Shunsuke Kitajima

RECK modulates Notch signaling during cortical neurogenesis by regulating ADAM10 activity

We report that during cortical development in the mouse embryo, reversion-inducing cysteine-rich protein with Kazal motifs (RECK) critically regulates Notch signaling by antagonizing the ectodomain shedding of Notch ligands, which is mediated by a disintegrin and metalloproteinase domain 10 (ADAM10). In the embryonic brain, RECK is specifically expressed in Nestin-positive neural precursor cells (NPCs). Reck-deficient NPCs undergo precocious differentiation that is associated with downregulated Nestin expression, impaired Notch signaling and defective self-renewal. These phenotypes were substantially rescued either by enhancing Notch signaling or by suppressing endogenous ADAM10 activity. Consequently, we found that RECK regulates the ectodomain shedding of Notch ligands by directly inhibiting the proteolytic activity of ADAM10. This mechanism appeared to be essential for Notch ligands to properly induce Notch signaling in neighboring cells. These findings indicate that RECK is a physiological inhibitor of ADAM10, an upstream regulator of Notch signaling and a critical modulator of brain development.

Rb Regulates DNA Damage Response and Cellular Senescence through E2F-Dependent Suppression of N-Ras Isoprenylation

Oncogene-induced cellular senescence is well documented, but little is known about how infinite cell proliferation induced by loss of tumor suppressor genes is antagonized by cellular functions. Rb heterozygous mice generate Rb-deficient C cell adenomas that progress to adenocarcinomas following biallelic loss of N-ras. Here, we demonstrate that pRb inactivation induces aberrant expression of farnesyl diphosphate synthase, many prenyltransferases, and their upstream regulators sterol regulatory element-binding proteins (SREBPs) in an E2F-dependent manner, leading to enhanced isoprenylation and activation of N-Ras. Consequently, elevated N-Ras activity induces DNA damage response and p130-dependent cellular senescence in Rb-deficient cells. Furthermore, Rb heterozygous mice additionally lacking any of Ink4a, Arf, or Suv39h1 generated C cell adenocarcinomas, suggesting that cellular senescence antagonizes Rb-deficient carcinogenesis.

STK11/LKB1 Deficiency Promotes Neutrophil Recruitment and Proinflammatory Cytokine Production to Suppress T-cell Activity in the Lung Tumor Microenvironment

STK11/LKB1 is among the most commonly inactivated tumor suppressors in non-small cell lung cancer (NSCLC), especially in tumors harboring KRAS mutations. Many oncogenes promote immune escape, undermining the effectiveness of immunotherapies, but it is unclear whether the inactivation of tumor suppressor genes, such as STK11/LKB1, exerts similar effects. In this study, we investigated the consequences of STK11/LKB1 loss on the immune microenvironment in a mouse model of KRAS-driven NSCLC. Genetic ablation of STK11/LKB1 resulted in accumulation of neutrophils with T-cell-suppressive effects, along with a corresponding increase in the expression of T-cell exhaustion markers and tumor-promoting cytokines. The number of tumor-infiltrating lymphocytes was also reduced in LKB1-deficient mouse and human tumors. Furthermore, STK11/LKB1-inactivating mutations were associated with reduced expression of PD-1 ligand PD-L1 in mouse and patient tumors as well as in tumor-derived cell lines. Consistent with these results, PD-1-targeting antibodies were ineffective against Lkb1-deficient tumors. In contrast, treating Lkb1-deficient mice with an IL6-neutralizing antibody or a neutrophil-depleting antibody yielded therapeutic benefits associated with reduced neutrophil accumulation and proinflammatory cytokine expression. Our findings illustrate how tumor suppressor mutations can modulate the immune milieu of the tumor microenvironment, and they offer specific implications for addressing STK11/LKB1-mutated tumors with PD-1-targeting antibody therapies.

ATM mediates pRB function to control DNMT1 protein stability and DNA methylation.

ABSTRACT The retinoblastoma tumor suppressor gene (RB) product has been implicated in epigenetic control of gene expression owing to its ability to physically bind to many chromatin modifiers. However, the biological and clinical significance of this activity was not well elucidated. To address this, we performed genetic and epigenetic analyses in an Rb-deficient mouse thyroid C cell tumor model. Here we report that the genetic interaction of Rb and ATM regulates DNMT1 protein stability and hence controls the DNA methylation status in the promoters of at least the Ink4a, Shc2, FoxO6, and Noggin genes. Furthermore, we demonstrate that inactivation of pRB promotes Tip60 (acetyltransferase)-dependent ATM activation; allows activated ATM to physically bind to DNMT1, forming a complex with Tip60 and UHRF1 (E3 ligase); and consequently accelerates DNMT1 ubiquitination driven by Tip60-dependent acetylation. Our results indicate that inactivation of the pRB pathway in coordination with aberration in the DNA damage response deregulates DNMT1 stability, leading to an abnormal DNA methylation pattern and malignant progression.

