A novel PD-1/PD-L1 pathway-related seven-gene signature for the development and validation of the prognosis prediction model for breast cancer

Background

Breast cancer (BC/BRCA) is the most common carcinoma in women. The average 5-year survival rate of BC patients with stage IV disease is 26%. A considerable proportion of patients still do not receive effective therapy. It is an unmet need to identify novel biomarkers for BC patients. Herein, we evaluated whether the programmed cell death protein 1/programmed cell death ligand 1 (PD-1/PD-L1) status is associated with the clinical outcomes of BC, based on data from The Cancer Genome Atlas (TCGA).

Methods

Clinical and transcriptome data of BC patients were obtained from TCGA dataset, and prognostic genes in BC patients were identified, as well as the PD-1/PD-L1 pathway mainly associating with the BC patients. Following the execution of the consensus clustering algorithm, BC patients were segregated into two clusters, and subsequent investigation of the potential mechanisms between them was carried out. A comparison of ferroptosis and N6-methyladenosine (m6A) was conducted between the two groups with the greatest difference in prognosis. Based on least absolute shrinkage and selection operator (LASSO) analysis, a signature associated with the PD-1/PD-L1 pathway was developed, and the prognosis outcome and the predictive accuracy of the signature model were further assessed.

Results

Prognostic genes in BC patients were studied using TCGA data and it was found that the PD-1/PD-L1 pathway was most associated with the BC patients. Then, a low-risk (C1) group and a high-risk (C2) group of BC patients were constructed based on a PD-1/PD-L1 pathway-related signature. The functional analyses suggested that the underlying mechanisms between these groups were mainly associated with immune-related pathways. We found that ferroptosis and m6A were significantly different between the two groups. A PD-1/PD-L1 pathway-related gene signature was further developed to predict survival of BC patients, including 7 genes [mitogen-activated protein kinase kinase 6 (MAP2K6), NF-kappa-B inhibitor alpha (NFKBIA), NFKB Inhibitor Epsilon (NFKBIE), Interferon gamma (IFNG), Toll/interleukin-1 receptor domain-containing adapter protein (TIRAP), IkappaB kinase (CHUK), and Casein kinase 2 alpha 3 gene (CSNK2A3)]. The receiver operating characteristic (ROC) curves were analyzed to further assess the prognostic values of these 7 genes. The 1-, 3-, and 5-year values of the areas under the curve (AUCs) for overall survival were 0.651, 0.658, and 0.653 in this seven gene signature model, respectively.

Conclusions

PD-1/PD-L1 pathway-related subtypes of BC were identified, which were closely associated with the immune microenvironment, the ferroptosis status, and m6A in BC patients. The gene signature involved in the PD-1/PD-L1 pathway might help to make a distinction and predict prognosis in BC patients.

Astragaloside IV enhances the sensitivity of breast cancer stem cells to paclitaxel by inhibiting stemness

Background

Chemotherapy is one of the common treatments for breast cancer. The induction of cancer stem cells (CSCs) is an important reason for chemotherapy failure and breast cancer recurrence. Astragaloside IV (ASIV) is one of the effective components of the traditional Chinese medicine (TCM) Astragalus membranaceus, which can improve the sensitivity of various tumors to chemotherapy drugs. Here, we explored the sensitization effect of ASIV to chemotherapy drug paclitaxel (PTX) in breast cancer from the perspective of CSCs.

Methods

The study included both in vitro and in vivo experiments. CSCs from the breast cancer cell line MCF7 with stem cell characteristics were successfully induced in vitro. Cell viability and proliferation were detected using the Cell Counting Kit-8 (CCK-8) and colony formation assays, and flow cytometry and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) methods were performed to detect cell apoptosis. Stemness-related protein expression was determined by western blotting (WB) and immunohistochemistry (IHC). Body weight, histopathology, and visceral organ damage of mice were used to monitor drug toxicity.

Results

The expression of stemness markers including Sox2, Nanog, and ALDHA1 was stronger in MCF7-CSCs than in MCF7. PTX treatment inhibited the proliferation of tumor cells by promoting cell apoptosis, whereas the stemness of breast cancer stem cells (BCSCs) resisted the effects of PTX. ASIV decreased the stemness of BCSCs, increased the sensitivity of BCSCs to PTX, and synergistically promoted PTX-induced apoptosis of breast cancer cells. Our results showed that the total cell apoptosis rate increased by about 25% after adding ASIV compared with BCSCs treated with PTX alone. The in vivo experiments demonstrated that ASIV enhanced the ability of PTX to inhibit the growth of breast cancer. WB and IHC showed that ASIV reduced the stemness of CSCs.

Conclusions

In this study, the resistance of breast cancer to PTX was attributed to the existence of CSCs; ASIV weakened the resistance of MCF7-CSCs to PTX by significantly attenuating the hallmarks of breast cancer stemness and improved the efficacy of PTX.

Comparison of hydrophilic and hydrophobic nano topographic surfaces of titanium alloys on pre-osteoblastic cell interaction

This work aimed to assess the influence of different structured substrates with hydrophilic and hydrophobic properties on micro and nano topographies developed on titanium alloys over pre-osteoblastic cell behavior. Nano topography influences small dimension levels of cell morphology by inducing filopodia formation in cell membranes, irrespectively to the wettability behavior of the surface. Therefore, micro and nanostructured surfaces of titanium-based samples using different techniques of surface modification processing, such as chemical treatments, micro-arc anodic oxidation (MAO), and MAO combined to laser irradiation were developed. Isotropic and anisotropic texture morphologies, wettability, topological parameters and compositional alterations were measured after the surface treatments. Finally, cell viability, adhesion and morphological responses were assessed to investigate the influence of distinct topologies on osteoblastic cells aiming to encounter the conditions to better promote mineralization events. Our study demonstrated that the hydrophilic behavior improves cell adhesion, amplified when effective surface area increases. Surfaces presenting nano topography have a direct influence on cell morphology and play a key role for filopodia formation.

Role of resistance training in bone macro and micro damages in an estrogen absence animal model

AIMS

We evaluated the effects of resistance training (RT) on bone properties, morphology, and bone extracellular matrix (ECM) remodeling markers in an ovariectomy (OVX) rat model.

MAIN METHODS

Thirty-six female rats were divided into four groups: sham sedentary, OVX sedentary, sham RT, and OVX RT. Rats performed RT for ten weeks, during which they climbed a ladder with progressive loads attached to the tail. Tibias were stored for dual-energy X-ray densitometry (DXA), micro-computed tomography (micro-CT), and biomechanical, biophysical, and biochemical analysis. Femurs were stored for morphological, gene expression, and gelatin zymography analysis.

KEY FINDINGS

OVX decreased bone mineral density, stiffness, maximal load, and calcium content, which was reversed by RT. The trabecular number, connectivity, and MMP-13 gene expression decreased in OVX groups. Furthermore, OVX increased run-related transcription factor-2 (RUNX-2) and osteoprotegerin (OPG) gene expression, and increased the number of adipocytes in bone marrow and MMP-2 activity.

SIGNIFICANCE

RT was efficient in preventing or reversing changes in bone biomechanical properties in OVX groups, improving fracture load and resilience, which is relevant to prevent fractures. On the other hand, RT did not decrease the number of bone adipocytes in the OVX-RT group. However, RT was efficient for increasing trabecular thickness and cortical bone volume, which improved bone resistance. Our findings provide further insights into the mechanisms involved in the role of RT in OVX damage protection.

