Cdc42 and beta1 integrin in cell migration

Cell migration plays a central role in the development and maintenance of multicellular organisms. It involves regulated cell adhesion, mediated by integrins, and polarized changes of the cytoskeleton, controlled by Rho GTPases such as Cdc42. Aim of this study was to investigate the role of integrins and Cdc42 in cell migration and in particular the cross-talk between these molecules. In addition, the structure–function relationship of beta1 integrin in mediating migration associated events was studied. To test whether Cdc42 is essential for directed cell migration in mammalian cells and to investigate the cross-talks between integrin and Cdc42 mediated signalling, fibroblastoid cell lines lacking a functional Cdc42 gene were established and analyzed in wound closure assays. Contrary to the expectations, we could show that Cdc42 is neither required for integrin activation nor for integrin mediated protrusion formation. Moreover, Cdc42 has no significant influence on the speed of directed migration. However, it contributes to the directionality of migration and to the re-orientation of the Golgi apparatus into the direction of migration by a mechanism independent of Gsk3beta phosphorylation. Furthermore, we demonstrated that Cdc42 controls cell morphology, quite likely by regulating Rac1 activity. Expression of dominant negative Cdc42 (dnCdc42) in Cdc42-null cells revealed that dnCdc42 non-specifically inhibits other Rho GTPases besides Cdc42, since it aggravates the impairments observed in Cdc42-null cells, resulting in strongly reduced directed migration, severely reduced single cell directionality, and complete loss of Golgi polarization and of directionality of protrusion formation towards the wound. Beta1 integrins were previously shown to activate Cdc42 in response to wounding and thus to regulate the directionality of migration. We demonstrated now, that fourfold reduction of beta1 integrin expression in keratinocytes in vivo did not impair wound healing. However, keratinocyte stem cells with normal levels of beta1 integrin had a competitive advantage over the hypomorphic cells and expanded steadily in the skin of mice harbouring both cell types in the epidermis. Finally, we analysed the importance of specific amino acids of the intracellular domain of beta1 integrin in keratinocytes in vivo by generating 8 mice strains which in skin express only point or deletion mutants of beta1 integrin. Our data are for the most part strikingly different from previous results obtained in vitro and significantly revise proposed models for the role of serine and tyrosine phosphorylation and the function of a salt bridge between the integrin beta subunits and the integrin alpha tails

Genetic analysis of β1 integrin “activation motifs” in mice

Akey feature of integrins is their ability to regulate the affinity for ligands, a process termed integrin activation. The final step in integrin activation is talin binding to the NPXY motif of the integrin β cytoplasmic domains. Talin binding disrupts the salt bridge between the α/β tails, leading to tail separation and integrin activation. We analyzed mice in which we mutated the tyrosines of the β1 tail and the membrane-proximal aspartic acid required for the salt bridge. Tyrosine-to-alanine substitutions abolished β1 integrin functions and led to a β1 integrin–null phenotype in vivo. Surprisingly, neither the substitution of the tyrosines with phenylalanine nor the aspartic acid with alanine resulted in an obvious defect. These data suggest that the NPXY motifs of the β1 integrin tail are essential for β1 integrin function, whereas tyrosine phosphorylation and the membrane-proximal salt bridge between α and β1 tails have no apparent function under physiological conditions in vivo

Analysis of the use of transistors based on SiC technology in inverters in the context of electromagnetic compatibility

Currently, manufacturers of power-electronic components are trying to introduce the silicon carbide (SiC) technology in their products and MOSFET transistors made with this technology are available on the market. They are characterised by a significantly higher operating frequency, reaching even 100 kHz and low switching losses. The application of this type of devices causes high voltage gradients at the inverter output, which can lead to increased inverter electromagnetic disturbances. This article presents test results and a high-frequency analysis, allowing for a preliminary evaluation of the use of SiC transistors in inverters in the context of electromagnetic compatibility

Activin promotes skin carcinogenesis by attraction and reprogramming of macrophages.

Activin has emerged as an important player in different types of cancer, but the underlying mechanisms are largely unknown. We show here that activin overexpression is an early event in murine and human skin tumorigenesis. This is functionally important, since activin promoted skin tumorigenesis in mice induced by the human papillomavirus 8 oncogenes. This was accompanied by depletion of epidermal γδ T cells and accumulation of regulatory T cells. Most importantly, activin increased the number of skin macrophages via attraction of blood monocytes, which was prevented by depletion of CCR2-positive monocytes. Gene expression profiling of macrophages from pre-tumorigenic skin and bioinformatics analysis demonstrated that activin induces a gene expression pattern in skin macrophages that resembles the phenotype of tumor-associated macrophages in different malignancies, thereby promoting angiogenesis, cell migration and proteolysis. The functional relevance of this finding was demonstrated by antibody-mediated depletion of macrophages, which strongly suppressed activin-induced skin tumor formation. These results demonstrate that activin induces skin carcinogenesis via attraction and reprogramming of macrophages and identify novel activin targets involved in tumor formation

β1 Integrin-Mediated Adhesion Signalling Is Essential for Epidermal Progenitor Cell Expansion

Background: There is a major discrepancy between the in vitro and in vivo results regarding the role of b1 integrins in the maintenance of epidermal stem/progenitor cells. Studies of mice with skin-specific ablation of b1 integrins suggested that epidermis can form and be maintained in their absence, while in vitro data have shown a fundamental role for these adhesion receptors in stem/progenitor cell expansion and differentiation. Methodology/Principal Findings: To elucidate this discrepancy we generated hypomorphic mice expressing reduced b1 integrin levels on keratinocytes that developed similar, but less severe defects than mice with b1-deficient keratinocytes. Surprisingly we found that upon aging these abnormalities attenuated due to a rapid expansion of cells, which escaped or compensated for the down-regulation of b1 integrin expression. A similar phenomenon was observed in aged mice with a complete, skin-specific ablation of the b1 integrin gene, where cells that escaped Cre-mediated recombination repopulated the mutant skin in a very short time period. The expansion of b1 integrin expressing keratinocytes was even further accelerated in situations of increased keratinocyte proliferation such as wound healing. Conclusions/Significance: These data demonstrate that expression of b1 integrins is critically important for the expansion of epidermal progenitor cells to maintain epidermal homeostasis

Kindlin-3–mediated signaling from multiple integrin classes is required for osteoclast-mediated bone resorption

Loss of kindlin-3 impairs activation of β1, β2, and β3 integrin classes, resulting in osteopetrotic defects in osteoclast adhesion and spreading

Keratinocyte Stem Cells: friends and foes

Skin and its appendages provide a protective barrier against the assaults of the environment. To perform its role, epidermis undergoes an ongoing renewal through a balance of proliferation and differentiation/apoptosis called homeostasis. Keratinocyte stem cells reside in a special microenvironment called niche in basal epidermis, adult hair follicle and sebaceous glands. While a definite marker has yet to be detected, data raised part in humans and part in the mouse system, point to a critical role of stem and its progeny transit amplifying cells in epidermal homeostasis. Stem cells are protected from apoptosis and are long-resident in adult epidermis. This renders them more prone to be the origin of skin cancer. In this review, we will outline the main features of adult stem cells in mouse and humans and discuss their fate in relation to differentiation, apoptosis and cancer