Mirela Anghelina

The antitumor effects of IFN-α are abrogated in a STAT1-deficient mouse

IFN-alpha activates the signal transducer and activator of transcription (STAT) family of proteins; however, it is unknown whether IFN-alpha exerts its antitumor actions primarily through a direct effect on malignant cells or by stimulating the immune system. To investigate the contribution of STAT1 signaling within the tumor, we generated a STAT1-deficient melanoma cell line, AGS-1. We reconstituted STAT1 into AGS-1 cells by retroviral gene transfer. The resulting cell line (AGS-1STAT1) showed normal regulation of IFN-alpha-stimulated genes (e.g., H2k, ISG-54) as compared with AGS-1 cells infected with the empty vector (AGS-1MSCV). However, mice challenged with the AGS-1, AGS-1STAT1, and AGS-1MSCV cell lines exhibited nearly identical survival in response to IFN-alpha treatment, indicating that restored STAT1 signaling within the tumor did not augment the antitumor activity of IFN-alpha. In contrast, STAT1-/- mice could not utilize exogenous IFN-alpha to inhibit the growth of STAT1+/+ melanoma cells in either an intraperitoneal tumor model or in the adjuvant setting. The survival of tumor-bearing STAT1-/- mice was identical regardless of treatment (IFN-alpha or PBS). Additional cell depletion studies demonstrated that NK cells mediated the antitumor effects of IFN-alpha. Thus, STAT1-mediated gene regulation within immune effectors was necessary for mediating the antitumor effects of IFN-alpha in this experimental system.

Biomechanical Signals Suppress TAK1 Activation to Inhibit NF-κB Transcriptional Activation in Fibrochondrocytes

Exercise/joint mobilization is therapeutic for inflammatory joint diseases like rheumatoid and osteoarthritis, but the mechanisms underlying its actions remain poorly understood. We report that biomechanical signals at low/physiological magnitudes are potent inhibitors of inflammation induced by diverse proinflammatory activators like IL-1β, TNF-α, and lipopolysaccharides, in fibrochondrocytes. These signals exert their anti-inflammatory effects by inhibiting phosphorylation of TAK1, a critical point where signals generated by IL-1β, TNF-α, and LPS converge to initiate NF-κB signaling cascade and proinflammatory gene induction. Additionally, biomechanical signals inhibit multiple steps in the IL-1β-induced proinflammatory cascade downstream of IκB kinase activation to regulate IκBα and IκBβ degradation and synthesis, and promote IκBα shuttling to export nuclear NF-κB and terminate its transcriptional activity. The findings demonstrate that biomechanical forces are but another important signal that uses NF-κB pathway to regulate inflammation by switching the molecular activation of discrete molecules involved in proinflammatory gene transcription.

The dual epigenetic role of PRMT5 in acute myeloid leukemia: gene activation and repression via histone arginine methylation.

Changes in the enzymatic activity of protein arginine methyltransferase (PRMT) 5 have been associated with cancer; however, the protein’s role in acute myeloid leukemia (AML) has not been fully evaluated. Here, we show that increased PRMT5 activity enhanced AML growth in vitro and in vivo while PRMT5 downregulation reduced it. In AML cells, PRMT5 interacted with Sp1 in a transcription repressor complex and silenced miR-29b preferentially via dimethylation of histone 4 arginine residue H4R3. As Sp1 is also a bona fide target of miR-29b, the miR silencing resulted in increased Sp1. This event in turn led to transcription activation of FLT3, a gene that encodes a receptor tyrosine kinase. Inhibition of PRMT5 via sh/siRNA or a first-in-class small-molecule inhibitor (HLCL-61) resulted in significantly increased expression of miR-29b and consequent suppression of Sp1 and FLT3 in AML cells. As a result, significant antileukemic activity was achieved. Collectively, our data support a novel leukemogenic mechanism in AML where PRMT5 mediates both silencing and transcription of genes that participate in a ‘yin-yang’ functional network supporting leukemia growth. As FLT3 is often mutated in AML and pharmacologic inhibition of PRMT5 appears feasible, the PRMT5–miR-29b–FLT3 network should be further explored as a novel therapeutic target for AML.

