-1,4-galactosylated carbohydrate chains. Morphological analysis showed that the chains were primarily expressed in neutrophils and partially expressed in macrophages, endothelial cells, and collagen. Our results suggest that beta-1,4-GalT-I and beta-1,4-galactosylated carbohydrate chains participate in leukocyte recruitment, angiogenesis, and collagen deposition in the skin wound-healing process.

Genome-wide identification and characterization of transcripts translationally regulated by bacterial lipopolysaccharide in macrophage-like J774.1 cells

Although Escherichia coli LPS is known to elicit various proinflammatory responses in macrophages, its effect on the translational states of transcripts has not yet been explored on a genome-wide scale. To address this, we investigated the mRNA profiles in polysomal and free messenger ribonucleoprotein particle (mRNP) fractions of mouse macrophage-like J774.1 cells, using Affymetrix Mouse Genome 430 2.0 GeneChips. Comparison of the mRNA profiles in total cellular, polysomal, and free mRNP fractions enabled us to identify transcripts that were modulated at the translational level by LPS: among 19,791 transcripts, 115 and 418 were up- and downregulated at 1, 2, or 4 h after LPS stimulation (100 ng/ml) in a translation-dependent manner. Interestingly, gene ontology-based analysis suggested that translation-dependent downregulated genes frequently include those encoding proteins in the mitochondrial respiratory chain. In fact, the mRNA levels of some transcripts for complexes I, IV, and V in the mitochondrial respiratory chain were translationally downregulated, eventually contributing to the decline of their protein levels. Moreover, the amount of metabolically labeled cytochrome oxidase subunit Va in complex IV was decreased without any change of its mRNA level in total cellular fraction after LPS stimulation. Consistently, the total amounts and activities of complexes I and IV were attenuated by LPS stimulation, and the attenuation was independent of nitric oxide. These results demonstrated that translational suppression may play a critical role in the LPS-mediated attenuation of mitochondrial oxidative phosphorylation in a nitric oxide-independent manner in J774.1 cells.

Lipopolysaccharide induces expression of SSeCKS in rat lung microvascular endothelial cell

Src-suppressed C kinase substrate (SSeCKS) plays a role in membrane-cytoskeletal remodeling to regulate mitogenesis, cell differentiation, and motility. Previous study showed that lipopolysaccharide (LPS) induced a selective and strong expression of SSeCKS in the vascular endothelial cells of lung. Here we show that LPS stimulation elevated expression of SSeCKS mRNA and protein in Rat pulmonary microvascular endothelial cell (RPMVEC). LPS potentiated SSeCKS phosphorylation in a time- and dose-dependent manner, and partly induced translocation of SSeCKS from the cytosol to the membrane after LPS challenge. The PKC inhibitor, Calphostin C, significantly decreased LPS-induced phosphorylation of SSeCKS, inhibited SSeCKS translocation and actin cytoskeleton reorganization after LPS challenge, suggesting that PKC may play a role in LPS-induced SSeCKS translocation and actin rearrangement. We conclude that SSeCKS is located downstream of PKC and that SSeCKS and PKC are both necessary for LPS-induced stress fiber formation.

Src suppressed C kinase substrate regulates the lipopolysaccharide-induced TNF-α biosynthesis in rat astrocytes

The protein kinase C (PKC) is known to be a critical component in the signaling cascades that lead to astrocyte-activation. To further understand the mechanism of PKC signaling in astrocyte-activation, we investigated the effect of SSeCKS, a PKC substrate, on LPS-induced cytokine expression in astrocytes by RT-PCR and enzyme-linked immunosorbent assay. Exposure of the cells to LPS induced rapid translocation of SSeCKS to the perinuclear sides, ERK activation and pronounced TNF-alpha production, which can be inhibited by the PKC inhibitor Gö6983. By using siRNA knockdown of SSeCKS expression, LPS-induced signaling events were partly inhibited, including ERK activation, inducible TNF-alpha biosynthesis and secretion. These results suggest that SSeCKS is involved in the LPS-induced TNF-alpha expression in astrocytes mediated by PKC.

Expression of beta-1,4-galactosyltransferase-I in rat during inflammation

beta-1,4-Galactosyltransferase-I (beta-1,4-GalT-I) which is one of the best-studied glycosyltransferases, plays a key role in the synthesis of selectin ligands such as sialy Lewis (sLe( x )) and sulfated sLe( x ). Previous studies showed that inflammatory responses of beta-1,4-GalT-I-deficient mice were impaired because of the defect in selectin-ligand biosynthesis. However, the expression of beta-1,4-GalT-I during inflammation and its biological function remains to be elucidated. Real-time PCR showed that intraperitoneal administration of LPS strongly induced beta-1,4-GalT-I mRNA expression in the lung, heart, liver, spleen, kidney, lymph node, hippocampus, and testis, as well as in the cerebral cortex. In the rat lung, liver and testis, LPS stimulation of beta-1,4-GalT-I mRNA expression is time-dependent and biphasic. Lectin-fluorescent staining with RCA-I showed that LPS induced expression of galactose-containing glycans in rat lung and liver to the higher lever. Morphology analysis observed that galactose-containing glycans and beta-1,4-GalT-I mRNA was mostly expressed in neutrophils, macrophages and endothelial cells. These findings indicated that beta-1,4-GalT-I may play an important role in the inflammation reaction.