The β1-Integrin-Dependent Function of RECK in Physiologic and Tumor Angiogenesis

Vascular endothelial cells produce considerable amounts of matrix metalloproteinases (MMP), including MMP-2, MMP-9, and membrane type 1 (MT1)–MMP. However, little is known about the regulatory mechanisms of these protease activities exhibited during vascular development. A glycosylphosphatidylinositol-anchored glycoprotein, reversion-inducing cysteine-rich protein with Kazal motifs (RECK), has been shown to attenuate MMP-2 maturation by directly interacting with MT1-MMP. Here, we show that an angiogenic factor angiopoietin-1 induces RECK expression in human umbilical vein endothelial cells (HUVEC), and RECK depletion in these cells results in defective vascular tube formation and cellular senescence. We further observed that RECK depletion downregulates β1-integrin activation, which was associated with decreased autophosphorylation of focal adhesion kinase and increased expression of a cyclin-dependent kinase inhibitor p21CIP1. In agreement, significant downregulation of β1-integrin activity was observed in vascular endothelial cells in Reck−/− mouse embryos. In HUVECs, specific inhibition of MMP-2 significantly antagonized the effect of RECK depletion on β1-integrin signaling, cell proliferation, and tube elongation. Furthermore, we observed that hypervascular tumor-derived cell lines can induce high RECK expression in convoluted vascular endothelial cells, and this in turn supports tumor growth. Targeting RECK specifically in tumor-associated vascular endothelial cells resulted in tumor regression. Therefore, we propose that RECK in tumor vascular endothelial cells can be an interesting target of cancer treatment via abortion of tumor angiogenesis. Mol Cancer Res; 8(5); 665–76. ©2010 AACR.

Ex Vivo Profiling of PD-1 Blockade Using Organotypic Tumor Spheroids

Ex vivo systems that incorporate features of the tumor microenvironment and model the dynamic response to immune checkpoint blockade (ICB) may facilitate efforts in precision immuno-oncology and the development of effective combination therapies. Here, we demonstrate the ability to interrogate ex vivo response to ICB using murine- and patient-derived organotypic tumor spheroids (MDOTS/PDOTS). MDOTS/PDOTS isolated from mouse and human tumors retain autologous lymphoid and myeloid cell populations and respond to ICB in short-term three-dimensional microfluidic culture. Response and resistance to ICB was recapitulated using MDOTS derived from established immunocompetent mouse tumor models. MDOTS profiling demonstrated that TBK1/IKKε inhibition enhanced response to PD-1 blockade, which effectively predicted tumor response in vivo Systematic profiling of secreted cytokines in PDOTS captured key features associated with response and resistance to PD-1 blockade. Thus, MDOTS/PDOTS profiling represents a novel platform to evaluate ICB using established murine models as well as clinically relevant patient specimens.Significance: Resistance to PD-1 blockade remains a challenge for many patients, and biomarkers to guide treatment are lacking. Here, we demonstrate feasibility of ex vivo profiling of PD-1 blockade to interrogate the tumor immune microenvironment, develop therapeutic combinations, and facilitate precision immuno-oncology efforts. Cancer Discov; 8(2); 196-215. ©2017 AACR.See related commentary by Balko and Sosman, p. 143See related article by Deng et al., p. 216This article is highlighted in the In This Issue feature, p. 127.

Autophagy Inhibition Dysregulates TBK1 Signaling and Promotes Pancreatic Inflammation

Autophagy inhibition has been proposed for treatment of KRAS-driven cancer, but this strategy resulted in a protumorigenic feedback loop that activated TBK1 and induced PD-L1 expression. Therapeutic approaches that counteract this feedback may be necessary to limit pancreatic dysplasia. Autophagy promotes tumor progression downstream of oncogenic KRAS, yet also restrains inflammation and dysplasia through mechanisms that remain incompletely characterized. Understanding the basis of this paradox has important implications for the optimal targeting of autophagy in cancer. Using a mouse model of cerulein-induced pancreatitis, we found that loss of autophagy by deletion of Atg5 enhanced activation of the IκB kinase (IKK)-related kinase TBK1 in vivo, associated with increased neutrophil and T-cell infiltration and PD-L1 upregulation. Consistent with this observation, pharmacologic or genetic inhibition of autophagy in pancreatic ductal adenocarcinoma cells, including suppression of the autophagy receptors NDP52 or p62, prolonged TBK1 activation and increased expression of CCL5, IL6, and several other T-cell and neutrophil chemotactic cytokines in vitro. Defective autophagy also promoted PD-L1 upregulation, which is particularly pronounced downstream of IFNγ signaling and involves JAK pathway activation. Treatment with the TBK1/IKKϵ/JAK inhibitor CYT387 (also known as momelotinib) not only inhibits autophagy, but also suppresses this feedback inflammation and reduces PD-L1 expression, limiting KRAS-driven pancreatic dysplasia. These findings could contribute to the dual role of autophagy in oncogenesis and have important consequences for its therapeutic targeting. Cancer Immunol Res; 4(6); 520–30. ©2016 AACR.

