Dataset Information

Actin assembly in electropermeabilized neutrophils: role of intracellular calcium.

ABSTRACT: Assembly of microfilaments involves the conversion of actin from the monomeric (G) to the filamentous (F) form. The exact sequence of events responsible for this conversion is yet to be defined and, in particular, the role of calcium remains unclear. Intact and electropermeabilized human neutrophils were used to assess more directly the role of cytosolic calcium [( Ca2+]i) in actin assembly. Staining with 7-nitrobenz-2-oxa-1,3-diazole-phallacidin and right angle light scattering were used to monitor the formation of F-actin. Though addition of Ca2+ ionophores can be known to induce actin assembly, the following observations suggest that an increased [Ca2+]i is not directly responsible for receptor-induced actin polymerization: (a) intact cells in Ca2(+)-free medium, depleted of internal Ca2+ by addition of ionophore, responded to the formyl peptide fMLP with actin assembly despite the absence of changes in [Ca2+]i, assessed with Indo-1; (b) fMLP induced a significant increase in F-actin content in permeabilized cells equilibrated with medium containing 0.1 microM free Ca2+, buffered with up to 10 mM EGTA; (c) increasing [Ca2+]i beyond the resting level by direct addition of CaCl2 to permeabilized cells resulted in actin disassembly. Conversely, lowering [Ca2+]i resulted in spontaneous actin assembly. To reconcile these findings with the actin-polymerizing effects of Ca2+ ionophores, we investigated whether A23187 and ionomycin induced actin assembly by a mechanism independent of, or secondary to the increase in [Ca2+]i. We found that the ionophore-induced actin assembly was completely inhibited by the leukotriene B4 (LTB4) antagonist LY-223982, implying that the ionophore effect was secondary to LTB4 formation, possibly by stimulation of phospholipase A2. We conclude that actin assembly is not mediated by an increase in [Ca2+]i, but rather that elevated [Ca2+]i facilitates actin disassembly, an effect possibly mediated by Ca2(+)-sensitive actin filament-severing proteins such as gelsolin. Sequential actin assembly and disassembly may be necessary for functions such as chemotaxis.

SUBMITTER: Downey GP

PROVIDER: S-EPMC2116117 | biostudies-other | 1990 Jun

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:Intracellular Ca2+ release through the Inositol 1,4,5-Triphosphate Receptor (InsP3R) is a feature of all multicellular organisms in which it shapes the temporal and spatial aspects of calcium signaling in cells, affecting several developmental and physiological processes. Mutants in the InsP3R gene of Drosophila (itpr) exhibit a range of defects which include growth defects and larval lethality.The Drosophila Insulin-like peptides (ILPs) are encoded by multigene families that are expressed in the brain and other tissues. Upon secretion, these peptides likely serve as hormones, neurotransmitters, and growth factors. In Drosophila melanogaster, molecular genetic studies have revealed Drosophila ILPs as elements of a conserved insulin signaling pathway, and as in other animal models, it appears to play a key role in metabolism, growth, reproduction, and aging. Previous work from our group has shown that InsP3R function can be rescued by ectopically expressing InsP3R in dilp cells or can be compensated by altering the activity of Sarco-Endoplasmic Reticulum Calcium-ATPase (SERCA). To understand the molecular basis of larval lethality and growth defect in Drosophila InsP3R mutants and to decipher possible cross talk of itpr gene with other signaling pathways we have carried out genome wide microarray experiments. We have compared the transcript profiles of i) itpr mutant larvae and wild type larvae, ii) dilp rescue larvae with itpr mutant larvae iii) itpr and SERCA double mutant larvae with itpr mutant larvae. By this we have identified genes whose levels are altered in itpr mutants and are restored towards wild type in dilp rescue larvae with itpr mutant larvae and itpr and SERCA double mutants. Our experiments help in identify genes that are regulated by changes in intracellular Ca2+ in the context of larval viability may contribute to the better understanding of the major human pathologies caused by calcium misbalance or by dysregulation of the insulin/IGF pathway. The 8x60k array AMADID: 27326 slide was scanned immediately by PerkinElmer Scan array Gx Microarray scanner. The Scan array software (PerkinElmer) was used for grid wise normalization of array images. Three were used with Mutant, three for Dilp Rescue and two for Kum Rescue experiments . The data was analysed by GeneSpring GX Agilent . The differential expression was considered if the Log 2 mean of at least -1 for the down regulated genes and +1 for the upregulated genes. We considered only the genes that were reproducible from biological triplicates for Mutant, biological treplicates for Dilp Rescue and biological duplicates for Kum Rescue.

Dataset Information

Actin assembly in electropermeabilized neutrophils: role of intracellular calcium.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets