Granzyme B-activated p53 interacts with Bcl-2 to promote cytotoxic lymphocyte-mediated apoptosis.

Granzyme B (GzmB) plays a major role in CTLs and NK cell-mediated elimination of virus-infected cells and tumors. Human GzmB preferentially induces target cell apoptosis by cleaving the proapoptotic Bcl-2 family member Bid, which, together with Bax, induces mitochondrial outer membrane permeabilization. We previously showed that GzmB also induces a rapid accumulation of the tumor-suppressor protein p53 within target cells, which seems to be involved in GzmB-induced apoptosis. In this article, we show that GzmB-activated p53 accumulates on target cell mitochondria and interacts with Bcl-2. This interaction prevents Bcl-2 inhibitory effect on both Bax and GzmB-truncated Bid, and promotes GzmB-induced mitochondrial outer membrane permeabilization. Consequently, blocking p53-Bcl-2 interaction decreases GzmB-induced Bax activation, cytochrome c release from mitochondria, and subsequent effector caspases activation leading to a decreased sensitivity of target cells to both GzmB and CTL/NK-mediated cell death. Together, our results define p53 as a new important player in the GzmB apoptotic signaling pathway and in CTL/NK-induced apoptosis.

Cutting edge: Hypoxia-induced Nanog favors the intratumoral infiltration of regulatory T cells and macrophages via direct regulation of TGF-ß1.

Emerging evidence suggests a link between tumor hypoxia and immune suppression. In this study, we investigated the role of hypoxia-induced Nanog, a stemness-associated transcription factor, in immune suppression. We observed that hypoxia-induced Nanog correlated with the acquisition of stem cell-like properties in B16-F10 cells. We further show that Nanog was selectively induced in hypoxic areas of B16-F10 tumors. Stable short hairpin RNA-mediated depletion of Nanog, combined with melanocyte differentiation Ag tyrosinase-related protein-2 peptide-based vaccination, resulted in complete inhibition of B16-F10 tumor growth. Nanog targeting significantly reduced immunosuppressive cells (regulatory T cells and macrophages) and increased CD8(+) T effector cells in tumor bed in part by modulating TGF-ß1 production. Additionally, Nanog regulated TGF-ß1 under hypoxia by directly binding the TGF-ß1 proximal promoter. Collectively, our data establish a novel functional link between hypoxia-induced Nanog and TGF-ß1 regulation and point to a major role of Nanog in hypoxia-driven immunosuppression.

A noninvasive photoactivatable split-Cre recombinase system for genome engineering in zebrafish.

The cyclic recombinase (Cre)/loxP recombination system is a powerful technique for in vivo cell labeling and tracking. However, achieving high spatiotemporal precision in cell tracking using this system is challenging due to the requirement for reliable tissue-specific promoters. In contrast, light-inducible systems offer superior regional confinement, tunability, and non-invasiveness compared to conventional lineage-tracing methods. Here, we took advantage of the unique strengths of the zebrafish to develop an easy-to-use highly efficient, genetically encoded, magnets-based, light-inducible transgenic Cre/loxP system. We demonstrate that our system does not exhibit phototoxicity or leakiness in the dark, and it enables efficient and robust Cre/loxP recombination in various tissues and cell types at different developmental stages through noninvasive illumination with blue light. Our newly developed tool is expected to open novel opportunities for light-controlled tracking of cell fate and migration in vivo.

Definitive hematopoiesis is dispensable to sustain erythrocytes and macrophages during zebrafish ontogeny.

In all organisms studied, from flies to humans, blood cells emerge in several sequential waves and from distinct hematopoietic origins. However, the relative contribution of these ontogenetically distinct hematopoietic waves to embryonic blood lineages and to tissue regeneration during development is yet elusive. Here, using a lineage-specific "switch and trace" strategy in the zebrafish embryo, we report that the definitive hematopoietic progeny barely contributes to erythrocytes and macrophages during early development. Lineage tracing further shows that ontogenetically distinct macrophages exhibit differential recruitment to the site of injury based on the developmental stage of the organism. We further demonstrate that primitive macrophages can solely maintain tissue regeneration during early larval developmental stages after selective ablation of definitive macrophages. Our findings highlight that the sequential emergence of hematopoietic waves in embryos ensures the abundance of blood cells required for tissue homeostasis and integrity during development.

Cancer stem-like cells evade CD8+CD103+ tumor-resident memory T (TRM) lymphocytes by initiating an epithelial-to-mesenchymal transition program in a human lung tumor model.

