Biomedical subjects

Edward F Labelle

Publications and source records attributed to Edward F Labelle.

4 recordsLinked to original sources

PubMed2006

Polyamines, PI(4,5)P2, and actin polymerization.

Spermine (SPM) and spermidine (SPD) activate isolated phosphatidylinositol-4-phosphate 5-kinases (PI(4)P5K), enzymes that convert phosphatidylinositol-4-phosphate to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). PI(4,5)P2 formation is known to be involved in cellular actin reorganization and motility, functions that are also influenced by polyamines. It has not been proven that endogenous polyamines can control inositol phospholipid metabolism. We evoked large decreases in SPD and putrescine (PUT) contents in HL60 cells, using the ornithine decarboxylase inhibitor, alpha-difluoromethylornithine (DFMO), which resulted in decreases in PI(4,5)P2 content per cell and inositol phosphate formation to 76.9 +/- 3.5% and 81.5 +/- 4.0% of control, respectively. Accurately reversing DFMO-evoked decreases in SPD content by incubating cells with exogenous SPD for 20 min rescued these decreases. DFMO treatment and SPD rescues also changed the ratio of total cellular PI(4,5)P2 to PIP suggesting involvement of a SPD-sensitive PI(4)P5K. PUT and SPM were not involved in DFMO-evoked changes in cellular PI(4,5)P2 contents. In DFMO-treated HL60 cells, the percent of total actin content that was filamentous was decreased to 59.1 +/- 5.8% of that measured in paired control HL60 cells, a finding that was rescued following reversal of DFMO-evoked decreases in SPD and PI(4,5)P2 contents. In slowly proliferating DMSO-differentiated HL60 cells, inositol phospholipid metabolism was uncoupled from SPD control. We conclude: in rapidly proliferating HL60 cells, but not in slowly proliferating differentiated HL60 cells, there are endogenous SPD-sensitive PI(4,5)P2 pools, probably formed via SPD-sensitive PI(4)P5K, that likely control actin polymerization.

Actins↗

PubMed2005

A membrane defect in the pathogenesis of the Smith-Lemli-Opitz syndrome.

The Smith-Lemli-Opitz syndrome (SLOS) is an often lethal birth defect resulting from mutations in the gene responsible for the synthesis of the enzyme 3beta-hydroxy-steroid-Delta7-reductase, which catalyzes the reduction of the double bond at carbon 7 on 7-dehydrocholesterol (7-DHC) to form unesterified cholesterol. We hypothesize that the deficiency in cholesterol biosynthesis and subsequent accumulation of 7-DHC in the cell membrane leads to defective composition, organization, dynamics, and function of the cell membrane. Using skin fibroblasts obtained from SLOS patients, we demonstrate that the SLOS membrane has increased 7-DHC and reduced cholesterol content and abnormal membrane fluidity. X-ray diffraction analyses of synthetic membranes prepared to mimic SLOS membranes revealed atypical membrane organization. In addition, calcium permeability is markedly augmented, whereas membrane-bound Na+/K+ATPase activity, folate uptake, inositol-1,4,5-trisphosphate signaling, and cell proliferation rates are markedly suppressed. These data indicate that the disturbance in membrane sterol content in SLOS, likely at the level of membrane caveolae, directly contributes to the widespread tissue abnormalities in this disease.

Calcium↗

PubMed2005

Mechanisms of hypotonicity-induced calcium signaling and integrin activation by arachidonic acid-derived inflammatory mediators in B cells.

We previously characterized the initial steps in the activation of novel (calcium-permeant) nonselective cation channels (NSCCs) and calcium release-activated calcium channels in primary murine B lymphocytes. Phospholipase C products, namely diacylglycerol and d-myo-inositol 1,4,5-trisphosphate, were identified as proximal intracellular agonists of these respective channels following mechanical stimulation of B cells. However, neither the distal steps in NSCC activation nor the contribution of these channels to sustained mechanical signaling were defined in these previous studies. In this study, single cell measurements of intracellular Ca(2+) were used to define the mechanisms of NSCC activation and demonstrate a requirement for arachidonic acid liberated from diacylglycerol. Several arachidonic acid-derived derivatives were identified that trigger Ca(2+) entry into B cells, including the lipoxygenase product 5-hydroperoxyeicosatetranenoic acid and the cytochrome P450 hydroxylase product 20-hydroxyeicosatetraenoic; however, the cytochrome P450 epoxygenase product 5,6-epoxyeicosatrienoic acid is primarily responsible for hypotonicity-induced responses. In addition to regulating calcium entry, our data suggest that eicosanoid-activated NSCCs have a separate and direct role in regulating the avidity of integrins on B cells for extracellular matrix proteins, including ICAM-1 and VCAM-1. Thus, in addition to defining a novel osmotically activated signal transduction pathway in B cells, our results have broad implications for understanding how inflammatory mediators dynamically and rapidly regulate B cell adhesion and trafficking.

Animals↗

PubMed2005

Nitric oxide stimulated vascular smooth muscle cells undergo apoptosis induced in part by arachidonic acid derived eicosanoids.

The role of eicosanoids in atherogenesis has not been thoroughly explained. This is partly due to the numerous eicosanoids and the variable effects that each has on different systems. Apoptosis of vascular smooth muscle cells has been shown to play a role in the atherosclerotic disease leading to lesion formation and further destabilization of the formed lesion. In this study, we have investigated the role of arachidonic acid derived eicosanoids in nitric oxide (NO)-stimulated vascular smooth muscle cells. We have shown previously that the nitric oxide (NO)-induced apoptosis of vascular smooth muscle cells was accompanied by arachidonic acid release via cytoplasmic phospholipase A(2) (cPLA(2)) activation. Also, arachidonic acid, but not oleic acid, induced apoptosis of these cells at low concentrations (5-10 microM). Our results revealed that the cPLA(2) specific inhibitor, arachidonyl trifluoromethyl ketone (AACOCF(3)), blocked NO-induced eicosanoid production, while the presence of arachidonic acid enhanced the ability of the cells to make prostaglandin E(2) (PGE(2)). Also, inhibitors of the cyclo-oxygenase (Cox) enzymes, such as N-[2-cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide (NS-398), a specific Cox-2 inhibitor, or indomethacin, a non-specific Cox inhibitor, blocked NO-induced PGE(2) production and apoptosis of vascular smooth muscle cells to the same extent, indicating that apoptosis might be induced by a Cox-2 metabolic product. In addition to these observations, the eicosanoids investigated, namely, PGE(2), PGI(2) LTB(4), and PGJ(2), showed different effects on vascular smooth muscle cells. Both PGJ(2) and LTB(4) decreased the percentage of viable cells and induced apoptosis of vascular smooth muscle cells, while PGE(2) and PGI(2) had no effect on cell viability and failed to induce apoptosis. These data suggest that eicosanoids, such as PGJ(2), but not PGE(2) or PGI(2), are involved in NO-induced apoptosis of vascular smooth muscle cells and that the eicosanoid synthesis pathways might be utilized for vascular therapeutic strategies.

Apoptosis↗