Biomedical subjects

V Benard

Publications and source records attributed to V Benard.

6 recordsLinked to original sources

PubMed2001

Characterisation of Rac activation in thrombin- and collagen-stimulated human blood platelets.

In this study, we characterised the mechanisms of Rac GTPase activation in human platelets stimulated by two physiological agonists, either thrombin, acting through membrane receptors coupled to heterotrimeric G-proteins, or collagen which is known to mobilise a tyrosine kinase-dependent pathway. Both agonists induced a rapid activation of Rac that was not significantly affected by the inhibition of integrin alpha(IIb)beta(3) engagement. Using pharmacological inhibitors, we found that phospholipase C activation and calcium mobilisation were essential for platelet Rac activation by either thrombin or collagen whereas protein kinase C inhibition was without effect. In contrast to Rac, Cdc42 activation was independent of phospholipase C activation, indicating that the two GTPases are differently regulated. We also found that phosphoinositide 3-kinase was not required for Rac activation in response to thrombin but was involved in its activation by collagen.

Benzylamines↗

PubMed2000

Rho family proteins modulate rapid apoptosis induced by cytotoxic T lymphocytes and Fas.

Little is known about the role of Rho proteins in apoptosis produced by stimuli evolved specifically to produce apoptosis, such as granzymes from cytotoxic T lymphocytes (CTLs) and Fas. Here we demonstrate that all three Rho family members are involved in CTL- and Fas-induced killing. Dominant-negative mutants of each Rho family member and Clostridium difficile toxin B, an inhibitor of all family members, strongly inhibited the susceptibility of cells to CTL- and Fas-induced apoptosis. Fas-induced caspase-3 activation was inhibited by C. difficile toxin. Activated mutants of each GTPase increased susceptibility to apoptosis, and activation of Cdc42 increased within 5 min of Fas stimulation. In contrast, during the time required for CTL and Fas killing, no apoptosis was produced by dominant-negative or activated mutants or by C. difficile toxin alone. Inhibition of actin polymerization using latrunculin A reduced the ability of constitutively active GTPase mutants to stimulate apoptosis and blocked Fas-induced activation of caspase-3. Furthermore, the ability of Rac to enhance apoptosis was decreased by point mutations reported to block Rac induction of actin polymerization. Rho family proteins may regulate apoptosis through their effects on the actin cytoskeleton.

Actins↗

PubMed2000

Endogenous, hyperactive Rac3 controls proliferation of breast cancer cells by a p21-activated kinase-dependent pathway.

Uncontrolled cell proliferation is a major feature of cancer. Experimental cellular models have implicated some members of the Rho GTPase family in this process. However, direct evidence for active Rho GTPases in tumors or cancer cell lines has never been provided. In this paper, we show that endogenous, hyperactive Rac3 is present in highly proliferative human breast cancer-derived cell lines and tumor tissues. Rac3 activity results from both its distinct subcellular localization at the membrane and altered regulatory factors affecting the guanine nucleotide state of Rac3. Associated with active Rac3 was deregulated, persistent kinase activity of two isoforms of the Rac effector p21-activated kinase (Pak) and of c-Jun N-terminal kinase (JNK). Introducing dominant-negative Rac3 and Pak1 fragments into a breast cancer cell line revealed that active Rac3 drives Pak and JNK kinase activities by two separate pathways. Only the Rac3-Pak pathway was critical for DNA synthesis, independently of JNK. These findings identify Rac3 as a consistently active Rho GTPase in human cancer cells and suggest an important role for Rac3 and Pak in tumor growth.

Breast Neoplasms↗

PubMed2000

Downregulation of a mitogen-activated protein kinase signaling pathway in the placentas of women with preeclampsia.

OBJECTIVE: To investigate whether the activity of the three mitogen-activated protein kinases (Jun aminoterminal kinase, extracellular regulated kinase, and p38) is altered in placental tissue of women with preeclampsia and hemolysis, elevated liver enzymes, low platelets (HELLP) syndrome. METHODS: Placental activity (measured by immunoprecipitation-kinase assay) and protein expression (measured by western blot) of Jun aminoterminal kinase, extracellular regulated kinase, and p38 mitogen-activated protein kinase were measured in four groups of eight women each with preeclampsia, HELLP syndrome, and normal vaginal or cesarean deliveries. To further characterize the Jun aminoterminal kinase signal transduction pathway, phosphorylation of c-Jun, a downstream effector of Jun aminoterminal kinase- mitogen-activated protein kinase, was analyzed by western blotting, and the activity of Rac1, an upstream activator of the Jun aminoterminal kinase signaling pathway, was determined by pull-down assay. RESULTS: The activity of Jun aminoterminal kinase was significantly lower in placentas of women with preeclampsia or HELLP syndrome compared with those who had normal vaginal or cesarean delivery, whereas levels of Jun aminoterminal kinase protein expression were similar. Phosphorylation of the transcription factor c-Jun and Rac1 activity also were significantly lower in women with preeclampsia and HELLP than in controls. p38 mitogen-activated protein kinase activity was significantly higher in women with preeclampsia than with HELLP syndrome. There was no change in extracellular regulated kinase activity or protein expression between subgroups. CONCLUSION: In placentas of women with preeclampsia or HELLP syndrome, a Rac1-Jun aminoterminal kinase-c-Jun-dependent signal transduction pathway was downregulated.

Adult↗

PubMed1999

Characterization of rac and cdc42 activation in chemoattractant-stimulated human neutrophils using a novel assay for active GTPases.

A major function of Rac2 in neutrophils is the regulation of oxidant production important in bacterial killing. Rac and the related GTPase Cdc42 also regulate the dynamics of the actin cytoskeleton, necessary for leukocyte chemotaxis and phagocytosis of microorganisms. Although these GTPases appear to be critical downstream components of chemoattractant receptor signaling in human neutrophils, the pathways involved in direct control of Rac/Cdc42 activation remain to be determined. We describe an assay that measures the formation of Rac-GTP and Cdc42-GTP based on their specific binding to the p21-binding domain of p21-activated kinase 1. A p21-binding domain glutathione S-transferase fusion protein specifically binds Rac and Cdc42 in their GTP-bound forms both in vitro and in cell samples. Binding is selective for Rac and Cdc42 versus RhoA. Using this assay, we investigated Rac and Cdc42 activation in neutrophils and differentiated HL-60 cells. The chemoattractant fMet-Leu-Phe and the phorbol ester phorbol myristate acetate stimulate formation of Rac-GTP and Cdc42-GTP with distinct time courses that parallel cell activation. We also show that the signaling pathways leading to Rac and Cdc42 activation in HL-60 cells involve G proteins sensitive to pertussis toxin, as well as tyrosine kinase and phosphatidylinositol 3-kinase activities.

Animals↗

PubMed1999

Potential drug targets: small GTPases that regulate leukocyte function.

Leukocytes are not only important mediators of innate immunity, but they also induce and perpetuate inflammatory responses that are harmful to the host. Although inflammatory mediators activate leukocytes through a common heterotrimeric G protein (Gi) signalling intermediate, many downstream inflammatory functions are regulated by distinct small GTPases, which suggests that pharmacological modulation of small GTPase activity would be useful in developing specific anti-inflammatory therapies. The recent identification of multiple small GTPase effectors, the recognition of the role of GTPase regulatory proteins in directing downstream signalling from small GTPases, and detailed structural information on the GTPases themselves suggests new possibilities for the development of effective and selective anti-inflammatory drugs.

Anti-Inflammatory Agents↗