[Show abstract][Hide abstract] ABSTRACT: Acute lymphoblastic leukemia (ALL) initiates and progresses in the bone marrow, and as such, the marrow microenvironment is a critical regulatory component in development of this cancer. However, ALL studies were conducted mainly on flat plastic substrates, which do not recapitulate the characteristics of marrow microenvironments. To study ALL in a model of in vivo relevance, we have engineered a 3-D microfluidic cell culture platform. Biologically relevant populations of primary human bone marrow stromal cells, osteoblasts and human leukemic cells representative of an aggressive phenotype were encapsulated in 3-D collagen matrix as the minimal constituents and cultured in a microfluidic platform. The matrix stiffness and fluidic shear stress were controlled in a physiological range. The 3-D microfluidic as well as 3-D static models demonstrated coordinated cell-cell interactions between these cell types compared to the compaction of the 2-D static model. Tumor cell viability in response to an antimetabolite chemotherapeutic agent, cytarabine in tumor cells alone and tri-culture models for 2-D static, 3-D static and 3-D microfluidic models were compared. The present study showed decreased chemotherapeutic drug sensitivity of leukemic cells in 3-D tri-culture models from the 2-D models. The results indicate that the bone marrow microenvironment plays a protective role in tumor cell survival during drug treatment. The engineered 3-D microfluidic tri-culture model enables systematic investigation of effects of cell-cell and cell-matrix interactions on cancer progression and therapeutic intervention in a controllable manner, thus improving our limited comprehension of the role of microenvironmental signals in cancer biology.
PLoS ONE 10/2015; 10(10):e0140506. DOI:10.1371/journal.pone.0140506 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Leptin has been considered to modulate cardiac electrical properties via β-adrenergic receptor activation. The presence of leptin receptors and adipocytes in myocardium raised a question as to whether leptin can directly modulate cardiac electrical properties such as heart rate and QT interval via its receptor. In this work, the role of local direct actions of leptin on heart rate and ventricular repolarization was investigated. We identified the protein expression of leptin receptors at cell surface of sinus node, atrial and ventricular myocytes isolated from rat heart. Leptin at low doses (0.1-30μg/kg) decreased resting heart rate; at high doses (150-300μg/kg) leptin induced a biphasic effect (decrease and then increase) on heart rate. In the presence of high-dose propranolol (30mg/kg), high-dose leptin only reduced heart rate, sometimes caused sinus pauses and ventricular tachycardia. The leptin-induced inhibition of resting heart rate was fully reversed by leptin antagonist. Leptin also increased heart-rate corrected QT interval (QTc) and leptin antagonist did not. In isolated ventricular myocytes leptin (0.03 - 0.3μg/ml) reversibly increased the action potential duration. These results supported our hypothesis that leptin can directly inhibit heart rate and increase QT interval via its receptor, independent of β-adrenergic receptor stimulation.
[Show abstract][Hide abstract] ABSTRACT: Acute lymphoblastic leukemia (ALL) treatment regimens have dramatically improved the survival of ALL patients. However, chemoresistant minimal residual disease (MRD) that persists following cessation of therapy contributes to aggressive relapse. The bone marrow microenvironment (BMM) is an established "site of sanctuary" for ALL as well as myeloid lineage hematopoietic disease, with signals in this unique anatomical location contributing to drug resistance. Several models have been developed to recapitulate the interactions between the BMM and ALL cells. However, many in vitro models fail to accurately reflect the level of protection afforded to the most resistant sub-set of leukemic cells during co-culture with BMM elements. Pre-clinical in vivo models have advantages, but can be costly, and are often not fully informed by optimal in vitro studies. In the current report we describe an innovative extension of 2D co-culture wherein ALL cells uniquely interact with bone marrow derived stromal cells. Tumor cells in this model bury beneath primary human bone marrow derived stromal cells or osteoblasts, termed "phase dim" (PD) ALL, and exhibit a unique phenotype characterized by altered metabolism, distinct protein expression profiles, increased quiescence, and pronounced chemotherapy resistance. Investigation focused on the PD subpopulation may more efficiently inform pre-clinical design and investigation of MRD and relapse that arises from BMM supported leukemic tumor cells.
