Myosin-X provides a motor-based link between integrins and the cytoskeleton

Unconventional myosins are actin-based motors with a growing number of attributed functions. Interestingly, it has been proposed that integrins are transported by unidentified myosins to facilitate cellular remodelling. Here we present an interaction between the unconventional myosin-X (Myo10) FERM (band 4.1/ezrin/radixin/moesin) domain and an NPXY motif within beta-integrin cytoplasmic domains. Importantly, knock-down of Myo10 by short interfering RNA impaired integrin function in cell adhesion, whereas overexpression of Myo10 stimulated the formation and elongation of filopodia in an integrin-dependent manner and relocalized integrins together with Myo10 to the tips of filopodia. This integrin relocalization and filopodia elongation did not occur with Myo10 mutants deficient in integrin binding or with a beta(1)-integrin point mutant deficient in Myo10 binding. Taken together, these results indicate that Myo10-mediated relocalization of integrins might serve to form adhesive structures and thereby promote filopodial extension.     

Molecular Analysis of Anaplasma phagocytophilum Isolated from Patients with Febrile Diseases of Unknown Etiology in China

Although anaplasmosis cases have been nationally identified in China, no human isolates of A. phagocytophilum have been obtained, which limits the analysis of any molecular and genetic contributions to patients'' severe clinical manifestations and the study of the bacteria''s pathogeneses in China. Given this situation, a joint project was conducted in 2009–2010. A total of 421 febrile cases of unknown etiology were collected and the patients'' blood samples were collected for laboratory diagnoses including serologic diagnosis based on the four-fold rise in the anti- A. phagocytophilum IgG titer by indirect micro-immunofluorescence assay (IFA), positive PCR assay and confirmation of A. phagocytophilum DNA and positive culture of A. phagocytophilum and confirmed by amplification and sequencing of the 16S rRNA and ank A genes of the A. phagocytophilum isolates. A total of 570 ticks were collected from the patients'' domestic animals (456) and from wild fields (114) for culturing and amplifying and sequencing the 16S rRNA gene of A. phagocytophilum. Phylogenetic analyses were performed on the 16S rRNA and ank A gene sequences of the isolates and the ticks tested in the study. A total of 46 (10.9%) confirmed and 16 (3.8%) probable cases were diagnosed and severe clinical features and higher mortality rates were observed in these Chinese patients. Five isolates were obtained and the 16S rRNA genes of the 5 isolates were conserved but variety for ank A genes. Two human isolates and 1 tick isolate from Shandong Peninsula, where all patients exhibited severe clinical manifestations, were grouped as one clan based on the phylogenetic analyses, while 2 other human isolates were clustered in a second clan. 43.5% of H. longicornis were infected with A. phagocytophilum.The present study is the first to obtain clinical isolates of A. phagocytophilum in China. The diversity of the ank A genes of Chinese isolates will help us to further discern the relationship between the variations in the ank A genes and the severity of the disease''s clinical manifestations in China.     

Integrin-mediated Cell Attachment Induces a PAK4-dependent Feedback Loop Regulating Cell Adhesion through Modified Integrin αvβ5 Clustering and Turnover

Cell-to-extracellular matrix adhesion is regulated by a multitude of pathways initiated distally to the core cell–matrix adhesion machinery, such as via growth factor signaling. In contrast to these extrinsically sourced pathways, we now identify a regulatory pathway that is intrinsic to the core adhesion machinery, providing an internal regulatory feedback loop to fine tune adhesion levels. This autoinhibitory negative feedback loop is initiated by cell adhesion to vitronectin, leading to PAK4 activation, which in turn limits total cell–vitronectin adhesion strength. Specifically, we show that PAK4 is activated by cell attachment to vitronectin as mediated by PAK4 binding partner integrin αvβ5, and that active PAK4 induces accelerated integrin αvβ5 turnover within adhesion complexes. Accelerated integrin turnover is associated with additional PAK4-mediated effects, including inhibited integrin αvβ5 clustering, reduced integrin to F-actin connectivity and perturbed adhesion complex maturation. These specific outcomes are ultimately associated with reduced cell adhesion strength and increased cell motility. We thus demonstrate a novel mechanism deployed by cells to tune cell adhesion levels through the autoinhibitory regulation of integrin adhesion.     

