Signaling pathways controlling cell polarity and chemotaxis

Many important biological processes, including chemotaxis (directional cell movement up a chemoattractant gradient), require a clearly established cell polarity and the ability of the cell to respond to a directional signal. Recent advances using Dictyostelium cells and mammalian leukocytes have provided insights into the biochemical and molecular pathways that control chemotaxis. Phosphoinositide 3-kinase plays a central and possibly pivotal role in establishing and maintaining cell polarity by regulating the subcellular localization and activation of downstream effectors that are essential for regulating cell polarity and proper chemotaxis. This review outlines our present understanding of these pathways.     

Hexosamine induction of oxidative stress, hypertrophy and laminin expression in renal mesangial cells: effect of the anti-oxidant alpha-lipoic acid

We have previously shown that one of the potential mediators of the deleterious effects of high glucose on extracellular matrix protein (ECM) expression in renal mesangial cells is its metabolic flux through the hexosamine biosynthesis pathway (HBP). Here, we investigate further whether the hexosamines induce oxidative stress, cell-cycle arrest and ECM expression using SV-40-transformed rat mesangial (MES) cells and whether the anti-oxidant alpha-lipoic acid will reverse some of these effects. Culturing renal MES cells with high glucose (HG, 25 mM) or glucosamine (GlcN, 1.5 mM) for 48 h stimulates laminin gamma1 subunit expression significantly approximately 1.5 +/- 0.2- and 1.9 +/- 0.3-fold, respectively, when compared to low glucose (LG, 5 mM). Similarly, HG and GlcN increase the level of G0/G1 cell-cycle progression factor cyclin D1 significantly approximately 1.7 +/- 0.2- and 1.4 +/- 0.04-fold, respectively, versus LG (p < 0.01 for both). Azaserine, an inhibitor of glutamine:fruc-6-PO(4) amidotransferase (GFAT) in the HBP, blocks the HG-induced expression of laminin gamma1 and cyclin D1, but not GlcN's effect because it exerts its metabolic function distal to GFAT. HG and GlcN also elevate reactive oxygen species (ROS) generation, pro-apoptotic caspase-3 activity, and lead to mesangial cell death as revealed by TUNEL and Live/Dead assays. FACS analysis of cell-cycle progression shows that the cells are arrested at G1 phase; however, they undergo cell growth and hypertrophy as the RNA/DNA ratio is significantly (p < 0.05) increased in HG or GlcN-treated cells relative to LG. The anti-oxidant alpha-lipoic acid (150 microM) reverses ROS generation and mesangial cell death induced by HG and GlcN. Alpha-lipoic acid also reduces HG and GlcN-induced laminin gamma1 and cyclin D1 expression in MES cells. In addition, induction of diabetes in rats by streptozotocin (STZ) increases both laminin gamma1 and cyclin D1 expression in the renal cortex and treatment of the diabetic rats with alpha-lipoic acid (400 mg kg(-1) body weight) reduces the level of both proteins significantly (p < 0.05) when compared to untreated diabetic rats. These results support the hypothesis that the hexosamine pathway mediates mesangial cell oxidative stress, ECM expression and apoptosis. Anti-oxidant alpha-lipoic acid reverses the effects of high glucose, hexosamine and diabetes on oxidative stress and ECM expression in mesangial cells and rat kidney.     

Signaling pathways regulating ectodermal cell fate choices

Although embryonic patterning and early development of the nervous system have been studied for decades, our understanding of how signals instruct ectodermal derivatives to acquire specific identities has only recently started to form a coherent picture. In this mini-review, we summarize recent findings and models of how a handful of well-known secreted signals influence progenitor cells in successive binary decisions to adopt various cell type specific differentiation programs.     

Investigation of VHL gene associated with miR-223 in clear cell renal cell carcinoma

Background

Clear cell type renal cell carcinoma (ccRCC) is the most common renal cell carcinoma (RCC). In this study, we examined the expressions of VHL and miR-223 in ccRCC patients? tissues to investigate the possible role in the development of ccRCC.

Methods and results

This study collected five expression profiles (GSE36139, GSE3, GSE73731, GSE40435, and GSE26032) from Gene Omnibus Data. Expressions of VHL and miR-223 in paraffinized tumor and normal tissues of 100 Turkish patients' ccRCC tissues were determined by bioinformatic data mining and real-time quantitative polymerase chain reaction (qRT-PCR). The VHL gene was subjected to mutational analysis by DNA sequencing, and pVHL was analyzed using western blotting. Our study's t-test and Pearson correlation analysis showed that VHL gene expression in tumoral tissues with a???0.39-fold decrease was not significantly lower than normal tissues (p?=?0.441), and a 0.97-fold increase miR-223 (p?=?0.045) was determined by real-time PCR. Also, as a result of DNA sequence analysis performed in the VHL gene, it was found that 26% of the patients have mutations. The mutations for (VHL):c.60C>A (p.Val20=) and (VHL):c.467delA (p.Tyr156Leu) was detected for the first time in Turkish patients.

Conclusions

The present study demonstrated that the differences in the expression levels of miR-223 have the potential to be biomarkers to determine the poor prognosis in ccRCC.