[Show abstract][Hide abstract] ABSTRACT: Epidemiological studies provide strong evidence that obesity and the associated adipose tissue inflammation are risk factors for breast cancer; however, the molecular mechanisms are poorly understood. We evaluated the effect of a high-fat/high-calorie diet on mammary carcinogenesis in the immunocompetent MMTV-PyMT murine model. Four-week old female mice (20/group) were randomized to receive either a high-fat (HF; 60% kcal as fat) or a low-fat (LF; 16% kcal) diet for eight weeks. Body weights were determined, and tumor volumes measured by ultrasound, each week. At necropsy, the tumors and abdominal visceral fat were weighed and plasma collected. The primary mammary tumors, adjacent mammary fat, and lungs were preserved for histological and immunohistochemical examination and quantification of infiltrating macrophages, crown-like structure (CLS) formation, and microvessel density. The body weight gains, visceral fat weights, the primary mammary tumor growth rates and terminal weights, were all significantly greater in the HF-fed mice. Adipose tissue inflammation in the HF group was indicated by hepatic steatosis, pronounced macrophage infiltration and CLS formation, and elevations in plasma monocyte chemoattractant protein-1 (MCP-1), leptin and proinflammatory cytokine concentrations. HF intake was also associated with higher tumor-associated microvascular density and the proangiogenic factor MCP-1. This study provides preclinical evidence in a spontaneous model of breast cancer that mammary adipose tissue inflammation induced by diet, enhances the recruitment of macrophages and increases tumor vascular density suggesting a role for obesity in creating a microenvironment favorable for angiogenesis in the progression of breast cancer.
[Show abstract][Hide abstract] ABSTRACT: The High Mobility Group box protein SOX9 and the GLI1 transcription factor play protumorigenic roles in pancreatic ductal adenocarcinoma (PDA). In Kras transgenic mice each of these factors are critical for development of PDA precursor lesions. SOX9 transcription is directly regulated by GLI1, but how SOX9 functions downstream of GLI1 is unclear. We observed positive feedback, such that SOX9-deficient PDA cells have severely repressed levels of endogenous GLI1, attributed to loss of GLI1 protein stability. Sox9 associated with the F-box domain of the SKP1/CUL1/F-box (SCF) E3 ubiquitin ligase component, β-TrCP, and suppressed its association with SKP1 and GLI1, a substrate of SCF-β-TrCP. SOX9 also tethered β-TrCP within the nucleus and promoted its degradation. SOX9 bound to β-TrCP through its C-terminal PQA/S domain that mediates transcriptional activation. Suppression of β-TrCP in SOX9-deficient PDA cells restored GLI1 levels and promoted SOX9-dependent cancer stem cell properties. These studies identify SOX9-GLI1 positive feedback as a major determinant of GLI1 protein stability and implicate β-TrCP as a latent, SOX9-bound tumor suppressor with the potential to degrade oncogenic proteins in tumor cells.
[Show abstract][Hide abstract] ABSTRACT: We developed a three-dimensional
fibroblastic nodule model for
fibrogenicity testing of nanomaterials and investigated the role of
fibroblast stemlike cells (FSCs) in the fibrogenic process. We showed
that carbon nanotubes (CNTs) induced fibroblastic nodule formation
in primary human lung fibroblast cultures resembling the fibroblastic
foci in clinical fibrosis and promoted FSCs that are highly fibrogenic
and a potential driving force of fibrogenesis. This study provides
a predictive 3D model and mechanistic insight on CNT fibrogenesis.
[Show abstract][Hide abstract] ABSTRACT: Despite initial response to therapy, most acute myeloid leukemia (AML) patients relapse. To eliminate relapse-causing leukemic stem/progenitor cells (LPCs), patient-specific immune therapies may be required. In vitro cellular engineering may require increasing the "stemness" or immunogenicity of tumor cells and activating or restoring cancer-impaired immune-effector and antigen-presenting cells. Leukapheresis samples provide the cells needed to engineer therapies: LPCs to be targeted, normal hematopoietic stem cells to be spared, and cancer-impaired immune cells to be repaired and activated. This study sought to advance development of LPC-targeted therapies by exploring nongenetic ways to slow the decay and to increase the immunogenicity of primary CD34(+) AML cells. CD34(+) AML cells generally displayed more colony-forming and aldehyde dehydrogenase activity than CD34(-) AML cells. Along with exposure to bone marrow stromal cells and low (1%-5%) oxygen, culture with RepSox (a reprogramming tool and inhibitor of transforming growth factor-β receptor 1) consistently slowed decline of CD34(+) AML and myelodysplastic syndrome (MDS) cells. RepSox-treated AML cells displayed higher CD34, CXCL12, and MYC mRNA levels than dimethyl sulfoxide-treated controls. RepSox also accelerated loss of T cell immunoglobulin mucin-3 (Tim-3), an immune checkpoint receptor that impairs antitumor immunity, from the surface of AML and MDS cells. Our results suggest RepSox may reduce Tim-3 expression by inhibiting transforming growth factor-β signaling and slow decay of CD34(+) AML cells by increasing CXCL12 and MYC, two factors that inhibit AML cell differentiation. By prolonging survival of CD34(+) AML cells and reducing Tim-3, RepSox may promote in vitro immune cell activation and advance development of LPC-targeted therapies.
