Specific Cell Interactions Research Articles

Platelets Promote Breast Cancer Metastasis By Reprogramming Tumor Cells to Produce IL-8

Platelets, primarily known for their role in hemostasis, are now recognized to play an integral role in cancer progression and metastasis. Recent evidence has established that platelets are activated by contact with breast tumor cells, leading to the release of hundreds of growth factors, cytokines, chemokines and angiogenesis mediators that could influence tumor growth and metastasis. Indeed, work from our group has demonstrated that factors released from activated platelets promote both metastasis and angiogenesis. However, little is known about the specific factors and signaling pathways that mediate this critical platelet-tumor cell cross-talk. To address this question, we performed an angiogenesis array (Ray Biotech) to identify specific pro-angiogenic and pro-metastatic factors released by tumor cells during platelet-tumor cell interactions. We identified several factors that were secreted by MCF-7 breast tumor cells in response to activated platelet releasate, including high levels of interleukin 8 (IL-8, CXCL8). IL-8 is a cytokine known to play a critical role in metastasis and angiogenesis and is elevated in the serum and tumor tissue of breast cancer patients. We confirmed that exposure to platelets strongly induced the production of IL-8 in several human breast cancer cell lines (MDA-MB-231, BT-20, SKBR-3 and MCF-7) by ELISA and found that platelets themselves do not contain detectable levels of IL-8. Furthermore, IL-8 production was highest in the more aggressive, triple negative MDA-MB-231 and BT-20 lines, suggesting a link between platelet-induced IL-8 and tumor subtype. To identify the specific component or components of platelet releasate responsible for driving tumor cell IL-8, we first characterized the contents of activated platelet releasate by array (Ray Biotech) and found an abundance of both chemokine (C-C motif) ligand 5 (CCL5, RANTES) and epidermal growth factor (EGF). Next, we treated breast tumor cell lines directly with recombinant CCL5 or EGF and observed an increase in IL-8 production, however sensitivity to CCL5, EGF or the combination varied among the cell lines tested and may depend on receptor expression. To determine if platelet-derived CCL5 or EGF drives tumor cell IL-8, breast tumor cells were pretreated with the CCL5 receptor (CCR5) blocker maraviroc or the EGFR blocker AG-1478 and then exposed to platelets. Blocking CCR5 abrogated the induction of IL-8 in response to platelets in the cell lines that were sensitive to CCL5 while EGFR inhibition diminished induction of IL-8 in response to platelets in the cell lines that were sensitive to EGF. Next we sought to determine the role of platelet-induced IL-8 in metastasis. We performed standard invasion assays using MDA-MB-231 cells transfected with IL-8shRNA or control cells. Platelets were able to increase the invasion of control MDA-MD-231 cells by 5 fold, while IL-8 knockdown reduced the effect of platelets on invasion by 50%. Furthermore, ability of platelets to promote tumor cell migration across an endothelialized membrane was reduced 87% in IL-8 knockdown MDA-MB-231s compared to controls in standard transendothelial migration assays. These results suggest that platelets promote metastasis, in part, by driving tumor cell IL-8. Studies are currently underway to further elucidate the mechanism by which platelets reprogram tumor cells to produce IL-8 and to confirm these findings in vivo. Taken together, these results suggest that platelets, through release of soluble factors, drive tumor cells to produce IL-8 and that blocking this communication can disrupt the pro-metastatic potential of platelets. Ultimately, these studies support targeting specific platelet-tumor cell interaction as a novel means of limiting disease progression in breast cancer. DisclosuresNo relevant conflicts of interest to declare.

Photoresponsive Cucurbit[8]uril-Mediated Adhesion of Bacteria on Supported Lipid Bilayers.