     

Signaling pathways and effector mechanisms pre-programmed cell death.

Apoptosis is a complex biochemical process that involves all aspects of the cell from the plasma membrane to the nucleus. Apoptosis stimuli are mediated by many different cellular processes including protein synthesis and degradation, the alteration in protein phosphorylation states, the activation of lipid second messenger systems, and disruption of normal mitochondrial function. Despite this diversity in signal transduction, all apoptotic pathways are believed to converge ultimately with the activation of caspases leading to the characteristic morphological changes of apoptosis. In this review, we discuss what is known about these pathways and its implication for normal cellular function.     

Irradiation of rat mesangial cells alters the expression of gene products associated with the development of renal fibrosis.

To determine the ability of radiation to modulate mesangial cell expression of various molecules involved in promoting extracellular matrix (ECM) accumulation [fibronectin, plasminogen activator-inhibitor 1 (Pai1), and tissue inhibitor of metalloproteinase-2 (Timp2)] and degradation (Tgfb, plasminogen activators u-PA or t-PA, matrix metalloproteinases Mmp2 and Mmp9), primary cultures of rat mesangial cells (passage number 6-11) were placed in serum-free medium 24 h prior to irradiation with single doses of 0.5-20 Gy (137)Cs gamma rays. After irradiation, cells were maintained in serum-free medium for a further 48 h. Irradiation of quiescent mesangial cells resulted in significant (P < 0.05) time- and dose-dependent increases in Fn and Pai1 mRNA and/or immunoreactive protein. Despite an increase in Tgfb1 mRNA, there was little evidence for an increase in total Tgfb protein. Indeed, active levels remained unaltered after irradiation. Irradiation led to differential changes in MMP expression; active Mmp2 levels increased, while Mmp9 levels appeared unaltered. In addition, secretion of plasminogen activators into the medium was unchanged after irradiation, while secretion of Timp2 increased. We conclude that irradiating mesangial cells leads to altered production of various molecules involved in accumulation and degradation of extracellular matrix.     

Apoptosis. Signaling pathways and cell ion and water balance

Current data on the alteration of the monovalent ion balance, pH and the membrane potential during apoptosis are summarized and considered with respect to ionic mechanisms of the apoptotic cell shrinkage. A brief survey of the main signaling pathways involved in apoptosis, such as receptor-and mitochondria-mediated pathways of the caspase-dependent and caspase-independent apoptosis is given. The data on the alteration of the distinct ion transporters and channels of the plasma membrane during apoptosis are considered.     

调节表皮干细胞增殖和分化的信号通路

表皮干细胞能够维持正常表皮的新陈代谢、毛囊周期循环以及参与创伤情况下创面的修复,皮肤肿瘤的发生也与其密切相关。表皮干细胞的增殖和分化受到严格的调控,了解表皮干细胞增殖与分化的调控机制将有助于治疗脱发、创伤以及皮肤肿瘤等疾病。文章着重概述了Wnt和Bmp信号对于控制干细胞命运的重要作用。     

Hypoxia enhances prostaglandin synthesis in renal mesangial cell cultures

In view of recent findings which suggest that renal prostaglandins mediate the effect of hypoxia on erythropoietin production, we have studied whether hypoxia is a stimulus for in vitro prostaglandin synthesis. Studies were carried out in rat renal mesangial cell cultures which produce erythropoietin in an oxygen-dependent manner. Production rates of PGE2 and in specified samples also of 6-keto-PGF1 alpha, as a measure of PGI2, and PGF2 alpha were determined by radioimmunoassay after incubation at either 20% O2 (normoxic) or 2% O2 (hypoxic) in gas permeable dishes for 24 hrs. Considerable variation in PGE2 production was noted among independent cell lines. PGE2 production appeared to be inversely correlated to the cellular density of the cultures. In addition, PGE2 production was enhanced in hypoxic cell cultures. The mean increase was 50 to 60%. PGF2 alpha and 6-keto-PGF1 alpha increased by about the same rate. These results indicate that hypoxia is a stimulus for in vitro prostaglandin production.     

Hypoxia enhances prostaglandin synthesis in renal mesangial cell cultures

In view of recent findings which suggest that renal prostaglandins mediate the effect of hypoxia on erythropoietin production, we have studied whether hypoxia is a stimulus for in vitro prostaglandin synthesis. Studies were carried out in rat renal mesangial cell cultures which produce erythropoietin in an oxygen-dependent manner. Production rates of PGE₂ and in specified samples also of 6-keto-PGF_1α, as a measure of PGI₂, and PGF_2α were determined by radioimmunoassay after incubation at either 20% O₂ (normoxic) or 2% O₂ (hypoxic) in gas permeable dishes for 24 hrs. Considerable variation in PGE₂ production was noted among independent cell lines. PGE₂ production appeared to be inversely correlated to the cellular density of the cultures. In addition, PGE₂ production was enhanced in hypoxic cell cultures. The mean increase was 50 to 60%. PGF_2α and 6-keto-PGF_1α increased by about the same rate. These results indicate that hypoxia is a stimulus for in vitro prostaglandin production.     

