The effect of ADAMTS13 on graft-versus-host disease.

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) can potentially cure malignant blood disorders and benign conditions such as haemoglobinopathies and immunologic diseases. However, allo-HSCT is associated with significant complications. The most common and debilitating among them is graft-versus-host disease (GVHD). In GVHD, donor-derived T cells mount an alloimmune response against the recipient. The alloimmune response involves several steps, including recognition of recipient antigens, activation and proliferation of T cells in secondary lymphoid organs, and homing into GVHD-targeted organs. Adhesion molecules on T cells and endothelial cells mediate homing of T cells into lymphoid and non-lymphoid tissues. In this study, we showed that Von Willebrand factor (VWF), an adhesion molecule secreted by activated endothelial cells, plays an important role in mouse models of GVHD. We investigated the effect of the VWF-cleaving protease ADAMTS13 on GVHD. We found that ADAMTS13 reduced the severity of GVHD after bone marrow transplantation from C57BL6 donor to BALB/C recipient mice. A recombinant VWF-A2 domain peptide also reduced GVHD in mice. We showed that ADAMTS13 and recombinant VWF-A2 reduced the binding of T cells to endothelial cells and VWF in vitro, and reduced the number of T cells in lymph nodes, Peyer's patches and GVHD-targeted organs in vivo. We identified LFA-1 (αLß2) as the binding site of VWF on T cells. Our results showed that blocking T-cell homing by ADAMTS13 or VWF-A2 peptide reduced the severity of the GVHD after allo-HSCT, a potentially novel method for treating and preventing GVHD.

Role of ADP receptors on platelets in the growth of ovarian cancer.

We investigated the effect of platelets on ovarian cancer and the role of adenosine diphosphate (ADP) receptors (P2Y12 and P2Y1) on platelets in the growth of primary ovarian cancer tumors. We showed that in murine models of ovarian cancer, a P2Y12 inhibitor (ticagrelor) reduced tumor growth by 60% compared with aspirin and by 75% compared with placebo. In P2Y12-/- mice, the growth of syngeneic ovarian cancer tumors was reduced by >85% compared with wild-type (WT) mice. In contrast, there was no difference in tumor growth between P2Y1-/- and WT mice. Reconstitution of hematopoiesis in irradiated P2Y12-/- mice by hematopoietic progenitor cells from WT mice (WT→P2Y12-/-) restored tumor growth in P2Y12-/- mice. Finally, knockdown of ecto-apyrase (CD39) on ovarian cancer cells increased tumor growth in tumor-bearing mice. Although in the absence of platelets, ADP, the P2Y12 inhibitor, recombinant apyrase, or knockdown of CD39 did not affect cancer cell proliferation, in the presence of platelets, the P2Y12 inhibitor and recombinant apyrase reduced and knockdown of CD39 increased platelet-enhanced cancer cell proliferation. These results suggest that P2Y12 on platelets and ADP concentration at the interface between cancer cells and platelets affect the growth of primary ovarian cancer tumors in mice. If additional studies in mice and in pilot human trials confirm our results, inhibition of P2Y12 might be a new therapeutic option that can be used in adjuvant to the traditional surgery and chemotherapy in patients with ovarian cancer.

Complement Component 3 Is Regulated by TWIST1 and Mediates Epithelial-Mesenchymal Transition.

We have previously shown that complement component 3 (C3) is secreted by malignant epithelial cells. To understand the mechanism of upregulation of C3 expression in tumor cells, we studied the C3 promoter and identified that twist basic helix-loop-helix transcription factor 1 (TWIST1) binds to the C3 promoter and enhances its expression. Because TWIST1 mediates epithelial-mesenchymal transition (EMT), we studied the effect of C3 on EMT and found that C3 decreased E-cadherin expression on cancer cells and promoted EMT. We showed that C3-induced reduction in E-cadherin expression in ovarian cancer cells was mediated by C3a and is Krüppel-like factor 5 dependent. We investigated the association between TWIST1 and C3 in malignant tumors and in murine embryos. TWIST1 and C3 colocalized at the invasive tumor edges, and in the neural crest and limb buds of mouse embryos. Our results identified TWIST1 as a transcription factor that regulates C3 expression during pathologic and physiologic EMT.

