Integrin αvß3 and disulfide bonds play important roles in NGR-retargeted adenovirus transduction efficiency.

AIMS: Adenoviruses that have CNGRCVSGCAGRC peptide inserted into fiber (AdFNGR) or hexon (AdHNGR) protein, respectively, showed increased transduction of endothelial cells. In this study we investigated if cysteines within the CNGRCVSGCAGRC sequence inserted into Ad serotype 5 Ad5 fiber or hexon protein form disulfide bond(s) and whether they play a role in retargeting potential of AdFNGR and AdHNGR. METHODS: Transduction efficiency of adenoviruses was done by counting infected cells under the microscope. Adenovirus attachment and internalization were measured by qPCR. Flow cytometry was used to evaluate the expression of CD13 and integrins. Gene knockdown was achieved by transfection of small interfering RNA. Mass spectrometry was used for determining disulfide bonds in adenovirus fiber and hexon protein. Molecular modeling was use to predict interaction of CNGRCVSGCAGRC peptide and CD13. KEY FINDINGS: AdFNGR and AdHNGR attach better to CD13 and/or αvß3 integrin-positive cells than Adwt. Reducing disulfide bonds using DTT decreased transduction efficiency and attachment of both AdFNGR and AdHNGR. Cysteins from CNGRCVSGCAGRC peptide within AdHNGR do not form disulfide bonds. Knockdown of αvß3 integrin reduced increased transduction efficiency of both AdFNGR and AdHNGR, while CD13 knockdown had no effect, indicating that retargeting properties of these viruses rely mainly on αvß3 integrin expression. SIGNIFICANCE: Insertion site of NGR-containing peptides as well as NGR flanking residues are critical for receptor binding affinity/specificity and transduction efficiency of NGR retargeted adenoviral vectors.

Targeting the Achilles' heel of cancer cells via integrin-mediated delivery of ROS-generating dihydrolipoamide dehydrogenase.

Cancer cells frequently exhibit higher levels of reactive oxygen species (ROS) than normal cells and when ROS levels increase beyond a cellular tolerability threshold, cancer cell death is enhanced. The mitochondrial dihydrolipoamide dehydrogenase (DLDH) is an enzyme which produces ROS in association with its oxidoreductive activity and may be thus utilized as an exogenous anticancer agent. As cancer cells often overexpress integrins that recognize RGD-containing proteins, we have bioengineered the human DLDH with RGD motifs (DLDHRGD) for integrin-mediated drug delivery. The modified protein fully retained its enzyme activity and ROS-production capability. DLDHRGD uptake by cells was shown to depend on the presence of cell-associated integrin αvß3, as comparatively demonstrated with normal kidney cells (HEK293) transfected with either ß1 (αvß1 positive) or ß3 integrins (αvß3 positive). The interaction with ß3 integrins was shown to be competitively inhibited by an RGD peptide. In mice melanoma cells (B16F10), which highly express an endogenous αvß3 integrin, fast cellular uptake of DLDHRGD which resulted in cell number reduction, apoptosis induction, and a parallel intracellular ROS production was shown. Similar results were obtained with additional human melanoma cell models (A375, WM3314, and WM3682). In contrast, HEK293ß3 cells remained intact following DLDHRGD uptake. The high pharmacological safety profile of DLDHRGD has been observed by several modes of administrations in BALB/C or C57Bl/6 mouse strains. Treatments with DLDHRGD in a subcutaneous melanoma mice model resulted in significant tumor inhibition. Our study demonstrated, in vitro and in vivo, the development of a unique platform, which targets cancer cells via integrin-mediated drug delivery of an exogenous ROS-generating drug.

Estrogen deficiency impairs integrin αvß3-mediated mechanosensation by osteocytes and alters osteoclastogenic paracrine signalling.

