Sudarshan Anand

MicroRNA-132–mediated loss of p120RasGAP activates the endothelium to facilitate pathological angiogenesis

Although it is well established that tumors initiate an angiogenic switch, the molecular basis of this process remains incompletely understood. Here we show that the miRNA miR-132 acts as an angiogenic switch by targeting p120RasGAP in the endothelium and thereby inducing neovascularization. We identified miR-132 as a highly upregulated miRNA in a human embryonic stem cell model of vasculogenesis and found that miR-132 was highly expressed in the endothelium of human tumors and hemangiomas but was undetectable in normal endothelium. Ectopic expression of miR-132 in endothelial cells in vitro increased their proliferation and tube-forming capacity, whereas intraocular injection of an antagomir targeting miR-132, anti–miR-132, reduced postnatal retinal vascular development in mice. Among the top-ranking predicted targets of miR-132 was p120RasGAP, which we found to be expressed in normal but not tumor endothelium. Endothelial expression of miR-132 suppressed p120RasGAP expression and increased Ras activity, whereas a miRNA-resistant version of p120RasGAP reversed the vascular response induced by miR-132. Notably, administration of anti–miR-132 inhibited angiogenesis in wild-type mice but not in mice with an inducible deletion of Rasa1 (encoding p120RasGAP). Finally, vessel-targeted nanoparticle delivery of anti–miR-132 restored p120RasGAP expression in the tumor endothelium, suppressed angiogenesis and decreased tumor burden in an orthotopic xenograft mouse model of human breast carcinoma. We conclude that miR-132 acts as an angiogenic switch by suppressing endothelial p120RasGAP expression, leading to Ras activation and the induction of neovascularization, whereas the application of anti–miR-132 inhibits neovascularization by maintaining vessels in the resting state.

B7-H1/CD80 interaction is required for the induction and maintenance of peripheral T-cell tolerance.

T-cell tolerance is the central program that prevents harmful immune responses against self-antigens, in which inhibitory PD-1 signal given by B7-H1 interaction plays an important role. Recent studies demonstrated that B7-H1 binds CD80 besides PD-1, and B7-H1/CD80 interaction also delivers inhibitory signals in T cells. However, a role of B7-H1/CD80 signals in regulation of T-cell tolerance has yet to be explored. We report here that attenuation of B7-H1/CD80 signals by treatment with anti-B7-H1 monoclonal antibody, which specifically blocks B7-H1/CD80 but not B7-H1/PD-1, enhanced T-cell expansion and prevented T-cell anergy induction. In addition, B7-H1/CD80 blockade restored Ag responsiveness in the previously anergized T cells. Experiments using B7-H1 or CD80-deficient T cells indicated that an inhibitory signal through CD80, but not B7-H1, on T cells is responsible in part for these effects. Consistently, CD80 expression was detected on anergic T cells and further up-regulated when they were re-exposed to the antigen (Ag). Finally, blockade of B7-H1/CD80 interaction prevented oral tolerance induction and restored T-cell responsiveness to Ag previously tolerized by oral administration. Taken together, our findings demonstrate that the B7-H1/CD80 pathway is a crucial regulator in the induction and maintenance of T-cell tolerance.

An integrin β 3 –KRAS–RalB complex drives tumour stemness and resistance to EGFR inhibition

Tumour cells, with stem-like properties, are highly aggressive and often show drug resistance. Here, we reveal that integrin αvβ3 serves as a marker of breast, lung and pancreatic carcinomas with stem-like properties that are highly resistant to receptor tyrosine kinase inhibitors such as erlotinib. This was observed in vitro and in mice bearing patient-derived tumour xenografts or in clinical specimens from lung cancer patients who had progressed on erlotinib. Mechanistically, αvβ3, in the unliganded state, recruits KRAS and RalB to the tumour cell plasma membrane, leading to the activation of TBK1 and NF-κB. In fact, αvβ3 expression and the resulting KRAS–RalB–NF-κB pathway were both necessary and sufficient for tumour initiation, anchorage independence, self-renewal and erlotinib resistance. Pharmacological targeting of this pathway with bortezomib reversed both tumour stemness and erlotinib resistance. These findings not only identify αvβ3 as a marker/driver of carcinoma stemness but also reveal a therapeutic strategy to sensitize such tumours to RTK inhibition.

