A 130-kDa Protein 4.1B Regulates Cell Adhesion,Spreading, and Migration of Mouse Embryo Fibroblasts by Influencing Actin Cytoskeleton Organization

Protein 4.1B is a member of protein 4.1 family, adaptor proteins at the interface of membranes and the cytoskeleton. It is expressed in most mammalian tissues and is known to be required in formation of nervous and cardiac systems; it is also a tumor suppressor with a role in metastasis. Here, we explore functions of 4.1B using primary mouse embryonic fibroblasts (MEF) derived from wild type and 4.1B knock-out mice. MEF cells express two 4.1B isoforms: 130 and 60-kDa. 130-kDa 4.1B was absent from 4.1B knock-out MEF cells, but 60-kDa 4.1B remained, suggesting incomplete knock-out. Although the 130-kDa isoform was predominantly located at the plasma membrane, the 60-kDa isoform was enriched in nuclei. 130-kDa-deficient 4.1B MEF cells exhibited impaired cell adhesion, spreading, and migration; they also failed to form actin stress fibers. Impaired cell spreading and stress fiber formation were rescued by re-expression of the 130-kDa 4.1B but not the 60-kDa 4.1B. Our findings document novel, isoform-selective roles for 130-kDa 4.1B in adhesion, spreading, and migration of MEF cells by affecting actin organization, giving new insight into 4.1B functions in normal tissues as well as its role in cancer.     

Isolation and identification of antimicrobial secondary metabolites from Bacillus cereus associated with a rhabditid entomopathogenic nematode

The cell-free culture filtrate of Bacillus cereus associated with an entomopathogenic nematode, Rhabditis (Oscheius) sp., exhibited strong antimicrobial activity. The ethyl acetate extract of the bacterial culture filtrate was purified by silica gel column chromatography to obtain six bioactive compounds. The structure and absolute stereochemistry of these compounds were determined based on extensive spectroscopic analyses (LCMS, FABMS, ¹H NMR, ¹³C NMR, ¹H ?¹H COSY, ¹H ?¹³C HMBC) and Marfey’s method. The compounds were identified as cyclo(D-Pro-D-Leu), cyclo(L-Pro-D-Met), cyclo (L-Pro-D-Phe), cyclo (L-Pro-L-Val), 3,5-dihydroxy-4-ethyl-trans-stilbene, and 3,5-dihydroxy-4-isopropylstilbene, respectively. Compounds recorded antibacterial activity against all four tested bacteria strains of Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. 3,5-dihydroxy-4-isopropylstilbene recorded activity only against Gram-positive bacteria while cyclo(L-Pro-L-Val) recorded no antibacterial activity. Best antibacterial activity was recorded by 3,5-dihydroxy-4-ethyl-trans-stilbene (4 μg/ml) against Escherichia coli. The six compounds recorded significant antifungal activities against five fungal strains tested (Aspergillus flavus, Candida albicans, Fusarium oxysporum, Rhizoctonia solani and Penicillium expansum) and they were more effective than bavistin, the standard fungicide. The activity of cyclo(D-Pro-D-Leu), cyclo(L-Pro-D-Met), 3,5-dihydroxy-4-ethyl-trans-stilbene, and 3,5-dihydroxy-4-isopropylstilbene against Candida albicans was better than amphotericin B. To the best of our knowledge, this is the first report of antifungal activity of the bioactive compounds against the plant pathogenic fungi Fusarium oxysporum, Rhizoctonia solani, and Penicillium expansum. We conclude that the Bacillus cereus strain associated with entomopathogenic nematode is a promising source of natural bioactive secondary metabolites which may receive great benefit as potential sources of new drugs in the agricultural and pharmacological industry.     

Protein 4.1R links E-cadherin/β-catenin complex to the cytoskeleton through its direct interaction with β-catenin and modulates adherens junction integrity

Protein 4.1R (4.1R) is the prototypical member of the protein 4.1 superfamily comprising of the protein 4.1 family (4.1R, 4.1B, 4.1G and 4.1N) and ERM family (ezrin, radixin and meosin). These proteins in general serve as adaptors between the membrane and the cytoskeleton. Here we show that 4.1R expressed in the gastric epithelial cells associates with adherens junction protein β-catenin. Biochemical examination of 4.1R-deficient stomach epithelia revealed a selective reduction of β-catenin which is accompanied by a weaker linkage of E-cadherin to the cytoskeleton. In addition, organization of actin cytoskeleton was altered in 4.1R-deficient cells. Moreover, histological examination revealed that cell-cell contacts are impaired and gastric glands are disorganized in 4.1R null stomach epithelia. These results demonstrate an important and previously unidentified role of 4.1R in linking the cadherin/catenin complex to the cytoskeleton through its direct interaction with β-catenin and in regulating the integrity of adherens junction.     