In this work, the development of a photoresponsive platform for the presentation of bioactive ligands to study receptor-ligand interactions has been described. For this purpose, supramolecular host-guest chemistry and supported lipid bilayers (SLBs) have been combined in a microfluidic device. Quartz crystal microbalance with dissipation monitoring (QCM-D) studies on methyl viologen (MV)-functionalized oligo ethylene glycol-based self-assembled monolayers, gel and liquid-state SLBs have been compared for their nonfouling properties in the case of ConA and bacteria. In combination with bacterial adhesion test, negligible nonspecific bacterial adhesion is observed only in the case of methyl-viologen-modified liquid-state SLBs. Therefore, liquid-state SLBs have been identified as most suitable for studying specific cell interactions when MV is incorporated as a guest on the surface. The photoswitchable supramolecular ternary complex is formed by assembling cucurbit[8]uril (CB[8]) and an azobenzene-mannose conjugate (Azo-Man) onto MV-functionalized liquid-state SLBs and the assembly process has been characterized using QCM-D and fluorescence techniques. Mannose has been found to enable binding of E. coli via cell-surface receptors on the nonfouling supramolecular SLBs. Optical switching of the azobenzene moiety allows us to "erase" the bioactive surface after bacterial binding, providing the potential to develop reusable sensors. Localized photorelease of bacterial cells has also been shown indicating the possibility of optically guiding cellular growth, migration, and intercellular interactions.

Antiviral therapies and prospects for a cure of chronic hepatitis B.

Current therapies of chronic hepatitis B (CHB) remain limited to either pegylated interferon-α (Peg-IFN-α), or one of the five approved nucleoside analog (NA) treatments. Although viral suppression can be achieved in the majority of patients with high-barrier-to-resistance new-generation NAs (i.e., entecavir and tenofovir), HBsAg loss is achieved in only 10% of patients with both classes of drugs after a follow-up of 5 years. Attempts to improve the response by administering two different NAs or a combination of NA and Peg-IFN-α have been unsuccessful. Therefore, there is a renewed interest to investigate a number of steps in the hepatitis B virus (HBV) replication cycle and specific virus-host cell interactions as potential targets for new antivirals. Novel targets and compounds could readily be evaluated using both relevant in vitro and newly developed in vivo models of HBV infection. The addition of one or several new drugs to current regimens should offer the prospect of markedly improving the response to therapy, thus reducing the burden of drug resistance, as well as the incidence of cirrhosis and hepatocellular carcinoma (HCC).

The apicomplexan glideosome and adhesins - Structures and function.

The apicomplexan family of pathogens, which includes Plasmodium spp. and Toxoplasma gondii, are primarily obligate intracellular parasites and invade multiple cell types. These parasites express extracellular membrane protein receptors, adhesins, to form specific pathogen-host cell interaction complexes. Various adhesins are used to invade a variety of cell types. The receptors are linked to an actomyosin motor, which is part of a complex comprised of many proteins known as the invasion machinery or glideosome. To date, reviews on invasion have focused primarily on the molecular pathways and signals of invasion, with little or no structural information presented. Over 75 structures of parasite receptors and glideosome proteins have been deposited with the Protein Data Bank. These structures include adhesins, motor proteins, bridging proteins, inner membrane complex and cytoskeletal proteins, as well as co-crystal structures with peptides and antibodies. These structures provide information regarding key interactions necessary for target receptor engagement, machinery complex formation, how force is transmitted, and the basis of inhibitory antibodies. Additionally, these structures can provide starting points for the development of antibodies and inhibitory molecules targeting protein-protein interactions, with the aim to inhibit invasion. This review provides an overview of the parasite adhesin protein families, the glideosome components, glideosome architecture, and discuss recent work regarding alternative models.

Bispecific single-chain diabody-immunoliposomes targeting endoglin (CD105) and fibroblast activation protein (FAP) simultaneously

Liposomes are well-established drug delivery systems with cancer chemotherapy as main focus. To increase the cellular drug delivery, liposomes can be endowed with ligands, e.g. recombinant antibody fragments, which ensure specific cell interaction. Multispecific immunoliposomes can be prepared to improve the liposome to cell interaction by targeting multiple different targets at the same time, for instance by coupling two or more different ligands to the liposomal surface, resulting in a synergistic or additive increase in binding. An alternative approach is the use of bispecific ligands to address at least two different targets. For this purpose we cloned a single-chain diabody fragment (scDb`), a bispecific molecule targeting two antigens, endoglin (CD105) and fibroblast activation protein (FAP), expressed on cells of the tumor microenvironment. As model cell system, a human fibrosarcoma cell line was used expressing endoglin and FAP simultaneously. Monospecific immunoliposomes directed either against endoglin or FAP were compared in vitro for cell binding and cytotoxic activity with bispecific dual-targeted scFv`-IL (bispecific scFv`FAP/CD105-IL) and bispecific single-chain diabody`-IL (scDb`CD105/FAP-IL) targeting endoglin and FAP simultaneously. In the underlying study, bispecific scFv`FAP/CD105-IL interacted stronger with cells expressing FAP and endoglin (both targets simultaneously) compared to the monospecific immunoliposomes. Furthermore, bispecific scDb`-immunoliposomes increased the cell interaction massively and showed enhanced cytotoxicity against target cells using doxorubicin-loaded immunoliposomes. The use of recombinant bispecific ligands as scDb`-molecules facilitates the generation of bispecific immunoliposomes by using the established post-insertion technique, enabling an extension of the ligand specificity spectrum via genetic modification.