A small amount of cyclooxygenase 2 (COX2) is constitutively expressed in platelets.

Cyclooxygenase (COX) is the rate-limiting enzyme in conversion of arachidonic acid to prostanoids, and has two isoforms, COX1 and COX2, which share ~65% amino acid homology. COX1 is universally expressed in many cell types including platelets; however, expression of COX2 is known to be more limited. We examined expression of COX2 mRNA and protein in platelets and platelet-derived microparticles (MPs); using quantitative RT-PCR, immunostaining, and Western blotting. We have detected a significant amount of COX2 in platelets, both at mRNA and protein levels. We found that COX1/COX2 mRNA and protein ratios in platelets were 370:1 and 17:1, respectively. Expression level of COX2 in platelets was less than COX1, but comparable to the expression of COX2 in malignant epithelial cells. Considering the important role of COX2 in tumorigenesis and thrombosis, and the large number of circulating platelets, we propose that platelet COX2 may play an important role in physiologic and pathologic conditions.

Induced multipotency in adult keratinocytes through down-regulation of ΔNp63 or DGCR8.

The roles of microRNAs (miRNAs) and the miRNA processing machinery in the regulation of stem cell biology are not well understood. Here, we show that the p53 family member and p63 isoform, ΔNp63, is a transcriptional activator of a cofactor critical for miRNA processing (DGCR8). This regulation gives rise to a unique miRNA signature resulting in reprogramming cells to multipotency. Strikingly, ΔNp63(-/-) epidermal cells display profound defects in terminal differentiation and express a subset of markers and miRNAs present in embryonic stem cells and fibroblasts induced to pluripotency using Yamanaka factors. Moreover, ΔNp63(-/-) epidermal cells transduced with an inducible DGCR8 plasmid can differentiate into multiple cell fates in vitro and in vivo. We found that human primary keratinocytes depleted of ΔNp63 or DGCR8 can be reprogrammed in 6 d and express a unique miRNA and gene expression signature that is similar but not identical to human induced pluripotent stem cells. Our data reveal a role for ΔNp63 in the transcriptional regulation of DGCR8 to reprogram adult somatic cells into multipotent stem cells.

Anti-vascular therapies in ovarian cancer: moving beyond anti-VEGF approaches.

Resistance to chemotherapy is among the most important issues in the management of ovarian cancer. Unlike cancer cells, which are heterogeneous as a result of remarkable genetic instability, stromal cells are considered relatively homogeneous. Thus, targeting the tumor microenvironment is an attractive approach for cancer therapy. Arguably, anti-vascular endothelial growth factor (anti-VEGF) therapies hold great promise, but their efficacy has been modest, likely owing to redundant and complementary angiogenic pathways. Components of platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), and other pathways may compensate for VEGF blockade and allow angiogenesis to occur despite anti-VEGF treatment. In addition, hypoxia induced by anti-angiogenesis therapy modifies signaling pathways in tumor and stromal cells, which induces resistance to therapy. Because of tumor cell heterogeneity and angiogenic pathway redundancy, combining cytotoxic and targeted therapies or combining therapies targeting different pathways can potentially overcome resistance. Although targeted therapy is showing promise, much more work is needed to maximize its impact, including the discovery of new targets and identification of individuals most likely to benefit from such therapies.

TAp63 suppresses metastasis through coordinate regulation of Dicer and miRNAs.