[Show abstract][Hide abstract] ABSTRACT: Increasing evidence has demonstrated the potential risks of cardiac arrhythmias (such as prolonged QT interval) using tyrosine kinase inhibitors for cancer therapy. We report here that a widely used selective inhibitor of Src tyrosine kinases, PP2, can inhibit and prevent isoproterenol stimulation of cardiac pacemaker activity. In dissected rat sinus node PP2 inhibited and prevented isoproterenol stimulation of spontaneous beating rate. In isolated sinus node myocytes PP2 suppressed the hyperpolarization-activated "funny" current (If) by negatively shifting the activation curve and decelerating activation kinetics, associated with decreased cell surface expression and reduced tyrosine phosphorylation of hyperpolarization-activated, cyclic nucleotide-modulated channel 4 (HCN4) channel proteins. In human embryonic kidney 293 cells overexpressing recombinant human HCN4 channels, PP2 reversed isoproterenol stimulation of HCN4 and inhibited HCN4-573x, a cAMP insensitive human HCN4 mutant. Isoprotenrenol had little effects on HCN4-573x. These results demonstrated that inhibition of presumably tyrosine Src kinase activity in heart by PP2 decreased and prevented the potential β-adrenergic stimulation of cardiac pacemaker activity. These effects are mediated, at least partially, by a cAMP-independent attenuation of channel activity and cell surface expression of HCN4, the key channel protein that controls the heart rate.
[Show abstract][Hide abstract] ABSTRACT: Cancer patients are known to be highly susceptible to Pseudomonas aeruginosa (Pa) infection, but it remains unknown whether alterations at the tumor cell level can contribute to infection. This study explored how cellular changes associated with tumor metastasis influence Pa infection using highly metastatic MTLn3 cells and non-metastatic MTC cells as cell culture models. MTLn3 cells were found to be more sensitive to Pa infection than MTC cells based on increased translocation of the type III secretion effector, ExoS, into MTLn3 cells. Subsequent studies found that higher levels of ExoS translocation into MTLn3 cells related to Pa entry and secretion of ExoS within MTLn3 cells, rather than conventional ExoS translocation by external Pa. ExoS includes both Rho GTPase activating protein (GAP) and ADP-ribosyltransferase (ADPRT) enzyme activities, and differences in MTLn3 and MTC cell responsiveness to ExoS were found to relate to the targeting of ExoS-GAP activity to Rho GTPases. MTLn3 cell migration is mediated by RhoA activation at the leading edge, and inhibition of RhoA activity decreased ExoS translocation into MTLn3 cells to levels similar to those of MTC cells. The ability of Pa to be internalized and transfer ExoS more efficiently in association with Rho activation during tumor metastasis confirms that alterations in cell migration that occur in conjunction with tumor metastasis contribute to Pa infection in cancer patients. This study also raises the possibility that Pa might serve as a biological tool for dissecting or detecting cellular alterations associated with tumor metastasis.
Biology Open 09/2013; 2(9):891-900. DOI:10.1242/bio.20133632 · 2.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Wounds are known to serve as portals of entry for group A Streptococcus (GAS). Subsequent tissue colonization is mediated by interactions between GAS surface proteins and host extracellular matrix components. We recently reported that the streptococcal collagen-like protein-1, Scl1, selectively binds the cellular form of fibronectin (cFn) and also contributes to GAS biofilm formation on abiotic surfaces. One structural feature of cFn, which is predominantly expressed in response to tissue injury, is the presence of a spliced variant containing extra domain A (EDA/EIIIA). We now report that GAS biofilm formation is mediated by the Scl1 interaction with EDA-containing cFn. Recombinant Scl1 proteins that bound cFn also bound recombinant EDA within the C-C' loop region recognized by the α(9) β(1) integrin. The extracellular 2-D matrix derived from human dermal fibroblasts supports GAS adherence and biofilm formation. Altogether, this work identifies and characterizes a novel molecular mechanism by which GAS utilizes Scl1 to specifically target an extracellular matrix component that is predominantly expressed at the site of injury in order to secure host tissue colonization.