Judicious use of biologicals in juvenile idiopathic arthritis.

Juvenile idiopathic arthritis (JIA) is a chronic inflammatory disorder that may cause joint destruction. Biological treatments targeting specific cytokines and cell interactions have transformed the outcomes of JIA. This review focuses on the selection of patients for and the timing and selection of biological treatment in JIA. Tumor necrosis factor (TNF) inhibitors remain the first choice for polyarticular JIA, followed by abatacept and tocilizumab. Monoclonal-antibody TNF inhibitors and abatacept are usually chosen for methotrexate-resistant uveitis. Recent clinical trials of canakinumab, rilonacept, and tocilizumab have obtained great improvement in both systemic and arthritic features in chronic systemic JIA patients. Current guidelines support the early use of a short-acting IL-1 antagonist for macrophage activation syndrome, a life-threatening complication. TREAT and ACUTE studies suggest that a therapeutic window of opportunity during early disease may exist in JIA. Early initiation of biological therapy may be associated with slower progression of joint damage and longer remission.

Mechanisms of cellular invasion by intracellular parasites

Numerous disease-causing parasites must invade host cells in order to prosper. Collectively, such pathogens are responsible for a staggering amount of human sickness and death throughout the world. Leishmaniasis, Chagas disease, toxoplasmosis, and malaria are neglected diseases and therefore are linked to socio-economical and geographical factors, affecting well-over half the world's population. Such obligate intracellular parasites have co-evolved with humans to establish a complexity of specific molecular parasite-host cell interactions, forming the basis of the parasite's cellular tropism. They make use of such interactions to invade host cells as a means to migrate through various tissues, to evade the host immune system, and to undergo intracellular replication. These cellular migration and invasion events are absolutely essential for the completion of the lifecycles of these parasites and lead to their for disease pathogenesis. This review is an overview of the molecular mechanisms of protozoan parasite invasion of host cells and discussion of therapeutic strategies, which could be developed by targeting these invasion pathways. Specifically, we focus on four species of protozoan parasites Leishmania, Trypanosoma cruzi, Plasmodium, and Toxoplasma, which are responsible for significant morbidity and mortality.

Functional fibrils derived from the peptide TTR1-cycloRGDfK that target cell adhesion and spreading

Peptide self-assembly offers a route for the production of fibrous nanomaterials with advanced bioactive properties that promote specific cell interactions. In this study the peptide TTR1-cycloRGDfK was designed to form amyloid-like fibrils that display the functional cyclic RGDfK pentapeptide ligand to target mammalian cell surface α Vβ 3 integrin receptors. The TTR 105–115 (or TTR1) sequence was used as the self-assembling domain. Once assembled, TTR1-cycloRGDfK fibrils display a characteristic cross-β core structure by X-ray fibre diffraction that was preserved following dehydration. Thin films of fibrils were characterised by infrared synchrotron mapping, scanning electron microscopy and atomic force microscopy. Cell adhesion and spreading were promoted on thin films of TTR1-cycloRGDfK fibrils via specific interactions with the cyclic RGDfK ligand. Low levels of non-specific interactions were also observed between cells and non-functionalised fibrils. TTR1-cycloRGDfK fibrils are an advance on bioactive fibrils previously designed to interact with a range of RGD binding integrins and our findings show that the assembly of amyloid-like fibrils based on the TTR1 sequence is robust and can be directed to form materials with specific properties.