Rb/E2F1 regulates the innate immune receptor Toll-like receptor 3 in epithelial cells.

ABSTRACT Tumor suppressor genes regulate the antiviral host defense through molecular mechanisms that are not yet well explored. Here, we show that the tumor suppressor retinoblastoma (Rb) protein positively regulates Toll-like receptor 3 (TLR3) expression, the sensing receptor for viral double-stranded RNA and poly(I·C). TLR3 expression was lower in Rb knockout (Rb−/−) mouse embryonic fibroblasts (MEF) and in mammalian epithelial cells transfected with Rb small-interfering RNA (siRNA) than in control cells. Consequently, induction of cytokines interleukin-8 and beta interferon after poly(I·C) stimulation was impaired in Rb−/− MEF and Rb siRNA-transfected cells compared to controls. TLR3 promoter analysis showed that Rb modulates the transcription factor E2F1, which directly binds to the proximal promoter of TLR3. Exogenous addition of E2F1 decreased TLR3 promoter activity, while Rb dose dependently curbed the effect of E2F1. Interestingly, poly(I·C) increased the Rb expression, and the poly(I·C)-induced TLR3 expression was impaired in Rb-depleted cells, suggesting the importance of Rb in TLR3 induction by poly(I·C). Together, these data indicated that E2F1 suppresses TLR3 transcription, but during immune stimulation, Rb is upregulated to block the inhibitory effect of E2F1 on TLR3, highlighting a role of Rb-E2F1 axis in the innate immune response in epithelial cells.

Reversion-inducing cysteine-rich protein with Kazal motifs interferes with epidermal growth factor receptor signaling

The reversion-inducing cysteine-rich protein with Kazal motifs (RECK) gene had been isolated as an antagonist to RAS signaling; however, the mechanism of its action is not clear. In this study, the effect of loss of RECK function was assessed in various ways and cell systems. Successive cell cultivation of mouse embryonic fibroblasts (MEFs) according to 3T3 protocol revealed that the germline knockout of RECK confers accelerated cell proliferation and early escape from cellular senescence associated with downregulation of p19Arf, Trp53 and p21Cdkn1a. In contrast, short hairpin RNA-mediated depletion of RECK induced irreversible growth arrest along with several features of the Arf, Trp53 and Cdkn1a-dependent cellular senescence. Within 2 days of RECK depletion, we observed a transient increase in protein kinase B (AKT) and extracellular signal-regulated kinase (ERK) phosphorylation associated with an upregulated expression of cyclin D1, p19Arf, Trp53, p21Cdkn1a and Sprouty 2. On further cultivation, RAS, AKT and ERK activities were then downregulated to a level lower than control, indicating that RECK depletion leads to a negative feedback to RAS signaling and subsequent cellular senescence. In addition, we observed that epidermal growth factor receptor (EGFR) activity was transiently upregulated by RECK depletion in MEFs, and continuously downregulated by RECK overexpression in colon cancer cells. These findings indicate that RECK is a novel modulator of EGFR signaling.

Inflammation as a driver and vulnerability of KRAS mediated oncogenesis

While important strides have been made in cancer therapy by targeting certain oncogenes, KRAS, the most common among them, remains refractory to this approach. In recent years, a deeper understanding of the critical importance of inflammation in promoting KRAS-driven oncogenesis has emerged, and applies across the different contexts of lung, pancreatic, and colorectal tumorigenesis. Here we review why these tissue types are particularly prone to developing KRAS mutations, and how inflammation conspires with KRAS signaling to fuel carcinogenesis. We discuss multiple lines of evidence that have established NF-κB, STAT3, and certain cytokines as key transducers of these signals, and data to suggest that targeting these pathways has significant clinical potential. Furthermore, recent work has begun to uncover how inflammatory signaling interacts with other KRAS regulated survival pathways such as autophagy and MAPK signaling, and that co-targeting these multiple nodes may be required to achieve real benefit. In addition, the impact of KRAS associated inflammatory signaling on the greater tumor microenvironment has also become apparent, and taking advantage of this inflammation by incorporating approaches that harness T cell anti-tumor responses represents another promising therapeutic strategy. Finally, we highlight the likelihood that the genomic complexity of KRAS mutant tumors will ultimately require tailored application of these therapeutic approaches, and that targeting inflammation early in the course of tumor development could have the greatest impact on eradicating this deadly disease.