Cell adhesion and communication最新文献

We studied the distribution of alpha-catenin, beta-catenin and gamma-catenin/plakoglobin in developing, adult and denervated mouse skeletal muscle. During primary myogenesis, all three catenins present a subsarcolemmal distribution within primary myotubes. During secondary myogenesis they accumulate at myotube-myotube contacts. In contrast to the other catenins, gamma-catenin is strongly expressed in the sarcoplasm. In adult muscle, all three catenins are localized on the presynaptic elements of the neuromuscular junction. In denervated muscles, alpha- and beta-catenins are upregulated like N- and M-cadherin, while the levels of gamma-catenin/plakoglobin remain unchanged. The developmental changes in localization and regulation of alpha- and beta-catenins in muscle compared to gamma-catenin/plakoglobin are suggestive of a privileged association of alpha- and beta-catenins with N- and M-cadherins, while gamma-catenin/plakoglobin appears to be expressed quite independently and must assume a different role during myogenesis.

Microinjection and scrape-loading have been used to load cells in culture with soluble protein tyrosine phosphatases (PTPs). The introduction of protein tyrosine phosphatases into cells caused a rapid (within 5 minutes) decrease in tyrosine phosphorylation of major tyrosine phosphorylated substrates, including the focal adhesion kinase and paxillin. This decrease was detected both by blotting whole cell lysates with anti-phosphotyrosine antibodies and visualizing the phosphotyrosine in focal adhesions by immunofluorescence microscopy. After 30 minutes, many of the cells injected with tyrosine phosphatases revealed disruption of focal adhesions and stress fibers. To determine whether this disruption was due to the dephosphorylation of FAK and its substrates in focal adhesions, we have compared the effects of protein tyrosine phosphatase microinjection with the effects of displacing FAK from focal adhesions by microinjection of a dominant negative FAK construct. Although both procedures resulted in a marked decrease in the level of phosphotyrosine in focal adhesions, disruption of focal adhesions and stress fibers only occurred in cells loaded with exogenous protein tyrosine phosphatases. These results lead us to conclude that although tyrosine phosphorylation regulates focal adhesion and stress fiber stability, this does not involve FAK nor does it appear to involve tyrosine-phosphorylated proteins within focal adhesions. The critical tyrosine phosphorylation event is upstream of focal adhesions, a likely target being in the Rho pathway that regulates the formation of stress fibers and focal adhesions.

Dynamics of alterations of focal adhesions (FA) induced by a microtubule-depolymerizing drug, colcemid, was examined in several types of fibroblastic cells. Evolution of individual FA in cultured cells was monitored by interference-reflection microscopy (IRM); at the end of the monitoring period (3 hours) the cells were fixed and immunofluorescence microscopy of the same FA was performed with an antibody against vinculin. Control and colcemid-treated cells remained non-motile and did not show lamellipodial activity at the edges. During the incubation, formation of new FA or disappearance of pre-existing FA did not occur in either colcemid-treated or control cultures. However, FA in colcemid-treated cells significantly increased in size in the course of a 3 hour incubation. The growth of FA was centripetal and sometimes was accompanied by the fusion of several adjacent FA. Immunofluorescence examination showed that colcemid-induced growth of FA was accompanied by accumulation of several proteins specific for these structures including vinculin, talin, paxillin and pp125FAK kinase. Immunoblotting with anti-vinculin antibody showed that incubation with colcemid considerably increased the amount of vinculin associated with the ventral membranes due to its partial redistribution from a soluble pool into the growing adhesions. A substantial increase in tyrosine phosphorylation of pp125FAK was also observed in colcemid-treated cells. In cells plated on elastic silicone rubber films, colcemid induced formation of wrinkles in the films and these wrinkles relaxed after treatment with cytochalasin D. These results confirm that microtubule depolymerization increases traction transmitted to the substratum by the actin cortex and shows that an increase in cortical tension accompanies maturation of FA. Taken together, these data show that short-term incubation with colcemid does not affect the formation of initial FA. In contrast, microtubule depolymerization considerably stimulates the maturation FA, manifested by their centripetal growth. Maturation is proposed to be mediated by increased cortical tension, which is caused by microtubule depolymerization.