Dusty protein kinases: primary structure, gene evolution, tissue specific expression and unique features of the catalytic domain

Ser/Thr- and Tyr-Protein kinases constitute a key switch underlying the dynamic nature and graded regulation of signal transduction and pathway activities in cellular organization. Here we describe the identification and characterization of Dusty, a single-copy gene that arose in metazoan evolution and encodes a putative dual Ser/Thr and Tyr protein kinase with unique structural features. Dusty is widely expressed in vertebrates, broadly distributed in the central nervous system, and deregulated in certain human cancers. Confocal imaging of transiently expressed human Dusty-GFP fusion proteins showed a cytoplasmic distribution. Dusty proteins from lower to higher species display an increasing degree of sequence conservation from the N-terminal non-catalytic domain to C-terminal catalytic domain. The non-catalytic region has eight conserved cysteine residues, multiple potential kinase-docking motifs and phosphorylation sites, whereas the catalytic domain is divergent and about equally distant of Ser/Thr and Tyr protein kinases. Homology analyses identified the essential catalytic residues, suggesting that Dusty homologues all possess the enzymatic activity of a protein kinase. Taken together, Dusty is a unique evolutionarily selected group of divergent protein kinases that may play important functional roles in the brain and other tissues of vertebrates.     

Peptides based on alphaV-binding domains of erythrocyte ICAM-4 inhibit sickle red cell-endothelial interactions and vaso-occlusion in the microcirculation

Growing evidence shows that adhesion molecules on sickle erythrocytes interact with vascular endothelium leading to vaso-occlusion. Erythrocyte intercellular adhesion molecule-4 (ICAM-4) binds V-integrins, including V3 on endothelial cells. To explore the contribution of ICAM-4 to vascular pathology of sickle cell disease, we tested the effects of synthetic peptides, V(16)PFWVRMS (FWV) and T(91)RWATSRI (ATSR), based on V-binding domains of ICAM-4 and capable of inhibiting ICAM-4 and V-binding in vitro. For these studies, we utilized an established ex vivo microvascular model system that enables intravital microscopy and quantitation of adhesion under shear flow. In this model, the use of platelet-activating factor, which causes endothelial oxidant generation and endothelial activation, mimicked physiological states known to occur in sickle cell disease. Infusion of sickle erythrocytes into platelet-activating factor-treated ex vivo rat mesocecum vasculature produced pronounced adhesion of erythrocytes; small-diameter venules were sites of maximal adhesion and frequent blockage. Both FWV and ATSR peptides markedly decreased adhesion, and no vessel blockage was observed with either of the peptides, resulting in improved hemodynamics. ATSR also inhibited adhesion in unactivated microvasculature. Although infused fluoresceinated ATSR colocalized with vascular endothelium, pretreatment with function-blocking antibody to V3-integrin markedly inhibited this interaction. Our data strengthen the thesis that ICAM-4 on sickle erythrocytes binds endothelium via V3 and that this interaction contributes to vaso-occlusion. Thus peptides or small molecule mimetics of ICAM-4 may have therapeutic potential. sickle cell disease; intercellular adhesion molecule-4; V3-integrin; peripheral resistance unit; endothelium; erythrocytes     

Effect of complete protein 4.1R deficiency on ion transport properties of murine erythrocytes