Essential role of TNF family molecule LIGHT as a cytokine in the pathogenesis of hepatitis

LIGHT is an important costimulatory molecule for T cell immunity. Recent studies have further implicated its role in innate immunity and inflammatory diseases, but its cellular and molecular mechanisms remain elusive. We report here that LIGHT is upregulated and functions as a proinflammatory cytokine in 2 independent experimental hepatitis models, induced by concanavalin A and Listeria monocytogenes. Molecular mutagenesis studies suggest that soluble LIGHT protein produced by cleavage from the cell membrane plays an important role in this effect through the interaction with the lymphotoxin-beta receptor (LTbetaR) but not herpes virus entry mediator. NK1.1+ T cells contribute to the production, but not the cleavage or effector functions, of soluble LIGHT. Importantly, treatment with a mAb that specifically interferes with the LIGHT-LTbetaR interaction protects mice from lethal hepatitis. Our studies thus identify a what we believe to be a novel function of soluble LIGHT in vivo and offer a potential target for therapeutic interventions in hepatic inflammatory diseases.

B7-H4 deficient mice display augmented neutrophil-mediated innate immunity

B7-H4 is an immunoglobulin superfamily molecule and shown to be inhibitory for T-cell responses. To explore physiologic roles of B7-H4, we created B7-H4-deficient (KO) mice by genetic targeting. B7-H4KO mice are healthy and their T- and B-cell responses to polyclonal antigens are in normal range. However, B7-H4KO mice are more resistant to infection by Listeria monocytogenes than their littermates. Within 3 days after infection, bacterial colonies in livers and spleens are significantly lower than the controls, suggesting a role of B7-H4 in enhancing innate immunity. Further studies demonstrate that neutrophils increase in peripheral organs of B7-H4KO mice more so than their littermates but their bactericidal functions remain unchanged. Augmented innate resistance is completely dependent on neutrophils, even in the absence of adaptive immunity. In vitro B7-H4 inhibits the growth of bone marrow-derived neutrophil progenitors, suggesting an inhibitory function of B7-H4 in neutrophil expansion. Our results identify B7-H4 as a negative regulator of the neutrophil response to infection and provide a new target for manipulation of innate immunity.

MicroRNA-mediated regulation of the angiogenic switch

Purpose of reviewIt has been known for decades that in order to grow, tumors need to activate quiescent endothelial cells to form a functional vascular network, a process termed ‘angiogenesis’. However, the molecular determinants that reverse this endothelial quiescence to facilitate pathological angiogenesis are not yet completely understood. This review examines a critical regulatory switch at the level of Ras that activates this angiogenic switch process and the role that microRNAs play in this process. Recent findingsIn the last few years, microRNAs, a new class of small RNA molecules, have emerged as key regulators of several cellular processes, including angiogenesis. MicroRNAs such as miR-126, miR-296, and miR-92a have been shown to play important roles in angiogenesis. We recently described how miR-132, an angiogenic growth factor inducible microRNA in the endothelium, facilitates pathological angiogenesis by downregulating p120RasGAP, a molecular brake for Ras. Importantly, targeting miR-132 with a complementary, synthetic antimicroRNA restored the brake and decreased angiogenesis and tumor burden in multiple tumor models. Taken together, emerging evidence suggests a central role for microRNAs downstream of multiple growth factors in regulating endothelial proliferation, migration, and vascular patterning. SummaryFurther research into miR-132–p120RasGAP biology and more broadly, microRNA regulation of Ras pathways in the endothelium will not only advance our understanding of angiogenesis but also provide opportunities for therapeutic intervention.

Disruption of angiogenesis and tumor growth with an orally active drug that stabilizes the inactive state of PDGFRβ/B-RAF

Kinases are known to regulate fundamental processes in cancer including tumor proliferation, metastasis, neovascularization, and chemoresistance. Accordingly, kinase inhibitors have been a major focus of drug development, and several kinase inhibitors are now approved for various cancer indications. Typically, kinase inhibitors are selected via high-throughput screening using catalytic kinase domains at low ATP concentration, and this process often yields ATP mimetics that lack specificity and/or function poorly in cells where ATP levels are high. Molecules targeting the allosteric site in the inactive kinase conformation (type II inhibitors) provide an alternative for developing selective inhibitors that are physiologically active. By applying a rational design approach using a constrained amino-triazole scaffold predicted to stabilize kinases in the inactive state, we generated a series of selective type II inhibitors of PDGFRβ and B-RAF, important targets for pericyte recruitment and endothelial cell survival, respectively. These molecules were designed in silico and screened for antivascular activity in both cell-based models and a Tg(fli1-EGFP) zebrafish embryogenesis model. Dual inhibition of PDGFRβ and B-RAF cellular signaling demonstrated synergistic antiangiogenic activity in both zebrafish and murine models of angiogenesis, and a combination of previously characterized PDGFRβ and RAF inhibitors validated the synergy. Our lead compound was selected as an orally active molecule with favorable pharmacokinetic properties which demonstrated target inhibition in vivo leading to suppression of murine orthotopic tumors in both the kidney and pancreas.