P21-activated kinase 4 interacts with integrin alpha v beta 5 and regulates alpha v beta 5-mediated cell migration

p21-activated kinase 1 (PAK1) can affect cell migration (Price et al., 1998; del Pozo et al., 2000) and modulate myosin light chain kinase and LIM kinase, which are components of the cellular motility machinery (Edwards, D.C., L.C. Sanders, G.M. Bokoch, and G.N. Gill. 1999. Nature Cell Biol. 1:253-259; Sanders, L.C., F. Matsumura, G.M. Bokoch, and P. de Lanerolle. 1999. SCIENCE: 283:2083-2085). We here present a novel cell motility pathway by demonstrating that PAK4 directly interacts with an integrin intracellular domain and regulates carcinoma cell motility in an integrin-specific manner. Yeast two-hybrid screening identified PAK4 binding to the cytoplasmic domain of the integrin beta 5 subunit, an association that was also found in mammalian cells between endogenous PAK4 and integrin alpha v beta 5. Furthermore, we mapped the PAK4 binding to the membrane-proximal region of integrin beta 5, and identified an integrin-binding domain at aa 505-530 in the COOH terminus of PAK4. Importantly, engagement of integrin alpha v beta 5 by cell attachment to vitronectin led to a redistribution of PAK4 from the cytosol to dynamic lamellipodial structures where PAK4 colocalized with integrin alpha v beta 5. Functionally, PAK4 induced integrin alpha v beta 5-mediated, but not beta1-mediated, human breast carcinoma cell migration, while no changes in integrin cell surface expression levels were observed. In conclusion, our results demonstrate that PAK4 interacts with integrin alpha v beta 5 and selectively promotes integrin alpha v beta 5-mediated cell migration.     

Alantolactone exhibits antiproliferative and apoptosis-promoting properties in colon cancer model via activation of the MAPK-JNK/c-Jun signaling pathway

Molecular and Cellular Biochemistry - Colorectal cancer (CRC) is one of the most common human malignancies in the digestive tract with high mortality. Alantolactone (ATL), as a plant-derived...     

p21-activated Kinase 4 Phosphorylation of Integrin β5 Ser-759 and Ser-762 Regulates Cell Migration

Modulation of integrin αvβ5 regulates vascular permeability, angiogenesis, and tumor dissemination. In addition, we previously found a role for p21-activated kinase 4 (PAK4) in selective regulation of integrin αvβ5-mediated cell motility (Zhang, H., Li, Z., Viklund, E. K., and Strömblad, S. (2002) J. Cell Biol. 158, 1287–1297). This report focuses on the molecular mechanisms of this regulation. We here identified a unique PAK4-binding membrane-proximal integrin β5-SERS-motif involved in controlling cell attachment and migration. We also mapped the integrin β5-binding site within PAK4. We found that PAK4 binding to integrin β5 was not sufficient to promote cell migration, but that PAK4 kinase activity was required for PAK4 promotion of cell motility. Importantly, PAK4 specifically phosphorylated the integrin β5 subunit at Ser-759 and Ser-762 within the β5-SERS-motif. Point mutation of these two serine residues abolished the PAK4-induced cell migration, indicating a functional role for these phosphorylations in migration. Our results may give important leads to the functional regulation of integrin αvβ5, with implications for vascular permeability, angiogenesis, and cancer dissemination.     

