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Abstract: In the field of tumor biology, increasing attention is now focused on the complex interactions between various constituent cell types within the tumor microenvironment as being functionally important for the etiology of the disease. The detailed description of tumor-promoting properties of cancer-associated fibroblasts, endothelial cells, pericytes, and immune cells, introduces novel potential drug targets for improved cancer treatments, as well as a rationale for exploring the tumor stroma as a previously unchartered source for prognostic or predictive biomarkers. However, recent work highlights the fact that cellular identity is perhaps too broadly defined and that subdivision of each cell type may reveal functionally distinct subsets of cells. Here, we will review our current understanding of the diversity of different subsets of mesenchymal cells, i.e., cancer-associated fibroblasts and pericytes, residing within the tumor parenchyma. [Copyright &y& Elsevier]

Introduction. The initial clinical experience from targeted therapy for breast cancer has been mixed. While important progress has been made in the care of a subset of patients characterized by amplification of HER2 through the use of trastuzumab, other targeted therapies have failed to improve the outcome for large, unselected groups of patients. Thus, efforts to find prognostic or predictive biomarkers to enable tailored therapy are highly warranted. Genetically engineered mouse models of human cancer provide a convenient setting in which to perform explorative studies. However, there is a paucity of comparative studies between mouse and human tumours in order to validate the use of mouse models as discovery tools. Materials and methods. Here, we have compared the localization of markers for cancer-associated fibroblasts in the MMTV-PyMT mouse model of mammary carcinoma with that of human breast cancer. The expression of α-smooth muscle actin, platelet-derived growth factor receptor-α, and fibroblast-specific protein-1 was assessed by immunostaining of sections from tumours of MMTV-PyMT mice. Information about the distribution of the same markers in human breast cancer was derived from the publicly available database the Human Protein Atlas. Results. Both mouse and human mammary carcinomas were infused by a rich fibrotic stroma. While no marker was capable of identifying all stromal fibroblasts, the expression pattern of each marker was remarkably similar in mouse and human. Discussion. We conclude that the MMTV-PyMT mouse model of breast cancer will have utility as a discovery tool for biomarkers of cancer-associated fibroblasts during malignant conversion. [ABSTRACT FROM AUTHOR]

Endothelial cells (ECs) in blood vessels under formation are stabilized by the recruitment of pericytes, both in normal tissues and during angiogenesis in pathologic situations, including neoplasia. In the tumor vasculature, besides supporting the functionality of blood flow, pericytes protect ECs from antiangiogenic therapies, and have thus been implicated in clinical resistance to vascular targeting drugs. However, the molecular nature of the crosstalk between pericytes and ECs is largely unchartered. Herein, we identified pericyte-induced survival signals in ECs by isolation of vascular fragments derived from tumors that had been genetically or pharmacologically engineered to be either pericyte-rich or pericyte-poor. Pericytes induced the antiapoptotic protein Bcl-w in tumor ECs both in vivo and in vitro, thereby conveying protection from cytotoxic damage. The pericyte-dependent survival signaling in ECs was consequential to enforcement of an autocrine loop involving VEGF-A expression in ECs. Through molecular and functional studies, we delineated a signal transduction pathway in ECs downstream of integrin αv involving activation of NF-κB as the initiating event of the protective crosstalk from pericytes. Our elucidation of pericyte-derived pro-survival signaling in tumor ECs has potentially important implications for clinical development of antiangiogenic drugs, and suggests new therapeutic targets for rational multitargeting of cancer. [ABSTRACT FROM AUTHOR]

Background: CGGBP1 is a CGG-triplet repeat binding protein, which affects transcription from CGG-triplet-rich promoters such as the FMR1 gene and the ribosomal RNA gene clusters. Earlier, we reported some previously unknown functions of CGGBP1 in gene expression during heat shock stress response. Recently we had found CGGBP1 to be a cell cycle regulatory midbody protein required for normal cytokinetic abscission in normal human fibroblasts, which have all the cell cycle regulatory mechanisms intact. Results: In this study we explored the role of CGGBP1 in the cell cycle in various cancer cell lines. CGGBP1 depletion by RNA interference in tumor-derived cells caused an increase in the cell population at G0/G1 phase and reduced the number of cells in the S phase. CGGBP1 depletion also increased the expression of cell cycle regulatory genes CDKN1A and GAS1, associated with reductions in histone H3 lysine 9 trimethylation in their promoters. By combining RNA interference and genetic mutations, we found that the role of CGGBP1 in cell cycle involves multiple mechanisms, as single deficiencies of CDKN1A, GAS1 as well as TP53, INK4A or ARF failed to rescue the G0/G1 arrest caused by CGGBP1 depletion. Conclusions: Our results show that CGGBP1 expression is important for cell cycle progression through multiple parallel mechanisms including the regulation of CDKN1A and GAS1 levels. [ABSTRACT FROM AUTHOR]

