Inhibition of integrin-linked kinase/protein kinase B/Akt signaling: mechanism for ganglioside-induced apoptosis

Endocytic Roles of Glycans on Proteins and Lipids

Most cell surface proteins are decorated by glycans, and the plasma membrane is rich in glycosylated lipids. The mechanisms by which the enormous complexity of these glycan structures on proteins and lipids is exploited to control glycoprotein activity by setting their cell surface residence time and the ways by which they are taken up into cells are still under active investigation. Here, two mechanisms are presented, termed galectin lattices and glycolipid-lectin (GL-Lect)-driven endocytosis, which are among the most prominent to establish a link between glycan information and endocytosis. Types of glycans on glycoproteins and glycolipids are reviewed from the angle of their interaction with glycan-binding proteins that are at the heart of galectin lattices and GL-Lect-driven endocytosis. Examples are given to show how these mechanisms affect cellular functions ranging from cell migration and signaling to vascularization and immune modulation. Finally, outstanding challenges on the link between glycosylation and endocytosis are discussed.

A network-based integration for understanding racial disparity in prostate cancer

Compared to Caucasians (CAs), African Americans (AAs) have a higher rate of incidence and mortality in prostate cancer and are prone to be diagnosed at later stages. To understand this racial disparity, molecular features of different types, including gene expression, DNA methylation and other genomic alterations, have been compared between tumor samples from the two races, but led to different disparity associated genes (DAGs). In this study, we applied a network-based algorithm to integrate a comprehensive set of genomic datasets and identified 130 core DAGs. Out of these genes, 78 were not identified by any individual dataset but prioritized and selected through network propagation. We found DAGs were highly enriched in several critical prostate cancer-related signaling transduction and cell cycle pathways and were more likely to be associated with patient prognosis in prostate cancer. Furthermore, DAGs were over-represented in prostate cancer risk genes identified from previous genome wide association studies. We also found DAGs were enriched in kinase and transcription factor encoding genes. Interestingly, for many of these prioritized kinases their association with racial disparity did not manifest from the original genomic/transcriptomic data but was reflected by their differential phosphorylation levels between AA and CA prostate tumor samples. Similarly, the disparity relevance of some transcription factors was not reflected at the mRNA or protein expression level, but at the activity level as demonstrated by their differential ability in regulating target gene expression. Our integrative analysis provided new candidate targets for improving prostate cancer treatment and addressing the racial disparity problem.

Iron Oxide Nanoparticles Carrying 5-Fluorouracil in Combination with Magnetic Hyperthermia Induce Thrombogenic Collagen Fibers, Cellular Stress, and Immune Responses in Heterotopic Human Colon Cancer in Mice

In this study we looked for the main protein pathway regulators which were responsible for the therapeutic impact on colon cancers when combining magnetic hyperthermia with the chemotherapeutic agent 5-fluorouracil (5FU). To this end, chitosan-coated magnetic nanoparticles (MNP) functionalized with 5FU were intratumorally injected into subcutaneous human colon cancer xenografts (HT-29) in mice and exposed to an alternating magnetic field. A decreased tumor growth was found particularly for the combined thermo-chemotherapy vs. the corresponding monotherapies. By using computational analysis of the tumor proteome, we found upregulated functional pathway categories termed "cellular stress and injury", "intracellular second messenger and nuclear receptor signaling", "immune responses", and "growth proliferation and development". We predict TGF-beta, and other mediators, as important upstream regulators. In conclusion, our findings show that the combined thermo-chemotherapy induces thrombogenic collagen fibers which are able to impair tumor nutrient supply. Further on, we associate several responses to the recognition of damage associated molecular patterns (DAMPs) by phagocytic cells, which immigrate into the tumor area. The activation of some pathways associated with cell survival implies the necessity to conduct multiple therapy sessions in connection with a corresponding monitoring, which could possibly be performed on the base of the identified protein regulators.

D-Limonene Is a Potential Monoterpene to Inhibit PI3K/Akt/IKK-α/NF-κB p65 Signaling Pathway in Coronavirus Disease 2019 Pulmonary Fibrosis

At the time of the prevalence of coronavirus disease 2019 (COVID-19), pulmonary fibrosis (PF) related to COVID-19 has become the main sequela. However, the mechanism of PF related to COVID (COVID-PF) is unknown. This study aimed to explore the key targets in the development of COVID-PF and the mechanism of d-limonene in the COVID-PF treatment. The differentially expressed genes of COVID-PF were downloaded from the GeneCards database, and their pathways were analyzed. d-Limonene was molecularly docked with related proteins to screen its pharmacological targets, and a rat lung fibrosis model was established to verify d-limonene's effect on COVID-PF-related targets. The results showed that the imbalance between collagen breakdown and metabolism, inflammatory response, and angiogenesis are the core processes of COVID-PF; and PI3K/AKT signaling pathways are the key targets of the treatment of COVID-PF. The ability of d-limonene to protect against PF induced by bleomycin in rats was reported. The mechanism is related to the binding of PI3K and NF-κB p65, and the inhibition of PI3K/Akt/IKK-α/NF-κB p65 signaling pathway expression and phosphorylation. These results confirmed the relationship between the PI3K–Akt signaling pathway and COVID-PF, showing that d-limonene has a potential therapeutic value for COVID-PF.

Glycosylation and raft endocytosis in cancer

Changes in glycosylation on proteins or lipids are one of the hallmarks of tumorigenesis. In many cases, it is still not understood how glycan information is translated into biological function. In this review, we discuss at the example of specific cancer-related glycoproteins how their endocytic uptake into eukaryotic cells is tuned by carbohydrate modifications. For this, we not only focus on overall uptake rates, but also illustrate how different uptake processes-dependent or not on the conventional clathrin machinery-are used under given glycosylation conditions. Furthermore, we discuss the role of certain sugar-binding proteins, termed galectins, to tune glycoprotein uptake by inducing their crosslinking into lattices, or by co-clustering them with glycolipids into raft-type membrane nanodomains from which the so-called clathrin-independent carriers (CLICs) are formed for glycoprotein internalization into cells. The latter process has been termed glycolipid-lectin (GL-Lect) hypothesis, which operates in a complementary manner to the clathrin pathway and galectin lattices.

Identification of single-nucleotide variants associated with susceptibility to Salmonella in pigs using a genome-wide association approach

BACKGROUND

Salmonella enterica serovars are a major cause of foodborne illness and have a substantial impact on global human health. In Canada, Salmonella is commonly found on swine farms and the increasing concern about drug use and antimicrobial resistance associated with Salmonella has promoted research into alternative control methods, including selecting for pig genotypes associated with resistance to Salmonella. The objective of this study was to identify single-nucleotide variants in the pig genome associated with Salmonella susceptibility using a genome-wide association approach. Repeated blood and fecal samples were collected from 809 pigs in 14 groups on farms and tonsils and lymph nodes were collected at slaughter. Sera were analyzed for Salmonella IgG antibodies by ELISA and feces and tissues were cultured for Salmonella. Pig DNA was genotyped using a custom 54 K single-nucleotide variant oligo array and logistic mixed-models used to identify SNVs associated with IgG seropositivity, shedding, and tissue colonization.

RESULTS

Variants in/near PTPRJ (p = 0.0000066), ST6GALNAC3 (p = 0.0000099), and DCDC2C (n = 3, p < 0.0000086) were associated with susceptibility to Salmonella, while variants near AKAP12 (n = 3, p < 0.0000358) and in RALGAPA2 (p = 0.0000760) may be associated with susceptibility.

CONCLUSIONS

Further study of the variants and genes identified may improve our understanding of neutrophil recruitment, intracellular killing of bacteria, and/or susceptibility to Salmonella and may help future efforts to reduce Salmonella on-farm through genetic approaches.