Small Extracellular Vesicles from Hypoxic Triple-Negative Breast Cancer Cells Induce Oxygen-Dependent Cell Invasion

Hypoxia, a condition of low oxygenation frequently found in triple-negative breast tumors (TNBC), promotes extracellular vesicle (EV) secretion and favors cell invasion, a complex process in which cell morphology is altered, dynamic focal adhesion spots are created, and ECM is remodeled. Here, we investigated the invasive properties triggered by TNBC-derived hypoxic small EV (SEVh) in vitro in cells cultured under hypoxic (1% O₂) and normoxic (20% O₂) conditions, using phenotypical and proteomic approaches. SEVh characterization demonstrated increased protein abundance and diversity over normoxic SEV (SEVn), with enrichment in pro-invasive pathways. In normoxic cells, SEVh promotes invasive behavior through pro-migratory morphology, invadopodia development, ECM degradation, and matrix metalloprotease (MMP) secretion. The proteome profiling of 20% O₂-cultured cells exposed to SEVh determined enrichment in metabolic processes and cell cycles, modulating cell health to escape apoptotic pathways. In hypoxia, SEVh was responsible for proteolytic and catabolic pathway inducement, interfering with integrin availability and gelatinase expression. Overall, our results demonstrate the importance of hypoxic signaling via SEV in tumors for the early establishment of metastasis.

Resistance training variable manipulations is less relevant than intrinsic biology in affecting muscle fiber hypertrophy

We aimed to investigate whether muscle fiber cross-sectional area (fCSA) and associated molecular processes could be differently affected at the group and individual level by manipulating resistance training (RT) variables. Twenty resistance-trained subjects had each leg randomly allocated to either a standard RT (RT-CON: without specific variables manipulations) or a variable RT (RT-VAR: manipulation of load, volume, muscle action, and rest interval at each RT session). Muscle fCSA, satellite cell (SC) pool, myonuclei content, and gene expression were assessed before and after training (chronic effect). Gene expression was assessed 24h after the last training session (acute effect). RT-CON and RT-VAR increased fCSA and myonuclei domain in type I and II fibers after training (P < 0.05). SC and myonuclei content did not change for both conditions (P > 0.05). Pax-7, MyoD, MMP-2 and COL3A1 (chronic) and MGF, Pax-7, and MMP-9 (acute) increased similar for RT-CON and RT-VAR (P < 0.05). The increase in acute MyoG expression was significantly higher for the RT-VAR than RT-CON (P < 0.05). Significant correlation between RT-CON and RT-VAR for the fCSA changes (r = 0.89). fCSA changes were also correlated to satellite cells (r = 0.42) and myonuclei (r = 0.50) changes. Heatmap analyses showed coupled changes in fCSA, SC, and myonuclei responses at the individual level, regardless of the RT protocol. The high between and low within-subject variability regardless of RT protocol suggests that the intrinsic biological factors seem to be more important to explain the magnitude of fCSA gains in resistance-trained subjects.

Abstract PO034: Hypoxia-derived extracellular vesicles promote triple-negative breast cancer invasion in vitro

The increase of tumor mass and complexity triggers cell invasion, a key step of the metastatic cascade, through hypoxia-derived signalization. The decrease in oxygen levels on the inner tumor mass stimulates the secretion of extracellular vesicles (EV) to the microenvironment, whose cargo may induce an invasive behavior of breast cancer cells. In an attempt to identify key players in hypoxic EV-mediated cell invasion in breast cancer, we are investigating the molecular, cellular and biochemical changes triggered by hypoxic-EVs to triple-negative breast cancer cells (MDA-MB-231). EVs have been isolated from conditioned culture media by differential ultracentrifugation and characterized by particle analysis (NTA), transmission electron microscopy (TEM), protein quantification and western blot of EV markers according to the MISEV2018. EV-treated cells were submitted to invasion assays in i) invasion chamber with extracellular matrix-based hydrogel and ii) a fluorescent gelatin-coated surface. Cell lysate and EV samples were probed for matrix metalloproteases by western blot and zymography. Morphological analysis of cells after EV treatment have been conducted after cytoskeleton staining using fluorescent probes. EVs derived from hypoxia and normoxia-cultured MDA-MB-231 are similarly sized and enriched with CD63, FLOT-1 and ALIX, although hypoxic-EVs have displayed higher protein concentration and particle concentration. Hypoxic EVs promoted cell invasion in an extracellular matrix-based hydrogel after 6h and 16h under normal oxygen conditions. Gelatin degradation has also been observed after EV treatment in normoxia, with results akin to degradation found in cells under hypoxia. While protease activity has been detected in EVs via zymography, we have yet to confirm the role of matrix metalloproteases in EV-related cell invasion. While little morphological changes have been observed upon EV treatment in gelatin-adhered cells, they acquire an epithelial morphology in uncoated circumstances, thus indicating a key role of adhesion molecules to hypoxia-derived invasive behavior. In conclusion, hypoxia-derived EVs from breast cancer cells generate morphological and physiological changes to tumor cells in regular oxygen levels, leading to an invasive behavior in collagen-based matrixes.

Citation Format: Bianca Cruz Pachane, Wanessa Fernanda Altei, Heloisa Sobreiro Selistre-de-Araujo. Hypoxia-derived extracellular vesicles promote triple-negative breast cancer invasion in vitro [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr PO034.

Snake Venom Metalloproteinases (SVMPs): A structure-function update

Snake venom metalloproteinases (SVMPs) represent a diverse group of multi-domain proteins with several biological activities such as the ability to induce hemorrhage, proteolytic degradation of fibrinogen and fibrin, induction of apoptosis and inhibition of platelet aggregation. Due to these activities, SVMPs are responsible for many of the well-known pathological phenotypes in snake envenomations caused particularly by species from the Viperidae family and the Crotalinae subfamily. These proteins have been classified based on their size and domain structure into P–I, P-II and P-III classes. Comparatively, members of the P–I SVMPs possess the simplest structures, formed by the catalytic metalloproteinase domain only; the P-II SVMPs are moderately more complex, having the canonical disintegrin domain in addition to the metalloproteinase domain; members of the P-III class are more structurally varied, comprising the metalloproteinase, disintegrin-like, and cysteine-rich domains. Proteolytic cleavage, repeated domain loss and presence of other ancillary domains are responsible for structural diversities in the P-III class. However, studies continue to unveil the relationship between the structure and function of these proteins. In this review, we recovered evidences from literature on the structural peculiarities and functional classification of Snake Venom Metalloproteinases. In addition, we reflect on diversities that exist among each class while taking into account specific and up-to-date class-based activities.

Metastasis inhibition in breast cancer by targeting cancer cell extravasation

The spread of cells from primary tumors toward distant tissues and organs, also known as metastasis, is responsible for most cancer-associated deaths. The metastasis cascade comprises a series of events, characterized by the displacement of tumor cells (TCs) from the primary tumor to distant organs by traveling through the bloodstream, and their subsequent colonization. The first step in metastasis involves loss of cell-cell and cell-matrix adhesions, increased invasiveness and migratory abilities, leading to intravasation of TCs into the blood or lymphatic vessels. Stationary TCs must undergo the process of epithelial-mesenchymal transition in order to achieve this migratory and invasive phenotype. Circulating tumor cells that have survived in the circulation and left the blood or lymphatic vessels will reach distant sites where they may stay dormant for many years or grow to form secondary tumors. To do this, cells need to go through the mesenchymal-epithelial transition to revert the phenotype in order to regain epithelial cell-to-cell junctions, grow and become a clinically relevant and detectable tumor mass. This work will review the main steps of the metastatic cascade and describe some strategies to inhibit metastasis by reducing cancer cell extravasation presenting recent studies in the context of breast cancer.