The integrin αvß3 has been shown to play an important role in osteocyte mechanotransduction. It has been reported that there are fewer ß3 integrin-containing cells in osteoporotic bone cells. Osteocytes cultured in vitro under estrogen deficient conditions demonstrate altered mechanotransduction. However, it is unknown whether the altered mechanotransduction in estrogen deficient osteocytes is directly associated with defective αvß3 expression or signalling. The objective of this study is to investigate the role of estrogen deficiency for regulating MLO-Y4 cell morphology, αvß3 expression, focal adhesion formation and mechanotransduction by osteocytes. Here, we report that estrogen withdrawal leads to a smaller focal adhesion area and reduced αvß3 localisation at focal adhesion sites, resulting in an increased Rankl/Opg ratio and defective Cox-2 responses to oscillatory fluid flow. Interestingly, αvß3 antagonism had a similar effect on focal adhesion assembly, Rankl/Opg ratio, and Cox-2 responses to oscillatory fluid flow. Taken together, our results provide the first evidence for a relationship between estrogen withdrawal and defective αvß3-mediated signalling. Specifically, this study implicates estrogen withdrawal as a putative mechanism responsible for altered αvß3 expression and resultant changes in downstream signalling in osteocytes during post-menopausal osteoporosis, which might provide an important, but previously unidentified, contribution to the bone loss cascade.

Osteopontin plays important roles in pulmonary arterial hypertension induced by systemic-to-pulmonary shunt.

Recent studies indicated that osteopontin (OPN) was involved in the genesis and progression of pulmonary arterial hypertension (PAH); however, its role in congenital heart disease-associated PAH (CHD/PAH) remains unknown. Our results showed that OPN was increased in lungs and plasma of patients with Eisenmenger syndrome; moreover, OPN and αVß3-integrin expression levels were augmented in rat lungs exposed to systemic-to-pulmonary shunt. Cell culture assay demonstrated that distal pulmonary arterial smooth muscle cells (PASMCs) from rat lungs suffering from volume and pressure overload exhibited enhanced proliferation compared with those from healthy rats. Mechanical stretch (20% at 1 Hz) increased OPN expression and activated ERK1/2 and protein kinase B (Akt) signal pathway in distal PASMCs from healthy rats. Interestingly, OPN enhanced the proliferation and migration of PASMCs while blocking αVß3-integrin with neutralizing antibody LM609 or Arg-Gly-Asp peptidomimetic antagonist cyclo(Ala-Arg-Gly-Asp-3-aminomethylbenzoyl) (XJ735), rectified the proliferative and migratory effects of OPN, which were partially mediated via ERK1/2 and Akt signaling pathways. Furthermore, surgical correction of systemic-to-pulmonary shunt, particularly XJ735 supplementation after surgical correction of systemic-to-pulmonary shunt, significantly alleviated the pulmonary hypertensive status in terms of pulmonary hemodynamic indices, pulmonary vasculopathy, and right ventricular hypertrophy. In summary, OPN alteration in lungs exposed to systemic-to-pulmonary shunt exerts a deteriorative role in pulmonary vascular remodeling through modulating the proliferation and migration of PASMCs, at least in part, via ανß3-ERK1/2 and ανß3-Akt signaling pathways. Antagonizing OPN receptor ανß3-integrin accelerated the regression of pulmonary vasculopathy after surgical correction of systemic-to-pulmonary shunt, indicating a potential therapeutic strategy for patients with CHD/PAH.-Meng, L., Liu, X., Teng, X., Gu, H., Yuan, W., Meng, J., Li, J., Zheng, Z., Wei, Y., Hu, S. Osteopontin plays important roles in pulmonary arterial hypertension induced by systemic-to-pulmonary shunt.

Nonthyroidal Illness Syndrome and Thyroid Hormone Actions at Integrin αvß3.

Context: The nonthyroidal illness syndrome (NTIS) is a constellation of changes in circulating thyroid hormone levels that occur in euthyroid patients with acute or chronic systemic diseases. The changes that occur include a reduction in serum T3, an increase in serum rT3, and variable changes in circulating T4 levels. No consensus exists regarding therapeutic intervention for NTIS. Methods: We briefly review the published literature on the physiological actions of T4 and of rT3-hormones that until recently have been seen to have little or no bioactivity-and analyze the apparent significance of changes in circulating T4 and T3 encountered in the setting of NTIS in patients with cancer. In the case of T4, these actions may be initiated at a cancer or endothelial cell plasma membrane receptor on integrin αvß3 or at the cytoskeleton. Results: This review examines possible therapeutic intervention in NTIS in patients with cancer in terms of T4 reduction and T3 support. Evidence also exists that rT3 may support cancer. Conclusions: Prospective study is proposed of pharmacological reduction of normal or elevated T4 in cancer-associated NTIS. We also support investigation of normally circulating levels of T3 in such patients.