Aberrant expression of microRNAs (miRNAs) and the enzymes that control their processing have been reported in multiple biological processes including primary and metastatic tumours, but the mechanisms governing this are not clearly understood. Here we show that TAp63, a p53 family member, suppresses tumorigenesis and metastasis, and coordinately regulates Dicer and miR-130b to suppress metastasis. Metastatic mouse and human tumours deficient in TAp63 express Dicer at very low levels, and we found that modulation of expression of Dicer and miR-130b markedly affected the metastatic potential of cells lacking TAp63. TAp63 binds to and transactivates the Dicer promoter, demonstrating direct transcriptional regulation of Dicer by TAp63. These data provide a novel understanding of the roles of TAp63 in tumour and metastasis suppression through the coordinate transcriptional regulation of Dicer and miR-130b and may have implications for the many processes regulated by miRNAs.

Platelets increase the proliferation of ovarian cancer cells.

Platelets promote metastasis and angiogenesis, but their effect on tumor cell growth is uncertain. Here we report a direct proliferative effect of platelets on cancer cells both in vitro and in vivo. Incubation of platelets with ovarian cancer cells from murine (ID8 and 2C6) or human (SKOV3 and OVCAR5) origin increased cell proliferation. The proliferative effect of platelets was not dependent on direct contact with cancer cells, and preincubation of platelets with blocking antibodies against platelet adhesion molecules did not alter their effect on cancer cells. The proliferative effect of platelets was reduced by fixing platelets with paraformaldehyde, preincubating platelets with a TGF-ß1-blocking antibody, or reducing expression of TGF-ßR1 receptor on cancer cells with siRNA. Infusing platelets into mice with orthotopic ovarian tumors significantly increased the proliferation indices in these tumors. Ovarian cancer patients with thrombocytosis had higher tumor proliferation indices compared with patients with normal platelet counts.

Rescue of key features of the p63-null epithelial phenotype by inactivation of Ink4a and Arf.

Mice lacking p63 cannot form skin, exhibit craniofacial and skeletal defects, and die soon after birth. The p63 gene regulates a complex network of target genes, and disruption of p63 has been shown to affect the maintenance of epithelial stem cells, the differentiation of keratinocytes, and the preservation of the adhesive properties of stratified epithelium. Here, we show that inactivation of p63 in mice is accompanied by aberrantly increased expression of the Ink4a and Arf tumour suppressor genes. In turn, anomalies of the p63-null mouse affecting the skin and skeleton are partially ameliorated in mice lacking either Ink4a or Arf. Rescue of epithelialization is accompanied by restoration of keratinocyte proliferative capacity both in vivo and in vitro and by expression of markers of squamous differentiation. Thus, in the absence of p63, abnormal upregulation of Ink4a and Arf is incompatible with skin development.

Interactions between Platelets and Tumor Microenvironment Components in Ovarian Cancer and Their Implications for Treatment and Clinical Outcomes.

Platelets, the primary operatives of hemostasis that contribute to blood coagulation and wound healing after blood vessel injury, are also involved in pathological conditions, including cancer. Malignancy-associated thrombosis is common in ovarian cancer patients and is associated with poor clinical outcomes. Platelets extravasate into the tumor microenvironment in ovarian cancer and interact with cancer cells and non-cancerous elements. Ovarian cancer cells also activate platelets. The communication between activated platelets, cancer cells, and the tumor microenvironment is via various platelet membrane proteins or mediators released through degranulation or the secretion of microvesicles from platelets. These interactions trigger signaling cascades in tumors that promote ovarian cancer progression, metastasis, and neoangiogenesis. This review discusses how interactions between platelets, cancer cells, cancer stem cells, stromal cells, and the extracellular matrix in the tumor microenvironment influence ovarian cancer progression. It also presents novel potential therapeutic approaches toward this gynecological cancer.

Role of circulating mitochondria in venous thrombosis in glioblastoma.