BACKGROUND: Cancer stem cells (CSC) define a population of rare malignant cells endowed with 'stemness' properties, such as self-renewing, multipotency and tumorigenicity. They are responsible for tumor initiation and progression, and could be associated with resistance to immunotherapies by negatively regulating antitumor immune response and acquiring molecular features enabling escape from CD8 T-cell immunity. However, the immunological hallmarks of human lung CSC and their potential interactions with resident memory T (TRM) cells within the tumor microenvironment have not been investigated. METHODS: We generated a non-small cell lung cancer model, including CSC line and clones, and autologous CD8+CD103+ TRM and CD8+CD103- non-TRM clones, to dissect out immune properties of CSC and their susceptibility to specific T-cell-mediated cytotoxic activity. RESULTS: Unlike their parental tumor cells, lung CSC are characterized by the initiation of an epithelial-to-mesenchymal transition program defined by upregulation of the SNAIL1 transcription factor and downregulation of phosphorylated-GSK-3ß and cell surface E-cadherin. Acquisition of a CSC profile results in partial resistance to TRM-cell-mediated cytotoxicity, which correlates with decreased surface expression of the CD103 ligand E-cadherin and human leukocyte antigen-A2-neoepitope complexes. On the other hand, CSC gained expression of intercellular adhesion molecule (ICAM)-1 and thereby sensitivity to leukocyte function-associated antigen (LFA)-1-dependent non-TRM-cell-mediated killing. Cytotoxicity is inhibited by anti-ICAM-1 and anti-major histocompatibility complex class I neutralizing antibodies further emphasizing the role of LFA-1/ICAM-1 interaction in T-cell receptor-dependent lytic function. CONCLUSION: Our data support the rational design of immunotherapeutic strategies targeting CSC to optimize their responsiveness to local CD8+CD103+ TRM cells for more efficient anticancer treatments.

Selection of tumor­resistant variants following sustained natural killer cell­mediated immune stress.

Resistance of tumor cells to cell­mediated cytotoxicity remains an obstacle to the immunotherapy of cancer and its molecular basis is poorly understood. To investigate the acquisition of tumor resistance to cell­mediated cytotoxicity, resistant variants were selected following long­term natural killer (NK) cell selection pressure. It was observed that these variants were resistant to NK cell­mediated lysis, but were sensitive to autologous cytotoxic T lymphocytes or cytotoxic drugs. This resistance appeared to be dependent, at least partly, on an alteration of target cell recognition by NK effector cells, but did not appear to involve any alterations in the expression of KIR, DNAM1 or NKG2D ligands on resistant cells, nor the induction of protective autophagy. In the present study, in order to gain further insight into the molecular mechanisms underlying the acquired tumor resistance to NK cell­mediated cytotoxicity, a comprehensive analysis of the variant transcriptome was conducted. Comparative analysis identified an expression profile of genes that best distinguished resistant variants from parental sensitive cancer cells, with candidate genes putatively involved in NK cell­mediated lysis resistance, but also in adhesion, migration and invasiveness, including upregulated genes, such as POT1, L1CAM or ECM1, and downregulated genes, such as B7­H6 or UCHL1. Consequently, the selected variants were not only resistant to NK cell­mediated lysis, but also displayed more aggressive properties. The findings of the present study emphasized that the role of NK cells may span far beyond the mere killing of malignant cells, and NK cells may be important effectors during cancer immunoediting.

Integrin-αV-mediated activation of TGF-ß regulates anti-tumour CD8 T cell immunity and response to PD-1 blockade.

TGF-ß is secreted in the tumour microenvironment in a latent, inactive form bound to latency associated protein and activated by the integrin αV subunit. The activation of latent TGF-ß by cancer-cell-expressed αV re-shapes the tumour microenvironment, and this could affect patient responses to PD-1-targeting therapy. Here we show, using multiplex immunofluorescence staining in cohorts of anti-PD-1 and anti-PD-L1-treated lung cancer patients, that decreased expression of cancer cell αV is associated with improved immunotherapy-related, progression-free survival, as well as with an increased density of CD8+CD103+ tumour-infiltrating lymphocytes. Mechanistically, tumour αV regulates CD8 T cell recruitment, induces CD103 expression on activated CD8+ T cells and promotes their differentiation to granzyme B-producing CD103+CD69+ resident memory T cells via autocrine TGF-ß signalling. Thus, our work provides the underlying principle of targeting cancer cell αV for more efficient PD-1 checkpoint blockade therapy.

Regulation of antitumour CD8 T-cell immunity and checkpoint blockade immunotherapy by Neuropilin-1.