Author Correction: Resistance training regulates gene expression of molecules associated with intramyocellular lipids, glucose signaling and fiber size in old rats

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Detraining and Anabolic-Androgenic Steroid Discontinuation Change Calcaneal Tendon Morphology

Several side effects of anabolic-androgenic steroid (AAS) administration associated with training are reported in the biomechanical properties of the calcaneal tendon (CT) of rats. Thus, the aim of the present study is to evaluate the effects of the detraining and discontinuation of AAS administration on the CT morphology of rats submitted to exercise in water. Animals were divided into two groups (20/group): (1) Immediately after training (IA), and (2) Six weeks of detraining and AAS discontinuation (6W). The IA group included four subgroups: Sedentary (S), Trained (T), Sedentary with AAS administration (SAAS), and trained with AAS administration (TAAS). The 6W group included four subgroups: Sedentary (6W-S), six weeks of detrained (6W-T), six weeks of sedentary with AAS discontinuation (6W-SAAS), and six weeks of detrained with AAS discontinuation (6W-TAAS). Data show significant reduction in adipose cells volume density (Vv%) in the distal CT in 6W-TAAS group, indicating that training can exert a positive effect on the tendon. The 6W-SAAS group exhibited increased adipose cells Vv% in the distal region, compared with the W6-S and W6-T groups. A decrease in tendon proper cells Vv% and in peritendinous sheath cells Vv% of proximal and distal regions was also observed. In 6W-TAAS group showed increase in adipose cells, blood vessels, peritendinous sheath cells, and tendon proper cells Vv% in the distal region of the CT. The vertical jumps in water were not able to protect CT regions from the negative effects of AAS discontinuation for six weeks. However, after detraining and AAS discontinuation, many protective factors of the mechanical load in the long-term could be observed.

Estrogen deficiency in ovariectomized rats: can resistance training re-establish angiogenesis in visceral adipose tissue?

OBJECTIVE

The purpose of this study was to investigate the effects of resistance training on angiogenesis markers of visceral adipose tissue in ovariectomized rats.

METHOD

Adult Sprague-Dawley female rats were divided into four groups (n=6 per group): sham-sedentary, ovariectomized sedentary, sham-resistance training and ovariectomized resistance training. The rats were allowed to climb a 1.1-m vertical ladder with weights attached to their tails and the weights were progressively increased. Sessions were performed three times per week for 10 weeks. Visceral adipose tissue angiogenesis and morphology were analyzed by histology. VEGF-A mRNA and protein levels were analyzed by real-time PCR and ELISA, respectively.

RESULTS

Ovariectomy resulted in higher body mass (p=0.0003), adipocyte hypertrophy (p=0.0003), decreased VEGF-A mRNA (p=0.0004) and protein levels (p=0.0009), and decreased micro-vascular density (p=0.0181) in the visceral adipose tissue of the rats. Resistance training for 10 weeks was not able to attenuate the reduced angiogenesis in the visceral adipose tissue of the ovariectomized rats.

CONCLUSION

Our findings indicate that the resistance training program used in this study could not ameliorate low angiogenesis in the visceral adipose tissue of ovariectomized rats.

ADAM9 silencing inhibits breast tumor cells transmigration through blood and lymphatic endothelial cells

ADAMs are transmembrane multifunctional proteins that contain disintegrin and metalloprotease domains. ADAMs act in a diverse set of biological processes, including fertilization, inflammatory responses, myogenesis, cell migration, cell proliferation and ectodomain cleavage of membrane proteins. These proteins also have additional functions in pathological processes as cancer and metastasis development. ADAM9 is a member of ADAM protein family that is overexpressed in several types of human carcinomas. The aim of this study was to investigate the role of ADAM9 in hematogenous and lymphatic tumor cell dissemination assisting the development of new therapeutic tools. The role of ADAM9 in the interaction of breast tumor cells (MDA-MB-231) and endothelial cells was studied through RNA silencing. ADAM9 silencing in MDA-MB-231 cells had no influence in expression of several genes related to the metastatic process such as ADAM10, ADAM12, ADAM17, cMYC, MMP9, VEGF-A, VEGF-C, osteopontin and collagen XVII. However, there was a minor decrease in ADAM15 expression but an increase in that of MMP2. Moreover, ADAM9 silencing had no effect in the adhesion of MDA-MB-231 cells to vascular (HMEC-1 and HUVEC) and lymphatic cells (HMVEC-dLyNeo) under flow condition. Nevertheless, siADAM9 in MDA-MB-231 decreased transendothelial cell migration in vitro through HUVEC, HMEC-1 and HMVEC-dLyNeo (50%, 40% and 32% respectively). These results suggest a role for ADAM9 on the extravasation step of the metastatic cascade through both blood and lymph vessels.

Resistance Training and Ovariectomy: Antagonic Effects in Mitochondrial Biogenesis Markers in Rat Skeletal Muscle

Estrogen reduction is associated with a decline in skeletal muscle mitochondrial biogenesis. Molecular events associated with improvements in markers of mitochondrial biogenesis after resistance training and estradiol replacement are unknown. This study aimed to investigate the effects of ovariectomy, resistance training, and estradiol replacement on markers of mitochondrial biogenesis and protein expression related to oxidative capacity in the rat gastrocnemius pool. Estradiol replacement was performed using Silastic(®) capsules. During the 12-week resistance training, animals climbed a ladder with weights attached to their tails. Gene expression was analysed by RT-PCR, and protein content was determined by western blotting. Ovariectomy decreased the gene expression of the mitochondrial biogenesis markers PGC-1α (~73%), NRF-1 (~44%), and TFAM (~53%) (p<0.05) and decreased the protein expression of phosphorylated AMPK, CREB and AKT, which are related to oxidative capacity. Resistance training increased PGC-1α (~59%) and TFAM (~48%) expression compared to the Ovariectomy-Sedentary group. The combination of resistance training and estradiol replacement was superior to the ovariectomy-sedentary and ovariectomy-resistance training treatments regarding the gastrocnemius muscle. Estrogen deficiency altered the expression of genes and proteins that favour the development of a mitochondrial dysfunction phenotype, which was improved with resistance training and was partially improved by estradiol replacement.