Baicalin alleviates bleomycin‑induced pulmonary fibrosis and fibroblast proliferation in rats via the PI3K/AKT signaling pathway

Baicalin is an important flavonoid compound THAT is isolated from the Scutellaria baicalensis Georgi Chinese herb and plays a critical role in anti‑oxidative, anti‑inflammatory, anti‑infection and anti‑tumor functions. Although baicalin can suppress the proliferation of tumor cells, the underlying mechanisms of baicalin in bleomycin (BLM)‑induced pulmonary fibrosis remain to be elucidated. Thus, the aim of the present study was to determine the role of baicalin in pulmonary fibrosis and fibroblast proliferation in rats. Hematoxylin and eosin (H&E) and Masson staining were used to measure the morphology of pulmonary fibrosis, ELIASA kits were used to test the ROS and inflammation, and western blotting and TUNEL were performed to study the apoptosis proteins. In vitro, MTT assay, flow cytometry, western blotting and immunofluorescence were performed to investigate the effects of baicalin on proliferation of fibroblasts. The most significantly fibrotic changes were identified in the lungs of model rats at day 28. Baicalin (50 mg/kg) attenuated the degree of pulmonary fibrosis, and the hydroxyproline content of the lung tissues was decreased in the baicalin group, compared with the BLM group. Further investigation revealed that baicalin significantly increased glutathione peroxidase (GSH‑px), total‑superoxide dismutase (T‑SOD) and glutathione (GSH) levels, whilst decreasing that of serum malondialdehyde (MDA). TUNEL‑positive cells were significantly decreased in rats treated with baicalin group, compared with the model group. Furthermore, it was found that BLM promoted fibroblasts viability in a dose‑dependent manner in vivo, which was restricted following treatment with different concentrations of baicalin. Moreover, BLM promoted the expression levels of cyclin A, D and E, proliferating cell nuclear antigen, phosphorylated (p)‑AKT and p‑calcium/calmodulin‑dependent protein kinase type. BLM also promoted the transition of cells from the G0/G1 phase to the G2/M and S phases, and increased the intracellular Ca2+ concentration, which was subsequently suppressed by baicalin. Collectively, the results of the present study suggested that baicalin exerted a suppressive effect on BLM‑induced pulmonary fibrosis and fibroblast proliferation.

Mutation and expression of ABCA12 in keratosis pilaris and nevus comedonicus

Keratosis pilaris (KP) and nevus comedonicus (NC) are congenital keratinized dermatoses; however, the exact etiology of these two diseases is unclear. The objective of the present study was to identify the disease-causing genes and their association with functional alterations in the development of KP and NC. Peripheral blood samples of one KP family, two NC families and 100 unrelated healthy controls were collected. The genomic sequences of 147 genes associated with 143 genetic skin diseases were initially analyzed from the KP proband using a custom-designed GeneChip. A novel heterozygous missense mutation in the ATP-binding cassette sub-family A member 12 (ABCA12) gene, designated c.6694G>T (p.Asp2232Tyr), was identified in the KP proband and confirmed by Sanger sequencing. The same mutation was also present in the affected family members but not in the healthy family members, the two patients with NC or population-matched controls. The predictions provided by PolyPhen-2 and SIFT analyses suggested that the mutation may produce a damaged protein. The region surrounding the mutation is the extra-membrane domain, which is conserved among particular species, as suggested by ClustalX; however, no ABCA12 mutations were reported in the patients with NC. As observed by immunofluorescence, ABCA12 expression was upregulated in the sebaceous glands of the patients with NC compared with that of normal controls. In summary, ABCA12-associated mutations or alterations in expression may exhibit causative or contributive effects to the development of keratinized dermatoses, including KP and NC.

The transient receptor potential vanilloid-3 regulates hypoxia-mediated pulmonary artery smooth muscle cells proliferation via PI3K/AKT signaling pathway

OBJECTVES

Transient receptor potential vanilloid 3 (TRPV3) is a member of the TRP channels family of Ca²⁺ -permeant cation channels. In this study, we aim to investigate the role of TRPV3 in pulmonary vascular remodeling and PASMCs proliferation under hypoxia.

MATERIALS AND METHODS

The expression of TRPV3 was evaluated in patients with pulmonary arterial hypertension (PAH) and hypoxic rats, using hematoxylin and eosin (H&E) and immunohistochemistry. In vitro, MTT assay, flow cytometry, Western blotting and immunofluorescence were performed to investigate the effects of TRPV3 on proliferation of PASMCs.

RESULTS

We found that, in vivo, the expression of TRPV3 was increased in patients with PAH and hypoxic rats. Right ventricular hypertrophy measurements and pulmonary pathomorphology data show that the ratio of the heart weight/tibia length (HW/TL), the right ventricle/left ventricle plus septum (RV/LV+S) and the medial width of the pulmonary artery were increased in chronic hypoxic rats. Moreover, the expression of proliferating cell nuclear antigen (PCNA), Cyclin D, Cyclin E and Cyclin A, phospho-CaMKII (p-CaMKII) were induced by hypoxia. In vitro, we revealed that hypoxia promoted PASMCs viability, increased the expression of PCNA, Cyclin D, Cyclin E, Cyclin A p-CaMKII, made more cells from G₀ /G₁ phase to G₂ /M + S phase, enhanced the microtubule formation, and increased [Ca²⁺ ]_i , which could be suppressed by Ruthenium Red, an inhibitor of TRPV3, and TRPV3 silencing has similar effects. Furthermore, the up-regulated expression of PCNA, Cyclin D, Cyclin E and Cyclin A, the increased number of cells in G₂ /M and S phase, and the enhanced activation and expression of PI3K and AKT proteins induced by hypoxia and in presence of carvacrol (an agonist of TRPV3), was significantly attenuated by incubation of LY 294002, a specific inhibitor for PI3K/AKT.

CONCLUSIONS

These findings suggest that TRPV3 is involved in hypoxia-induced pulmonary vascular remodeling and promotes proliferation of PASMCs and the effect is, at least in part, mediated via the PI3K/AKT pathway.

TGF-β1 inhibits the apoptosis of pulmonary arterial smooth muscle cells and contributes to pulmonary vascular medial thickening via the PI3K/Akt pathway

Previous studies have highlighted that the transforming growth factor‑β1 (TGF‑β1) pathway may be activated by hypoxic conditions. TGF‑β1 also participates in the regulation of proliferation, differentiation, migration and apoptosis of various cell types. Furthermore, TGF‑β1 has been reported to participate in the regulation of the progression of pulmonary arterial hypertension (PAH). However, the effect of TGF‑β1 on pulmonary arterial smooth muscle cells (PASMCs) and the corresponding molecular mechanisms remain unclear. The present study aimed to determine whether TGF‑β1 protects against cell apoptosis in PASMCs, and identify the underlying molecular mechanisms. Western blotting, MTT and lactate dehydrogenase activity assays were performed, and the activity of caspase‑3 and caspase‑9 was detected in order to investigate the hypothesis. It was determined that TGF‑β1 may facilitate cell growth in a dose‑dependent manner in serum‑starved PASMCs. Furthermore, it was observed that apoptosis in serum‑starved PASMCs was inhibited by TGF‑β1 via regulation of the expression levels of mitochondrial membrane proteins. Additionally, the phosphatidylinositol 3‑kinase/protein kinase B (PI3K/Akt) pathway was found to be activated by TGF‑β1 in PASMCs, while the inhibition of PI3K/Akt signaling also prevented the apoptosis‑limiting effects of TGF‑β1. These observations suggest that TGF‑β1 protects PASMCs from apoptosis and contributes to pulmonary vascular medial thickening via the PI3K/Akt pathway.

BMP4 protects rat pulmonary arterial smooth muscle cells from apoptosis by PI3K/AKT/Smad1/5/8 signaling

Bone morphogenetic protein-4 (BMP4), a member of the transforming growth factor β (TGF-β) family of growth factors, is activated and increased under hypoxic conditions, which plays an important role in the progression of pulmonary arterial hypertension (PAH). Previous studies have shown that BMP4 is involved in the regulation of proliferation, differentiation, migration and apoptosis of various cell types. However, the precise mechanisms involved in the regulation of pulmonary artery smooth muscle cells (PASMCs) in PAH are still incompletely understood. It has been reported that AKT is a critical regulator of cell survival and vascular remodeling. Therefore, there may be crosstalk between BMP4 anti-apoptotic processes and PI3K/AKT survival effect in rat PASMCs. To test this hypothesis, we performed confocal, cell viability measurement, mitochondrial potential, real-time polymerase chain reaction (PCR), and Western blot analysis to determine the role of BMP4 on cell survival and apoptosis. We found that hypoxia up-regulated the expression of BMP4. BMP4 promoted cell survival, reduced mitochondrial depolarization, and increased the expression of Bcl-2 and procaspase-3 in PASMCs under serum-deprived condition. These effects were reversed by PI3K/AKT inhibitors (LY294002 and wortmannin). Thus, these findings indicate that BMP4 protects PASMCs from apoptosis at least in part, mediated via the PI3K/AKT pathway.