Leukosialin is a negatively-charged mucin-like membrane protein of leukocytes. This anti-adhesive molecule prevents uncontrolled cellular interactions and is proteolytically cleaved during neutrophil activation. CD43 is shed in vivo during neutrophil migration to the inflammatory site. We have analysed the decrease in CD43 expression during in vitro adherence of TNF-alpha activated PMN. CD43 was quantitated by flow cytometry on TNF-alpha-activated PMN either maintained in suspension or allowed to adhere then detached with EDTA. Although TNF did not induce significant modification of CD43 expression on suspended cells, we showed that 40% of membrane CD43 is released during neutrophil TNF-induced adhesion to serum-coated plates or endothelial cells, and that migration through the endothelial monolayer did not result in further shedding. Adhesion-blocking anti-beta 2 integrin mAbs prevented CD43 shedding. beta 2 integrin "activation" by anti-CD 18 mAbs or Mn ions did not decrease CD43 expression if adhesion was prevented by stirring. Inhibitors of signal transduction or of cytoskeleton association, which allowed cells to adhere but not to spread, inhibited the shedding of CD43 during adhesion. We conclude that CD43 shedding is not promoted by beta 2 integrins engagement or adhesion but is concomitant with spreading of adherent cells.

It has become apparent that extracellular matrix components and their cellular receptors, the integrins, are important regulators of glomerular development and function. In this rapidly evolving field we studied the production of extracellular matrix components and integrins by rat glomerular visceral epithelial and mesangial cells, using molecular probes and antibodies that have recently become available. Special attention was paid to laminin isoforms and to splice variants of the integrin subunits alpha 3 and alpha 6. Results were compared to the in vivo expression in human fetal, newborn and adult kidneys. The mesangial cells were found to produce laminin-1, nidogen and two as yet unidentified laminin isoforms with putative alpha chains of about 395 (alpha x) and of 375 kDa (alpha y), tentatively described before as bovine kidney laminin. Furthermore, they expressed the integrins alpha 1 beta 1, alpha 2 beta 1, alpha 3A beta 1, alpha 5 beta 1, alpha v beta 3, alpha v beta 5, and small amounts of alpha 6A beta 1 and alpha 6B beta 1. The glomerular visceral epithelial cells produced the two new laminin isoforms mentioned above, laminin-5, but no laminin-1 or nidogen. The integrins alpha 2 beta 1, alpha 3A beta 1, alpha 6A beta 4, alpha 6B beta 4 and the integrin subunit alpha v were found to be expressed. We show that during nephrogenesis, the laminin alpha 1 chain disappears and is replaced by another alpha chain, possibly one of the two as yet unidentified alpha chains mentioned above. The laminin beta 1 chain is replaced by the beta 2 chain somewhat later in glomerular development. In general, the integrins found to be expressed in glomeruli of adult kidney were consistent with those found in cultured glomerular visceral epithelial and mesangial cells. No splice variant switch of the integrin alpha 3 or alpha 6 subunits could be demonstrated during nephrogenesis. Our results suggest an important role for the mesangial cell in providing nidogen as a crucial component of the supramolecular structure of the glomerular basement membrane. Furthermore our results indicate that laminin alpha x beta 2 gamma 1 and alpha y beta 2 gamma 1 isoforms are important in the glomerulus of adult kidney and that the integrin alpha 3A beta 1 is the main integrin receptor for laminin isoforms on glomerular visceral epithelial and mesangial cells, both in vitro and in vivo.