BIOMEDICAL MATERIALS: Compact and Stable Quantum Dots with Positive, Negative, or Zwitterionic Surface: Specific Cell Interactions and Non‐Specific Adsorptions by the Surface Charges (Adv. Funct. Mater. 9/2011)

AbstractA new type of quantum dot (QD) ligand chemistry is introduced that can provide positive, negative, or zwitterionic surface QDs. CdSe/CdZnS core‐shell QDs are decorated with ligands, and the non‐specific and specific interactions of the QDs through their surface charge are investigated with the focus on cellular adsorptions and endocytosis. Zwitterionic QDs are compact with a ligand hydrodynamic thickness of less than 2 nm, they are colloidally very stable over a broad pH range and even in saturated NaCl solution, and they show minimal non‐specific adsorptions. Positive and negative QDs show a very different behavior for cellular adsorption and subsequent incorporation, suggesting mostly energy‐independent pathways for positive QDs and exclusively adenosine triphosphate (ATP)‐dependent pathways for negative QDs. The zwitterionic QD surface ligands can also be used in conjunction with other functional groups, which allows simple conjugations for highly specific targeting whereas retaining the advantages of a zwitterionic QD surface. This QD surface chemistry can provide highly specific and very sensitive imaging with very low background level. Using the mixed QD surface ligand system, we demonstrated streptavidin and antibody QD conjugates that show a signal‐to‐noise ratio that is over 4000 times higher than the unconjugated mixture, which was used as a control case. The QD chemistry reported herein can be easily extended to other functional groups, such as alkynes, azides, or other amines, and can be further used in many future applications, including single‐QD level experiments, sensitive assays, or in vivo applications using anti‐fouling QD probes.

What chick and mouse models have taught us about the role of the endocardium in congenital heart disease

Specific cell and tissue interactions drive the formation and function of the vertebrate cardiovascular system. Although much attention has been focused on the muscular components of the developing heart, the endocardium plays a key role in the formation of a functioning heart. Endocardial cells exhibit heterogeneity that allows them to participate in events such as the formation of the valves, septation of the outflow tract, and trabeculation. Here we review, the contributions of the endocardium to cardiovascular development and outline useful approaches developed in the chick and mouse that have revealed endocardial cell heterogeneity, the signaling molecules that direct endocardial cell behavior, and how these insights have contributed to our understanding of cardiovascular development and disease.

Compact and Stable Quantum Dots with Positive, Negative, or Zwitterionic Surface: Specific Cell Interactions and Non‐Specific Adsorptions by the Surface Charges

AbstractA new type of quantum dot (QD) ligand chemistry is introduced that can provide positive, negative, or zwitterionic surface QDs. CdSe/CdZnS core‐shell QDs are decorated with ligands, and the non‐specific and specific interactions of the QDs through their surface charge are investigated with the focus on cellular adsorptions and endocytosis. Zwitterionic QDs are compact with a ligand hydrodynamic thickness of less than 2 nm, they are colloidally very stable over a broad pH range and even in saturated NaCl solution, and they show minimal non‐specific adsorptions. Positive and negative QDs show a very different behavior for cellular adsorption and subsequent incorporation, suggesting mostly energy‐independent pathways for positive QDs and exclusively adenosine triphosphate (ATP)‐dependent pathways for negative QDs. The zwitterionic QD surface ligands can also be used in conjunction with other functional groups, which allows simple conjugations for highly specific targeting whereas retaining the advantages of a zwitterionic QD surface. This QD surface chemistry can provide highly specific and very sensitive imaging with very low background level. Using the mixed QD surface ligand system, we demonstrated streptavidin and antibody QD conjugates that show a signal‐to‐noise ratio that is over 4000 times higher than the unconjugated mixture, which was used as a control case. The QD chemistry reported herein can be easily extended to other functional groups, such as alkynes, azides, or other amines, and can be further used in many future applications, including single‐QD level experiments, sensitive assays, or in vivo applications using anti‐fouling QD probes.