Alternagin-C (ALT-C), a disintegrin-like protein from Rhinocerophis alternatus snake venom promotes positive inotropism and chronotropism in fish heart

Alternagin-C (ALT-C) is a disintegrin-like protein purified from the venom of the snake, Rhinocerophis alternatus. Recent studies showed that ALT-C is able to induce vascular endothelial growth factor (VEGF) expression, endothelial cell proliferation and migration, angiogenesis and to increase myoblast viability. This peptide, therefore, can play a crucial role in tissue regeneration mechanisms. The aim of this study was to evaluate the effects of a single dose of alternagin-C (0.5 mg kg(-1), via intra-arterial) on in vitro cardiac function of the freshwater fish traíra, Hoplias malabaricus, after 7 days. ALT-C treatment increased the cardiac performance promoting: 1) significant increases in the contraction force and in the rates of contraction and relaxation with concomitant decreases in the values of time to the peak tension and time to half- and 90% relaxation; 2) improvement in the cardiac pumping capacity and maximal electrical stimulation frequency, shifting the optimum frequency curve upward and to the right; 3) increases in myocardial VEGF levels and expression of key Ca(2+)-cycling proteins such as SERCA (sarcoplasmic reticulum Ca(2+)-ATPase), PLB (phospholamban), and NCX (Na(+)/Ca(2+) exchanger); 4) abolishment of the typical negative force-frequency relationship of fish myocardium. In conclusion, this study indicates that ALT-C improves cardiac function, by increasing Ca(2+) handling efficiency leading to a positive inotropism and chronotropism. The results suggest that ALT-C may lead to better cardiac output regulation indicating its potential application in therapies for cardiac contractile dysfunction.

Recombinant disintegrin domain of human ADAM9 inhibits migration and invasion of DU145 prostate tumor cells

One of the most important features of malignant cells is their capacity to invade adjacent tissues and metastasize to distant organs. This process involves the creation, by tumor and stroma cells, of a specific microenvironment, suitable for proliferation, migration and invasion of tumor cells. The ADAM family of proteins has been involved in these processes. This work aimed to investigate the role of the recombinant disintegrin domain of the human ADAM9 (rADAM9D) on the adhesive and mobility properties of DU145 prostate tumor cells. rADAM9D was able to support DU145 cell adhesion, inhibit the migration of DU145 cells, as well as the invasion of this cell line through matrigel in vitro. Overall this work demonstrates that rADAM9D induces specific cellular migratory properties when compared with different constructs having additional domains, specially those of metalloproteinase and cysteine-rich domains. Furthermore, we showed that rADAM9D was able to inhibit cell adhesion, migration and invasion mainly through interacting with α6β1 in DU145 tumor cell line. These results may contribute to the development of new therapeutic strategies for prostate cancer.

Resistance training suppresses intra-abdominal fatty acid synthesis in ovariectomized rats

Ovarian hormone loss is associated with a shift in fat distribution to intra-abdomin al adipose tissue (intra-AAT) depots and with lipid metabolism disorders, which predisposes individuals to developing insulin resistance. Resistance training (RT) prevents increases in intra-AAT after ovarian hormone loss. However, the molecular mechanisms underlying these changes remain unclear. We investigated the effects of ovariectomy and RT on gene expression related to lipogenesis and fat oxidation in the intra-AAT of ovariectomized rats. Sprague-Dawley rats (n=6/group) were divided into the groups: sham-sedentary, ovariectomized-sedentary, sham-RT and ovariectomized-RT. RT groups performed a 10-week climbing program on a ladder with progressive overload. Intra-AAT was subjected to morphometric and mRNA analysis. Ovariectomized-sedentary group had larger adipocytes and higher expression of peroxisome proliferator-activated receptor-γ (PPAR-γ), sterol regulatory element-binding protein-1c (SREBP-1c), stearoyl-CoA desaturase-1 (SCD-1), acetyl-CoA carboxylase (ACC), hormone-sensitive lipase (HSL) and lower expression of the oxidative carnitinepalmitoyltransferase-I (CPT-1). RT counteracted OVX-induced increases in PPAR-γ and SCD-1 and decreased SREBP-1c. ACC and HSL were downregulated in ovariectomized-RT compared with the ovariectomized-sedentary group. Ovariectomized-RT group had the highest CPT-1 gene expression. Adipocyte size decreased in ovariectomized-RT group. Results suggest that RT reduces intra-AAT adipocyte size in ovariectomized rats by suppressing intra-AAT fatty acid synthesis and enhancing fatty acid β-oxidation.

Effects of Blocking αvβ₃ integrin by a recombinant RGD disintegrin on remodeling of wound healing after induction of incisional hernia in rats

PURPOSE

Incisional hernia (IH) is characterized by defective wound healing process. Disba-01, a αvb₃ integrin blocker has shown to control the rate of wound repair and therefore it could be a target for new wound healing therapies.The objective of the study was to determine the changes induced by Disba-01 on repair of wound healing after induced IH in rats.

METHODS

Thirty two male albino rats were submitted to IH and divided into 4 experimental groups: G1, placebo control; G2, DisBa-01-treated; G3, anti-αvβ₃ antibodies-treated and G4, anti-α₂ antibodies-treated. Histological. biochemical and extracellular matrix remodeling analysis of abdominal wall were evaluated.

RESULTS

After 14 days, 100% of the G2 did not present hernia, and the hernia ring was closed by a thin membrane. In contrast, all groups maintained incisional hernia. DisBa-01 also increased the number macrophages and fibroblasts and induced the formation of new vessels. Additionally, MMP-2 was strongly activated only in G2 (P<0.05). Anti- αvβ₃-integrin antibodies produced similar results than Disba-01 but not anti-α₂ integrin blocking antibodies.

CONCLUSION

These results strongly indicate that Disba-01 has an important role in the control of wound healing and the blocking of this integrin may be an interesting therapeutical strategy in IH.

Abstract B44: A role for endothelial αvβ3 integrin in breast tumor cell migration

Vascular endothelial growth factor (VEGF) and αvβ3 integrin are key molecules that actively participate in tumor angiogenesis and metastasis. Some integrin-blocking molecules are currently under clinical trials for cancer and metastasis treatment. However, the mechanism of action of such inhibitors is not completely understood and evasive resistance of antiangiogenic therapy has been reported. We have previously demonstrated the anti-angiogenic and anti-metastatic properties of DisBa-01, a recombinant His-tag RGD-disintegrin from Bothrops alternatus snake venom in experimental models. DisBa-01 blocks αvβ3 integrin binding to vitronectin and inhibits integrin mediated downstream signaling cascades and cell migration. Recently, we reported that DisBa-01 strongly decreases the expression of VEGF mRNA and of its receptors, vascular endothelial growth factor receptors 1 and 2 (VEGFR1 and VEGFR2) in endothelial cells. Here, DisBa-01 was submitted to adhesion under flow and transmigration assays, both using different DisBa-01 concentrations and β3-siMDA-MB-231 cells. In the first assay, labeled tumor cells incubated with Disba-01 perfused for 5 minutes through a chamber containing endothelial cells as coat. In the second, labeled tumor cells incubated with DisBa-01 were attracted by complete medium and transmigrated through an endothelial cell coat. Individually, assays were photographed and the cells quantified. Results show that DisBa-01 dose-dependently inhibited adhesion of MDA-MB-231 cells to human endothelial cells under flow conditions, similarly to the effect observed by β3-siMDA-MB-231 cells. In addition, the disintegrin or β3-silencing inhibited the transmigration of tumor cells through endothelial cells in vitro. These results demonstrate that endothelial αvβ3 integrin has a key role in tumor cell adhesion and transmigration through the endothelium under flow conditions.

Support: Fapesp (grant no. 1998/14138-2), CNPq, and CAPES (Brazil)

Citation Format: Cyntia Freitas Montenegro, Araceli Cristina Durante, Kelli Cristina Micocci, Antonio Carlos Manucci Pereira, Jr., Heloisa Sobreiro Selistre-de-Araujo. A role for endothelial αvβ3 integrin in breast tumor cell migration. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr B44.