Signaling pathways and cell mechanics involved in wound closure by epithelial cell sheets

BACKGROUND: Sheets of cells move together as a unit during wound healing and embryonic tissue movements, such as those occurring during gastrulation and neurulation. We have used epithelial wound closure as a model system for such movements and examined the mechanisms of closure and the importance of the Rho family of Ras-related small GTPases in this process. RESULTS: Wounds induced in Madin-Darby canine kidney (MDCK) epithelial cell monolayers close by Rac- and phosphoinositide-dependent cell crawling, with formation of lamellipodia at the wound margin, and not by contraction of a perimarginal actomyosin purse-string. Although Rho-dependent actin bundles usually form at the margin, neither Rho activity nor formation of these structures is required for wound closure to occur at a normal rate. Cdc42 activity is also not required for closure. Inhibition of Rho or Cdc42 results, however, in statistically significant decreases in the regularity of wound closure, as determined by the ratio of wound margin perimeter over the remaining denuded area at different times. The Rac-dependent force generation for closure is distributed over several rows of cells from the wound margin, as inhibition of motility in the first row of cells alone does not inhibit closure and can be compensated for by generation of motile force in cells behind the margin. Furthermore, we observed high levels of Rac-dependent actin assembly in the first few rows of cells from the wound margin. CONCLUSIONS: Wounds in MDCK cell sheets do not close by purse-string contraction but by a crawling behavior involving Rac, phosphoinositides and active movement of multiple rows of cells. This finding suggests a new distributed mode of signaling and movement that, nevertheless, resembles individual cell motility. Although Rho and Cdc42 activities are not required for closure, they have a role in determining the regularity of closure.     

Signaling pathways associated with macrophage-activating polysaccharide isolated from the fermentation liquor of Rhizopus nigricans

Our previous reports showed that the structural features and immunologic enhancement of polysaccharide (EPS1-1) from Rhizopus nigricans. However, the molecular mechanism in cellular immunomodulatory of EPS1-1 remains unclear. Here the experiments for the molecular mechanisms of EPS1-1 on the peritoneal macrophages were performed. The results demonstrated that the expression of TLR4 was significantly improved by EPS1-1. Subsequently, the phosphorylation of p38MAPK, ERK1/2, JNK and IKKα/β were promoted. Moreover, EPS1-1 enhanced the expressions of IL-2, TNF-α and iNOS in EPS1-1-induced macrophages which were pretreated with MAPK signaling pathway inhibitors, and reduced the blocking effects of the inhibitors to the expressions of p-p38MAPK, p-ERK1/2 and p-IKKα/β. Therefore, these results illustrated that EPS1-1 could improve the immune functions of peritoneal macrophages by promoting the gene expressions of IL-2, TNF-α and iNOS via the MAPK and NF-κB signaling pathways.     

Signaling pathways in sensitization: toward a nociceptor cell biology

The electrophysiological properties of peripheral neurons activated by noxious stimuli, the primary afferent nociceptors, have been investigated intensively, and our knowledge about the molecular basis of transducers for noxious stimuli has increased greatly. In contrast, understanding of the intracellular signaling mechanisms regulating nociceptor sensitization downstream of ligand binding to the receptors is still at a relatively nascent stage. After outlining the initiated signaling cascades, we discuss the emerging plasticity within these cascades and the importance of subcellular compartmentalization. In addition, the recently realized importance of functional interactions with the extracellular matrix, cytoskeleton, intracellular organelles such as mitochondria, and sex hormones will be introduced. This burgeoning literature establishes new cellular features crucial for the function of nociceptive neurons and argues that additional focus should be placed on understanding the complex integration of cellular events that make up the "cell biology of pain."     

The von Hippel-Lindau gene product inhibits renal cell apoptosis via Bcl-2-dependent pathways

Previous studies have reported a protective role for the von Hippel-Lindau (VHL) gene products against pro-apoptotic cellular stresses, but the mechanisms remain unclear. In this study, we examined the role of VHL in renal cells subjected to chemical hypoxia, using four VHL-negative and two VHL-positive cell lines. VHL-negative renal carcinoma cells underwent apoptosis following chemical hypoxia (short-term glucose deprivation and antimycin treatment), as evidenced by morphologic changes and internucleosomal DNA cleavage. Reintroduction of VHL expression prevented this apoptosis. VHL-negative cells displayed a significant (greater than 5-fold) activation of caspase 9 and release of cytochrome c into the cytosol following chemical hypoxia. In contrast, VHL-positive cells showed minimal caspase 9 activation, and absence of cytochrome c release under the same conditions. Caspase 8 was only minimally activated in both VHL-negative and -positive cells. In addition, VHL-positive cells displayed a striking up-regulation of Bcl-2 expression (5-fold) following chemical hypoxia. Antisense oligonucleotides to Bcl-2 significantly down-regulated Bcl-2 protein expression in VHL-positive cells and rendered them sensitive to apoptosis. Overexpression of Bcl-2 in VHL-negative cells conferred resistance to apoptosis. Our results suggest that VHL protects renal cells from apoptosis via Bcl-2-dependent pathways.