Peptide-grafted lactide-based poly(ethylene glycol) porous scaffolds for specific cell adhesion

While biodegradable polyesters or their copolymers have been used widely as scaffolding materials in tissue engineering, these polymers intrinsically lack the cell-binding motifs on the surface. In this study, a GL-PEG, which is a poly(ethylene glycol) monoacrylate combined with glycerol (G)-lactide (L) triols, was synthesized and fabricated into a porous three dimensional (3D) structure. In addition, peptide ligands, Arg-Gly-Asp (RGD) or Arg-Glu-Asp-Val (REDV) were grafted directly onto the GL-PEG, producing GL-PEG-GRGD and GL-PEG-GREDV scaffolds to improve the specific cell adhesion. Both GL-PEG and GL-PEG-GRDG scaffolds were also prepared as a control. The ESCA spectra showed that peptide-grafted GL-PEG carried a nitrogen peak, which is indicative of the amine group in the peptide sequence. The nitrogen content in the GL-PEG-peptides was significantly higher than that on the the GL-PEG. When the peptide-grafted GL-PEG scaffolds were seeded with fibroblasts and endothelial cells (ECs) and cultured for up to 4 days, specific cell interactions were identified by scanning electron microscopy (SEM). More fibroblasts were found on the GL-PEG-GRGD scaffold but more ECs were found attached to GL-PEGGREDV. The total protein assay also supported the same trend that the fibroblasts/GL-PEG-GRGD or EC/GL-PEGGREDV constructs had the highest protein content with the specific cells, compared with the other groups. This data suggests that cell adhesion could be specific and dependent on the type of peptide ligands. Such 3D porous and crosslinked peptide-grafted GL-PEG scaffolds can be very useful for harboring specific cell populations for tissue engineering and vascular stents.

Conventional splenic dendritic cells regulate development of graft-versus-host disease. (145.10)

Abstract The use of allogeneic hematopoietic stem cell transplant (HSCT) to treat hematologic malignancies is associated with the development of graft-versus-host disease (GVHD), a frequently fatal complication that limits successful outcomes. The treatment of GVHD often requires potent immunosuppressive drugs and can predispose to relapse of the original cancer and the development of opportunistic infection. Understanding how GVHD is initiated may help to identify targets for therapeutic interventions that do not require wholesale suppression of the immune response. Prior studies have shown that host antigen presenting cells (APCs) are critical to GVHD induction. We examined how functionally distinct host splenic DC subpopulations (CD4+ vs. CD8+) regulate the development of GVHD mediated by donor CD4+ T cells. When compared to purified Balb/c CD4+ DCs, we found that Balb/c CD8+ DCs significantly increased C57BL/6 CD4+ T cell proliferation and cytolytic activity in vitro. To control the source of T cell stimulation for in vivo HSCT studies, we created chimeric Balb/c mice that have C57BL/6 APCs (C57BL/6 → Balb/c). Subsequently, we found that transplantation of C57BL/6 CD4+ T cells stimulated ex vivo by CD8+ Balb/c DCs resulted in more robust GVHD (survival, clinical score, pathology) compared to T cells activated by CD4+ DCs. Targeting specific DC-T cell interactions early in HSCT may help to control the severity of GVHD without requiring wholesale suppression of the immune system.

A comparative analysis of oncofetal fibronectin and tenascin-C incorporation in tumour vessels using human recombinant SIP format antibodies

Tumour angioneogenesis is associated with the reexpression of oncofetal fibronectin (oncFn) and tenascin-C (oncTn-C) splice variants, which may serve as targets for antibody-based pharmacodelivery. Knowledge of the vascular distribution and organization in different tumours is of importance for the understanding of tumour vessel formation and might be crucial for therapy. Therefore, human SIP format antibodies against Fn ED-A, Fn ED-B and Tn-C A and C splice domains were used for immunofluorescence labelling in renal, lung, oral, colon, breast and urinary bladder carcinoma specimens and in a renal carcinoma xenograft. The spatial relation to stroma, vessels and vascular basement membrane (vBM) was analysed including CD31 and laminin alpha4 chain antibodies. Renal cell carcinomas and atypical carcinoid of the lung revealed vessel-restricted oncFn and/or oncTn-C depositions; all other entities showed a variable stroma positivity including vessels. The individual pattern of oncFn/oncTn-C incorporation in the vBM depended on tumour type, vessel size and intratumoural heterogeneity. There was a stratification of the vessel wall showing luminal oncFn and extraluminal oncTn-C depositions. As shown in the xenograft, perivascular oncTn-C is provided by carcinoma cells. In conclusion, tumours differ in the pattern of Fn or Tn-C isoform positivity in the vessel wall, potentially representing a tumour type specific endothelial cell-tumour cell-stromal cell interaction. Carcinoma cells themselves are involved in vascular Tn-C matrix organization. Up to antigen distribution, Fn and Tn-C domain antibodies may serve as vehicles for antiangiogenetic and antifibrotic agents; oncFn/oncTn-C based targeting should be adapted individually.