Background: A better definition of biomarkers and biological processes related to local recurrence and disease progression is highly warranted for ductal breast carcinoma in situ (DCIS). Stromal-epithelial interactions are likely of major importance for the biological, clinical, and pathological distinctions between high- and low-risk DCIS cases.Methods: Stromal platelet derived growth factor receptor (PDGFR) was immunohistochemically assessed in two DCIS patient cohorts (n = 458 and n = 80). Cox proportional hazards models were used to calculate the hazard ratios of recurrence. The molecular mechanisms regulating stromal PDGFR expression were investigated in experimental in vitro co-culture systems of DCIS cells and fibroblasts and analyzed using immunoblot and quantitative real-time PCR. Knock-out of JAG1 in DCIS cells and NOTCH2 in fibroblasts was obtained through CRISPR/Cas9. Experimental data were validated by mammary fat pad injection of DCIS and DCIS-JAG1 knock-out cells (10 mice per group). All statistical tests were two-sided.Results: PDGFRα(low)/PDGFRβ(high) fibroblasts were associated with increased risk for recurrence in DCIS (univariate hazard ratio = 1.59, 95% confidence interval [CI] = 1.02 to 2.46; P = .04 Wald test; multivariable hazard ratio = 1.78, 95% CI = 1.07 to 2.97; P = .03). Tissue culture and mouse model studies indicated that this fibroblast phenotype is induced by DCIS cells in a cell contact-dependent manner. Epithelial Jagged1 and fibroblast Notch2 were identified through loss-of-function studies as key juxtacrine signaling components driving the formation of the poor prognosis-associated fibroblast phenotype.Conclusions: A PDGFRα(low)/PDGFRβ(high) fibroblast subset was identified as a marker for high-risk DCIS. The Jagged-1/Notch2/PDGFR stroma-epithelial pathway was described as a novel signaling mechanism regulating this poor prognosis-associated fibroblast subset. In general terms, the study highlights epithelial-stromal crosstalk in DCIS and contributes to ongoing efforts to define clinically relevant fibroblast subsets and their etiology. [ABSTRACT FROM AUTHOR]

Background: Pericytes are members of the tumor stroma; however, little is known about their origin, function, or interaction with other tumor components. Emerging evidence suggest that pericytes may regulate leukocyte transmigration. Myeloid-derived suppressor cells (MDSC) are immature myeloid cells with powerful inhibitory effects on T-cell-mediated antitumor reactivity.Methods: We generated subcutaneous tumors in a genetic mouse model of pericyte deficiency (the pdgfb (ret/ret) mouse) and littermate control mice (n = 6-25). Gene expression profiles from 253 breast cancer patients (stage I-III) were evaluated for clinic-pathological parameters and survival using Cox proportional hazard ratios (HRs) and 95% confidence intervals (CIs) based on a two-sided Wald test.Results: We report that pericyte deficiency leads to increased transmigration of Gr1(+)/CD11b(+) cells in experimentally induced tumors. Pericyte deficiency produced defective tumor vasculature, resulting in a more hypoxic microenvironment promoting IL-6 upregulation in the malignant cells. Silencing IL-6 expression in tumor cells attenuated the observed differences in MDSC transmigration. Restoring the pericyte coverage in tumors abrogated the increased MDSC trafficking to pericyte-deficient tumors. MDSC accumulation in tumors led to increases in tumor growth and in circulating malignant cells. Finally, gene expression analysis from human breast cancer patients revealed increased expression of the human MDSC markers CD33 and S100A9 with concomitant decreased expression of pericyte genes and was associated with poor prognosis (HR = 1.88, 95% CI = 1.08 to 3.25, P = .03).Conclusions: Our data uncovers a novel paracrine interaction between tumor pericytes and inflammatory cells and delineates the cellular events resulting in the recruitment of MDSC to tumors. Furthermore, we propose for the first time a role for tumor pericytes in modulating the expression of immune mediators in malignant cells by promoting a hypoxic microenvironment. [ABSTRACT FROM AUTHOR]

Exploration of new strategies for the prevention of breast cancer metastasis is justifiably at the center of clinical attention. In this study, we combined a computational biology approach with mechanism-based preclinical trials to identify inhibitors of activin-like receptor kinase (ALK) 1 as effective agents for blocking angiogenesis and metastasis in breast cancer. Pharmacologic targeting of ALK1 provided long-term therapeutic benefit in mouse models of mammary carcinoma, accompanied by strikingly reduced metastatic colonization as a monotherapy or part of combinations with chemotherapy. Gene-expression analysis of breast cancer specimens from a population-based nested case-control study encompassing 768 subjects defined endothelial expression of ALK1 as an independent and highly specific prognostic factor for metastatic manifestation, a finding that was corroborated in an independent clinical cohort. Overall, our results suggest that pharmacologic inhibition of endothelial ALK1 constitutes a tractable strategy for interfering with metastatic dissemination of breast cancer. [ABSTRACT FROM AUTHOR]