[Show abstract][Hide abstract] ABSTRACT: Ultrasound and Duplex ultrasonography in particular are routinely used to diagnose cardiovascular disease (CVD), which is the leading cause of morbidity and mortality worldwide. However, these techniques may not be able to characterize vascular tissue compositional changes due to CVD. This work describes an ultrasound-based hybrid imaging technique that can be used for vascular tissue characterization and the diagnosis of atherosclerosis. Ultrasound radiofrequency (RF) data were acquired and processed in time, frequency, and wavelet domains to extract six parameters including time integrated backscatter (T(IB)), time variance (T(var)), time entropy (T(E)), frequency integrated backscatter (F(IB)), wavelet root mean square value (W(rms)), and wavelet integrated backscatter (W(IB)). Each parameter was used to reconstruct an image co-registered to morphological B-scan. The combined set of hybrid images were used to characterize vascular tissue in vitro and in vivo using three mouse models including control (C57BL/6), and atherosclerotic apolipoprotein E-knockout (APOE-KO) and APOE/A(1) adenosine receptor double knockout (DKO) mice. The technique was tested using high-frequency ultrasound including single-element (center frequency=55MHz) and commercial array (center frequency=40MHz) systems providing superior spatial resolutions of 24μm and 40μm, respectively. Atherosclerotic vascular lesions in the APOE-KO mouse exhibited the highest values (contrast) of -10.11±1.92dB, -12.13±2.13dB, -7.54±1.45dB, -5.10±1.06dB, -5.25±0.94dB, and -10.23±2.12dB in T(IB), T(var), T(E), F(IB), W(rms), W(IB) hybrid images (n=10, p<0.05), respectively. Control segments of normal vascular tissue showed the lowest values of -20.20±2.71dB, -22.54±4.54dB, -14.94±2.05dB, -9.64±1.34dB, -10.20±1.27dB, and -19.36±3.24dB in same hybrid images (n=6, p<0.05). Results from both histology and optical images showed good agreement with ultrasound findings within a maximum error of 3.6% in lesion estimation. This study demonstrated the feasibility of a high-resolution hybrid imaging technique to diagnose atherosclerosis and characterize plaque components in mouse. In the future, it can be easily implemented on commercial ultrasound systems and eventually translated into clinics as a screening tool for atherosclerosis and the assessment of vulnerable plaques.
[Show abstract][Hide abstract] ABSTRACT: Head and neck squamous cell carcinoma (HNSCC) has a proclivity for locoregional invasion. HNSCC mediates invasion in part through invadopodia-based proteolysis of the extracellular matrix (ECM). Activation of Src, Erk1/2, Abl and Arg downstream of epidermal growth factor receptor (EGFR) modulates invadopodia activity through phosphorylation of the actin regulatory protein cortactin. In MDA-MB-231 breast cancer cells, Abl and Arg function downstream of Src to phosphorylate cortactin, promoting invadopodia ECM degradation activity and thus assigning a pro-invasive role for Ableson kinases. We report that Abl kinases have an opposite, negative regulatory role in HNSCC where they suppress invadopodia and tumor invasion. Impairment of Abl expression or Abl kinase activity with imatinib mesylate enhanced HNSCC matrix degradation and 3D collagen invasion, functions that were impaired in MDA-MB-231. HNSCC lines with elevated EGFR and Src activation did not contain increased Abl or Arg kinase activity, suggesting that Src could bypass Abl/Arg to phosphorylate cortactin and promote invadopodia ECM degradation. Src-transformed Abl(-/-)/Arg(-/-) fibroblasts produced ECM degrading invadopodia containing pY421 cortactin, indicating that Abl/Arg are dispensable for invadopodia function in this system. Imatinib-treated HNSCC cells had increased EGFR, Erk1/2 and Src activation, enhancing cortactin pY421 and pS405/418 required for invadopodia function. Imatinib stimulated shedding of the EGFR ligand heparin-binding EGF-like growth factor (HB-EGF) from HNSCC cells, where soluble HB-EGF enhanced invadopodia ECM degradation in HNSCC but not in MDA-MB-231. HNSCC cells treated with inhibitors of the EGFR-invadopodia pathway indicated that EGFR and Src are required for invadopodia function. Collectively, our results indicate that Abl kinases negatively regulate HNSCC invasive processes through suppression of an HB-EGF autocrine loop responsible for activating a EGFR-Src-cortactin cascade, in contrast to the invasion promoting functions of Abl kinases in breast and other cancer types. Our results provide mechanistic support for recent failed HNSCC clinical trials utilizing imatinib.Oncogene advance online publication, 12 November 2012; doi:10.1038/onc.2012.513.