Preferential activity of Tie2 promoter in arteriolar endothelium

The tyrosine kinase Tie2/Tek (the receptor for angiopoietins) is considered one of the most reliable markers of the endothelial phenotype, across organisms, organs, and developmental stages. However, endothelium is intrinsically heterogeneous in origin, composition and function, presenting an arteriolar/venular asymmetry. In this regard, the expression of Tie2 along the vascular tree, although thought to be homogenous, has not been systematically investigated. Therefore we questioned whether the activity of Tie2 promoter is uniform in the microvascular endothelium. To this end, we analyzed in situ the expression of the markers β‐galactosidase [LacZ(Tie2)] and green fluorescent protein (GFP) [GFP(Tie2)], placed under the Tie2 promoter in transgenic mice, in whole mount tissue samples, which allow the simultaneous evaluation of its relative distribution in various microvascular compartments. In the mesenteries of LacZ(Tie2) and GFP(Tie2) mice, we found that the activity of Tie2 promoter is asymmetrically distributed, being much stronger in arteries and arterioles than on the venular side of the vascular tree. This observation was replicated in the diaphragm of LacZ(Tie2) mice. The capillaries presented a mosaic pattern of Tie2 promoter activity. Stimulation of angiogenesis either by wounding, or by intraperitoneal injection of Vascular Endothelial Growth Factor (VEGF), revealed that the arteriolar/venular asymmetry is established at endothelial cellular level early during new capillary formation, even before the starting of the microvasular blood flow. In conclusion, a strong Tie2 promoter activity qualifies as a novel marker of the arteriolar phenotype in microvascular endothelium.

Pharmacological targeting of miR-155 via the NEDD8-activating enzyme inhibitor MLN4924 (Pevonedistat) in FLT3-ITD acute myeloid leukemia

High levels of microRNA-155 (miR-155) are associated with poor outcome in acute myeloid leukemia (AML). In AML, miR-155 is regulated by NF-κB, the activity of which is, in part, controlled by the NEDD8-dependent ubiquitin ligases. We demonstrate that MLN4924, an inhibitor of NEDD8-activating enzyme presently being evaluated in clinical trials, decreases binding of NF-κB to the miR-155 promoter and downregulates miR-155 in AML cells. This results in the upregulation of the miR-155 targets SHIP1, an inhibitor of the PI3K/Akt pathway, and PU.1, a transcription factor important for myeloid differentiation, leading to monocytic differentiation and apoptosis. Consistent with these results, overexpression of miR-155 diminishes MLN4924-induced antileukemic effects. In vivo, MLN4924 reduces miR-155 expression and prolongs the survival of mice engrafted with leukemic cells. Our study demonstrates the potential of miR-155 as a novel therapeutic target in AML via pharmacologic interference with NF-κB-dependent regulatory mechanisms. We show the targeting of this oncogenic microRNA with MLN4924, a compound presently being evaluated in clinical trials in AML. As high miR-155 levels have been consistently associated with aggressive clinical phenotypes, our work opens new avenues for microRNA-targeting therapeutic approaches to leukemia and cancer patients.

SPARC promotes leukemic cell growth and predicts acute myeloid leukemia outcome

Aberrant expression of the secreted protein, acidic, cysteine-rich (osteonectin) (SPARC) gene, which encodes a matricellular protein that participates in normal tissue remodeling, is associated with a variety of diseases including cancer, but the contribution of SPARC to malignant growth remains controversial. We previously reported that SPARC was among the most upregulated genes in cytogenetically normal acute myeloid leukemia (CN-AML) patients with gene-expression profiles predictive of unfavorable outcome, such as mutations in isocitrate dehydrogenase 2 (IDH2-R172) and overexpression of the oncogenes brain and acute leukemia, cytoplasmic (BAALC) and v-ets erythroblastosis virus E26 oncogene homolog (ERG). In contrast, SPARC was downregulated in CN-AML patients harboring mutations in nucleophosmin (NPM1) that are associated with favorable prognosis. Based on these observations, we hypothesized that SPARC expression is clinically relevant in AML. Here, we found that SPARC overexpression is associated with adverse outcome in CN-AML patients and promotes aggressive leukemia growth in murine models of AML. In leukemia cells, SPARC expression was mediated by the SP1/NF-κB transactivation complex. Furthermore, secreted SPARC activated the integrin-linked kinase/AKT (ILK/AKT) pathway, likely via integrin interaction, and subsequent β-catenin signaling, which is involved in leukemia cell self-renewal. Pharmacologic inhibition of the SP1/NF-κB complex resulted in SPARC downregulation and leukemia growth inhibition. Together, our data indicate that evaluation of SPARC expression has prognosticative value and SPARC is a potential therapeutic target for AML.

A subpopulation of peritoneal macrophages form capillary‐like lumens and branching patterns in vitro

Objective: We have previously shown that monocytes/macrophages (MC/Mph) influence neovascularization by extracellular matrix degradation, and by direct incorporation into growing microvessels. To date, neither the phenotype of these cells, nor the stages of their capillary‐like conversion were sufficiently characterized. Methods: We isolated mouse peritoneal Mph from transgenic mice expressing fluorescent proteins either ubiquitously, or specifically in the myelocytic lineage. These Mph were embedded in Matrigel which contained fluorescent protease substrates, exposed to an MCP‐1 chemotactic gradient, and then examined by confocal microscopy after various intervals. Results: Within 3 hrs after gel embedding, we detected TIMP‐1 and MMP‐12 dependent proteolysis of the matrix surrounding Mph, mostly in the direction of high concentrations of MCP‐1. After 2 days, Mph developed intracellular vacuoles containing degradation product. At 5 days these vacuoles were enlarged and/or fused to generate trans‐cellular lumens in approximately 10% of cells or more (depending on animals genetic background). At this stage, Mph became tubular, and occasionally organized in three‐dimensional structures resembling branched microvessels. Conclusion: Isolated mouse peritoneal Mph penetrate Matrigel and form tunnels via a metalloprotease‐driven proteolysis and phagocytosis. Following a morphological adjustment driven by occurrence, enlargement and/or fusion process of intracellular vacuoles, similar to that described in bona fide endothelium, a subpopulation of these cells end up by lining a capillary‐like lumen in vitro. Thus we show that adult Mph, not only the more primitive ‘endothelial progenitors’, have functional properties until now considered defining of the endothelial phenotype.