ADAM9 silencing inhibits breast tumor cell invasion in vitro

ADAM9 (A Disintegrin And Metalloproteinase 9) is a member of the ADAM protein family which contains a disintegrin domain. This protein family plays key roles in many physiological processes, including fertilization, migration, and cell survival. The ADAM proteins have also been implicated in various diseases, including cancer. Specifically, ADAM9 has been suggested to be involved in metastasis. To address this question, we generated ADAM9 knockdown clones of MDA-MB-231 breast tumor cells using silencing RNAs that were tested for cell adhesion, proliferation, migration and invasion assays. In RNAi-mediated ADAM9 silenced MDA-MB-231 cells, the expression of ADAM9 was lower from the third to the sixth day after silencing and inhibited tumor cell invasion in matrigel by approximately 72% when compared to control cells, without affecting cell adhesion, proliferation or migration. In conclusion, the generation of MDA-MB-231 knockdown clones lacking ADAM9 expression inhibited tumor cell invasion in vitro, suggesting that ADAM9 is an important molecule in the processes of invasion and metastasis.

Association of Bartonella spp bacteremia with Chagas cardiomyopathy, endocarditis and arrhythmias in patients from South America

Infection with Bartonella spp may cause cardiac arrhythmias, myocarditis and endocarditis in humans. The aim of the present study was to evaluate a possible association between Bartonella spp bacteremia and endocarditis, arrhythmia and Chagas cardiomyopathy in patients from Brazil and Argentina. We screened for the presence of bacterial 16S rRNA in human blood by PCR using oligonucleotides to amplify a 185-bp bacterial DNA fragment. Blood samples were taken from four groups of subjects in Brazil and Argentina: i) control patients without clinical disease, ii) patients with negative blood-culture endocarditis, iii) patients with arrhythmias, and iv) patients with chronic Chagas cardiomyopathy. PCR products were analyzed on 1.5% agarose gel to visualize the 185-bp fragment and then sequenced to confirm the identity of DNA. Sixty of 148 patients (40.5%) with cardiac disease and 1 of 56 subjects (1.8%) from the control group presented positive PCR amplification for Bartonella spp, suggesting a positive association of the bacteria with these diseases. Separate analysis of the four groups showed that the risk of a Brazilian patient with endocarditis being infected with Bartonella was 22 times higher than in the controls. In arrhythmic patients, the prevalence of infection was 45 times higher when compared to the same controls and 40 times higher for patients with Chagas cardiomyopathy. To the best of our knowledge this is the first report of the association between Bartonella spp bacteremia and Chagas disease. The present data may be useful for epidemiological and prevention studies in Brazil and Argentina.

Purification and characterization of Ts15, the first member of a new α-KTX subfamily from the venom of the Brazilian scorpion Tityus serrulatus

Voltage-gated potassium channel toxins (KTxs) are basic short chain peptides comprising 23-43 amino acid residues that can be cross-linked by 3 or 4 disulfide bridges. KTxs are classified into four large families: α-, β-, γ- and κ-KTx. These peptides display varying selectivity and affinity for K(v) channel subtypes. In this work, a novel toxin from the Tityus serrulatus venom was isolated, characterized and submitted to a wide electrophysiological screening on 5 different subtypes of Na(V) channels (Na(V)1.4; Na(V)1.5; Na(V)1.6; Na(V)1.8 and DmNa(V)1) and 12 different subtypes of K(V) channels (K(V)1.1 - K(V)1.6; K(V)2.1; K(V)3.1; K(V)4.2; K(V)4.3; Shaker IR and ERG). This novel peptide, named Ts15, has 36 amino acids, is cross-linked by 3 disulfide bridges, has a molecular mass of 3956 Da and pI around 9. Electrophysiological experiments using patch clamp and the two-electrode voltage clamp techniques show that Ts15 preferentially blocks K(V)1.2 and K(V)1.3 channels with an IC₅₀ value of 196 ± 25 and 508 ± 67 nM, respectively. No effect on Na(V) channels was observed, at all tested concentrations. Since Ts15 shows low amino acid identity with other known KTxs, it was considered a bona fide novel type of scorpion toxin. Ts15 is the unique member of the new α-Ktx21 subfamily and therefore was classified as α-Ktx21.1.

Biomechanical responses of different rat tendons to nandrolone decanoate and load exercise

Androgenic-anabolic steroids (AAS) have been associated with an increased incidence of tendon rupture. The aim of this study was to compare the biomechanical properties of the rat calcaneal tendon (CT), superficial flexor tendon (SFT), and deep flexor tendon (DFT), and to determine the effect of jump training in association with AAS. Animals were separated into four groups: sedentary, trained, AAS-treated sedentary rats (AAS), and AAS-treated and trained animals. Mechanical testing showed that the CT differed from the DFT and SFT, which showed similar mechanical properties. Jump caused the CT to exhibit an extended toe region, an increased resistance to tensional load, and a decreased elastic modulus, characteristics of an elastic tendon capable of storing energy. AAS caused the tendons to be less compliant, and the effects were reinforced by simultaneous training. The DFT was the most affected by training, AAS, and the interaction of both, likely because of its involvement in the toe-off step of jumping, which we suggest is related to the rapid transmission of force as opposed to energy storage. In conclusion, tendons are differently adapted to exercise, but responded equally to AAS, showing reduced flexibility, which is suggested to increase the risk of tendon rupture in AAS consumers.

Effects of the myotoxic Lys49 phospholipase A2 from Agkistrodon contortrix laticinctus snake venom on water transport in the toad bladder epithelium: evidence for a role of microtubules and calmodulin

ACLMT is a myotoxic Lys49 phospholipase A2 isolated from the venom of the snake Agkistrodon contortrix laticinctus. We have previously demonstrated that ACLMT affects the water transport in toad bladders through a mechanism partially mediated by an increase in the cytosolic calcium. This study aims to further investigate the sites and mechanisms involved in the effects of ACLMT on water transport in toad bladders by examining the role of microtubules and calmodulin. Water flow across the membrane was gravimetrically measured in bladder sac preparations. ACLMT increased basal water transport and inhibited water transport stimulated by vasopressin. Colchicine and trifluoperazine reduced the effect of the toxin on basal water transport and enhanced it on vasopressin-stimulated water transport. The results suggest that both microtubules and calmodulin may be involved in the effect of ACLMT on basal water transport. On the other hand, the effect of the toxin on vasopressin-stimulated water transport appears to be neither dependent on the microtubules integrity nor directly mediated by calmodulin. This study provides a deeper understanding of the effects of the Lys49 PLA2 myotoxins on membrane permeability, thus contributing to elucidate the toxicity mechanism of these myotoxins on biological tissues.