Single-molecule measurements of the effect of force on Thy-1/αvß3-integrin interaction using nonpurified proteins.

Thy-1 and αvß3 integrin mediate bidirectional cell-to-cell communication between neurons and astrocytes. Thy-1/αvß3 interactions stimulate astrocyte migration and the retraction of neuronal prolongations, both processes in which internal forces are generated affecting the bimolecular interactions that maintain cell-cell adhesion. Nonetheless, how the Thy-1/αvß3 interactions respond to mechanical cues is an unresolved issue. In this study, optical tweezers were used as a single-molecule force transducer, and the Dudko-Hummer-Szabo model was applied to calculate the kinetic parameters of Thy-1/αvß3 dissociation. A novel experimental strategy was implemented to analyze the interaction of Thy-1-Fc with nonpurified αvß3-Fc integrin, whereby nonspecific rupture events were corrected by using a new mathematical approach. This methodology permitted accurately estimating specific rupture forces for Thy-1-Fc/αvß3-Fc dissociation and calculating the kinetic and transition state parameters. Force exponentially accelerated Thy-1/αvß3 dissociation, indicating slip bond behavior. Importantly, nonspecific interactions were detected even for purified proteins, highlighting the importance of correcting for such interactions. In conclusion, we describe a new strategy to characterize the response of bimolecular interactions to forces even in the presence of nonspecific binding events. By defining how force regulates Thy-1/αvß3 integrin binding, we provide an initial step towards understanding how the neuron-astrocyte pair senses and responds to mechanical cues.

Evidence that activation of ASIC1a by acidosis increases osteoclast migration and adhesion by modulating integrin/Pyk2/Src signaling pathway.

Activated acid-sensing ion channel 1a (ASIC1a) is involved in acid-induced osteoclastogenesis by regulating activation of the transcription factor NFATc1. These results indicated that ASIC1a activation by extracellular acid may cause osteoclast migration and adhesion through Ca2+-dependent integrin/Pyk2/Src signaling pathway. INTRODUCTION: Osteoclast adhesion and migration are responsible for osteoporotic bone loss. Acidic conditions promote osteoclastogenesis. ASIC1a in osteoclasts is associated with acid-induced osteoclastogenesis through modulating transcription factor NFATc1 activation. However, the influence and the detailed mechanism of ASIC1a in regulating osteoclast adhesion and migration, in response to extracellular acid, are not well characterized. METHODS: In this study, knockdown of ASIC1a was achieved in bone marrow macrophage cells using small interfering RNA (siRNA). The adhesion and migration abilities of osteoclast precursors and osteoclasts were determined by adhesion and migration assays, in vitro. Bone resorption was performed to measure osteoclast function. Cytoskeletal changes were assessed by F-actin ring formation. αvß3 integrin expression in osteoclasts was measured by flow cytometry. Western blotting and co-immunoprecipitation were performed to measure alterations in integrin/Pyk2/Src signaling pathway. RESULTS: Our results showed that blockade of ASIC1a using ASIC1a-siRNA inhibited acid-induced osteoclast precursor migration and adhesion, as well as osteoclast adhesion and bone resorption; we also demonstrated that inhibition of ASIC1a decreased the cell surface αvß3 integrin and ß3 protein expression. Moreover, blocking of ASIC1a inhibited acidosis-induced actin ring formation and reduced Pyk2 and Src phosphorylation in osteoclasts and also inhibited the acid-induced association of the αvß3 integrin/Src/Pyk2. CONCLUSION: Together, these results highlight a key functional role of ASIC1a/αvß3 integrin/Pyk2/Src signaling pathway in migration and adhesion of osteoclasts.

The role of integrins in glaucoma.

Integrins are a family of heterodimeric transmembrane receptors that mediate adhesion to the extracellular matrix (ECM). In addition to their role as adhesion receptors, integrins can act as ''bidirectional signal transducers'' that coordinate a large number of cellular activities in response to the extracellular environment and intracellular signaling events. This bidirectional signaling helps maintain tissue homeostasis. Dysregulated bidirectional signaling, however, could trigger the propagation of feedback loops that can lead to the establishment of a disease state such as glaucoma. Here we discuss the role of integrins and bidirectional signaling as they relate to the glaucomatous phenotype with special emphasis on the αvß3 integrin. We present evidence that this particular integrin may have a significant impact on the pathogenesis of glaucoma.