Galectin-3 drives glycosphingolipid-dependent biogenesis of clathrin-independent carriers

Several cell surface molecules including signalling receptors are internalized by clathrin-independent endocytosis. How this process is initiated, how cargo proteins are sorted and membranes are bent remains unknown. Here, we found that a carbohydrate-binding protein, galectin-3 (Gal3), triggered the glycosphingolipid (GSL)-dependent biogenesis of a morphologically distinct class of endocytic structures, termed clathrin-independent carriers (CLICs). Super-resolution and reconstitution studies showed that Gal3 required GSLs for clustering and membrane bending. Gal3 interacted with a defined set of cargo proteins. Cellular uptake of the CLIC cargo CD44 was dependent on Gal3, GSLs and branched N-glycosylation. Endocytosis of β1-integrin was also reliant on Gal3. Analysis of different galectins revealed a distinct profile of cargoes and uptake structures, suggesting the existence of different CLIC populations. We conclude that Gal3 functionally integrates carbohydrate specificity on cargo proteins with the capacity of GSLs to drive clathrin-independent plasma membrane bending as a first step of CLIC biogenesis.

Disialoganglioside GD3-synthase over expression inhibits survival and angiogenesis of pancreatic cancer cells through cell cycle arrest at S-phase and disruption of integrin-β1-mediated anchorage

Gangliosides play important roles in the development, differentiation and proliferation of mammalian cells. They bind to other cell membrane components through their terminal sialic acids. Different gangliosides influence cellular functions based on the positions and linkages of sialic acids. Expression of gangliosides mainly depends on the status of sialic acid-modulatory enzymes, such as different types of sialyltransferases and sialidases. One such sialyltransferase, disialoganglioside GD3 synthase, is specifically responsible for the production of GD3. Pancreatic ductal adenocarcinoma, making up more than 90% of pancreatic cancers, is a fatal malignancy with poor prognosis. Despite higher sialylation status, the disialoganglioside GD3 level is very low in this cancer. However, the exact status and function of this disialoganglioside is still unknown. Here, we intended to study the intracellular mechanism of disialoganglioside GD3-induced apoptosis and its correlation with the adhesion and angiogenic pathways in pancreatic cancer. We demonstrated that disialoganglioside GD3 synthase-transfected cells showed enhanced apoptosis and it caused the arrest of these cells in the S-phase of the cell cycle. Integrins, a family of transmembrane proteins play important role in cell-cell recognition, invasion, adhesion and migration. disialoganglioside GD3 co-localised with integrin-β1 and thereby inhibited it's downstream signalling in transfected cells. Transfected cells exhibited inhibition of cell adhesion with extracellular matrix proteins. Enhanced GD3 expression down regulated angiogenesis-regulatory proteins and inhibited epidermal growth factor/vascular endothelial growth factor-driven angiogenic cell growth in these cells. Taken together, our study provides support for the GD3-induced cell cycle arrest, disruption of integrin-β1-mediated anchorage, inhibition of angiogenesis and thereby induced apoptosis in pancreatic cancer cells.

The roles of ABCA12 in epidermal lipid barrier formation and keratinocyte differentiation

ATP-binding cassette (ABC) transporters form a large superfamily of transporters that bind and hydrolyze ATP to transport various molecules across limiting membranes or into vesicles. The ABCA subfamily members are thought to transport lipid materials. ABCA12 is a keratinocyte transmembrane lipid transporter protein associated with the transport of lipids via lamellar granules. ABCA12 is considered to transport lipids including ceramides to form extracellular lipid layers in the stratum corneum of the epidermis, which is essential for skin barrier function. ABCA12 mutations are known to underlie the three major types of autosomal recessive congenital ichthyoses: harlequin ichthyosis, lamellar ichthyosis and congenital ichthyosiform erythroderma. ABCA12 mutations result in defective lipid transport via lamellar granules in the keratinocytes, leading to ichthyosis phenotypes from malformation of the stratum corneum lipid barrier. Studies on ABCA12-deficient bioengineered models have revealed that lipid transport by ABCA12 is required for keratinocyte differentiation and epidermal morphogenesis. Defective lipid transport due to loss of ABCA12 function leads to the accumulation of intracellular lipids, including glucosylceramides and gangliosides, in the epidermal keratinocytes. The accumulation of gangliosides seems to result in the apoptosis of Abca12(-/-) keratinocytes. It was reported that AKT activation occurs in Abca12(-/-) granular-layer keratinocytes, which suggests that AKT activation serves to prevent the cell death of Abca12(-/-) keratinocytes. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Deacetylated GM3 promotes uPAR-associated membrane molecular complex to activate p38 MAPK in metastatic melanoma

GM3, the simplest ganglioside, regulates cell proliferation, migration, and invasion by influencing cell signaling at the membrane level. Although the classic N-acetylated form of GM3 (NeuAcLacCer) is commonly expressed and has been well studied, deacetylated GM3 (NeuNH2LacCer, d-GM3) has been poorly investigated, despite its presence in metastatic tumors but not in noninvasive melanomas or benign nevi. We have recently found that d-GM3 stimulates cell migration and invasion by activating urokinase plasminogen activator receptor (uPAR) signaling to augment matrix metalloproteinase-2 (MMP-2) function. However, the mechanisms by which d-GM3/uPAR increase MMP-2 expression and activation are not clear. By modifying the expression of d-GM3 genetically and biochemically, we found that decreasing d-GM3 expression inhibits, whereas overexpressing d-GM3 stimulates, p38 mitogen-activated protein kinase (MAPK) activity to influence MMP-2 expression and activation. p38 MAPK (p38) activation requires the formation of a membrane complex that contains uPAR, caveolin-1, and integrin α5β1 in membrane lipid rafts. In addition, knocking down or inhibiting focal adhesion kinase (FAK), phosphoinositide 3-kinase (PI3K), or Src kinase significantly reduces d-GM3-induced p38 phosphorylation and activation. Taken together, these results suggest that d-GM3 enhances the metastatic phenotype by activating p38 signaling through uPAR/integrin signaling with FAK, PI3K, and Src kinase as intermediates. Elucidation of the mechanisms by which d-GM3, a newly discovered, potential biomarker of metastatic melanomas, promotes cell metastasis will help us to understand the function of d-GM3 in metastatic melanomas and may lead to novel GM3-based cancer therapies.

The ganglioside G(D2) induces the constitutive activation of c-Met in MDA-MB-231 breast cancer cells expressing the G(D3) synthase

We have recently established and characterized cellular clones deriving from MDA-MB-231 breast cancer cells that express the human G(D3) synthase (GD3S), the enzyme that controls the biosynthesis of b- and c-series gangliosides. The GD3S positive clones show a proliferative phenotype in the absence of serum or growth factors and an increased tumor growth in severe immunodeficient mice. This phenotype results from the constitutive activation of the receptor tyrosine kinase c-Met in spite of the absence of ligand and subsequent activation of mitogen-activated protein kinase/extracellular signal-regulated kinase and phosphoinositide 3-kinase/Akt pathways. Here, we show by mass spectrometry analysis of total glycosphingolipids that G(D3) and G(D2) are the main gangliosides expressed by the GD3S positive clones. Moreover, G(D2) colocalized with c-Met at the plasma membrane and small interfering RNA silencing of the G(M2)/G(D2) synthase efficiently reduced the expression of G(D2) as well as c-Met phosphorylation and reversed the proliferative phenotype. Competition assays using anti-G(D2) monoclonal antibodies also inhibit proliferation and c-Met phosphorylation of GD3S positive clones in serum-free conditions. Altogether, these results demonstrate the involvement of the disialoganglioside G(D2) in MDA-MB-231 cell proliferation via the constitutive activation of c-Met. The accumulation of G(D2) in c-Met expressing cells could therefore reinforce the tumorigenicity and aggressiveness of breast cancer tumors.