Effect of rACLF, a recombinant snake venom metallopeptidase on cell viability, chemokine expression and degradation of extracellular matrix proteins

Snake venom metallopeptidases (SVMPs) comprise a family of zinc-dependent enzymes, which display many different biological activities. ACLF is a 23kDa fibrinolytic non-hemorrhagic metallopeptidase from the venom of the snake Agkistrodon contortrix laticinctus. We have previously developed an expression system for production of recombinant ACLF (rACLF) in bacteria. To achieve a better understanding of the role of such enzyme in envenoming cases, we have studied the biological properties of rACLF, including the ability of enzyme to degrade extracellular proteins, as well its cytotoxic effect in human fibroblasts and HeLa cells. Our results showed that rACLF hydrolyzed laminin, fibronectin, type IV collagen and thrombospondin. rACLF decreased HeLa cell viability, changed cell morphology and induced detachment, while for human fibroblasts no cytotoxic effects were observed after treatment with rACLF. In addition, growth-related oncogene (GRO) and monocyte chemoattractant protein 1 (MCP-1/CCL2) were chemokines detected in the culture supernatant of human fibroblasts incubated with rACLF for 48h. These chemokines could contribute to the severe local lesion induced by Agkistrodon contortrix lacticinctus venom. These findings suggest a relevant role for ACLF in envenomation.

Insights into the substrate specificity of a novel snake venom serine peptidase by molecular modeling

The cDNA encoding BthaTL, a serine peptidase from the venom of the snake Bothrops alternatus, was cloned and sequenced. The deduced primary structure shows over 62% of identity with snake venom thrombin-like enzymes (SVTLEs), molecules with high substrate specificity toward different natural substrates. Indeed, a phylogenetic reconstruction by two different methods clustered this enzyme close to other SVTLEs. These enzymes generally affect the hemostatic system in several ways, and therefore are used as tools in pharmacology and clinical diagnosis. A three-dimensional model of BthaTL was built by homology modeling using TSV-PA (Trimeresurus stejnegeri venom plasminogen activator) crystal structure as template. BthaTL model showed that the typical catalytic triad conformation of serine peptidases was preserved. The calcium coordination ligands were absent or adopt an unfavorable conformation, preventing interactions with metals. On the other hand, the Asp97-Arg174 saline bridge of TSV-PA was not found and its specificity determinant Phe193 is replaced by a Gly in BthaTL. The substitution of essential residues in the neighborhoods of the catalytic site cleft of BthaTL indicates that these two proteins do not share the same enzymatic specificity, what means that BthaTL will probably not activate plasminogen. Such observations may be helpful in the understanding of the molecular mechanism for substrate specificity of these enzymes.

The effect of the myotoxic Lys49 phospholipase A(2) from Agkistrodon contortrix laticinctus snake venom on Na+/K+ -ATPase activity of toad bladders

ACLMT is a myotoxic Lys49 phospholipase A(2) isolated from the venom of the snake Agkistrodon contortrix laticinctus. We have previously shown that ACLMT increases baseline water transport and partially inhibits vasopressin-stimulated water transport across toad bladders due to an increase in cytosolic calcium. However, these evidences provide insufficient insight into the mechanisms involved in the effects of ACLMT on membrane permeability. In an attempt to better understand such mechanisms, the current study aimed to investigate whether the Na(+)/K(+)-ATPase activity of isolated toad bladders can be affected by the ACLMT and the synthetic peptide from its C-terminal region. The toxin significantly decreased the Na(+)/K(+)-ATPase, while the peptide did not alter it. These findings suggest that the effects of ACLMT on membrane permeability may be due to the inhibition of the Na(+)/K(+)-ATPase activity, and that the C-terminal region may not play a relevant role in this effect. This study contributes toward a better understanding of the mechanisms involved in the toxicity of the snake venom Lys49 PLA(2) myotoxins on biological tissues.

Snake venom metalloproteases--structure and function of catalytic and disintegrin domains

Snake venoms are relevant sources of toxins that have evolved towards the engineering of highly active compounds. In the last years, research efforts have produced great advance in their understanding and uses. Metalloproteases with disintegrin domains are among the most abundant toxins in many Viperidae snake venoms. This review will focus on the structure, function and possible applications of the metalloprotease and disintegrin domains.

Alternagin-C, a disintegrin-like protein from the venom of Bothrops alternatus, modulates alpha2beta1 integrin-mediated cell adhesion, migration and proliferation

The alpha2beta1 integrin is a major collagen receptor that plays an essential role in the adhesion of normal and tumor cells to the extracellular matrix. Alternagin-C (ALT-C), a disintegrin-like protein purified from the venom of the Brazilian snake Bothrops alternatus, competitively interacts with the alpha2beta1 integrin, thereby inhibiting collagen binding. When immobilized in plate wells, ALT-C supports the adhesion of fibroblasts as well as of human vein endothelial cells (HUVEC) and does not detach cells previously bound to collagen I. ALT-C is a strong inducer of HUVEC proliferation in vitro. Gene expression analysis was done using an Affimetrix HU-95A probe array with probe sets of approximately 10,000 human genes. In human fibroblasts growing on collagen-coated plates, ALT-C up-regulates the expression of several growth factors including vascular endothelial growth factor, as well as some cell cycle control genes. Up-regulation of the vascular endothelial growth factor gene and other growth factors could explain the positive effect on HUVEC proliferation. ALT-C also strongly activates protein kinase B phosphorylation, a signaling event involved in endothelial cell survival and angiogenesis. In human neutrophils, ALT-C has a potent chemotactic effect modulated by the intracellular signaling cascade characteristic of integrin-activated pathways. Thus, ALT-C acts as a survival factor, promoting adhesion, migration and endothelial cell proliferation after binding to alpha2beta1 integrin on the cell surface. The biological activities of ALT-C may be helpful as a therapeutic strategy in tissue regeneration as well as in the design of new therapeutic agents targeting alpha2beta1 integrin.

Comparative analysis of the catalytic domain of hemorrhagic and non-hemorrhagic snake venom metallopeptidases using bioinformatic tools

Snake venom metalloproteases (SVMPs) are a set of interesting enzymes that are one of the major components of venom affecting hemostasis. A great challenge since their discovery has been to find molecular features responsible for their hemorrhagic potency and many attempts have been made without any consistent result. Here we describe a series of comparisons between the catalytic domains of hemorrhagic and non-hemorrhagic SVMPs made with the help of bioinformatics. These involved sequence and structure-based multiple alignments, phylogenetic reconstruction, predicted physical and chemical properties, motif scanning and structural analyses. Although hemorrhagic activity seems to be complex, involving multiple factors, we found some molecular characteristics that may influence the toxic effects. Among these findings, it was possible to use a molecular surface feature to subdivide the P-I class in hemorrhagic and non-hemorrhagic SVMPs. It was also possible to suggest a role for the conserved Asp148 and Ser176 residues in the stabilization of the active site.

Effect of a recombinant Lys49PLA2 myotoxin and Lys49PLA2-derived synthetic peptides from Agkistrodon species on membrane permeability to water

The aim of this work was to study the effect of recombinant ACL myotoxin, a Lys49PLA2 from Agkistrodon contortrix laticinctus snake venom and Lys49PLA2-derived synthetic peptides corresponding to the region 115-129 of venom of the two different Agkistrodon species on water permeability in the toad urinary bladder. The water flow through the membrane was measured gravimetrically in bag preparations of the bladder. The addition of recombinant ACL myotoxin-MBP (maltose binding protein) fusion protein (10 nM) to the bathing solution significantly increased (above 60%) the water transport compared with the control hemibladders. The addition of the Lys49PLA2-derived synthetic peptides in several concentrations to the bathing solution did not affect the water transport across membrane. These results suggest that the ACL myotoxin effect on water transport is not related to the cytotoxic C-terminal region.