Osteopontin in Spontaneous Germinal Centers Inhibits Apoptotic Cell Engulfment and Promotes Anti-Nuclear Antibody Production in Lupus-Prone Mice.

Disposal of apoptotic cells is important for tissue homeostasis. Defects in this process in immune tissues may lead to breakdown of self-tolerance against intracellular molecules, including nuclear components. Development of diverse anti-nuclear Abs (ANAs) is a hallmark of lupus, which may arise, in part, due to impaired apoptotic cell clearance. In this work, we demonstrate that spontaneous germinal centers (GCs) in lupus-prone mice contain significantly elevated levels of unengulfed apoptotic cells, which are otherwise swiftly engulfed by tingible body macrophages. We indicate that osteopontin (OPN) secreted by CD153(+) senescence-associated T cells, which selectively accumulate in the GCs of lupus-prone mice, interferes with phagocytosis of apoptotic cells specifically captured via MFG-E8. OPN induced diffuse and prolonged Rac1 activation in phagocytes via integrin αvß3 and inhibited the dissolution of phagocytic actin cup, causing defective apoptotic cell engulfment. In wild-type B6 mice, administration of TLR7 ligand also caused spontaneous GC reactions with increasing unengulfed apoptotic cells and ANA production, whereas B6 mice deficient for Spp1 encoding OPN showed less apoptotic cells and developed significantly reduced ANAs in response to TLR7 ligand. Our results suggest that OPN secreted by follicular CD153(+) senescence-associated T cells in GCs promotes a continuous supply of intracellular autoantigens via apoptotic cells, thus playing a key role in the progression of the autoreactive GC reaction and leading to pathogenic autoantibody production in lupus-prone mice.

Dendritic cell expression of ADAM23 governs T cell proliferation and cytokine production through the α(v)ß(3) integrin receptor.

ADAM23 is a member of the brain macrophage-derived chemokine family. Structural homology of ADAM proteins suggests their function as integrin receptors. Previous studies have linked ADAM23 as a dominant contributor to brain development and cancer metastasis. The present studies now show that ADAM23 expression on DCs partially governs antigen-presentation capacities to responder CD4+ T cells. With the use of RNAi approaches, knockdown of ADAM23 in murine BMDCs resulted in impaired T cell activation, proliferation, and cytokine production. Knockdown did not alter the maturation profile of DCs (i.e., costimulatory molecule expression or production of proinflammatory cytokines) but markedly impaired cognate T cell responses. There was a significant decrease in antigen-specific clonal expansion coupled with a global decrease in Th cytokine production. Impaired early activation and proliferation did not alter/skew the balance of Th polarization but significantly depressed total levels of IL-2, IFN-γ, IL-4, and IL-17 cytokine production in CD4+ T cells primed by ADAM23 knockdown versus control DCs. Finally, neutralizing antibodies targeting the α(v)ß(3) integrin receptors resulted in similar phenotypes of impaired CD4+ T cell responses. Taken together, these studies show a novel role of ADAM23 in governing DC antigen presentation to cognate CD4+ T cells.

MYC Is a Crucial Mediator of TGFß-Induced Invasion in Basal Breast Cancer.

Basal subtype breast cancers have a particularly poor prognosis, with high invasiveness and resistance to most targeted therapies. TGFß and MYC drive central features of basal breast cancer: TGFß is an autocrine and paracrine signaling factor that drives cell invasion and metastasis, and MYC is a central regulator of cellular proliferation that is upregulated in many cancer types. We show here that genetic or pharmacologic inhibition of MYC in MCF10A basal breast cells results in increased sensitivity to TGFß-stimulated invasion and metastasis and also show that this signaling loop is dependent on activation of SRC. Analysis of human breast cancer datasets and additional experiments with breast cancer cell lines further suggest the relevance of this signaling loop in basal, but not luminal, breast cancers. Our results imply precaution should be taken when utilizing therapeutic inhibitors of MYC with basal breast cancer patients as this could lead to increased metastasis; however, simultaneous pharmacologic inhibition of SRC and MYC for these patients could facilitate the antiproliferative effects of MYC inhibition while blocking the consequent promotion of metastasis. Cancer Res; 76(12); 3520-30. ©2016 AACR.