BACKGROUND: Many patients with glioblastoma multiforme (GBM) develop deep venous thrombosis or pulmonary emboli. Cell-free circulating mitochondria increase after brain injury and are associated with coagulopathy. OBJECTIVES: This study evaluated whether mitochondria play a role in the GBM-induced hypercoagulable state. METHODS: We examined the correlation between cell-free circulating mitochondria and venous thrombosis in patients with GBM and the impact of mitochondria on venous thrombosis in mice with inferior vena cava stenosis. RESULTS: Using plasma samples of 82 patients with GBM, we found that patients with GBM had a higher number of mitochondria in their plasma (GBM with venous thromboembolism [VTE],: 2.8 × 107 mitochondria/mL; GBM without VTE, 1.9 × 107 mitochondria/mL) than that in healthy control subjects (n = 17) (0.3 × 107 mitochondria/mL). Interestingly, patients with GBM and VTE (n = 41) had a higher mitochondria concentration than patients with GBM without VTE (n = 41). In a murine model of inferior vena cava stenosis, intravenous delivery of mitochondria resulted in an increased rate of venous thrombosis compared with that in controls (70% and 28%, respectively). Mitochondria-induced venous thrombi were neutrophil-rich and contained more platelets than those in control thrombi. Furthermore, as mitochondria are the only source of cardiolipin in circulation, we compared the concentration of anticardiolipin immunoglobulin G in plasma samples of patients with GBM and found a higher concentration in patients with VTE (optical density, 0.69 ± 0.04) than in those without VTE (optical density, 0.51 ± 0.04). CONCLUSION: We concluded that mitochondria might play a role in the GBM-induced hypercoagulable state. We propose that quantifying circulating mitochondria or anticardiolipin antibody concentrations in patients with GBM might identify patients at increased risk of VTE.

Podoplanin promotes tumor growth, platelet aggregation, and venous thrombosis in murine models of ovarian cancer.

BACKGROUND: Podoplanin (PDPN) is a sialylated membrane glycoprotein that binds to C-type lectin-like receptor 2 on platelets resulting in platelet activation. PDPN is expressed on lymphatic endothelial cells, perivascular fibroblasts/pericytes, cancer cells, cancer-associated fibroblasts, and tumor stromal cells. PDPN's expression on malignant epithelial cells plays a role in metastasis. Furthermore, the expression of PDPN in brain tumors (high-grade gliomas) was found to correlate with an increased risk of venous thrombosis. OBJECTIVE: We examined the expression of PDPN and its role in tumor progression and venous thrombosis in ovarian cancer. METHODS: We used mouse models of ovarian cancer and venous thrombosis. RESULTS: Ovarian cancer cells express PDPN and release PDPN-rich extracellular vesicles (EVs), and cisplatin and topotecan (chemotherapies commonly used in ovarian cancer) increase the expression of podoplanin in cancer cells. The expression of PDPN in ovarian cancer cells promotes tumor growth in a murine model of ovarian cancer and that knockdown of PDPN gene expression results in smaller primary tumors. Both PDPN-expressing ovarian cancer cells and their EVs cause platelet aggregation. In a mouse model of venous thrombosis, PDPN-expressing EVs released from HeyA8 ovarian cancer cells produce more frequent thrombosis than PDPN-negative EVs derived from PDPN-knockdown HeyA8 cells. Blood clots induced by PDPN-positive EVs contain more platelets than those in blood clots induced by PDPN-negative EVs. CONCLUSIONS: In summary, our findings demonstrate that the expression of PDPN by ovarian cancer cells promotes tumor growth and venous thrombosis in mice.

Novel Markers for Liquid Biopsies in Cancer Management: Circulating Platelets and Extracellular Vesicles.

Although radiologic imaging and histologic assessment of tumor tissues are classic approaches for diagnosis and monitoring of treatment response, they have many limitations. These include challenges in distinguishing benign from malignant masses, difficult access to the tumor, high cost of the procedures, and tumor heterogeneity. In this setting, liquid biopsy has emerged as a potential alternative for both diagnostic and monitoring purposes. The approaches to liquid biopsy include cell-free DNA/circulating tumor DNA, long and micro noncoding RNAs, proteins/peptides, carbohydrates/lectins, lipids, and metabolites. Other approaches include detection and analysis of circulating tumor cells, extracellular vesicles, and tumor-activated platelets. Ultimately, reliable use of liquid biopsies requires bioinformatics and statistical integration of multiple datasets to achieve approval in a Clinical Laboratory Improvement Amendments setting. This review provides a balanced and critical assessment of recent discoveries regarding tumor-derived biomarkers in liquid biopsies along with the potential and pitfalls for cancer detection and longitudinal monitoring.