Uptake ability of hepatic sinusoidal endothelial cells and enhancement by lipopolysaccharide

The liver is one of the major organs that remove exogenous substances and waste products from the blood circulation. Hepatic macrophages (Kupffer cells) and sinusoidal endothelial cells are responsible for the scavenger function of the liver. The sinusoidal endothelial cells, called scavenger endothelial cells, are believed to take up only soluble substances and nanometer-sized particles under normal conditions, while Kupffer cells can ingest larger particles and whole cells. However, the sinusoidal endothelial cells may have the potential to take up considerably large particles under special conditions. In this morphological study, we compared the uptake ability between sinusoidal endothelial cells and Kupffer cells after intravenous injections of latex beads (20 nm, 100 nm and 500 nm in diameter), bovine serum albumin (BSA) and dextran. Under normal conditions, the sinusoidal endothelial cells vigorously took up 100-nm-sized latex beads as well as 20-nm latex beads. BSA and dextran were ingested by the endothelial cells but not the Kupffer cells. The administration of lipopolysaccharide (LPS), which mimics inflammation, stimulated the uptake by endothelial cells. The uptake of latex beads by Kupffer cells was also elevated under LPS-stimulated conditions, but the uptake of BSA and dextran by them was not. These findings suggest that the sinusoidal endothelial cells can ingest not only soluble substances but also larger particles than those expected, and their uptake ability is strengthened under inflammatory conditions.

The expression of src-suppressed C kinase substrate (SSeCKS) and uptake of exogenous particles in endothelial and reticular cells

Src-suppressed C kinase substrate (SSeCKS), a potent tumor suppressor, plays a role in membrane-cytoskeletal remodeling to regulate mitogenesis, cell differentiation, and motility. Our previous study showed that lipopolysaccharide (LPS) induced a selective and strong expression of SSeCKS in the vascular endothelial cells of several organs, such as hepatic sinusoids, and in the reticular cells of lymphoid organs. In the present immunocyto-chemical study, we determined the detailed cellular and subcellular localization of SSeCKS in mouse tissues after LPS administration, and examined the involvement of SSeCKS in the uptake of exogenous particles. SSeCKS immunoreactivity in the liver and lymph nodes was below the detectable level under normal conditions. After LPS stimulation, an intense immunoreactivity for SSeCKS became noticeable in sinusoidal endothelial cells of the liver and medullary reticular cells of the lymph node. Electron-microscopically, the immunoreactivity was localized predominantly along the cytoplasmic membrane of both cell types. These cells in normal mice incorporated a small amount of injected particles (carbon particles and latex beads), while after LPS stimulation, the uptake of particles increased in terms of the amount and extent of the uptaking sites. Endothelial cells and reticular cells without SSeCKS expression could not incorporate any particles even after LPS stimulation. The subcellular localization of SSeCKS in endothelial cells correlated with some pinocytic pits and phago-lysosomes, although a diffuse distribution of SSeCKS in the cytoplasm was also visible. Taken together, these findings indicate that SSeCKS expression in endothelial cells and reticular cells is a functional index of the reticulo-endothelial system and is involved in the uptake of particles from blood and lymph circulation.

Ligand-specific control of src-suppressed C kinase substrate gene expression

The src-suppressed C-kinase substrate, SSeCKS, is now recognized as a key regulator of cell signaling and cytoskeletal dynamics. However, few ligands that control SSeCKS expression have been identified. We report that platelet-derived growth factor-BB (PDGF-BB), lysophosphatidic acid (LPA), and eicosapentaenoic acid (EPA) potently modulate SSeCKS gene expression in cultured smooth muscle (RASM) cells relative to other bioactive ligands tested. In addition, EPA-dependent regulation of SSeCKS expression correlates with distinct changes in cell morphology and adhesion in RASM cells. Independent evidence that ligand-specific control of SSeCKS expression links to the regulation of cell adhesion and morphology was obtained using ras-transformed fibroblasts, KNRK. Sodium butyrate (NaB) upregulates SSeCKS mRNA and protein expression corresponding to increased cell-spreading and adhesion. In addition, ectopic expression of recombinant SSeCKS recapitulates attributes of NaB-induced morphogenesis in KNRK cells. The data provide novel evidence that SSeCKS functions in PDGF-BB-, LPA-, EPA-, and NaB-mediated cell signaling.