Integrin αvß3 expression in tongue squamous carcinoma cells Cal27 confers anticancer drug resistance through loss of pSrc(Y418).

Integrins play key roles in the regulation of tumor cell adhesion, migration, invasion and sensitivity to anticancer drugs. In the present study we investigate the mechanism of resistance of tongue squamous carcinoma cells Cal27 with de novo integrin αvß3 expression to anticancer drugs. Cal27-derived cell clones, obtained by transfection of plasmid containing integrin subunit ß3 cDNA, as compared to control cells demonstrate: expression of integrin αvß3; increased expression of integrin αvß5; increased adhesion to fibronectin and vitronectin; resistance to cisplatin, mitomycin C, doxorubicin and 5-fluorouracil; increased migration and invasion, increased amount of integrin-linked kinase (ILK) and decreased amounts of non-receptor tyrosine kinase (Src) and pSrc(Y418). Knockdown of ILK and integrin ß5 in cells expressing integrin αvß3 ruled out their involvement in drug resistance. Opposite, Src knockdown in Cal27 cells which led to a reduction in pSrc(Y418), as well as treatment with the pSrc(Y418) inhibitors dasatinib and PP2, conferred resistance to all four anticancer drugs, indicating that the loss of pSrc(Y418) is responsible for the observed effect. We identified differential integrin signaling between Cal27 and integrin αvß3-expressing cells. In Cal27 cells integrin αv heterodimers signal through pSrc(Y418) while this is not the case in integrin αvß3-expressing cells. Finally, we show that dasatinib counteracts the effect of cisplatin in two additional head and neck squamous cell carcinoma (HNSCC) cell lines Cal33 and Detroit562. Our results suggest that pSrc(Y418) inhibitors, potential drugs for cancer therapy, may reduce therapeutic efficacy if combined with chemotherapeutics, and might not be recommended for HNSCC treatment.

Human Parechovirus 1 Infection Occurs via αVß1 Integrin.

Human parechovirus 1 (HPeV-1) (family Picornaviridae) is a global cause of pediatric respiratory and CNS infections for which there is no treatment. Although biochemical and in vitro studies have suggested that HPeV-1 binds to αVß1, αVß3 and αVß6 integrin receptor(s), the actual cellular receptors required for infectious entry of HPeV-1 remain unknown. In this paper we analyzed the expression profiles of αVß1, αVß3, αVß6 and α5ß1 in susceptible cell lines (A549, HeLa and SW480) to identify which integrin receptors support HPeV-1 internalization and/or replication cycle. We demonstrate by antibody blocking assay, immunofluorescence microscopy and RT-qPCR that HPeV-1 internalizes and replicates in cell lines that express αVß1 integrin but not αVß3 or αVß6 integrins. To further study the role of ß1 integrin, we used a mouse cell line, GE11-KO, which is deficient in ß1 expression, and its derivate GE11-ß1 in which human integrin ß1 subunit is overexpressed. HPeV-1 (Harris strain) and three clinical HPeV-1 isolates did not internalize into GE11-KO whereas GE11-ß1 supported the internalization process. An integrin ß1-activating antibody, TS2/16, enhanced HPeV-1 infectivity, but infection occurred in the absence of visible receptor clustering. HPeV-1 also co-localized with ß1 integrin on the cell surface, and HPeV-1 and ß1 integrin co-endocytosed into the cells. In conclusion, our results demonstrate that in some cell lines the cellular entry of HPeV-1 is primarily mediated by the active form of αVß1 integrin without visible receptor clustering.

The thyroid hormone-αvß3 integrin axis in ovarian cancer: regulation of gene transcription and MAPK-dependent proliferation.