Phase I Study of the Sequential Combination of Interleukin-12 and Interferon Alfa-2b in Advanced Cancer: Evidence for Modulation of Interferon Signaling Pathways by Interleukin-12

PURPOSE To evaluate the safety of sequentially administered recombinant (r) human (h) interleukin-12 (IL-12) and interferon alfa-2b (IFN-alpha-2b) in patients with advanced cancer and to determine the effects of endogenously produced IFN-gamma on Janus kinase-signal transducer and activator of transcription (Jak-STAT) signal transduction in patient peripheral-blood mononuclear cells (PBMCs). PATIENTS AND METHODS Forty-nine patients with metastatic cancer received rhIL-12 on day 1 and IFN-alpha-2b on days 2 to 6 of either a 14-day (n = 43) or a 7-day treatment cycle (n = 6). rhIL-12 was initially administered subcutaneously at a dose of 100 ng/kg, whereas IFN-alpha-2b was escalated from 1 to 10 million units (MU) in cohorts of three patients (1, 3, 5, 7, or 10 MU). rhIL-12 was subsequently administered intravenously (IV) in escalating doses (100 to 500 ng/kg) to achieve greater IFN-gamma production. Peripheral blood was drawn for measurement of plasma IFN-gamma and the induction of Jak-STAT signal transduction in PBMCs. RESULTS No IL-12-or IFN-alpha-related dose-limiting toxicities were observed. There were no responses in 41 assessable patients. Five patients exhibited stable disease lasting 6 months or longer while on therapy. Optimal induction of IFN-gamma by IL-12 occurred after an IV dose of 250 ng/kg. Patient PBMCs exhibited increased levels of STAT1 after IL-12 administration. The peak level of IFN-gamma achieved with IL-12 therapy correlated with the peak level of intracellular STAT1 in patient PBMCs (r = 0.38, P = .021). CONCLUSION The combination of rhIL-12 and IFN-alpha-2b can be administered sequentially with minimal toxicity. IV administration of rhIL-12 modulates IFN-alpha-induced Jak-STAT signal transduction in patient PBMCs.

Changes in surface topologies of chondrocytes subjected to mechanical forces: an AFM analysis

The cartilage is composed of chondrocytes embedded in a matrix of collagen fibrils interspersed within a network of proteoglycans and is constantly exposed to biomechanical forces during normal joint movement. Characterization of the surface morphology, cytoskeletal structure, adherance and elastic properties of these mechanosensitive cells are crucial in understanding the effects of mechanical forces around a cell and how a cell responds to changes in its physical environment. In this work, we employed the atomic force microscope (AFM) to image cultured chondrocytes before and after subjecting them to mechanical forces in the presence or absence of interleukin-1beta to mimic inflammatory conditions. Nanoscale imaging and quantitative measurements from AFM data revealed that there are distinct changes in cell-surface topology and cytoskeleton arrangement in the cells following treatment with mechanical forces, IL-1beta or both. Our findings for the first time demonstrate that cultured chondrocytes are amenable to high-resolution AFM imaging and dynamic tensile forces may help overcome the effect of inflammatory factors on chondrocyte response.

Regulation of biomechanical signals by NF-κB transcription factors in chondrocytes

Physical therapies and exercise are beneficial not only for physiological recovery in inflamed or injured joints, but also for promoting a homeostatic equilibrium in healthy joints. Human joints provide the pivot points and physiological hinges essential for ambulation and movement to the body, and it is this mobility that in return promotes the health of the joints. But how mobilization regulates the joint microenvironment at the molecular level has remained enigmatic for many years. Recent advances in joint biomechanics and molecular approaches have facilitated an enriched understanding of how joints operate. Consequently, the mechanisms active during joint inflammation that lead to arthritic conditions, both in vivo in animal models, and in vitro at cell and tissue levels, have become increasingly detailed and defined. These efforts have produced mounting evidences supporting the premise that biomechanical signals play a fundamental role in both the etiopathogenesis of arthritic diseases and in the physiological restoration of joints. This report aims to summarize current peer-reviewed literature and available experimental data to explain how the signals generated by mechanical forces/joint mobilization generate beneficial effects on inflamed articular cartilage, and to propose the basis for using appropriate physical therapies for the optimal benefit to the patient suffering from joint associated injuries.