Neuropilin-1 (Nrp-1) is a marker for murine CD4+FoxP3+ regulatory T (Treg) cells, a subset of human CD4+ Treg cells, and a population of CD8+ T cells infiltrating certain solid tumours. However, whether Nrp-1 regulates tumour-specific CD8 T-cell responses is still unclear. Here we show that Nrp-1 defines a subset of CD8+ T cells displaying PD-1hi status and infiltrating human lung cancer. Interaction of Nrp-1 with its ligand semaphorin-3A inhibits migration and tumour-specific lytic function of cytotoxic T lymphocytes. In vivo, Nrp-1+PD-1hi CD8+ tumour-infiltrating lymphocytes (TIL) in B16F10 melanoma are enriched for tumour-reactive T cells exhibiting an exhausted state, expressing Tim-3, LAG-3 and CTLA-4 inhibitory receptors. Anti-Nrp-1 neutralising antibodies enhance the migration and cytotoxicity of Nrp-1+PD-1hi CD8+ TIL ex vivo, while in vivo immunotherapeutic blockade of Nrp-1 synergises with anti-PD-1 to enhance CD8+ T-cell proliferation, cytotoxicity and tumour control. Thus, Nrp-1 could be a target for developing combined immunotherapies.

Human preprocalcitonin self-antigen generates TAP-dependent and -independent epitopes triggering optimised T-cell responses toward immune-escaped tumours.

Tumours often evade CD8 T-cell immunity by downregulating TAP. T-cell epitopes associated with impaired peptide processing are immunogenic non-mutated neoantigens that emerge during tumour immune evasion. The preprocalcitonin (ppCT)16-25 neoepitope belongs to this category of antigens. Here we show that most human lung tumours display altered expression of TAP and frequently express ppCT self-antigen. We also show that ppCT includes HLA-A2-restricted epitopes that are processed by TAP-independent and -dependent pathways. Processing occurs in either the endoplasmic reticulum, by signal peptidase and signal peptide peptidase, or in the cytosol after release of a signal peptide precursor or retrotranslocation of a procalcitonin substrate by endoplasmic-reticulum-associated degradation. Remarkably, ppCT peptide-based immunotherapy induces efficient T-cell responses toward antigen processing and presenting machinery-impaired tumours transplanted into HLA-A*0201-transgenic mice and in NOD-scid-Il2rγnull mice adoptively transferred with human PBMC. Thus, ppCT-specific T lymphocytes are promising effectors for treatment of tumours that have escaped immune recognition.

Paxillin Binding to the Cytoplasmic Domain of CD103 Promotes Cell Adhesion and Effector Functions for CD8+ Resident Memory T Cells in Tumors.

CD8+/CD103+ tissue-resident memory T cells (TRM cells) accumulate in several human solid tumors, where they have been associated with a favorable prognosis. However, the role of CD103, the α subunit of the integrin αEß7 (also known as CD103), in the retention and functions of these TRM is undefined. In this report, we investigated the role of CD103 cytoplasmic domain and the focal adhesion-associated protein paxillin (Pxn) in downstream signaling and functional activities triggered through αE/CD103 chain. Binding to immobilized recombinant (r)E-cadherin-Fc of CD103 integrin expressed on tumor-specific CTL clones promotes phosphorylation of Pxn and Pyk2 and binding of Pxn to the αE/CD103 subunit tail. Inhibition of Pxn phosphorylation by the Src inhibitor saracatinib or its knockdown via shRNA dramatically altered adhesion and spreading of freshly isolated CD8+/CD103+ lung tumor-infiltrating lymphocytes and CD103+ tumor-specific CTL clones. Inhibition of Pxn phosphorylation with saracatinib in these CTL clones also severely compromised their functional activities toward autologous tumor cells. Using Jurkat T cells as a model to study CD103 integrin activation, we demonstrated a key role of serine residue S1163 of the αE chain intracellular domain in polarization of CD103 and recruitment of lysosomes and Pxn at the contact zone of T lymphocytes with rE-cadherin-Fc-coated beads. Overall, our results show how Pxn binding to the CD103 cytoplasmic tail triggers αEß7 integrin outside-in signaling that promotes CD8+ T-cell migratory behavior and effector functions. These results also explain the more favorable prognosis associated with retention of TRM cells in the tumor microenvironment. Cancer Res; 77(24); 7072-82. ©2017 AACR.

Acquisition of tumor cell phenotypic diversity along the EMT spectrum under hypoxic pressure: Consequences on susceptibility to cell-mediated cytotoxicity.

Tumor escape to immunosurveillance and resistance to immune attacks present a major hurdle in cancer therapy, especially in the current era of new cancer immunotherapies. We report here that hypoxia, a hallmark of most solid tumors, orchestrates carcinoma cell heterogeneity through the induction of phenotypic diversity and the acquisition of distinct epithelial-mesenchymal transition (EMT) states. Using lung adenocarcinoma cells derived from a non-metastatic patient, we demonstrated that hypoxic stress induced phenotypic diversity along the EMT spectrum, with induction of EMT transcription factors (EMT-TFs) SNAI1, SNAI2, TWIST1, and ZEB2 in a hypoxia-inducible factor-1α (HIF1A)-dependent or -independent manner. Analysis of hypoxia-exposed tumor subclones, with pronounced epithelial or mesenchymal phenotypes, revealed that mesenchymal subclones exhibited an increased propensity to resist cytotoxic T lymphocytes (CTL), and natural killer (NK) cell-mediated lysis by a mechanism involving defective immune synapse signaling. Additionally, targeting EMT-TFs, or inhibition of TGF-ß signaling, attenuated mesenchymal subclone susceptibility to immune attack. Together, these findings uncover hypoxia-induced EMT and heterogeneity as a novel driving escape mechanism to lymphocyte-mediated cytotoxicity, with the potential to provide new therapeutic opportunities for cancer patients.