Effects of a myotoxic Asp49 phospholipase A2 (ACL-I PLA2) isolated from Agkistrodon contortrix laticinctus snake venom on water transport in the isolated toad urinary bladder

An Asp49 PLA2 (ACL-I PLA2) was purified from the venom of Agkistrodon contortrix laticinctus by gel filtration and cation-exchange chromatography. It has a relative molecular mass of 14,000, and its N-terminal sequence has more than 65% of identity with other snake venom PLA2s. ACL-I PLA2 injected into the Tibialis anterior muscle of rats and mice at doses of 0.3 and 1.6 mg/kg, respectively, induced muscle fiber necrosis, cellular infiltration and edema 3 and 48 h after injection. The effect of the purified enzyme on water permeability was tested in the isolated toad urinary bladder. Water flow through the membrane was measured gravimetrically in bag preparations of the bladder. ACL-I PLA2 (20 nM) did not significantly alter the water permeability in the bladder preparations, whereas ACL myotoxin (ACLMT), a Lys49 PLA2 isolated from the same venom, at similar concentration significantly increased (81%) the water permeability. However, both toxins inhibited the AVP-stimulated water permeability. These results strongly suggest that PLA2 activity is not involved in the ACLMT effect on water transport and the effect of ACL-I PLA2 myotoxin on membrane permeability is mediated by mechanisms that are different in comparison to ACLMT.

The effect of post-translational modifications on the hemorrhagic activity of snake venom metalloproteinases

Metalloproteinases (MPs) are Zn(+)-dependent endoproteolytic enzymes, abundant in crotalid and viperid snake venoms. Most snake venom metalloproteinases (svMPs) are active on extracellular matrix components and this effect is thought to result in bleeding as a consequence of the basement membrane disruption in capillaries. Jararhagin and ACLH are hemorrhagic svMPs from Bothrops jararaca and Agkistrodon contortrix laticinctus venom, respectively. Both enzymes demonstrate proteolytic activity on fibrinogen and fibronectin and jararhagin inhibits collagen-induced platelet aggregation in vitro. This work describes the expression, purification and successful refolding of the recombinant ACLH zymogen (rPRO-ACLH) as well as the catalytic domain of jararhagin (rCDJARA). The heterologous proteins were produced in E. coli, an in vivo expression system that does not make post-translational modifications. The recombinant refolded proteins did not show any hemorrhagic activity in mice skin, as well as the native deglycosylated jararhagin and ACLH. However, they preserved their proteolytic activity on fibrinogen and fibronectin. It seems that the hemorrhagic properties of these hemorrhagins are dependent on post-translational modifications, whereas their proteolytic activity is not dependent on such modifications.

Effects of ACL myotoxin, a Lys49 phospholipase A2 from Agkistrodon contortrix laticinctus snake venom, on water transport in the isolated toad urinary bladder

ACL myotoxin (ACLMT) is a Lys49 phospholipase A(2)-like protein isolated from the venom of the snake Agkistrodon contortrix laticinctus. The aim of this work was to study the effect of ACLMT on water transport in the toad bladder. Water flow through the membrane was measured gravimetrically in bag preparations of the bladder. ACLMT (20 nM) increased the baseline water flow and partially inhibited arginine-vasopressin (AVP), 8-chlorophenylthio-cAMP (8-CPT-cAMP) and forskolin-stimulated water flow. The effect of ACLMT on baseline or AVP-stimulated water flow was prevented by lanthanum (0.1 mM) indicating that the effect of ACLMT on water transport may be mediated through an increase in intracellular calcium. The effect of ACLMT on baseline water flow was also prevented by nifedipine (0.1 mM) indicating the participation of exogenous calcium in this effect. Carbachol (0.1 mM) has been shown to enhance baseline water flow while inhibiting AVP-stimulated water flow. The effects of ACLMT and carbachol on baseline water flow and AVP-stimulated water flow were not additive, suggesting that both agents alter water transport by a similar mechanism. Indomethacin (10 microM) reduced the effect of ACLMT on forskolin-stimulated water flow, suggesting an increase in prostaglandin biosynthesis. These results suggest that the effects of ACLMT on water transport may be mediated by increasing intracellular calcium and stimulation prostaglandin biosynthesis.

BaG, a new dimeric metalloproteinase/disintegrin from the Bothrops alternatus snake venom that interacts with alpha5beta1 integrin

The alpha(5)beta(1) integrin is one of the major fibronectin receptors which plays an essential role in the adhesion of normal and tumor cells to extracellular matrix. Here, we describe the isolation and characterization of a novel dimeric metalloproteinase/disintegrin, which is an inhibitor of fibronectin binding to the alpha(5)beta(1) integrin. This protein (BaG) was isolated from the venom of the South American snake Bothrops alternatus by gelatin-Sepharose affinity and anion exchange chromatography. The molecular mass of BaG was approximately 130 kDa under non-reducing conditions and 55 kDa under reducing conditions by SDS-PAGE. BaG shows proteolytic activity on casein that was inhibited by EDTA. 1,10-phenanthroline-treated BaG (BaG-I) inhibits ADP-induced platelet aggregation with an IC(50) of 190 nM. BaG-I inhibits fibronectin-mediated K562 cell adhesion with an IC(50) of 3.75 microM. K562 cells bind to BaG-I probably through interaction with alpha(5)beta(1) integrin, since anti-alpha(5)beta(1) antibodies inhibited K562 cell adhesion to BaG-I. In addition, BaG-I induces the detachment of K562 cells that were bound to fibronectin. In summary, we have purified a novel, dimeric snake venom metalloproteinase/disintegrin that binds to the alpha(5)beta(1) integrin.

Cell adhesion and cytotoxicity studies over polyanionic collagen surfaces with variable negative charge and wettability

This work describes the cytotoxicity, and the cell adhesion behavior of K562 cell line from human erythroleukemia transfected with the DNA for the alpha(2)beta(1) integrin over type-I collagen matrices with variable degree of carboxyl group and wettability. The results showed that type-I collagen materials with variable degree of carboxyl group prepared by selective hydrolysis of carboxyamide side chains of Asn and Gln residues present in the protein, independently from the extent of side chain hydrolysis, was characterized by preserved triple helix structure for materials with a carboxyl group content up to 87 +/- 17. Imbibition and wettability increased linearly with increasing carboxyl group content from 46 +/- 12 to 87 +/- 17, and no signs of cytotoxicity were detected. Nevertheless, in comparison to native collagen, K562 cell adhesion to PACMs was significantly improved by factors ranging from 1.60 to 1.47x, with the reduction in cell adhesion observed with increasing carboxyl content attributed to a balance between the inhibition of increasing negative charge and the stimulation by increased wettability. On the other hand, the overall improvement of K562 cell adhesion to polyanionic collagen was attributed to the introduction of new distinct motifs described as the minimal active recognition sequence for alpha(2)beta(1) integrins binding with type-I collagen produced as a result of Asn-Gly Glu-Ala alpha2(I)294-297, and Gly Gln-Arg-Gly Val-Val carboxyamide side chains hydrolysis.