The Human Cathelicidin LL-37 Preferentially Promotes Apoptosis of Infected Airway Epithelium

Cationic host defense peptides are key, evolutionarily conserved components of the innate immune system. The human cathelicidin LL-37 is an important cationic host defense peptide up-regulated in infection and inflammation, specifically in the human lung, and was shown to enhance the pulmonary clearance of the opportunistic pathogen Pseudomonas aeruginosa in vivo by as yet undefined mechanisms. In addition to its direct microbicidal potential, LL-37 can modulate inflammation and immune mechanisms in host defense against infection, including the capacity to modulate cell death pathways. We demonstrate that at physiologically relevant concentrations of LL-37, this peptide preferentially promoted the apoptosis of infected airway epithelium, via enhanced LL-37-induced mitochondrial membrane depolarization and release of cytochrome c, with activation of caspase-9 and caspase-3 and induction of apoptosis, which only occurred in the presence of both peptide and bacteria, but not with either stimulus alone. This synergistic induction of apoptosis in infected cells was caspase-dependent, contrasting with the caspase-independent cell death induced by supraphysiologic levels of peptide alone. We demonstrate that the synergistic induction of apoptosis by LL-37 and Pseudomonas aeruginosa required specific bacteria-epithelial cell interactions with whole, live bacteria, and bacterial invasion of the epithelial cell. We propose that the LL-37-mediated apoptosis of infected, compromised airway epithelial cells may represent a novel inflammomodulatory role for this peptide in innate host defense, promoting the clearance of respiratory pathogens.

Natural Killer cell interactions with dendritic cells and tumor cells are mediated by different NK cell receptors (141.10)

Abstract NK cells infiltrate solid organ allografts early post-transplant. As NK cells can mediate both maturation and killing of dendritic cells (DC), a better understanding of NK-DC interactions after transplant is warranted. This study investigates the interaction of NK cells with DC and tumor cells, and the specific NK cell activation receptors (NKRs) involved. A rat NK cell line was co-cultured with rat bone marrow-derived DC and rat hepatoma McA-RH7777 (McA). Co-culture of NK cells with DC and McA resulted in significant IFNγ production. This IFNγ production required cell contact suggesting that specific NKRs are involved. To specifically address this possibility, the NKRs, NKp30, NKp46, NKG2D, were knocked down using RNAi. NK cell activation by DC is mediated by NKp46 as knockdown of this receptor markedly decreased IFNγ production. In contrast, NKp30, not NKp46, was responsible for NK cell activation by tumor. Flow cytometry on DC and McA with NKR fusion proteins indicated the presence of putative ligands. Interestingly, individual NKR knockdown did not markedly diminish NK cell killing suggesting NK cells use multiple receptors and/or other mechanisms to kill cells. In conclusion, both DC and tumor activate NK cells but NKp46 and NKp30 mediate these interactions respectively. These data suggest a means to manipulate specific NK cell interactions after transplantation. Funding: NIH AI44095, and Agency for Science, Technology and Research (Singapore).

TecoflexTM functionalization by curdlan and its effect on protein adsorption and bacterial and tissue cell adhesion

Curdlan modified polyurethane was created by physically entrapping the former on TecoflexTM surface. ATR-FT-IR, SEM-EDAX and AFM analysis revealed the formation of stable thin curdlan layer on the film. Contact-angle measurements showed that the modified film was highly hydrophilic. Confocal laser scanning microscopy showed the existence of entrapped layer of approximately 20-25 microm in depth. Surface entrapment of curdlan minimized both protein adsorption and mouse L929 fibroblast cell adhesion relative to the control. Surface induced cellular inflammatory response was determined from the expression levels of proinflammatory cytokine TNF-alpha, by measuring their mRNA profiles in the cells using real time polymerase chain reaction (RT-PCR) normalized to the housekeeping gene GAPDH. The inflammatory response was suppressed on the modified substrate as expression of TNF-alpha mRNA was found to be up regulated on TecoflexTM, while it was significantly lower on curdlan substrate. The adhesion of S. aureus decreased by 62% on curdlan modified surface. Using such simple surface entrapment process, it will be possible to develop well-defined surface modifications that promote specific cell interactions and perhaps better performance in the long-term as implant.

