The S1P2 receptor negatively regulates platelet-derived growth factor-induced motility and proliferation. (33/160)

Sphingosine-1-phosphate (S1P), a bioactive sphingolipid metabolite, is the ligand for five specific G protein-coupled receptors, named S1P(1) to S1P(5). In this study, we found that cross-communication between platelet-derived growth factor receptor and S1P(2) serves as a negative damper of PDGF functions. Deletion of the S1P(2) receptor dramatically increased migration of mouse embryonic fibroblasts toward S1P, serum, and PDGF but not fibronectin. This enhanced migration was dependent on expression of S1P(1) and sphingosine kinase 1 (SphK1), the enzyme that produces S1P, as revealed by downregulation of their expression with antisense RNA and small interfering RNA, respectively. Although S1P(2) deletion had no significant effect on tyrosine phosphorylation of the PDGF receptors or activation of extracellular signal-regulated kinase 1/2 or Akt induced by PDGF, it reduced sustained PDGF-dependent p38 phosphorylation and markedly enhanced Rac activation. Surprisingly, S1P(2)-null cells not only exhibited enhanced proliferation but also markedly increased SphK1 expression and activity. Conversely, reintroduction of S1P(2) reduced DNA synthesis and expression of SphK1. Thus, S1P(2) serves as a negative regulator of PDGF-induced migration and proliferation as well as SphK1 expression. Our results suggest that a complex interplay between PDGFR and S1P receptors determines their functions.  (+info)

Different pattern of pinopodes expression in stimulated mouse endometrium. (34/160)

Adult NMRI mice were superovulated using human menopausal chorionic gonadotropic hormones (hMG and hCG), and then some of them were daily injected with progesterone (1 mg/mouse). At 3.5 and 4.5 days after hCG injection scanning electron micrographs revealed that the hyperstimulated and progesterone-injected group had well-developed pinopodes while most of the hyperstimulated group without progesterone injection had no pinopodes 3.5 days after stimulation. The results suggest that the lifespan of pinopodes is short and changeable during hyperstimulation and that progesterone causes premature formation of the pinopodes and that implantation after ovarian stimulation might depend upon the timing of the pinopode expression.  (+info)

Circulating endothelial microparticles are associated with vascular dysfunction in patients with end-stage renal failure. (35/160)

Endothelial dysfunction and arterial stiffness are major determinants of cardiovascular risk in patients with end-stage renal failure (ESRF). Microparticles are membrane fragments shed from damaged or activated cells. Because microparticles can affect endothelial cells, this study investigated the relationship between circulating microparticles and arterial dysfunction in patients with ESRF and identified the cellular origin of microparticles associated with these alterations. Flow cytometry analysis of platelet-free plasma from 44 patients with ESRF indicated that circulating levels of Annexin V+ microparticles were increased compared with 32 healthy subjects, as were levels of microparticles derived from endothelial cells (three-fold), platelets (16.5-fold), and erythrocytes (1.6-fold). However, when arterial function was evaluated noninvasively in patients with ESRF, only endothelial microparticle levels correlated highly with loss of flow-mediated dilation (r = -0.543; P = 0.004), increased aortic pulse wave velocity (r = 0.642, P < 0.0001), and increased common carotid artery augmentation index (r = 0.463, P = 0.0017), whereas platelet-derived, erythrocyte-derived, and Annexin V+ microparticle levels did not. In vitro, microparticles from patients with ESRF impaired endothelium-dependent relaxations and cyclic guanosine monophosphate generation, whereas microparticles from healthy subjects did not. Moreover, in vitro endothelial dysfunction correlated with endothelial-derived (r = 0.891; P = 0.003) but not platelet-derived microparticle concentrations. In fact, endothelial microparticles alone decreased endothelial nitric oxide release by 59 +/- 7% (P = 0.025). This study suggests that circulating microparticles of endothelial origin are tightly associated with endothelial dysfunction and arterial dysfunction in ESRF.  (+info)

Magnetosomes are cell membrane invaginations organized by the actin-like protein MamK. (36/160)

Magnetosomes are membranous bacterial organelles sharing many features of eukaryotic organelles. Using electron cryotomography, we found that magnetosomes are invaginations of the cell membrane flanked by a network of cytoskeletal filaments. The filaments appeared to be composed of MamK, a homolog of the bacterial actin-like protein MreB, which formed filaments in vivo. In a mamK deletion strain, the magnetosome-associated cytoskeleton was absent and individual magnetosomes were no longer organized into chains. Thus, it seems that prokaryotes can use cytoskeletal filaments to position organelles within the cell.  (+info)

Cytoskeletal dynamics and cell signaling during planar polarity establishment in the Drosophila embryonic denticle. (37/160)