Integrins and bone metastasis: integrating tumor cell and stromal cell interactions

Integrins on both tumor cells and the supporting host stromal cells in bone (osteoclasts, new blood vessels, inflammatory cells, platelets and bone marrow stromal cells) play key roles in enhancing bone metastasis. Tumor cells localize to specific tissues through integrin-mediated contacts with extracellular matrix and stromal cells. Integrin expression and signaling are perturbed in cancer cells, allowing them to "escape" from cell-cell and cell-matrix tethers, invade, migrate and colonize within new tissues and matrices. Integrin signaling through αvβ3 and VLA-4 on tumor cells can promote tumor metastasis to and proliferation in the bone microenvironment. Osteoclast (OC) mediated bone resorption is a critical component of bone metastasis and can promote tumor growth in bone and αvβ3 integrins are critical to OC function and development. Tumors in the bone microenvironment can recruit new blood vessel formation, platelets, pro-tumor immune cells and bone marrow stromal cells that promote tumor growth and invasion in bone. Integrins and their ligands play critical roles in platelet aggregation (αvβ3 and αIIbβ3), hematopoietic cell mobilization (VLA-4 and osteopontin), neoangiogenesis (αvβ3, αvβ5, α6β4, and β1 integrin) and stromal function (osteopontin and VLA-4). Integrins are involved in the pathogenesis of bone metastasis at many levels and further study to define integrin dysregulation by cancer will yield new therapeutic targets for the prevention and treatment of bone metastasis.

Overexpression of ST6GalNAcV, a ganglioside-specific alpha2,6-sialyltransferase, inhibits glioma growth in vivo

Aberrant cell-surface glycosylation patterns are present on virtually all tumors and have been linked to tumor progression, metastasis, and invasivity. We have shown that expressing a normally quiescent, glycoprotein-specific alpha2,6-sialyltransferase (ST6Gal1) gene in gliomas inhibited invasivity in vitro and tumor formation in vivo. To identify other glycogene targets with therapeutic potential, we created a focused 45-mer oligonucleotide microarray platform representing all of the cloned human glycotranscriptome and examined the glycogene expression profiles of 10 normal human brain specimens, 10 malignant gliomas, and 7 human glioma cell lines. Among the many significant changes in glycogene expression observed, of particular interest was the observation that an additional alpha2,6-sialyltransferase, ST6 (alpha-N-acetyl-neuraminyl-2,3-beta-galactosyl-1,3)-N-acetylgalactosaminide alpha2,6-sialyltransferase 5 (ST6GalNAcV), was expressed at very low levels in all glioma and glioma cell lines examined compared with normal brain. ST6GalNAcV catalyzes the formation of the terminal alpha2,6-sialic acid linkages on gangliosides. Stable transfection of ST6GalNAcV into U373MG glioma cells produced (i) no change in alpha2,6-linked sialic acid-containing glycoproteins, (ii) increased expression of GM2alpha and GM3 gangliosides and decreased expression of GM1b, Gb3, and Gb4, (iii) marked inhibition of in vitro invasivity, (iv) modified cellular adhesion to fibronectin and laminin, (v) increased adhesion-mediated protein tyrosine phosphorylation of HSPA8, and (vi) inhibition of tumor growth in vivo. These results strongly suggest that modulation of the synthesis of specific glioma cell-surface glycosphingolipids alters invasivity in a manner that may have significant therapeutic potential.

GT1b-induced neurotoxicity is mediated by the Akt/GSK-3/tau signaling pathway but not caspase-3 in mesencephalic dopaminergic neurons

Background

Gangliosides, sialic acid-containing glycosphingolipids exist in mammalian cell membranes particularly neuronal membranes. The trisialoganglioside (GT1b) is one of the major brain gangliosides and acts as an endogenous regulator in the brain. We previously showed GT1b induces mesencephalic dopaminergic (DA) neuronal death, both in vivo and in vitro. We further investigate the underlying mechanisms of GT1b neurotoxicity.

Results

Consistent with earlier findings, GT1b attenuated the DA neuron number and dopamine uptake level in mesencephalic cultures. Morphological evidence revealed GT1b-induced chromatin condensation and nuclear fragmentation as well as an increased number of TUNEL-positive cells, compared to control cultures. Interestingly, while GT1b enhanced caspase-3 activity, DEVD, a caspase-3 inhibitor, failed to rescue DA neuronal death. Immunoblot analysis revealed that GT1b inactivates Akt through dephosphorylation at both Ser473 and Thr308, subsequent dephosphorylation of GSK-3β, a substrate of Akt, and hyperphosphorylation of tau, downstream of GSK-3β. Moreover, a GSK-3β specific inhibitor, L803-mt, attenuated tau phosphorylation and rescued DA neurons from cell death in mesencephalic cultures.

Conclusion

Our data provide novel evidence that a Akt/GSK-3β/tau-dependent, but not caspase-3 signaling pathway plays a pivotal role in GT1b-mediated neurotoxic actions on mesencephalic DA neurons.

15-HETE protects rat pulmonary arterial smooth muscle cells from apoptosis via the PI3K/Akt pathway

15-Hydroxyeicosatetraenoic acid (15-HETE), a metabolic product of arachidonic acid (AA), plays an important role in pulmonary vascular smooth muscle remodeling. Although its effects on the apoptotic responses are known, the underlying mechanisms are still poorly understood. Since Akt is a critical regulator of cell survival and vascular remodeling, there may be a crosstalk between 15-HETE anti-apoptotic process and PI3K/Akt survival effect in rat pulmonary arterial smooth muscle cells (PASMCs). To test this hypothesis, we studied the effect of 15-HETE on cell survival and apoptosis using Western blot, cell viability measurement, nuclear morphology determination, TUNEL assay and mitochondrial potential analysis. We found that activation of the PI3K/Akt signaling system was necessary for the 15-HETE to suppress PASMC apoptosis and improve cell survival. Our results indicated that 15-HETE inhibited the apoptotic responses of PASMCs, including morphological alterations, mitochondrial depolarization and the expression apoptosis-specific proteins. These effects were likely to be mediated through the activation of PI3K/Akt. Two downstream signal molecules of PI3K/Akt were identified. Both FasL and Bad were down-regulated by 15-HETE and 15-HETE phosphorylated Bad. These changes depended on the PI3K/Akt signaling pathway in PASMCs. Thus a signal transduction pathway was demonstrated which is necessary for the effects of 15-HETE in protection PASMCs from apoptosis.

Single-cell hydrogel encapsulation for enhanced survival of human marrow stromal cells

Inadequate extracellular matrix cues and subsequent apoptotic cell death are among crucial factors currently limiting cell viability and organ retention in cell-based therapeutic strategies for vascular regeneration. Here we describe the use of a single-cell hydrogel capsule to provide enhanced cell survival of adherent cells in transient suspension culture. Human marrow stromal cells (hMSCs) were singularly encapsulated in agarose capsules containing the immobilized matrix molecules, fibronectin and fibrinogen to ameliorate cell-matrix survival signals. MSCs in the enriched capsules demonstrated increased viability, greater metabolic activity and enhanced cell-cytoskeletal patterning. Increased cell viability resulted from the re-induction of cell-matrix interactions likely via integrin clustering and subsequent activation of the extracellular signal regulated MAPK (ERK)/mitogen activated protein kinase (MAPK) signaling cascade. Proof of principle in-vivo studies, investigating autologous MSC delivery into Fisher 344 rat hindlimb, depicted a significant increase in the number of engrafted cells using the single-cell encapsulation system. Incorporation of immobilized adhesion molecules compensates, at least in part, for the missing cell-matrix cues, thereby attenuating the initial anoikis stimuli and providing protection from subsequent apoptosis. Thus, this single-cell encapsulation strategy may markedly enhance therapeutic cell survival in targeted tissues.

Silencing of GM3 synthase suppresses lung metastasis of murine breast cancer cells

BACKGROUND

Gangliosides are sialic acid containing glycosphingolipids that are ubiquitously distributed on vertebrate plasma membranes. GM3, a precursor for most of the more complex ganglioside species, is synthesized by GM3 synthase. Although total ganglioside levels are significantly higher in breast tumor tissue than in normal mammary tissue, the roles played by gangliosides in breast cancer formation and metastasis are not clear.

METHODS

To investigate the roles of gangliosides in breast tumor development, GM3 synthase was silenced in the highly metastatic 4T1 cells and over-expressed in the non-metastatic 67NR cells. The behavior of breast cancer cells was examined in vitro using migration assay, invasion assay, and soft agar assay. Tumor formation and metastasis in vivo were examined using a well established mouse mammary tumor model.

