Guanine nucleotide exchange factors for the Rho GTPases: a role in human disease?

The Rho family of low molecular weight GTP-binding proteins control important aspects of cell shape, adhesion, movement and growth. The DBL-homology (DH) protein family of upstream regulators of Rho GTPases has recently been identified, and deregulated expression of these proteins can have dramatic cellular consequences. This review examines the possible role of DH proteins and Rho GTPases in oncogenesis, metastasis and development.     

Calcium stimulates intramitochondrial cholesterol transfer in bovine adrenal glomerulosa cells

In adrenal glomerulosa cells, angiotensin II (Ang II) stimulates aldosterone synthesis through rises of cytosolic calcium ([Ca2+]c). The rate-limiting step in this process is the transfer of cholesterol to the inner mitochondrial membrane, where it is converted to pregnenolone by the P450 side chain cleavage enzyme. The aim of the present study was to examine the effect of changes in [Ca2+]c and of Ang II on intramitochondrial cholesterol distribution. Freshly prepared bovine zona glomerulosa cells were submitted to a cytosolic Ca2+ clamp (600 nM) or stimulated with Ang II (10 nM). Mitochondria were isolated and subfractionated into outer membranes (OM), inner membranes (IM), and contact sites (CS). Cholesterol content was determined by the cholesterol oxidase assay. Stimulation of intact cells with Ca2+ led to a marked decrease in cholesterol content of OM (to 54 +/- 24% of controls, n = 5) and to a concomitant increase of cholesterol in CS and IM (to 145 +/- 14%, n = 5). When glomerulosa cells were exposed to Ang II, a marked increase of cholesterol in CS occurred (to 172 +/- 16% of controls, n = 5). No significant changes were detected in OM cholesterol, suggesting a stimulation of cholesterol supply to the mitochondria in response to Ang II. Cycloheximide specifically and significantly reduced Ca2+-activated cholesterol transfer to CS and IM. In conclusion, our data indicate that one of the main functions of the Ca2+ messenger is to increase cholesterol supply to the P450 side chain cleavage enzyme by enhancing endogenous intermembrane cholesterol transfer to a mitochondrial site containing the enzymes responsible for the initial steps of the steroidogenic cascade.     

Supplementation of coconut oil from different sources to the diet induces cellular damage and rapid changes in fatty acid composition of chick liver and hepatic mitochondria

PURPOSE OF THE STUDY: Impaction in pertrochanteric fracture sites is a well known phenomenon; the screw-plate system is designed to stabilise the fracture. Although easier to use, the risk with the nail-plate system is postoperative penetration of the nail into the joint. The present study was conducted to determine the exact conditions of the impaction, and to identify possible ways to improve the nail-plate system. MATERIAL-METHOD: The study included 129 cases of pertrochanteric fracture, excluding sub-trochanteric fractures. All fractures were fixed with a 130 degrees angulated nail-plate. In all cases, consolidation was uneventful after 8 to a 12 weeks. The anatomical type of fracture, i.e. stable or unstable, was determined according to the size of the intermediary fragment, including the trochanter minor. The displacement was measured as the difference between the length of the nail and the length of the femoral head and neck measured along the axis of the femoral neck. The parameters examined were: fracture stability degree, bony mineralisation (Singh Index), nail length, femoral neck, length nail position in the femoral head, and above all, fracture reduction. All these parameters were computerised and compared using Stat View statistics software. RESULTS: Impaction was observed in 43 per cent of cases. Among these, 25 per cent were rated as slight (1 to 5 mm), 18 per cent as moderate (over 5 mm) and 9 per cent as marked (10 to 25 mm). Impaction was associated with demineralisation of the bone tissue (p = 0.001). The anatomical classification of the fracture was not a determining factor (p = 0.19), as marked displacements were also recorded in stable fractures. A posterior and inferior position of the intramedullary nail in the femoral head is one of displacement determining factors (p = 0.004, two-sided 1 test). Valgus over-correction is the most important factor, especially when it is associated with bony demineralisation (p = 0.02) and an inadequately centred intramedullary pin (p = 0.02). Shorter the femoral neck, and shorter the nail, greater was the frequency of nail articular penetration. DISCUSSION: The risk of articular penetration therefore reaches 15 per cent in petrochanteric fractures repaired with a nail plate, set at an angle of 130 degrees. A short neck, a cervicodiaphyseal angle superior to 140 degrees, and demineralisation are the three determining parameters. Stable or unstable fracture has in fact little effect on displacement incidence, and therefore does not, on its own, warrant the use of a prosthesis in comminuted fractures. The authors compared their results to literature on progressive sliding system: the incidence of complications associated with this type of fracture treatment is identical, but the determining parameters are different. CONCLUSION: The study shows that the nail-plate is efficient and provides simple and solid fracture fixation. However, this osteosynthesis material needs to be modified in order to improve its fixation in the femoral head.     

Tissue factor pathway inhibitor in endothelial cells colocalizes with glycolipid microdomains/caveolae. Regulatory mechanism(s) of the anticoagulant properties of the endothelium

Tissue factor pathway inhibitor (TFPI), the main downregulator of the procoagulant activity of tissue factor.factor VIIa complex, locates in human endothelial cells (EC) in culture as well-defined clusters uniformly distributed both on the cell surface and intracellularly. We here demonstrate by immunofluorescence that TFPI colocalizes in EC with caveolin, urokinase-type plasminogen activator receptor, and glycosphingolipids. The localization of TFPI in caveolae in resting endothelium is proved by double immunogold electron microscopy for TFPI and caveolin. After ultracentrifugation of rat lung or EC homogenates through density gradients of Nycodenz, TFPI was highly enriched at densities of 1.05 to 1.08 g/mL, together with caveolin and alkaline phosphatase. By ELISA, more than half of the cellular TFPI was detected in Triton X-100-insoluble extracts of EC. TFPI incorporates [1-3H]ethanolamine and is cleaved from the cell surface by phosphatidylinositol-phospholipase C, indicating a specific glycosylphosphatidylinositol-anchorage mechanism for TFPI in the plasma membrane. Clustering of TFPI and its localization in caveolae are dependent on the presence of cholesterol in the membrane. Agonist-induced stimulation of EC caused marked changes of distribution for both TFPI and caveolin at subcellular level, with subsequent increase of the cell surface-associated inhibitory activity toward tissue factor.factor VIIa. Our findings suggest that, beside their function in transcytosis, potocytosis, cell surface proteolysis, and regulation of signal transduction, caveolae also play a direct role in the regulation of EC anticoagulant properties.