[Show abstract][Hide abstract] ABSTRACT: Tyrosine kinase-based signal transduction mediated by modular protein domains is critical for cellular function. The Src homology (SH)2 domain is an important conductor of intracellular signalling that binds to phosphorylated tyrosines on acceptor proteins, producing molecular complexes responsible for signal relay. Cortactin is a cytoskeletal protein and tyrosine kinase substrate that regulates actin-based motility through interactions with SH2 domain-containing proteins. The Src kinase SH2 domain mediates cortactin binding and tyrosine phosphorylation, but how Src interacts with cortactin is unknown. Here we demonstrate that Src binds cortactin through cystine bonding between Src C185 in the SH2 domain within the phosphotyrosine binding pocket and cortactin C112/246 in the cortactin repeats domain independent of tyrosine phosphorylation. Interaction studies in the presence of reducing agents ablate Src-cortactin binding, eliminates cortactin phosphorylation by Src, and prevents Src SH2 domain binding to cortactin. Tandem MS/MS sequencing demonstrates cystine bond formation between Src C185 and cortactin C112/246. Mutational studies indicate that an intact cystine binding interface is required for Src-mediated cortactin phosphorylation, cell migration, and pre-invadopodia formation. Our results identify a novel phosphotyrosine independent binding mode between the Src SH2 domain and cortactin. Besides Src, one quarter of all SH2 domains contain cysteines at or near the analogous Src C185 position. This provides a potential alternative mechanism to tyrosine phosphorylation for cysteine-containing SH2 domains to bind cognate ligands that may be widespread in propagating signals regulating diverse cellular functions.
[Show abstract][Hide abstract] ABSTRACT: Cellular invasion into local tissues is a process important in development and homeostasis. Malregulated invasion and subsequent cell movement is characteristic of multiple pathological processes, including inflammation, cardiovascular disease and tumor cell metastasis(1). Focalized proteolytic degradation of extracellular matrix (ECM) components in the epithelial or endothelial basement membrane is a critical step in initiating cellular invasion. In tumor cells, extensive in vitro analysis has determined that ECM degradation is accomplished by ventral actin-rich membrane protrusive structures termed invadopodia(2,3). Invadopodia form in close apposition to the ECM, where they moderate ECM breakdown through the action of matrix metalloproteinases (MMPs). The ability of tumor cells to form invadopodia directly correlates with the ability to invade into local stroma and associated vascular components(3). Visualization of invadopodia-mediated ECM degradation of cells by fluorescent microscopy using dye-labeled matrix proteins coated onto glass coverslips has emerged as the most prevalent technique for evaluating the degree of matrix proteolysis and cellular invasive potential(4,5). Here we describe a version of the standard method for generating fluorescently-labeled glass coverslips utilizing a commercially available Oregon Green-488 gelatin conjugate. This method is easily scaled to rapidly produce large numbers of coated coverslips. We show some of the common microscopic artifacts that are often encountered during this procedure and how these can be avoided. Finally, we describe standardized methods using readily available computer software to allow quantification of labeled gelatin matrix degradation mediated by individual cells and by entire cellular populations. The described procedures provide the ability to accurately and reproducibly monitor invadopodia activity, and can also serve as a platform for evaluating the efficacy of modulating protein expression or testing of anti-invasive compounds on extracellular matrix degradation in single and multicellular settings.