Moderate hemolytic anemia, abnormal erythrocyte morphology (spherocytosis), and decreased membrane stability are observed in mice with complete deficiency of all erythroid protein 4.1 protein isoforms (4.1^–/–; Shi TS et al. J Clin Invest 103: 331, 1999). We have examined the effects of erythroid protein 4.1 (4.1R) deficiency on erythrocyte cation transport and volume regulation. 4.1^–/– mice exhibited erythrocyte dehydration that was associated with reduced cellular K and increased Na content. Increased Na permeability was observed in these mice, mostly mediated by Na/H exchange with normal Na-K pump and Na-K-2Cl cotransport activities. The Na/H exchange of 4.1^–/– erythrocytes was markedly activated by exposure to hypertonic conditions (18.2 ± 3.2 in 4.1^–/– vs. 9.8 ± 1.3 mmol/10¹³ cell x h in control mice), with an abnormal dependence on osmolality (EC₅₀ = 417 ± 42 in 4.1^–/– vs. 460 ± 35 mosmol/kgH₂O in control mice), suggestive of an upregulated functional state. While the affinity for internal protons was not altered (K_0.5 = 489.7 ± 0.7 vs. 537.0 ± 0.56 nM in control mice), the V_max of the H-induced Na/H exchange activity was markedly elevated in 4.1^–/– erythrocytes (V_max 91.47 ± 7.2 compared with 46.52 ± 5.4 mmol/10¹³ cell x h in control mice). Na/H exchange activation by okadaic acid was absent in 4.1^–/– erythrocytes. Altogether, these results suggest that erythroid protein 4.1 plays a major role in volume regulation and physiologically downregulates Na/H exchange in mouse erythrocytes. Upregulation of the Na/H exchange is an important contributor to the elevated cell Na content of 4.1^–/– erythrocytes. spherocytosis; cell Na; Na/H exchange     

In vitro synergistic activity of diketopiperazines alone and in combination with amphotericin B or clotrimazole against Candida albicans

The synergistic anticandidal activity of three diketopiperazines [cyclo-(l-Pro-l-Leu) (1), cyclo-(d-Pro-l-Leu) (2), and cyclo-(d-Pro-l-Tyr) (3)] purified from a Bacillus sp. N strain associated with entomopathogenic nematode Rhabditis (Oscheius) in combination with amphotericin B and clotrimazole was investigated using the macrodilution method. The minimum inhibitory concentration and minimum fungicidal concentration of the diketopiperazines was compared with that of the standard antibiotics. The synergistic anticandidal activities of diketopiperazines with amphotericin B or clotrimazole were assessed using the checkerboard and time-kill methods. The results of the present study showed that the combined effects of diketopiperazines with amphotericin B or clotrimazole predominantly recorded synergistic (<0.5). Time-kill study showed that the growth of the Candida was completely attenuated after 12–24 h of treatment with 50:50 ratios of diketopiperazines and antibiotics. These results suggest that diketopiperazines combined with antibiotics may be microbiologically beneficial and not antagonistic. These findings have potential implications in delaying the development of resistance as the anticandidal effect is achieved with lower concentrations of both drugs (diketopiperazines and antibiotics). The cytotoxicity of diketopiperazines was also tested against two normal human cell lines (L231 lung epithelial and FS normal fibroblast) and no cytotoxicity was recorded for diketopiperazines up to 200 μg/mL. The in vitro synergistic activity of diketopiperazines with antibiotics against Candida albicans is reported here for the first time.     

Antifungal activity of crude extract produced by Bacillus sp. associated with entomopathogenic nematode from media formulated by six nitrogen sources with fructose against Penicillium expansum

A specific symbiotic Bacillus species isolated from a rhabditid entomopathogenic nematode, Rhabditis (Oscheius) sp. was found to produce a number of bioactive compounds. The present study was conducted to determine the effect of six different nitrogen sources in combination with fructose on the production of antifungal crude extract by Bacillus sp. against Penicillium expansum. The yield of crude extract and antifungal activity against the test fungi differed significantly when the nitrogen sources in the fermentation media were changed. The highest yield was recorded for beef extract plus fructose (921?mg/L). The antifungal activity was higher in yeast extract plus fructose [P. expansum (46.5?±?2.12?mm)], followed by beef extract. High performance liquid chromatography analysis of the crude antimicrobial substances revealed different peaks with different retention times indicating that they produced different compounds. When a carbon source was not included in the fermentation medium, the antimicrobial production was substantially reduced almost eight times. Carbon source in the fermentation medium plays a vital role in the production of antimicrobial substances. Yeast extract and fructose as nitrogen and carbon sources in the fermentation medium produced maximum antimicrobial activity.