beta 1D is a recently identified isoform of the beta 1 integrin subunit selectively expressed in skeletal and cardiac muscles. In the present study we determined the temporal expression of beta 1D and its association with alpha subunits during mouse development. By immunohistochemistry and western blot analysis we demonstrated that beta 1D begins to be expressed in skeletal muscles of 17 days embryo (stage E17). Its level progressively increases reaching maximal values few days after birth and remaining high in adult mice. At earlier stages of development (E11-E17) the beta 1A isoform is expressed in skeletal muscle cells. After E17 beta 1A is downregulated and disappears from muscle fibers few days after birth. In cardiac muscle the regulation of the beta 1D expression is different: beta 1D and beta 1A are coexpressed in the heart of E11 embryo. Subsequently expression of beta 1A declines, while beta 1D increases until it becomes the unique beta 1 isoform in cardiomyocytes few days after birth. Previous studies (Belkin et al J. Cell Biol. 132: 211-226, 1996) demonstrated that beta 1D in adult mouse cardiomyocytes is exclusively associated with alpha 7B. Western blot analysis shows that alpha 7B starts to be expressed in the heart only at stage E17, while beta 1D is expressed already at E11 embryo, indicating that alpha subunits other than alpha 7 should associate with beta 1D in early developmental stages. To investigate this aspect, beta 1 associated alpha subunits were identified by western blotting from cardiomyocytes integrin complexes immunoprecipitated with alpha subunit specific antibodies. We found that, during cardiomyocyte development, beta 1D associates with several alpha subunits namely with alpha 5, alpha 6A and alpha 7B. In conclusion these data show that the expression of the beta 1D muscle specific integrin during development occurs much earlier in heart than in skeletal muscle and it can dimerize with different alpha subunits.

Lysophosphatidate (LPA) is an intercellular phospholipid messenger with a wide range of biologic effects. The first discovered source of LPA in the human body were activated platelets, but several other sites of LPA generation are now known. The number of cellular interactions is also growing steadily and responses to the compound range wide, from induction of mitogenesis to neurite retraction. LPA acts via a specific G protein-coupled receptor, of which one or more subtypes may exist. Intracellularly, this receptor activates several heterotrimeric G proteins. LPA induces cell proliferation via the small GTP-binding proteins ras, and triggers actin-based cytoskeletal events through rho. This review describes the most relevant recent developments in our understanding of LPA signaling.

CD44 is the principle transmembrane receptor for the extracellular matrix glycosaminoglycan, hyaluronan. This receptor: ligand interaction is required for many normal cellular processes including lymphocyte homing into inflammatory sites, assembly of a pericellular matrix during chondrogenesis, wound healing and tissue morphogenesis during development. In order to mediate these diverse events, CD44 expressing cells must be able to regulate, and respond to, interactions with hyaluronan. The mechanisms responsible have been subject to scrutiny over the past few years as it has become clear that their disruption can underlie the progression of both metastatic tumours and chronic inflammatory diseases. Here we describe recent data identifying discrete regions within the transmembrane and cytoplasmic domains of CD44 which regulate this important adhesion receptor.

It has been clearly shown that continuous recirculation of lymphocytes is crucial for the development of primary immune responses and that naive CD4 cells are distinguished from memory CD4 cells by differences in expression of several adhesion molecules. These findings suggest that changes in migratory behavior accompany the naive to memory cell transition. This area is first reviewed and then to evaluate this hypothesis, we compare the tissue distributions of highly purified naive and memory CD4 cells after transfer to syngeneic recipients. Naive cells which express high levels of L-selectin, and low levels of alpha 4 and beta 2 integrins, and CD44 localized in secondary lymphoid organs and were detectable in these tissues and in the blood for several weeks after transfer. Memory cells, which have a reciprocal phenotype, showed a markedly different distribution, particularly with respect to tissues where entry is controlled through high endothelial venules.

To study the diversity of protocadherins, a rat brain cDNA library was screened using a cDNA for the cytoplasmic domain of human protocadherin Pcdh2 as a probe. The resultant clones contained three different types. One type corresponds to rat Pcdh2; the other two types are distinct from Pcdh2 but contain the same sequence in their cytoplasmic domains and part of the 3' flanking sequence. To clarify the structure of the proteins defined by the new clones, a putative entire coding sequence corresponding to one of the clones was determined. The overall structure is essentially the same as Pcdh2, indicating that the proteins defined by this clone, and probably by other clones, belong to the protocadherin family. Two PCR experiments and an RNase protection assay showed the existence of the corresponding mRNAs in rat brain preparations. Human and mouse cDNA clones with the same sequence properties were also isolated. Taken together, these results indicate that the clones are not cloning artifacts and that corresponding mRNAs are actually expressed in brains of various species. The results of in situ hybridization showed that the mRNAs corresponding to these clones were expressed in different regions in brain. Since protocadherins encoded by these mRNAs are likely to have different specificity in their interaction and share a common activity at their cytoplasmic domains, these protocadherins may provide a molecular basis, in part, to support the complex cell cell interaction in brain.