[Show abstract][Hide abstract] ABSTRACT: The opportunistic pathogen Pseudomonas aeruginosa targets wounded epithelial barriers, but the cellular alteration that increases susceptibility to P. aeruginosa infection remains unclear. This study examined how cell migration contributes to the establishment of P. aeruginosa infections using (i) highly migratory T24 epithelial cells as a cell culture model, (ii) mutations in the type III secretion (T3S) effector ExoS to manipulate P. aeruginosa infection, and (iii) high-resolution immunofluorescent microscopy to monitor ExoS translocation. ExoS includes both GTPase-activating (GAP) and ADP-ribosyltransferase (ADPRT) activities, and P. aeruginosa cells expressing wild-type ExoS preferentially bound to the leading edge of T24 cells, where ExoS altered leading-edge architecture and actin anchoring in conjunction with interrupting T3S translocation. Inactivation of ExoS GAP activity allowed P. aeruginosa to be internalized and secrete ExoS within T24 cells, but as with wild-type ExoS, translocation was limited in association with disruption of actin anchoring. Inactivation of ExoS ADPRT activity resulted in significantly enhanced T3S translocation by P. aeruginosa cells that remained extracellular and in conjunction with maintenance of actin-plasma membrane association. Infection with P. aeruginosa expressing ExoS lacking both GAP and ADPRT activities resulted in the highest level of T3S translocation, and this occurred in conjunction with the entry and alignment of P. aeruginosa and ExoS along actin filaments. Collectively, in using ExoS mutants to modulate and visualize T3S translocation, we were able to (i) confirm effector secretion by internalized P. aeruginosa, (ii) differentiate the mechanisms underlying the effects of ExoS GAP and ADPRT activities on P. aeruginosa internalization and T3S translocation, (iii) confirm that ExoS ADPRT activity targeted a cellular substrate that interrupted T3S translocation, (iv) visualize the ability of P. aeruginosa and ExoS to align with actin filaments, and (v) demonstrate an association between actin anchoring at the leading edge of T24 cells and the establishment of P. aeruginosa infection. Our studies also highlight the contribution of ExoS to the opportunistic nature of P. aeruginosa infection through its ability to exert cytotoxic effects that interrupt T3S translocation and P. aeruginosa internalization, which in turn limit the P. aeruginosa infectious process.
Infection and immunity 06/2012; 80(9):3049-64. DOI:10.1128/IAI.00231-12 · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hematopoietic reconstitution, following bone marrow or stem cell transplantation, requires a microenvironment niche capable of supporting both immature progenitors and stem cells with the capacity to differentiate and expand. Osteoblasts comprise one important component of this niche. We determined that treatment of human primary osteoblasts (HOB) with melphalan or VP-16 resulted in increased phospho-Smad2, consistent with increased TGF-β1 activity. This increase was coincident with reduced HOB capacity to support immature B lineage cell chemotaxis and adherence. The supportive deficit was not limited to committed progenitor cells, as human embryonic stem cells (hESC) or human CD34+ bone marrow cells co-cultured with HOB pre-exposed to melphalan, VP-16 or rTGF-β1 had profiles distinct from the same populations co-cultured with untreated HOB. Functional support deficits were downstream of changes in HOB gene expression profiles following chemotherapy exposure. Melphalan and VP-16 induced damage of HOB suggests vulnerability of this critical niche to therapeutic agents frequently utilized in pre-transplant regimens and suggests that dose escalated chemotherapy may contribute to post-transplantation hematopoietic deficits by damaging structural components of this supportive niche.
PLoS ONE 02/2012; 7(2):e30758. DOI:10.1371/journal.pone.0030758 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Group A Streptococcus (GAS) is a human-specific pathogen responsible for a number of diseases characterized by a wide range of clinical manifestations. During host colonization GAS-cell aggregates or microcolonies are observed in tissues. GAS biofilm, which is an in vitro equivalent of tissue microcolony, has only recently been studied and little is known about the specific surface determinants that aid biofilm formation. In this study, we demonstrate that surface-associated streptococcal collagen-like protein-1 (Scl1) plays an important role in GAS biofilm formation.
Biofilm formation by M1-, M3-, M28-, and M41-type GAS strains, representing an intraspecies breadth, were analyzed spectrophotometrically following crystal violet staining, and characterized using confocal and field emission scanning electron microscopy. The M41-type strain formed the most robust biofilm under static conditions, followed by M28- and M1-type strains, while the M3-type strains analyzed here did not form biofilm under the same experimental conditions. Differences in architecture and cell-surface morphology were observed in biofilms formed by the M1- and M41-wild-type strains, accompanied by varying amounts of deposited extracellular matrix and differences in cell-to-cell junctions within each biofilm. Importantly, all Scl1-negative mutants examined showed significantly decreased ability to form biofilm in vitro. Furthermore, the Scl1 protein expressed on the surface of a heterologous host, Lactococcus lactis, was sufficient to induce biofilm formation by this organism.