A MEK-independent role for CRAF in mitosis and tumor progression.

RAF kinases regulate cell proliferation and survival and can be dysregulated in tumors. The role of RAF in cell proliferation has been linked to its ability to activate mitogen-activated protein kinase kinase 1 (MEK) and mitogen-activated protein kinase 1 (ERK). Here we identify a MEK-independent role for RAF in tumor growth. Specifically, in mitotic cells, CRAF becomes phosphorylated on Ser338 and localizes to the mitotic spindle of proliferating tumor cells in vitro as well as in murine tumor models and in biopsies from individuals with cancer. Treatment of tumors with allosteric inhibitors, but not ATP-competitive RAF inhibitors, prevents CRAF phosphorylation on Ser338 and localization to the mitotic spindle and causes cell-cycle arrest at prometaphase. Furthermore, we identify phospho-Ser338 CRAF as a potential biomarker for tumor progression and a surrogate marker for allosteric RAF blockade. Mechanistically, CRAF, but not BRAF, associates with Aurora kinase A (Aurora-A) and Polo-like kinase 1 (Plk1) at the centrosomes and spindle poles during G2/M. Indeed, allosteric or genetic inhibition of phospho-Ser338 CRAF impairs Plk1 activation and accumulation at the kinetochores, causing prometaphase arrest, whereas a phospho-mimetic Ser338D CRAF mutant potentiates Plk1 activation, mitosis and tumor progression in mice. These findings show a previously undefined role for RAF in tumor progression beyond the RAF-MEK-ERK paradigm, opening new avenues for targeting RAF in cancer.

Ras pathway inhibition prevents neovascularization by repressing endothelial cell sprouting

Vascular networks develop from a growing vascular front that responds to VEGF and other guidance cues. Angiogenesis is required for normal tissue function, but, under conditions of stress, inappropriate vascularization can lead to disease. Therefore, inhibition of angiogenic sprouting may prevent neovascularization in patients with blinding neovascular eye diseases, including macular degeneration. VEGF antagonists have therapeutic benefits but also can elicit off-target effects. Here, we found that the Ras pathway, which functions downstream of a wide range of cytokines including VEGF, is active in the growing vascular front of developing and pathological vascular networks. The endogenous Ras inhibitor p120RasGAP was expressed predominately in quiescent VEGF-insensitive endothelial cells and was ectopically downregulated in multiple neovascular models. MicroRNA-132 negatively regulated p120RasGAP expression. Experimental delivery of α-miR-132 to developing mouse eyes disrupted tip cell Ras activity and prevented angiogenic sprouting. This strategy prevented ocular neovascularization in multiple rodent models even more potently than the VEGF antagonist, VEGF-trap. Targeting microRNA-132 as a therapeutic strategy may prove useful for treating multiple neovascular diseases of the eye and for preventing vision loss regardless of the neovascular stimulus.

A brief primer on microRNAs and their roles in angiogenesis

Development of the vasculature is a complex, dynamic process orchestrated by a balance of pro and anti-angiogenic signaling pathways. The same signaling pathways are mis-regulated and exploited during pathological angiogenesis in cancer, inflammation and cardiovascular diseases and contribute to disease progression. In the last decade, small non-coding RNA molecules termed microRNAs (miRs) have emerged as key regulators of several cellular processes including angiogenesis. It is becoming clear that miRs function in complex networks and regulate gene expression both at the mRNA and protein levels thereby altering cellular signaling responses to specific stimuli. In the vasculature, miRs can function either in a pro-angiogenic manner and potentiate angiogenesis or act as anti-angiogenic miRs by enhancing cell death and decreasing endothelial proliferation. This review aims to provide an update on how microRNAs regulate gene expression and illustrate miR function in the vasculature with a discussion of potential applications of miRs as anti-angiogenic therapeutics.