MiR-125a-3p inhibits cell proliferation and inflammation responses in fibroblast-like synovial cells in rheumatoid arthritis by mediating the Wnt/β-catenin and NF-κB pathways via targeting MAST3

Objectives:To explore the role and mechanism of miR-125a-3p in rheumatoid arthritis (RA) progression.Methods:The RA-tissues and fibroblast-like synovial cells in rheumatoid arthritis (RA-FLS) were used in this study. qRT-PCR, western blot and ELISA assay were performed to detect the expression levels of IL-6, IL-β and ΤΝF-α. Dual-luciferase reporter gene assay was used to observe the binding effect of miR-125a-3p and MAST3, and CCK-8 was used to observe the effect of miR-125a-3p on the proliferation of RA-FLS.Results:miR-125a-3p was significantly downregulated in the RA-tissues and RA-FLS, and miR-125a-3p could inhibit the proliferation and reduce the inflammation response of RA-FLS. Besides, MAST3 was found as a target of miR-125a-3p, and increased MAST3 could reverse the effects of miR-125a-3p on RA-FLS including decreased proliferation, reduced inflammation level and the inactivation of Wnt/β-catenin and NF-κB pathways.Conclusions:This study suggests that miR-125a-3p could inactivate the Wnt/β-catenin and NF-κB pathways to reduce the proliferation and inflammation response of RA-FLS via targeting MAST3.     

Opposite Role of Kindlin-1 and Kindlin-2 in Lung Cancers

Lung cancer is highly heterogenous and is composed of various subtypes that are in diverse differential stages. The newly identified integrin-interacting proteins Kindlin-1 and Kindlin-2 are the activators of transmembrane receptor integrins that play important roles in cancer progression. In this report we present the expression profiles of Kindlin-1 and Kindlin-2 in lung cancers using patient specimens and established their correlation with lung cancer progression. We found that Kindlin-1 was expressed in epithelia-derived non-small-cell lung cancer, especially in squamous cell lung cancer but expressed at low levels in poorly differentiated large cell lung cancer. However, Kindlin-2 was highly expressed in large cell lung cancer. Both Kindlin-1 and Kindlin-2 were found not expressed or expressed at very low levels in neuroendocrine-derived small cell lung cancer. Importantly, the Kindlin-1 expression level was positively correlated with the differentiation of squamous cell lung cancer. Surprisingly, we found that the very homologous Kindlin family proteins, Kindlin-1 and Kindlin-2, displayed counteracting functional roles in lung cancer cells. Ectopic expression of Kindlin-1 in non-small-cell lung cancer cells inhibited in vitro cell migration and in vivo tumor growth, while Kindlin-2 promoted these functions. Mechanistically, Kindlin-1 prohibited epithelail to mesenchymal transition in non-small-cell lung cancer cells, while Kindlin-2 enhanced epithelail to mesenchymal transition in these cells. Taken together, we demonstrated that Kindlin-1 and Kindlin-2 differentially regulate lung cancer cell progression. Further, the expression levels of Kindlin-1 might be potentially used as a marker for lung cancer differentiation and targeting Kindlin-2 might block the invasive growth of large cell lung cancer.     

Apoptosis induced by NO via phosphorylation of p38 MAPK that stimulates NF-kappaB, p53 and caspase-3 activation in rabbit articular chondrocytes

Nitric oxide (NO), reported as an important inducer of apoptosis, plays a considerable role in the pathogenetic mechanisms of articular diseases. This research aimed at investigating the role of p38 MAPK signal transduction pathway on apoptosis induced by NO in rabbit articular chondrocytes. In the present study, NO was produced by a novel NO donor NOC-18. Rabbit articular chondrocytes were cultured as monolayer, and the first passage cells were used for the experiments. We detected apoptosis induced by NO using Annexin V-FITC/PI flow cytometry and TUNEL assay. Measurement of caspase-3 has reflected its activity level. Western blotting was performed to show the protein expressions of p38, NF-kappaB, p53 and caspase-3. Furthermore, we examined the inhibitory effects in the NO pathway with p38-specific inhibitor SB203580. Treatment with NOC-18 caused accelerated apoptosis in a concentration dependent manner. This acceleration was able to be reduced when added to SB203580. Besides, the inhibitor could significantly decrease NO-induced p38, NF-kappaB, p53 and caspase-3 protein expressions, as well as caspase-3 intracellular activity (P<0.05). These results suggest that p38 MAPK signal transduction pathway is critical to NO-induced chondrocyte apoptosis, and p38 plays a role by way of stimulating NF-kappaB, p53 and caspase-3 activation.