Regulation of Melanoma Progression through the TCF4/miR-125b/NEDD9 Cascade.

Melanoma progression from a primary lesion to a distant metastasis is a complex process associated with genetic alterations, epigenetic modifications, and phenotypic switches. Elucidation of these phenomena may indicate how to interfere with this fatal disease. The role of microRNAs as key negative regulators of gene expression, controlling all cellular processes including cell migration and invasion, is now being recognized. Here, we used in silico analysis of microRNA expression profiles of primary and metastatic melanomas and functional experiments to show that microRNA-125b (miR-125b) is a determinant candidate of melanoma progression: (i) miR-125b is more strongly expressed in aggressive metastatic than primary melanomas, (ii) there is an inverse correlation between the amount of miR-125b and overall patient survival, (iii) invasion/migration potentials in vitro are inversely correlated with the amount of miR-125b in a series of human melanoma cell lines, and (iv) inhibition of miR-125b reduces migratory and invasive potentials without affecting cell proliferation in vitro. Furthermore, we show that neural precursor cell expressed developmentally down-regulated protein 9 (i.e., NEDD9) is a direct target of miR-125b and is involved in modulating melanoma cell migration and invasion. Also, transcription factor 4, associated with epithelial-mesenchymal transition and invasion, induces the transcription of miR-125b-1. In conclusion, the transcription factor 4/miR-125b/NEDD9 cascade promotes melanoma cell migration/invasion.

TGFß Signaling Intersects with CD103 Integrin Signaling to Promote T-Lymphocyte Accumulation and Antitumor Activity in the Lung Tumor Microenvironment.

Homing of CD8(+) T lymphocytes to the tumor microenvironment is an important step for mounting a robust antitumor immune response. TGFß is responsible for CD103 (αEß7) integrin induction in activated intraepithelial CD8(+) T lymphocytes. However, the interplay between TGFß and CD103 and their contribution to T-cell infiltration and antitumor activity remain unknown. Here, we used viable human lung tumor slices and autologous tumor antigen-specific T-lymphocyte clones to provide evidence that CD103 is directly involved in T-lymphocyte recruitment within epithelial tumor islets and intratumoral early T-cell signaling. Moreover, TGFß enhanced CD103-dependent T-cell adhesion and signaling, whereas it inhibited leukocyte function-associated antigen (LFA)-1 (αLß2) integrin expression and LFA-1-mediated T-lymphocyte functions. Mechanistic investigations revealed that TGFß bound to its receptors (TGFBR), which promoted the recruitment and phosphorylation of integrin-linked kinase (ILK) by TGFBR1. We further show that ILK interacted with the CD103 intracellular domain, resulting in protein kinase B (PKB)/AKT activation, thereby initiating integrin inside-out signaling. Collectively, our findings suggest that the abundance of TGFß in the tumor microenvironment may in fact engage with integrin signaling pathways to promote T-lymphocyte antitumor functions, with potential implications for T-cell-based immunotherapies for cancer. Cancer Res; 76(7); 1757-69. ©2016 AACR.

A caveolin-dependent and PI3K/AKT-independent role of PTEN in ß-catenin transcriptional activity.

Loss of the tumour suppressor PTEN is frequent in human melanoma, results in MAPK activation, suppresses senescence and mediates metastatic behaviour. How PTEN loss mediates these effects is unknown. Here we show that loss of PTEN in epithelial and melanocytic cell lines induces the nuclear localization and transcriptional activation of ß-catenin independent of the PI3K-AKT-GSK3ß axis. The absence of PTEN leads to caveolin-1 (CAV1)-dependent ß-catenin transcriptional modulation in vitro, cooperates with NRAS(Q61K) to initiate melanomagenesis in vivo and induces efficient metastasis formation associated with E-cadherin internalization. The CAV1-ß-catenin axis is mediated by a feedback loop in which ß-catenin represses transcription of miR-199a-5p and miR-203, which suppress the levels of CAV1 mRNA in melanoma cells. These data reveal a mechanism by which loss of PTEN increases CAV1-mediated dissociation of ß-catenin from membranous E-cadherin, which may promote senescence bypass and metastasis.