RESULTS

GM3 synthase silencing in 4T1 cells significantly inhibited cell migration, invasion and anchorage-independent growth in vitro, and lung metastasis in vivo. In addition, over-expression of GM3 synthase in nonmetastatic 67NR cells significantly induced cell migration and anchorage-independent growth. Further studies indicated that activation of the phosphoinositide-3 kinase/Akt pathway, and consequently inhibition of nuclear factor of activated T cell (NFAT)1 expression, could be the mechanism underlying the suppression of breast cancer migration/invasion induced by GM3 synthase silencing.

CONCLUSION

Our findings indicate that GM3 synthase silencing suppressed lung metastasis in murine breast cancer cells. The molecular mechanism that underlies GM3 synthase mediated migration and invasion was inhibition of the phosphoinositide-3 kinase/Akt pathway. The findings suggest that GM3 synthase may be of value as a therapeutic target in breast cancer.

Suppression of epidermal growth factor receptor signaling by protein kinase C-alpha activation requires CD82, caveolin-1, and ganglioside

Activation of protein kinase C (PKC)-alpha decreases normal and neoplastic cell proliferation by inhibiting epidermal growth factor receptor (EGFR)-related signaling. The molecular interactions upstream to PKC-alpha that influence its suppression of EGFR, however, are poorly understood. We have found that caveolin-1, tetraspanin CD82, and ganglioside GM3 enable the association of EGFR with PKC-alpha, ultimately leading to inhibition of EGFR signaling. GM3- and CD82-induced inhibition of EGFR signaling requires PKC-alpha translocation and serine/threonine phosphorylation, which eventually triggers EGFR Thr654 phosphorylation and receptor internalization. Within this ordered complex of signaling molecules, the ability of CD82 to associate with PKC-alpha requires the presence of caveolin-1, whereas the interaction of caveolin-1 or PKC-alpha with EGFR requires the presence of CD82 and ganglioside GM3. Disruption of the membrane with methyl-beta-cyclodextrin dissociates the EGFR/GM3/caveolin-1/CD82/PKC-alpha complex and prevents the inhibitory effect of PKC-alpha on EGFR phosphorylation, suggesting that caveolin-1, CD82, and ganglioside interact with EGFR and PKC-alpha within intact cholesterol-enriched membrane microdomains. Given the role of these membrane molecules in suppressing EGFR signaling, up-regulation of GM3, caveolin-1, and CD82 function may be an effective adjunctive therapy for treating epithelial cell malignancies.

Sialic Acid and GM3 Ganglioside Expression in Papillomavirus-associated Urinary Bladder Tumours of Cattle with Chronic Enzootic Haematuria

This study was based on 30 papillomavirus-associated urinary bladder tumours from cattle with chronic haematuria, the animals having been kept since birth on pasture rich in bracken fern. The ganglioside content was assessed and compared with that of normal bovine urinary bladders, which was shown to be 28.6+/-3.3 (mean+/-SD) microg of lipid-bound sialic acid per gram of fresh tissue. In neoplastic bladder samples this value was higher but variable (120.9+/-80.6 in benign tumours, and 94.7+/-45.7 in malignant tumours). The main ganglioside, GM3, represented ca 75% of the total ganglioside mixture in normal tissues and 50-80% in tumour samples. GM1, GM2, GD1a, GD3 and FucGM1 were found as minor components. The study suggested that GM3 ganglioside may have a crucial role in "downregulation" of the metastatic potential of bovine urothelial cancers.

Osteopontin stimulates vascular smooth muscle cell migration by inducing FAK phosphorylation and ILK dephosphorylation

Focal adhesion kinase (FAK) and integrin-linked kinase (ILK) are both involved in integrin-mediated cell migration. However, the molecular mechanism, and the relationship between FAK and ILK activity in signaling transduction for the osteopontin (OPN)-induced migration of vascular smooth muscle cells (VSMCs) remain unclear. Here, we show that treating VSMCs with OPN could result in the dissociation of FAK with ILK by inducing phosphorylation of the former and dephosphorylation of the latter. Furthermore, we demonstrate that FAK phosphorylation induced by OPN is coupled with ILK dephosphorylation. We also provide evidence that ILK acts downstream of FAK in the signaling pathways that mediate OPN-induced VSMC migration. These findings suggest that FAK phosphorylation and ILK dephosphorylation play important roles in VSMC migration induced by OPN.

Diabetes alters sphingolipid metabolism in the retina: a potential mechanism of cell death in diabetic retinopathy

Dysregulated sphingolipid metabolism causes neuronal cell death and is associated with insulin resistance and diseases. Thus, we hypothesized that diabetes-induced changes in retinal sphingolipid metabolism may contribute to neuronal pathologies in diabetic retinopathy. ESI-MS/MS was used to measure ceramide content and ceramide metabolites in whole retinas after 2, 4, and 8 weeks of streptozotocin-induced diabetes. After 4 and 8 weeks of diabetes, a approximately 30% decrease in total ceramide content was observed, concomitant with a significant approximately 30% increase in glucosylceramide levels in fed diabetic rats compared with their age-matched controls. Acute insulin therapy as well as a short-term lowering of glucose via fasting did not affect the increase in glucosylceramide composition. To assess the putative biological consequences of the increase in glucosylceramide composition, R28 retinal neurons were treated with glucosylceramide synthase inhibitors. Inhibiting glycosphingolipid metabolism increased insulin sensitivity in retinal neurons. Glycosphingolipid inhibitors augmented insulin-stimulated p70 S6kinase activity in the presence of inhibitory concentrations of high glucose or glucosamine. Inhibition of glycosphingolipid synthesis also suppressed glucosamine- and interleukin-1beta-induced death. Consistent with these inhibitor studies, pharmacological accumulation of glycosphingolipids increased activation of the endoplasmic reticulum stress response, a putative modulator of insulin resistance and neuronal apoptosis. It is speculated that an increase in glucosylceramide, and possibly higher-order glycosphingolipids, could contribute to the pathogenesis of diabetic retinopathy by contributing to local insulin resistance, resulting in neuronal cell death. Thus, dysfunctional glycosphingolipid metabolism may contribute to metabolic stress in diabetes, and therapeutic strategies to restore normal sphingolipid metabolism may be a viable approach for treatment of diabetic retinopathy.

Molecular Mechanisms of GD3-Induced Apoptosis in U-1242 MG Glioma Cells

An increasing amount of evidence indicates that the disialoganglioside GD3 is involved in apoptosis in many cell lines. Our previous studies demonstrated that endogenous GD3 expression induced apoptosis in U-1242 MG glioma cells transfected with the GD3 synthase gene (U1242MG-GD3 cells). In this paper, we present further investigations on the molecular mechanisms of GD3-induced apoptosis in this cell line. We found that endogenously synthesized GD3 localizes to the caveolae of this cell line, where it promotes the localization of death receptor 5 (DR5), tumor necrosis factor receptor-1 (TNF-R1), and Fas (Apo-1) to the caveolae. In addition, caspase-8 was translocated to the caveolar fraction and cleaved; the cleaved proteins were then re-located into the high density fractions. However, GD3 had no effect on the distribution of the adapter protein Fas-associated death domain (FADD). We conclude that GD3 functions as a regulatory molecule early in the extrinsic apoptosis pathway.

Plasma-membrane-associated sialidase (NEU3) differentially regulates integrin-mediated cell proliferation through laminin- and fibronectin-derived signalling

We have found previously that human plasma-membrane-associated sialidase (NEU3), a key glycosidase for ganglioside degradation, was markedly up-regulated in human colon cancers, with an involvement in suppression of apoptosis. To elucidate the molecular mechanisms underlying increased NEU3 expression, in the present study we investigated its role in cell adhesion of human colon cancer cells. DLD-1 cells transfected with NEU3 exhibited increased adhesion to laminins and consequent cell proliferation, but decreased cell adhesion to fibronectin and collagens I and IV, compared with control cells. When triggered by laminins, NEU3 clearly stimulated phosphorylation of FAK (focal adhesion kinase) and ERK (extracellular-signal-regulated kinase), whereas there was no activation on fibronectin. NEU3 markedly enhanced tyrosine phosphorylation of integrin beta4 with recruitment of Shc and Grb-2 only on laminin-5, and NEU3 was co-immunoprecipitated by an anti-(integrin beta4) antibody, suggesting that association of NEU3 with integrin beta4 might facilitate promotion of the integrin-derived signalling on laminin-5. In addition, the promotion of phosphorylation of integrin beta1 and ILK (integrin-linked kinase) was also observed on laminins. G(M3) depletion as the result of NEU3 overexpression, assessed by TLC, appeared to be one of the causes of the increased adhesion on laminins and, in contrast, of the decreased adhesion on fibronectin - NEU3 probably having bimodal effects. These results indicate that NEU3 differentially regulates cell proliferation through integrin-mediated signalling depending on the extracellular matrix and, on laminins, NEU3 did indeed activate molecules often up-regulated in carcinogenesis, which may cause an acceleration of the malignant phenotype in cancer cells.