Regulation of Chondrocytic Gene Expression by Biomechanical Signals

Cartilage is a mechanosensitive tissue, which means that it can perceive and respond to biomechanical signals. Despite the known importance of biomechanical signals in the etiopathogenesis of arthritic diseases and their effectiveness in joint restoration, little is understood about their actions at the cellular level. Recent molecular approaches have revealed that specific biomechanical stimuli and cell interactions generate intracellular signals that are powerful inducers or suppressors of proinflammatory and reparative genes in chondrocytes. Biomechanical signals are perceived by cartilage in magnitude-, frequency-, and time-dependent manners. Static and dynamic biomechanical forces of high magnitudes induce proinflammatory genes and inhibit matrix synthesis. Contrarily, dynamic biomechanical signals of low/physiologic magnitudes are potent antiinflammatory signals that inhibit interleukin-1beta (IL-1beta)-induced proinflammatory gene transcription and abrogate IL-1beta/tumor necrosis factor-alpha-induced inhibition of matrix synthesis. Recent studies have identified nuclear factor-kB (NF-kB) transcription factors as key regulators of biomechanical signal-mediated proinflammatory and antiinflammatory actions. These signals intercept multiple steps in the NF-kappaB signaling cascade to regulate cytokine gene expression. Taken together, these findings provide insight into how biomechanical signals regulate inflammatory and reparative gene transcription, underscoring their potential in enhancing the ability of chondrocytes to curb inflammation in diseased joints.

Host CD147 blockade by small interfering RNAs suppresses growth of human colon cancer xenografts

Tumor cells can stimulate matrix metalloproteinase (MMP) production by stromal cells through cell-cell interactions mediated by cell adhesion molecules such as extracellular matrix metalloproteinase inducer (human CD147/EMMPRIN, mouse CD147/Basigin). This study sought to characterize whether specific tumor-stromal cell interactions mediated by CD147 promote colon cancer growth by utilizing small interfering (si)RNAs directed against human CD147/EMMPRIN or mouse CD147/Basigin in co-cultures of cancer cells with macrophages and fibroblasts and established human SW620 colon cancer xenograft models in immune deficient mice. We show that blockade of host (mouse) CD147/Basigin expression, but not cancer cell-derived CD147/EMMPRIN, suppresses tumor growth in human colon cancer xenografts. Experiments in vitro indicated that colon cancer cell-stromal cell interactions mediated by CD147 lead to increased MMP-2 expression in fibroblasts but not macrophages. Furthermore, expression of host VEGF-A in both fibroblasts and macrophages is independent of CD147 in vitro and in vivo. Interestingly, inhibition of cancer cell-derived EMMPRIN leads to increased MMP-9 levels in vivo. Our findings provide new insights into CD147-mediated tumor-host interactions mediating colon cancer growth.

Supported phospholipid bilayers as a platform for neural progenitor cell culture

Supported phospholipid bilayers constitute a biomimetic platform for cell behavior studies and a new approach to the design of cell culture substrates. Phosphocholine bilayers are resistant to cell attachment, but can be functionalized with bioactive molecules to promote specific cell interactions. Here, we explore phosphocholine bilayers, functionalized with the laminin-derived IKVAV pentamer, as substrates for attachment, growth, and differentiation of neural progenitor cells (AHPs). By varying peptide concentration (0-10%), we discovered a strongly nonlinear relationship between cell attachment and IKVAV concentration, with a threshold of 1% IKVAV required for attachment, and saturation in cell binding at 3% IKVAV. This behavior, together with the 10-fold reduction in cell attachment when using a jumbled peptide sequence, gives evidence for a specific interaction between IKVAV and its AHP cell-surface receptor. After 8 days in culture, the peptide-functionalized bilayers promoted a high degree of cell cluster formation. This is in contrast to the predominant monolayer growth, observed for these cells on the standard laminin coated growth substrates. The peptide-functionalized bilayer did not induce differentiation levels over those observed for the laminin coated substrates. These results are promising in that peptide-functionalized bilayers can allow attachment and growth of stem cells without induction of differentiation.