Overall, this work (i) identifies variations in biofilm formation capacity among pathogenically different GAS strains, (ii) identifies GAS surface properties that may aid in biofilm stability and, (iii) establishes that the Scl1 surface protein is an important determinant of GAS biofilm, which is sufficient to enable biofilm formation in the heterologous host Lactococcus. In summary, the GAS surface adhesin Scl1 may have an important role in biofilm-associated pathogenicity.
[Show abstract][Hide abstract] ABSTRACT: Loco-regional invasion of head and neck cancer is linked to metastatic risk and presents a difficult challenge in designing and implementing patient management strategies. Orthotopic mouse models of oral cancer have been developed to facilitate the study of factors that impact invasion and serve as model system for evaluating anti-tumor therapeutics. In these systems, visualization of disseminated tumor cells within oral cavity tissues has typically been conducted by either conventional histology or with in vivo bioluminescent methods. A primary drawback of these techniques is the inherent inability to accurately visualize and quantify early tumor cell invasion arising from the primary site in three dimensions. Here we describe a protocol that combines an established model for squamous cell carcinoma of the tongue (SCOT) with two-photon imaging to allow multi-vectorial visualization of lingual tumor spread. The OSC-19 head and neck tumor cell line was stably engineered to express the F-actin binding peptide LifeAct fused to the mCherry fluorescent protein (LifeAct-mCherry). Fox1(nu/nu) mice injected with these cells reliably form tumors that allow the tongue to be visualized by ex-vivo application of two-photon microscopy. This technique allows for the orthotopic visualization of the tumor mass and locally invading cells in excised tongues without disruption of the regional tumor microenvironment. In addition, this system allows for the quantification of tumor cell invasion by calculating distances that invaded cells move from the primary tumor site. Overall this procedure provides an enhanced model system for analyzing factors that contribute to SCOT invasion and therapeutic treatments tailored to prevent local invasion and distant metastatic spread. This method also has the potential to be ultimately combined with other imaging modalities in an in vivo setting.
Journal of Visualized Experiments 07/2011; DOI:10.3791/2941 · 1.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The filamentous (F)-actin regulatory protein cortactin plays an important role in tumor cell movement and invasion by promoting and stabilizing actin related protein (Arp)2/3-mediated actin networks necessary for plasma membrane protrusion. Cortactin is a substrate for ERK1/2 and Src family kinases, with previous in vitro findings demonstrating ERK1/2 phosphorylation of cortactin as a positive and Src phosphorylation as a negative regulatory event in promoting Arp2/3 activation through neuronal Wiskott Aldrich Syndrome protein (N-WASp). Evidence for this regulatory cortactin "switch" in cells has been hampered due to the lack of phosphorylation-specific antibodies that recognize ERK1/2-phosphorylated cortactin. Our findings with phosphorylation-specific antibodies against these ERK1/2 sites (pS405 and pS418) indicate that cortactin can be co-phosphorylated at 405/418 and tyrosine residues targeted by Src family tyrosine kinases. These results indicate that the ERK/Src cortactin switch is not the sole mechanism by which ERK1/2 and tyrosine phosphorylation events regulate cortactin function in cell systems.
[Show abstract][Hide abstract] ABSTRACT: The actin regulatory protein cortactin is involved in multiple signaling pathways impinging on the cortical actin cytoskeleton. Cortactin is phosphorylated by ERK1/2 and Src family tyrosine kinases, resulting in neuronal Wiskott Aldrich Syndrome protein (N-WASp) activation and enhanced actin related protein (Arp)2/3-mediated actin nucleation. Cortactin migrates as an 80/85 kDa doublet when analyzed by SDS-PAGE. Phosphorylation by ERK1/2 is associated with conversion of the 80 kDa to the 85 kDa form, postulated to occur by inducing a conformational alteration that releases the carboxyl-terminal SH3 domain from autoinhibition. Our recent analysis of the 80-85 kDa cortactin "shift" in tumor cells indicates that while ERK1/2 phosphorylation is associated with the 85 kDa shift, this phosphorylation event is not required for the shift to occur, nor does ERK1/2 phosphorylation appreciably alter global cortactin confirmation. These data indicate that additional factors besides ERK1/2 phosphorylation contribute to generating and/or maintaining the activated 85 kDa cortactin form in stimulated cells.