Expression of an active recombinant lysine 49 phospholipase A(2) myotoxin as a fusion protein in bacteria

ACL myotoxin (ACLMT) is a K49 phospholipase A(2)-like protein isolated from the venom of the snake Agkistrodon contortrix laticinctus (broad-banded copperhead) that induces necrosis of skeletal muscle. We have previously cloned and sequenced the cDNA coding for ACLMT from a venom gland cDNA library. In order to perform structure and function studies, we have developed an expression system for production of ACLMT as a fusion protein with maltose binding protein (MBP) from the periplasm of bacteria, using the pMAL-p2 expression vector. The cDNA coding for the mature toxin without the signal peptide was amplified by PCR and subcloned into the pMAL-p2 vector. The new plasmid (pMAL-MT) was used to transform BL21(DE3) E. coli cells. Culture of transformed cells induced with IPTG led to the expression of a 60 kDa fusion protein which strongly reacts with anti-native ACLMT antibodies. The fusion protein was purified from the bacterial periplasm by affinity chromatography in an amylose column and by gel filtration. The purified fusion protein (MBP-rACLMT) was able to induce necrosis of skeletal muscle of mice very similar to that caused by the native myotoxin.

Spectral characteristics of a compound altering cytochrome P450 spectra from vertebrate microsomes suggest that it is a functional protein

A peak near 420 nm interfering with the spectral detection of cytochrome P450 has been reported for invertebrates and fish. It has been variously suggested to be a breakdown product of P450, or a hemoprotein with unknown functions. Similar spectra were observed in the present work with a neotropical fish, an amphibian, and rodents. Comparative analysis showed that difference spectra resulted from an unknown hemoprotein and neither from P420, nor from hemoglobin, that may contaminate animal microsomes. Seasonal appearance of this protein was observed and its spectrum described. This protein completely substituted P450 in spectra of liver microsomes of fish and rodents collected in the summer, while in the winter the same animals displayed either the classic P450 spectra (rodents) or those accompanied with the low-intensity 421-nm peak (fish). We suggest that the compound visualized in P450 spectra is a functional protein and not an artifact. The possibility that an unknown protein may substitute for cytochrome P450 in microsomes under certain environmental conditions and play a role in animal adaptation to unfavorable environmental fluctuations is discussed.

Crystallization and preliminary X-ray analysis of jararhagin, a metalloproteinase/disintegrin from Bothrops jararaca snake venom

Jararhagin is a toxic protein, isolated from the venom of the snake Bothrops jararaca, which is composed of a metalloprotease domain coupled to a disintegrin/cysteine-rich domain. It induces local haemorrhage owing to the proteolytic digestion of the basement membrane of capillaries. Jararhagin also cleaves the alpha(2)beta(1) integrin on the surface of platelets, thereby acting as a potent inhibitor of collagen-induced platelet aggregation. Crystals of jararhagin were obtained by the vapour-diffusion technique at 273 K in 200 mM sodium acetate, 100 mM cacodylate buffer pH 6.5 and 30% PEG 8000. Diffraction data have been obtained to a resolution of 2.8 A from a single frozen crystal, which belonged to space group P2(1)2(1)2(1) with unit-cell parameters a = 73.7, b = 100.3, c = 133.4 A. The asymmetric unit contains two jararhagin molecules and has a solvent content of 45%. A molecular-replacement solution has been obtained using a homology-built model based on the crystal structure of acutolysin, a haemorrhagic zinc metalloproteinase from the venom of the snake Agkistrodon acutus; attempts are under way to locate the remaining domains.

The disintegrin-like domain of the snake venom metalloprotease alternagin inhibits alpha2beta1 integrin-mediated cell adhesion

The alpha2beta1 integrin is a major collagen receptor that plays an essential role in the adhesion of normal and tumor cells to the extracellular matrix. Here we describe the isolation of a novel metalloproteinase/disintegrin, which is a potent inhibitor of the collagen binding to alpha2beta1 integrin. This 55-kDa protein (alternagin) and its disintegrin domain (alternagin-C) were isolated from Bothrops alternatus snake venom. Amino acid sequencing of alternagin-C revealed the disintegrin structure. Alternagin and alternagin-C inhibit collagen I-mediated adhesion of K562-alpha2beta1-transfected cells. The IC50 was 134 and 100 nM for alternagin and alternagin-C, respectively. Neither protein interfered with the adhesion of cells expressing alphaIIbeta3, alpha1beta1, alpha5beta1, alpha4beta1 alphavbeta3, and alpha9beta1 integrins to other ligands such as fibrinogen, fibronectin, and collagen IV. Alternagin and alternagin-C also mediated the adhesion of the K562-alpha2beta1-transfected cells. Our results show that the disintegrin-like domain of alternagin is responsible for its ability to inhibit collagen binding to alpha2beta1 integrin.

Determination of the three-dimensional structure of toxins by protein crystallography

Protein crystallography has significantly contributed to the development of many areas of biochemical research, particularly in the understanding of phenomena related to molecular recognition. Examples include the formation of enzyme-substrate complexes (and their subsequent catalysis), host cell invasion by viruses, antigen neutralization and peptide display by proteins of the immune system and many others. More recently, protein crystallography has also proved to be of great value in unraveling the molecular basis of many diseases as well as in the development of new drugs for their treatment. The X-ray diffraction technique in the elucidation of macromolecular structures is situated at the interface between the traditional research fields of biology, biochemistry, chemistry and physics where researchers are united by a common interest in the detailed understanding of macromolecule function and its relationship to three-dimensional structure. The purpose of this review is to describe, without resort to mathematical detail, all of the necessary steps for the complete determination of a three-dimensional structure by X-ray diffraction techniques. The basic procedures used for protein isolation and crystallization, crystallographic data collection and analysis and, finally, structure determination and refinement are all briefly reviewed. As such our efforts are not directed towards the specialist. Rather, it is our hope that the information presented will aid interested readers from other fields in the understanding of more specialized literature and who may wish to employ the information contained therein in the planning of their biological research. We hope that in so doing we will make clear both the power and limitations of the technique.

Expression, refolding, and activity of a recombinant nonhemorrhagic snake venom metalloprotease

Snake venoms are rich sources of proteases that strongly affect the vascular system, by promoting blood coagulation, hemorrhage, and fibrinolysis. Hemorrhagic activity is mostly due to the enzymatic action of metalloproteases on capillary basement membrane components, such as collagen IV, laminin, and fibronectin. A few low-molecular-weight snake venom metalloproteases (svMP) have been described as being devoid of hemorrhagic activity, but they have strong direct-acting fibrinolytic activity that could be very helpful in thrombosis therapy. We have developed an expression system for production of a recombinant svMP from a cDNA (ACLPREF) coding for a small metalloprotease (ACLF) with three disulfide bonds from an Agkistrodon contortrix laticinctus (broad-banded copperhead) venom gland cDNA library. The mature protein-coding region was amplified by PCR and subcloned into the pET28a vector, and the resulting plasmid was used to transform BL21(DE3) Escherichia coli cells. Culture of the transformants at either 37 or 20 degrees C led to the overexpression of an insoluble and inactive 30-kDa protein after 1.0 mM IPTG induction. The expressed protein (rACLF) was recovered from inclusion bodies with 6 M buffered urea solution and purified on a nickel-Sepharose column followed by gel filtration chromatography, both under denaturing conditions. After treatment with dithiothreitol, protein refolding was performed by gradual removal of the denaturing agent by dialysis. The refolded recombinant protein was active in fibrin-agarose plates. The purified protein achieved a conformation similar to that of the native enzyme as judged by circular dichroism analysis.