Ovarian carcinoma is the fifth common cause of cancer death in women, despite advanced therapeutic approaches. αvß3 integrin, a plasma membrane receptor, binds thyroid hormones (L-thyroxine, T4; 3,5,3'-triiodo-L-thyronine, T3) and is overexpressed in ovarian cancer. We have demonstrated selective binding of fluorescently labeled hormones to αvß3-positive ovarian cancer cells but not to integrin-negative cells. Physiologically relevant T3 (1 nM) and T4 (100 nM) concentrations in OVCAR-3 (high αvß3) and A2780 (low αvß3) cells promoted αv and ß3 transcription in association with basal integrin levels. This transcription was effectively blocked by RGD (Arg-Gly-Asp) peptide and neutralizing αvß3 antibodies, excluding T3-induced ß3 messenger RNA, suggesting subspecialization of T3 and T4 binding to the integrin receptor pocket. We have provided support for extracellular regulated kinase (ERK)-mediated transcriptional regulation of the αv monomer by T3 and of ß3 monomer by both hormones and documented a rapid (30-120 min) and dose-dependent (0.1-1000 nM) ERK activation. OVCAR-3 cells and αvß3-deficient HEK293 cells treated with αvß3 blockers confirmed the requirement for an intact thyroid hormone-integrin interaction in ERK activation. In addition, novel data indicated that T4, but not T3, controls integrin's outside-in signaling by phosphorylating tyrosine 759 in the ß3 subunit. Both hormones induced cell proliferation (cell counts), survival (Annexin-PI), viability (WST-1) and significantly reduced the expression of genes that inhibit cell cycle (p21, p16), promote mitochondrial apoptosis (Nix, PUMA) and tumor suppression (GDF-15, IGFBP-6), particularly in cells with high integrin expression. At last, we have confirmed that hypothyroid environment attenuated ovarian cancer growth using a novel experimental platform that exploited paired euthyroid and severe hypothyroid serum samples from human subjects. To conclude, our data define a critical role for thyroid hormones as potent αvß3-ligands, driving ovarian cancer cell proliferation and suggest that disruption of this axis may present a novel treatment strategy in this aggressive disease.

The rational design of a gemcitabine prodrug with AIE-based intracellular light-up characteristics for selective suppression of pancreatic cancer cells.

An enzyme and reduction-activatable gemcitabine prodrug (TPE-GEM-RGD) with aggregation-induced emission (AIE) properties was designed for targeted and image-guided cancer therapy. TPE-GEM-RGD was successfully used for intracellular light-up imaging and glutathione (GSH)-responsive release of gemcitabine to suppress pancreatic cancer cells.

Thyroid hormones and tetrac: new regulators of tumour stroma formation via integrin αvß3.

To improve our understanding of non-genomic, integrin αvß3-mediated thyroid hormone action in tumour stroma formation, we examined the effects of triiodo-l-thyronine (T3), l-thyroxine (T4) and integrin-specific inhibitor tetrac on differentiation, migration and invasion of mesenchymal stem cells (MSCs) that are an integral part of the tumour's fibrovascular network. Primary human bone marrow-derived MSCs were treated with T3 or T4 in the presence of hepatocellular carcinoma (HCC) cell-conditioned medium (CM), which resulted in stimulation of the expression of genes associated with cancer-associated fibroblast-like differentiation as determined by qPCR and ELISA. In addition, T3 and T4 increased migration of MSCs towards HCC cell-CM and invasion into the centre of three-dimensional HCC cell spheroids. All these effects were tetrac-dependent and therefore integrin αvß3-mediated. In a subcutaneous HCC xenograft model, MSCs showed significantly increased recruitment and invasion into tumours of hyperthyroid mice compared to euthyroid and, in particular, hypothyroid mice, while treatment with tetrac almost completely eliminated MSC recruitment. These studies significantly improve our understanding of the anti-tumour activity of tetrac, as well as the mechanisms that regulate MSC differentiation and recruitment in the context of tumour stroma formation, as an important prerequisite for the utilisation of MSCs as gene delivery vehicles.

Single molecular force across single integrins dictates cell spreading.

Cells' ability to sense and interpret mechanical signals from the extracellular milieu modulates the degree of cell spreading. Yet how cells detect such signals and activate downstream signaling at the molecular level remain elusive. Herein, we utilize tension gauge tether (TGT) platform to investigate the underlying molecular mechanism of cell spreading. Our data from both differentiated cells of cancerous and non-cancerous origin show that for the same stiff underlying glass substrates and for same ligand density it is the molecular forces across single integrins that ultimately determine cell spreading responses. Furthermore, by decoupling molecular stiffness and molecular tension we demonstrate that molecular stiffness has little influence on cell spreading. Our data provide strong evidence that links molecular forces at the cell-substrate interface to the degree of cell spreading.