Many epithelial cells are polarized along the plane of the epithelium, a property termed planar cell polarity. The Drosophila wing and eye imaginal discs are the premier models of this process. Many proteins required for polarity establishment and its translation into cytoskeletal polarity were identified from studies of those tissues. More recently, several vertebrate tissues have been shown to exhibit planar cell polarity. Striking similarities and differences have been observed when different tissues exhibiting planar cell polarity are compared. Here we describe a new tissue exhibiting planar cell polarity - the denticles, hair-like projections of the Drosophila embryonic epidermis. We describe in real time the changes in the actin cytoskeleton that underlie denticle development, and compare this with the localization of microtubules, revealing new aspects of cytoskeletal dynamics that may have more general applicability. We present an initial characterization of the localization of several actin regulators during denticle development. We find that several core planar cell polarity proteins are asymmetrically localized during the process. Finally, we define roles for the canonical Wingless and Hedgehog pathways and for core planar cell polarity proteins in denticle polarity.  (+info)

The kinesin KIF1C and microtubule plus ends regulate podosome dynamics in macrophages. (38/160)

Microtubules are important for the turnover of podosomes, dynamic, actin-rich adhesions implicated in migration and invasion of monocytic cells. The molecular basis for this functional dependency, however, remained unclear. Here, we show that contact by microtubule plus ends critically influences the cellular fate of podosomes in primary human macrophages. In particular, we identify the kinesin KIF1C, a member of the Kinesin-3 family, as a plus-end-enriched motor that targets regions of podosome turnover. Expression of mutation constructs or small interfering RNA-/short hairpin RNA-based depletion of KIF1C resulted in decreased podosome dynamics and ultimately in podosome deficiency. Importantly, protein interaction studies showed that KIF1C binds to nonmuscle myosin IIA via its PTPD-binding domain, thus providing an interface between the actin and tubulin cytoskeletons, which may facilitate the subcellular targeting of podosomes by microtubules. This is the first report to implicate a kinesin in podosome regulation and also the first to describe a function for KIF1C in human cells.  (+info)

Inhibition of calpain stabilises podosomes and impairs dendritic cell motility. (39/160)

Podosomes, highly dynamic adhesion structures implicated in cell motility and extracellular matrix degradation, are characteristic of certain cells of the myeloid lineage and a limited range of other cell types. The nature and the mechanisms that regulate their high turnover are unknown at present. The cysteine protease calpain is involved in the regulation of cell migration in part by promoting either formation or disassembly of adhesion sites. Despite the fact that many known substrates of calpain are also structural components of the podosome complex, no studies have yet demonstrated that calpain participates in the regulation of podosome dynamics. In the present work, we show that inhibition of calpain in primary mouse dendritic cells leads to enhanced accumulation of actin filaments, the Wiskott Aldrich Syndrome protein (WASP), beta(2) integrins, talin, paxillin and vinculin in podosomes. This accumulation of components is associated with stabilisation of podosome turnover, overall reduction in velocity of cell locomotion and impaired transmigration across an endothelial monolayer. We also demonstrate that calpain cleaves the podosome components talin, Pyk2 and WASP in dendritic cells. In summary, our results provide evidence that calpain regulates podosome composition and turnover and that this process is required for efficient migration of dendritic cells.  (+info)

Tuba stimulates intracellular N-WASP-dependent actin assembly. (40/160)

Tuba is a multidomain scaffolding protein that links cytoskeletal dynamics and membrane trafficking pathways. The N-terminus of Tuba binds dynamin1, and the C-terminus contains domains that can interact with signaling pathways and cytoskeletal regulatory elements. We investigated Tuba localization, distribution and function in B16 melanoma cells. Tuba overexpression stimulated dorsal ruffles that occurred independently of dynamin function. Tuba expression induced actin-driven motility of small puncta that required the C-terminal SH3, GEF and BAR domains. Additionally, Tuba was recruited to lipid vesicles generated by overexpression of phosphatidylinositol-4-phosphate 5-kinase type Ialpha (PIP5Kalpha), localizing prominently to the head of the comets and at lower levels along the actin tail. We propose that Tuba facilitates dorsal ruffling of melanoma cells through direct interaction with actin-regulatory proteins and the recruitment of signaling molecules to lipid microdomains for the coordinated assembly of a cytoskeletal network. Knockdown of Tuba by RNA interference (RNAi) attenuated PIP5Kalpha-generated comet formation and the invasive behavior of B16 cells, implying that Tuba function is required for certain aspects of these processes. These results suggest first that Tuba-stimulated dorsal ruffling might represent a novel mechanism for the coordination of N-WASP-dependent cytoskeletal rearrangements and second that Tuba function is implicated in motility processes.  (+info)