Ganglioside GM3 promotes carcinoma cell proliferation via urokinase plasminogen activator-induced extracellular signal-regulated kinase-independent p70S6 kinase signaling

Overexpression of NeuAcalpha2-3Galbeta1-4Glcbeta1-Cer (GM3), a major ganglioside of cutaneous tumor cell membranes, inhibits ligand-dependent and ligand-independent activation of the epidermal growth factor (EGF) receptor in normal and neoplastic epithelial cells. This leads to the suppression of Ras/extracellular signal-regulated kinase (ERK) activation and, in the presence of EGF or fibronectin, inhibits cell proliferation. However, some tumor cells show increased levels of GM3, and vaccines that target GM3 can inhibit the growth of neoplastic cells in vivo, especially melanomas. We report that in the presence of urokinase plasminogen activator (uPA), overexpression of GM3 paradoxically increases the proliferation of carcinoma cells by augmenting ERK-independent p70S6 kinase activation. Functional blockade of uPA receptor (uPAR) or inhibition of p70S6 kinase, but not inhibition of Ras/ERK signaling, suppresses this GM3-induced stimulation of cell proliferation. The ERK-independent activation of p70S6 kinase involves phosphorylation at threonine-389, threonine-421/serine-424, and serine-411 sites with intermediate phosphatidylinositol 3 kinase and protein kinase C-zeta activation. These studies implicate gangliosides as enhancers of uPAR-related signaling and suggest that the response to GM3 depends on the local concentration of uPA. Therapeutic modalities that target or supplement gangliosides may require concomitant treatment that suppresses EGFR or uPAR signaling, respectively, to control neoplastic cell proliferation.

Integrin-linked kinase acts as a pro-survival factor against high glucose-associated osmotic stress in human mesangial cells

BACKGROUND

Integrin-linked kinase (ILK) is a protein that plays an important role in extracellular matrix-mediated signalling. Recent studies implicated ILK dysregulation in the development of diabetic nephropathy. However, little is known about the significance of ILK up-regulation in response to high glucose in mesangial cells.

METHODS

The ILK messenger (m)RNA and protein expression in human mesangial cells were analysed with quantitative real-time polymerase chain reaction (PCR) and western blotting after exposure to either 100, 200, or 500 mg/dl glucose, or 100 mg/dl glucose + 400 mg/dl mannitol. Activation of protein Kinase B (PKB)/Akt was also determined by western blot analysis. Cells were transfected with ILK siRNA to determine the effects of ILK knockdown on PKB/Akt activation and cell death following treatment with high glucose or mannitol.

RESULTS

High concentrations of glucose or mannitol for three days significantly up-regulated ILK mRNA and protein expression (P < 0.05 vs 100 mg/dl glucose). In contrast, ILK expression in cells exposed to the same conditions for seven days was unaffected. The time course of PKB/Akt phosphorylation was similar to that of ILK protein expression. The siRNA-mediated down-regulation of ILK expression inhibited the elevation of PKB/Akt phosphorylation induced by high glucose treatment. Furthermore, the inhibition of ILK expression promoted high glucose- or mannitol-induced apoptosis.

CONCLUSION

The ILK may act as a pro-survival factor and play a role in protecting mesangial cells from hyperglycaemic osmotic stress.

Targeting integrin-linked kinase inhibits Akt signaling pathways and decreases tumor progression of human glioblastoma

The phosphatidylinositol 3-kinase pathway is an important regulator of a wide spectrum of tumor-related biological processes, including cell proliferation, survival, and motility, as well as neovascularization. Protein kinase B/Akt is activated in a complex manner through the phosphorylation of protein kinase B/Akt on Thr308 and Ser473. Although protein-dependent kinase-1 has been shown to phosphorylate Akt at Thr308, it is not clear whether there is a distinct kinase that exclusively phosphorylates Akt at Ser473. A possible candidate is integrin-linked kinase (ILK), which has been shown to phosphorylate Akt at Ser473 in vitro. ILK is a multidomain focal adhesion protein that is believed to be involved in signal transmission from integrin and growth factor receptors. Further, ILK is implicated in the regulation of anchorage-dependent cell growth/survival, cell cycle progression, invasion and migration, and tumor angiogenesis. In this study, we tested the hypothesis that ILK inhibition would inhibit these processes in gliomas in which it is constitutively expressed. We found that a newly developed small-molecule compound (QLT0267) effectively inhibited signaling through the ILK/Akt cascade in glioma cells by blocking the phosphorylation of Akt and downstream targets, including mammalian target of rapamycin and glycogen synthase kinase-3beta. Treatment of glioma cells with 12.5 micromol/L QLT0267 inhibited cell growth by 50% at 48 hours. An anchorage-dependent cell growth assay confirmed the cell growth-inhibitory effect of QLT0267. Further, the decrease in cell growth was associated with a dramatic accumulation of cells in the G2-M phase of the cell cycle. Although the cell growth-inhibitory effects of the ILK inhibitor were achieved only at a high concentration, the QLT0267 was able to reduce cellular invasion and angiogenesis at much lower concentrations as shown by in vitro invasion assays and vascular endothelial growth factor secretion. Thus, blocking the ILK/Akt pathway is a potential strategy for molecular targeted therapy for gliomas.

Endogenous GD3 ganglioside induces apoptosis in U-1242 MG glioma cells

GD3 ganglioside induces apoptosis in several cell types, but the molecular events through which this occurs are largely unknown. We investigated the apoptotic effects of GD3 expression using U-1242 MG glioblastoma cells, as these cells synthesize almost exclusively GM3 and GM2 but not GD3. To express GD3 under the control of the TetOn system with minimum leakage, we modified the system by constructing a single tri-cistronic retrovirus vector containing three genes separated by two internal ribosome entry sites: (a) transcriptional silencer, tTS; (b) mutant of reverse transcriptional activator, rtTA2(S)-M2 (provided by H. Bujard, Heidelberg, Germany); and (c) enhanced green fluorescent protein (EGFP), as an indicator of the tri-cistronic gene expression. Using flow cytometry, we selected glioma cells (U1242MG-GD3 clone) that express high levels of GD3 in response to doxycycline. Expression of GD3 was associated with apoptosis as verified by annexin-V binding, TdT-mediated dUTPnick end-labelling assay (TUNEL), and EGFP degradation. GD3-induced apoptosis occurred via caspase-8 activation, as GD3 caused cleavage of caspase-8 and inhibition of caspase-8 activation by zlETD-fmk minimized GD3-induced apoptosis.

Role of the integrin-linked kinase/PINCH1/alpha-parvin complex in cardiac myocyte hypertrophy

Outside-in signaling from fibronectin (FN) through integrin receptors has been shown to play an important role in promoting cardiac myocyte hypertrophy and synergizes with other hypertrophic stimuli such as the alpha-adrenergic agonist phenylephrine (PE) and mechanical strain. The integrin-linked kinase (ILK) is a critical molecule involved in cell adhesion, motility and survival in nonmyocytes such as fibroblasts and epithelial cells. Its role in cardiac myocytes is unclear. In this study, we demonstrate that (1) ILK forms a complex with PINCH1 and alpha-parvin proteins (IPAP1 complex) in neonatal rat ventricular myocytes; (2) localization of IPAP1 complex proteins to costameres in cardiac myocytes is stimulated by FN, PE and synergistically by the combination of FN and PE in an integrin beta1-dependent manner; (3) a dominant-negative mutant lacking the PINCH-binding N-terminus of ILK (ILK-C) prevents costamere association of ILK and alpha-parvin, but not PINCH1; (4) FN- and PE-induced hypertrophy, measured by increased protein/DNA ratio, beating frequency and atrial natriuretic peptide expression, is stimulated by low levels of ILK-C but repressed by high ILK-C expression; and (5) overexpression of ILK-C, as well as deletion of the ILK gene in mouse neonatal ventricular myocytes, induces marked apoptosis of cardiac myocytes. These results suggest that the IPAP1 complex plays an important role in mediating integrin-signaling pathways that regulate cardiac myocyte hypertrophy and resistance to apoptosis.