Avß3 integrin: Pathogenetic role in osteotropic tumors.

The interplay of cancer cells and accessory cells within the microenvironment drives signals regulating the proliferation, migration and skeleton colonization. Osteotropism of tumor cells depends on chemokine activation, production of soluble factors and defective gene expression that cooperate within the metastatic niche to the bone resorbing functions of osteoclasts. Adhesion of cancer cells to the extracellular matrix is regulated by integrins as αvß3 that enhances their invasiveness, pro-tumor angiogenesis and skeleton invasion. Therefore, αvß3 signaling is implicated in enhancing osteotropism of breast and prostate cancers as well as of multiple myeloma. Targeting of αvß3 has been adopted to restrain the tumor progression in several cancer models leading to improvement of overall survival as effect of the reduction of both tumor burden and osteotropism by malignant cells. Here, we review both the role of αvß3 in malignant osteoclastogenesis and its potential targeting to restrain the bone colonization by skeleton invading cancers.

Tumor-derived osteopontin reprograms normal mammary fibroblasts to promote inflammation and tumor growth in breast cancer.

Breast tumors are characterized by an extensive desmoplastic stroma, abundantly populated by fibroblasts. Cancer-associated fibroblasts (CAF) support tumorigenesis by stimulating angiogenesis, cancer cell proliferation, and invasion. CAF also orchestrate tumor-promoting inflammation in multiple tumor types, including breast cancer. However, the mechanisms through which normal tissue fibroblasts are reprogrammed to tumor-promoting CAFs are mainly obscure. Here, we show that mammary fibroblasts can be educated by breast cancer cells to become activated to a proinflammatory state that supports malignant progression. Proteomic analysis of breast cancer cell-secreted factors identified the secreted proinflammatory mediator osteopontin, which has been implicated in inflammation, tumor progression, and metastasis. Osteopontin was highly secreted by mouse and human breast cancer cells, and tumor cell-secreted osteopontin activated a CAF phenotypes in normal mammary fibroblasts in vitro and in vivo. Osteopontin was sufficient to induce fibroblast reprogramming and neutralizing antibodies against osteopontin-blocked fibroblast activation induced by tumor cells. The ability of secreted osteopontin to activate mammary fibroblasts relied upon its known receptors CD44 and αVß3 integrin. Strikingly, osteopontin silencing in tumor cells in vivo attenuated stromal activation and inhibited tumor growth. Our findings establish a critical functional role for paracrine signaling by tumor-derived osteopontin in reprograming normal fibroblasts into tumor-promoting CAFs.

Role of milk fat globule-epidermal growth factor 8 in colonic inflammation and carcinogenesis.

BACKGROUND: Milk fat globule-epidermal growth factor 8 (MFG-E8) promotes phagocytic clearance of apoptotic cells to maintain normal tissue homeostasis. However, its functions in intestinal inflammation and carcinogenesis are unknown. METHODS: Experimental colitis was induced in MFG-E8 knockout (KO) and wild-type (WT) mice by dextran sodium sulfate (DSS) administration. Colon tissues were used for assessments of colitis activity and epithelial proliferation. A mouse colitis-associated cancer (CAC) model was induced by intraperitoneal injection of azoxymethane (AOM) and then the animals were given a single administration of DSS. A sporadic colon cancer model was established by repeated intraperitoneal injections of AOM. The role of MFG-E8 in epithelial proliferation with or without treatment of siRNA targeting α(v)-integrin was examined in vitro using a WST-1 assay. RESULTS: The severity of colitis in KO mice was greater than that in WT mice, while the proliferative potential of colonic epithelial cells in KO mice was lower during the regenerative phase. In both CAC and sporadic models, tumor size in KO was lower as compared to WT mice, while decreased tumor incidence was only found in the CAC model. In vitro findings showed that MFG-E8 promotes epithelial cell proliferation, and treatment with a siRNA targeting α(v)-integrin reduced the proliferation of Colon-26 cells stimulated with recombinant MFG-E8. CONCLUSIONS: MFG-E8 promotes tumor growth regardless of the presence or absence of colonic inflammation, whereas colon tumor development is initiated by MFG-E8 under inflammatory conditions. These MFG-E8 functions may be dependent on integrin-mediated cellular signaling.