Platelets Increase the Expression of PD-L1 in Ovarian Cancer.

The interactions between platelets and cancer cells activate platelets and enhance tumor growth. Platelets increase proliferation and epithelial-mesenchymal transition in cancer cells, inhibit anoikis, enhance the extravasation of cancer cells, and protect circulating tumor cells against natural killer cells. Here, we have identified another mechanism by which platelets dampen the immune attack on cancer cells. We found that platelets can blunt the antitumor immune response by increasing the expression of inhibitory immune checkpoint (PD-L1) on ovarian cancer cells in vitro and in vivo. Platelets increased PD-L1 in cancer cells via contact-dependent (through NF-κB signaling) and contact-independent (through TFGßR1/Smad signaling) pathways. Inhibition of NF-κB or TGFßR1 signaling in ovarian cancer cells abrogated platelet-induced PD-L1 expression. Reducing platelet counts or inhibiting platelet functions reduced the expression of PD-L1 in ovarian cancer. On the other hand, an increase in platelet counts increased the expression of PD-L1 in tumor-bearing mice.

Targeting DDX3X Triggers Antitumor Immunity via a dsRNA-Mediated Tumor-Intrinsic Type I Interferon Response.

Induction of nucleic acid sensing-mediated type I interferon (IFN) has emerged as a novel approach to activate the immune system against cancer. Here we show that the depletion of DEAD-box RNA helicase 3X (DDX3X) triggers a tumor-intrinsic type I IFN response in breast cancer cells. Depletion or inhibition of DDX3X activity led to aberrant cytoplasmic accumulation of cellular endogenous double-stranded RNAs (dsRNA), which triggered type I IFN production through the melanoma differentiation-associated gene 5 (MDA5)-mediated dsRNA-sensing pathway. Furthermore, DDX3X interacted with dsRNA-editing ADAR1 and dual depletion of DDX3X and ADAR1 synergistically activated the cytosolic dsRNA pathway in breast cancer cells. Loss of DDX3X in mouse mammary tumors enhanced antitumor activity by increasing the tumor-intrinsic type I IFN response, antigen presentation, and tumor infiltration of cytotoxic T and dendritic cells. These findings may lead to the development of a novel therapeutic approach for breast cancer by targeting DDX3X in combination with immune-checkpoint blockade. SIGNIFICANCE: This study elucidates the novel role of DDX3X in regulating endogenous cellular dsRNA homeostasis and type I IFN signaling in breast cancer. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/13/3607/F1.large.jpg.

The effect of platelet G proteins on platelet extravasation and tumor growth in the murine model of ovarian cancer.

We and other investigators have shown that platelets promote metastasis and the growth of tumors. Our rationale for conducting this study is that platelets' prometastatic and progrowth effects depend on a close encounter between platelets and cancer cells. This interaction occurs inside blood vessels with circulating tumor cells and outside blood vessels with cancer cells residing in the tumor parenchyma. Our hypothesis was that platelet extravasation is required for the effect of platelets on tumor growth. Platelets respond to environmental stimuli by activation of G protein-coupled receptors on their surface. We investigated the impact of various platelet G proteins on the growth of ovarian cancer tumors and platelet extravasation. We used mice with platelet-specific deficiency of Gαi2 (Gi), Gα13 (G13), or Gαq (Gq) in a syngeneic ovarian cancer model. We measured the total weight of tumor nodules resected from tumor-bearing mice. We developed methods for automated whole-slide image acquisition and unbiased computerized image analysis to quantify extravasated platelets. We compared the number of platelets inside tumor nodules of platelet G protein-deficient tumor-bearing mice. We found that deficiency of Gi and G13, but not Gq, in platelets resulted in smaller tumors compared with those in corresponding littermates. Deficiency of Gi and G13 in platelets reduced the number of extravasated platelets by >90%, but deficiency of Gq did not reduce the number of extravasated platelets significantly. The lack of Gi or G13 in platelets reduced platelet extravasation into the tumor and tumor growth.