Summary: Angiogenesis, the process by which new blood vessels arise from preexisting ones, is critical for embryonic development and is an integral part of many disease processes. Recent studies have provided detailed information on how angiogenic sprouts initiate, elongate, and branch, but less is known about how these processes cease. Here, we show that S1PR1, a receptor for the blood-borne bioactive lipid sphingosine-1-phosphate (S1P), is critical for inhibition of angiogenesis and acquisition of vascular stability. Loss of S1PR1 leads to increased endothelial cell sprouting and the formation of ectopic vessel branches. Conversely, S1PR1 signaling inhibits angiogenic sprouting and enhances cell-to-cell adhesion. This correlates with inhibition of vascular endothelial growth factor-A (VEGF-A)-induced signaling and stabilization of vascular endothelial (VE)-cadherin localization at endothelial junctions. Our data suggest that S1PR1 signaling acts as a vascular-intrinsic stabilization mechanism, protecting developing blood vessels against aberrant angiogenic responses. [Copyright &y& Elsevier]

Background: MicroRNAs (miRNAs) and their role during tumor development have been studied in great detail during the last decade, albeit their expression pattern and regulation during normal development are however not so well established. Previous studies have shown that miRNAs are differentially expressed in solid human tumors. Platelet-derived growth factor (PDGF) signaling is known to be involved in normal development of the brain as well as in malignant primary brain tumors, gliomas, but the complete mechanism is still lacking. We decided to investigate the expression of the oncogenic miR-21 during normal mouse development and glioma, focusing on PDGF signaling as a potential regulator of miR-21. Methods: We generated mouse glioma using the RCAS/tv-a system for driving PDGF-BB expression in a cellspecific manner. Expression of miR-21 in mouse cell cultures and mouse brain were assessed using Northern blot analysis and in situ hybridization. Immunohistochemistry and Western blot analysis were used to investigate SOX2 expression. LNA-modified siRNA was used for irreversible depletion of miR-21. For inhibition of PDGF signaling Gleevec (imatinib mesylate), Rapamycin and U0126, as well as siRNA were used. Statistical significance was calculated using double-sided unpaired Student´s t-test. Results: We identified miR-21 to be highly expressed during embryonic and newborn brain development followed by a gradual decrease until undetectable at postnatal day 7 (P7), this pattern correlated with SOX2 expression. Furthermore, miR-21 and SOX2 showed up-regulation and overlapping expression pattern in RCAS/tv-a generated mouse brain tumor specimens. Upon irreversible depletion of miR-21 the expression of SOX2 was strongly diminished in both mouse primary glioma cultures and human glioma cell lines. Interestingly, in normal fibroblasts the expression of miR-21 was induced by PDGF-BB, and inhibition of PDGF signaling in mouse glioma primary cultures resulted in suppression of miR-21 suggesting that miR-21 is indeed regulated by PDGF signaling. Conclusions: Our data show that miR-21 and SOX2 are tightly regulated already during embryogenesis and define a distinct population with putative tumor cell of origin characteristics. Furthermore, we believe that miR-21 is a mediator of PDGF-driven brain tumors, which suggests miR-21 as a promising target for treatment of glioma. [ABSTRACT FROM AUTHOR]

Mechanism(s) for generation of the high tumor interstitial fluid pressure (TIFP) that is characteristic of carcinoma is not known. We investigated the role of hyaluronan, the major water-binding polysaccharide of the extracellular matrix, for the generation of a high TIFP. A human anaplastic thyroid carcinoma (KAT-4) xenografted to athymic mice and a syngeneic rat colon carcinoma (PROb) were used. Neither KAT-4 nor PROb cells produced hyaluronan (HA) in culture, however, both cell lines produced factors that stimulated HA-synthesis by cultured fibroblasts. Modulating hyaluronan levels by transfection of PROb carcinoma cells with hyaluronan synthase-2 revealed no correlation between hyaluronan content and TIFP. Furthermore, lowering of TIFP by treating KAT-4 tumors with a specific inhibitor of TGF-β1 and -β3 did not change the concentration of hyaluronan in the tumors. In summary, our results suggest that a modulation of hyaluronan content is not a major pathogenetic mechanism for the generation of the characteristically high TIFP in malignant carcinomas. [Copyright &y& Elsevier]