Glucose-induced Akt1 activation mediates fibronectin synthesis in endothelial cells

AIMS/HYPOTHESIS

Increased expression and decreased degradation of extracellular matrix (ECM) proteins are key features of chronic diabetic complications. Fibronectin, a predominant ECM protein, has been shown to be overexpressed in all target organs of diabetic complications and in endothelial cells cultured in high levels of glucose. The present study was designed to elucidate the role of protein kinase B (Akt/PKB) in glucose-induced fibronectin mRNA expression and protein production in vascular endothelial cells.

METHODS

Human umbilical vein endothelial cells were cultured in the presence of high glucose to study Akt/PKB activation. The upstream and downstream mediators in the Akt/PKB pathway were also investigated using dominant negative transfections and specific inhibitors of signalling pathways. Cells were subjected to real time RT-PCR, western blotting, and confocal microscopy to assess Akt1/PKBalpha activation and fibronectin mRNA expression and protein production. To detect transcription factor activation, electrophoretic mobility shift assay was carried out.

RESULTS

Our data demonstrate that fibronectin mRNA expression and protein production that are induced by high glucose are mediated via activation of Akt/PKB, which is modulated by mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and protein kinase C. Glucose-induced fibronectin mRNA expression and protein production are also mediated by Akt1/PKBalpha-dependent activation of the transcription factors nuclear factor-kappaB and activating protein-1.

CONCLUSIONS/INTERPRETATION

Our study provides insight into the mechanical basis of glucose-induced increases in fibronectin mRNA expression and protein production. High levels of glucose may increase fibronectin mRNA expression and protein production by activating Akt/PKB.

Molecular determinants of Akt-induced keratinocyte transformation

The PI3K/PTEN/Akt signaling pathway has emerged in recent years as a main player in human cancers, increasing proliferation and decreasing apoptosis of transformed cells, and thus becoming a potential target for therapeutic intervention. Our previous data have demonstrated that Akt-mediated signaling is of a key relevance in the mouse skin carcinogenesis system, one of the best-known models of experimental carcinogenesis. Here, we investigated the involvement of several pathways as mediators of Akt-induced increased proliferation and tumorigenesis in keratinocytes. Tumors produced by subcutaneous injection of Akt-transformed keratinocytes showed increased Foxo3a phosphorylation, but no major alterations in p21(Cip1/WAF1), p27(Kip1) or mdm2 expression and/or localization. In contrast, we found increased expression and nuclear localization of DeltaNp63, beta-catenin and Lef1. Concomitantly, we also found increased expression of c-myc and CycD1, targets of the beta-catenin/Tcf pathway. Such increase is associated with increased phosphorylation and stabilization of c-myc protein as well as increased translation of c-myc and CycD1 due to mTOR activation. Using immunohistochemistry approaches in samples of oral dysplasias and human head and neck squamous cell carcinomas, we confirmed that increased Akt activation significantly correlates with increased DeltaNp63 and CycD expression, c-myc phosphorylation and nuclear accumulation of beta-catenin. Collectively, these results demonstrate that Akt is able to transform keratinocytes by specific mechanisms involving transcriptional and post-transcriptional processes.

Increased phospho-AKT is associated with loss of the androgen receptor during the progression of N-methyl-N-nitrosourea-induced prostate carcinogenesis in rats

BACKGROUND

Characterization of molecular events during N-methyl-N-nitrosourea (MNU)-induced rat prostate carcinogenesis enhances the utility of this model for the preclinical assessment of preventive strategies. Androgen independence is typical of advanced human prostate cancer and may occur through multiple mechanisms including the loss of androgen receptor (AR) expression and the activation of alternative signaling pathways.

METHODS

We examined the interrelationships between AR and p-AKT expression by immunohistochemical staining during MNU-androgen-induced prostate carcinogenesis in male Wistar-Unilever rats. Histone nuclear staining and image analysis was employed to assess parallel changes in chromatin and nuclear structure.

RESULTS

The percentage of AR positive nuclei decreased (P < 0.01) as carcinogenesis progressed: hyperplasia (92%), atypical hyperplasia (92%), well-differentiated adenocarcinoma (57%), moderately-differentiated adenocarcinoma (19%), and poorly-differentiated adenocarcinoma (10%). Conversely, p-AKT staining increased significantly during carcinogenesis. Sparse staining was observed in normal tissues (0.2% of epithelial area) and hyperplastic lesions (0.1%), while expression increased significantly (P < 0.001) in atypical hyperplasia (7.6%), well-differentiated adenocarcinoma (16.7%), moderately-differentiated adenocarcinoma (19.6%), and poorly-differentiated adenocarcinoma (17.4%). In parallel, nuclear morphometry revealed increased nuclear size, greater irregularity, and lower DNA compactness as cancers became more poorly differentiated.

CONCLUSIONS

In the MNU model, the progressive evolution of dominant tumor cell populations showing an increase in p-AKT in parallel with a decline in AR staining suggests that activation of AKT signaling may be one of several mechanisms contributing to androgen insensitivity during prostate cancer progression. Our observations mimic findings suggested by human studies and support the relevance of the MNU model in preclinical studies of preventive strategies.

The Ganglioside GD3 as the Greek Goddess Hecate: Several Faces Turned Towards as Many Directions

The disialoganglioside GD3 can mediate biological functions as diverse as proliferation, differentiation, and apoptosis. Since intracellular level of GD3 is crucial for the cell, understanding the mechanisms by which GD3 metabolism is tightly regulated seems of particular importance. GD3 can be enlisted among the most potent natural inducers of mitochondrial damage and apoptosis. However, some cell types resist GD3-mediated mitochondrial damage through complex mechanisms which are beginning to be unveiled.

Mechanisms for the apoptosis of small cell lung cancer cells induced by anti-GD2 monoclonal antibodies: roles of anoikis

Anti-GD2 ganglioside antibodies could be a promising, novel therapeutic approach to the eradication of human small cell lung cancers, as anti-GD2 monoclonal antibodies (mAbs) induced apoptosis of small cell lung cancer cells in culture. In this study, we analyzed the mechanisms for the apoptosis of these cells by anti-GD2 mAbs and elucidated the mechanisms by which apoptosis signals were transduced via reduction in the phosphorylation levels of focal adhesion kinase (FAK) and the activation of a MAPK family member, p38, upon the antibody binding. Knock down of FAK resulted in apoptosis and p38 activation. The inhibition of p38 activity blocked antibody-induced apoptosis, indicating that p38 is involved in this process. Immunoprecipitation-immunoblotting analysis of immune precipitates with anti-FAK or anti-integrin antibodies using an anti-GD2 mAb revealed that GD2 could be precipitated with integrin and/or FAK. These results suggested that GD2, integrin, and FAK form a huge molecular complex across the plasma membrane. Taken together with the fact that GD2+ cells showed marked detachment from the plate during apoptosis, GD2+ small cell lung cancer cells seemed to undergo anoikis through the conformational changes of integrin molecules and subsequent FAK dephosphorylation.

Gangliosides inhibit urokinase-type plasminogen activator (uPA)-dependent squamous carcinoma cell migration by preventing uPA receptor/alphabeta integrin/epidermal growth factor receptor interactions

The interaction of the urokinase-type plasminogen activator (uPA) receptor (uPAR) with integrins plays a critical role in the regulation of cell adhesion and migration. However, the molecular events underlying the modulation of the interaction of uPAR and integrin are poorly understood. Gangliosides are thought to regulate epithelial cell adhesion and migration by inhibiting alpha(5)beta(1) integrin and epidermal growth factor receptor (EGFR) signaling. We report here that increases in the expression of ganglioside NeuAcalpha2-->3Galbeta1-->3GalNAcbeta1-->4(NeuAcalpha2-->8NeuAcalpha2-->3)Galbeta1-->4Glcbeta1-Cer (GT1b) or NeuAcalpha2-->3Galbeta1-->4Glcbeta1-Cer (GM3) inhibit uPA-dependent cell migration by preventing the association of uPAR with alpha(5)beta(1) integrin or uPAR/alpha(5)beta(1) integrin with the EGFR, respectively. As a result, uPA-dependent focal adhesion kinase (FAK) and integrin-mediated EGFR signaling are suppressed. Both gangliosides inhibit uPAR signaling-stimulated migration; however, GM3 inhibits uPA-induced EGFR phosphorylation by blocking the crosstalk between integrin and EGFR, whereas GT1b suppresses both uPA-induced FAK and EGFR activation by preventing the activation of integrin alpha(5)beta(1).