The hidden role of paxillin: localization to nucleus promotes tumor angiogenesis.

Paxillin (PXN), a key component of the focal adhesion complex, has been associated with cancer progression, but the underlying mechanisms are poorly understood. The purpose of this study was to elucidate mechanisms by which PXN affects cancer growth and progression, which we addressed using cancer patient data, cell lines, and orthotopic mouse models. We demonstrated a previously unrecognized mechanism whereby nuclear PXN enhances angiogenesis by transcriptionally regulating SRC expression. SRC, in turn, increases PLAT expression through NF-ĸB activation; PLAT promotes angiogenesis via LRP1 in endothelial cells. PXN silencing in ovarian cancer mouse models reduced angiogenesis, tumor growth, and metastasis. These findings provide a new understanding of the role of PXN in regulating tumor angiogenesis and growth.

Disruption of the dynamic sub-cellular localization of the Xenopus tumorhead protein causes embryonic lethality at the early gastrula transition.

The Xenopus laevis tumorhead (TH) protein, a positive regulator of cell proliferation during embryogenesis, shuttles from the cell periphery into the nucleus during embryogenesis. In these studies, we performed a detailed analysis of TH's subcellular localization pattern to characterize its dynamic behavior. We found that TH exhibits distinct patterns of localization in different germ layers. At the blastula stage, TH is present in the apical cell periphery of prospective mesodermal and ectodermal cells. At the gastrula stage, TH is distributed throughout the entire cytoplasm of prospective mesodermal and ectodermal cells, whereas it shows nuclear localization in presumptive endodermal cells. TH moves into the nucleus of mesodermal and ectodermal cells during the neurula and early tailbud stages. To understand if TH is regulated by changes in its subcellular localization, we used a TH mutant containing signals for farnesylation and palmitoylation to tether the protein to the plasma membrane. Ubiquitous overexpression of this mutant causes embryonic lethality at the early gastrula transition. Further examination using TUNEL assays indicated that wild-type TH overexpression induces apoptosis during gastrulation, and that this effect is exacerbated by the overexpression of the membrane-bound TH mutant. Taken together, our results suggest that changes in the sub-cellular localization of the TH protein are important for its function because blocking the nuclear translocation of overexpressed TH increases apoptosis and causes embryos to die. Our data also suggest that TH plays a role outside the nucleus when it is present at the cell periphery.

Identification of TH-B, a new oligomeric variant of the Xenopus morphogenetic factor, tumorhead.

The Xenopus laevis gene tumorhead (TH) is a regulator of cell proliferation of the ectodermal germ layer during embryonic development. TH overexpression results in increased cell proliferation within the developing ectoderm, causing an expansion of the neural plate. Conversely, loss of TH function results in inhibition of proliferation of ectodermal cells. Embryos with altered levels of TH protein are unable to express neural differentiation markers, indicating that the effect of TH in proliferation is linked with differentiation in the nervous system. To date, the molecular mechanism by which TH affects cell proliferation during embryogenesis is unknown. We have utilized the yeast two-hybrid system to identify protein partners of TH that could lead us to define the mechanism or pathway through which TH functions. Using this assay we have identified a new variant of TH designated TH-B, as a potential protein partner of the original TH, now referred to as TH-A. The sequence for TH-B was found to be 85% identical at the amino acid level to the TH-A sequence. Further characterization of the TH-B variant using RT-PCR indicates that it is expressed ubiquitously throughout development from early cleavage stages until at least the tadpole stage. TH-B association with TH-A was confirmed in co-immnoprecipitation studies in Xenopus, indicating that the two variants may function as an oligomer in vivo. These studies reveal the presence of an isoform of TH that may possess novel functional capabilities.