Inhibition of integrin-linked kinase by a selective small molecule inhibitor, QLT0254, inhibits the PI3K/PKB/mTOR, Stat3, and FKHR pathways and tumor growth, and enhances gemcitabine-induced apoptosis in human orthotopic primary pancreatic cancer xenografts

Integrin-linked kinase (ILK) couples integrins and growth factors to downstream signaling pathways involving phosphatidylinositol 3-kinase, protein kinase B/Akt (PKB/Akt), and glycogen synthase kinase-3beta. The anticancer effects of ILK inhibitor QLT0254 were tested in an orthotopic primary xenograft model of pancreatic cancer. The pharmacodynamic effects of a single dose of QLT0254 on the phosphorylation of PKB/Akt were measured by immunohistochemistry and Western blotting, and showed a decrease of >80% after 2 hours, followed by recovery over 24 hours, consistent with the pharmacokinetic profile of this compound in mice. There was also suppression in phosphorylated PKB Thr(308), forkhead in rhabdomyosarcoma, S6K1, S6, 4E-BP1, and signal transducers and activators of transcription 3 Tyr(705) and Ser(727) protein levels with ILK inhibition by QLT0254. However, we did not observe an effect on phosphoinositide-dependent kinase 1, glycogen synthase kinase-3beta, and extracellular signal-regulated kinase phosphorylation or on total PKB and ILK protein expression levels with QLT0254 treatment. In tumor growth inhibition experiments, daily treatment with QLT0254 for 3 weeks was well tolerated and produced significant tumor growth inhibition compared with vehicle control (P = 0.001). When a single dose of QLT0254 and chemotherapy agent gemcitabine was administered, there was a significant 5.4-fold increase in acute apoptosis in the combination therapy group compared with vehicle controls (P = 0.002). However, the acute effects of QLT0254 on proliferation were not statistically significant. These results show in vivo evidence that ILK plays a prominent role in oncogenic phosphatidylinositol 3-kinase/PKB signaling in vivo with major impact on the mammalian target of rapamycin, signal transducers and activators of transcription 3, and forkhead in rhadomyosarcoma signaling pathways, suggesting that ILK inhibitors might show activity in pancreatic cancer patients.

Glycosphingolipids and mitochondria: role in apoptosis and disease

Glycosphingolipids (GSLs) comprise a class of lipids with important structural and signaling functions. Synthesized from ceramide in the Golgi, they are subsequently distributed to different compartments, most predominantly in the plasma membrane where they integrate signaling platforms. A recently characterized trafficking of ganglioside GD3 (GD3), a GSLs with two sialic-acid residues, to mitochondria has revealed a novel function of this lipid as a death effector. In addition to the interaction of GD3 with mitochondria recruiting these organelles to apoptotic pathways, GD3 disables survival paths dependent on NF-kappaB, thus favoring the balance towards cell death. The present review gathers the evidence documenting this emerging function of GSLs in cell death and their involvement in pathological states.

Integrin-linked kinase: a cancer therapeutic target unique among its ILK

Cancer development requires the acquisition of several capabilities that include increased replicative potential, anchorage and growth-factor independence, evasion of apoptosis, angiogenesis, invasion of surrounding tissues and metastasis. One protein that has emerged as promoting many of these phenotypes when dysregulated is integrin-linked kinase (ILK), a unique intracellular adaptor and kinase that links the cell-adhesion receptors, integrins and growth factors to the actin cytoskeleton and to a range of signalling pathways. The recent findings of increased levels of ILK in various cancers, and that inhibition of ILK expression and activity is antitumorigenic, makes ILK an attractive target for cancer therapeutics.

Integrin alpha5beta1 promotes survival of growth-arrested breast cancer cells: an in vitro paradigm for breast cancer dormancy in bone marrow

The mechanisms of long-term survival of occult breast cancer cells in the bone marrow microenvironment are not known. Using selected bone marrow stromal components with demonstrated roles in promoting growth arrest and survival of breast cancer cells, we reconstituted an in vitro model for dormancy of breast cancer cells in bone marrow. According to this model, basic fibroblast growth factor, a mammary differentiation factor abundant in the bone marrow stroma, induces growth arrest of relatively well-differentiated breast cancer cells, induces a spread appearance, and restricts their survival to fibronectin by up-regulating integrin alpha5beta1. Most of the basic fibroblast growth factor-arrested cells fail to establish optimal ligation to fibronectin and undergo cell death. Cells that do attach to fibronectin, another major constituent of the bone marrow microenvironment, stay alive and growth-arrested for many weeks. Although capable of adhering to other stromal proteins collagen and laminin, dormant cells do not gain a survival advantage from these interactions. Using function-blocking peptides, we show a specific contribution of alpha5beta1-fibronectin interaction in maintaining survival of growth-arrested cells, potentially by negatively modulating apoptotic response via signaling pathways. Blocking of phosphatidylinositol 3'-kinase and Akt inhibits survival of dormant clones, demonstrating this as one of those pathways. Experiments with human bone marrow stroma cocultures confirm the role of fibronectin ligation in maintaining survival of dormant clones.

Ganglioside GM3 Blocks the Activation of Epidermal Growth Factor Receptor Induced by Integrin at Specific Tyrosine Sites

The epidermal growth factor receptor (EGFR) can be activated by both direct ligand binding and cross-talk with other molecules, such as integrins. This integrin-mediated cross-talk with growth factor receptors participates in regulating cell proliferation, survival, migration, and invasion. Previous studies have shown that ligand-dependent EGFR activation is inhibited by GM3, the predominant ganglioside of epithelial cells, but the effect of GM3 on ligand-independent, integrin-EGFR cross-talk is unknown. Using a squamous carcinoma cell line we show that endogenous accumulation of GM3 disrupts the ligand-independent association of the integrin beta1 subunit with EGFR and results in inhibition of cell proliferation. Consistently, endogenous depletion of GM3 markedly increases the association of EGFR with tyrosine-phosphorylated integrin beta1 and promotes cell proliferation. The ligand-independent stimulation of EGFR does not require focal adhesion kinase phosphorylation or cytoskeletal rearrangement. Stimulation of EGFR and mitogen-activated protein kinase signaling by GM3 depletion involves the phosphorylation of EGFR at tyrosine residues 845, 1068, and 1148 but not 1086 or 1173. The specific blockade of phosphorylation at Tyr-845 with Src family kinase inhibition and at Tyr-1148 with phosphatidylinositol 3-kinase inhibition suggests that GM3 inhibits integrin-induced, ligand-independent EGFR phosphorylation (cross-talk) through suppression of Src family kinase and phosphatidylinositol 3-kinase signaling.

Ganglioside GM3 inhibits matrix metalloproteinase-9 activation and disrupts its association with integrin

Gangliosides GM3 and GT1b both inhibit epithelial cell adhesion and migration on fibronectin. GT1b binds to integrin alpha5beta1 and blocks the integrin-fibronectin interaction; GM3 does not interact with integrin, and its effect is poorly understood. We evaluated the effects of endogenous modulation of GM3 expression on epithelial cell motility on several matrices and the mechanism of these effects. Endogenous accumulation of GM3 decreased cell migration on fibronectin, types I, IV, and VII collagen matrices; depletion of GM3 dramatically increased cell migration, regardless of matrix. GM3 overexpression and depletion in vitro correlated inversely with the expression and activity of matrix metalloproteinase-9; consistently, the cell migration stimulated by GM3 depletion is reversed by inhibition of matrix metalloproteinase-9 activity. Accumulation and depletion of GM3 in epithelial cells grown on fibronectin also correlated inversely with epidermal growth factor receptor and mitogen activated protein kinase phosphorylation and with Jun expression. Ganglioside depletion facilitated the co-immunoprecipitation of matrix metal-loproteinase-9 and integrin alpha5beta1, while endogenous accumulation of GM3, but not GT1b, blocked the co-immunoprecipitation. These data suggest modulation of epidermal growth factor receptor signaling and dissociation of integrin/matrix metalloproteinase-9 as mechanisms for the GM3-induced effects on matrix metalloproteinase-9 function.