Natural killer (NK) cells are a powerful weapon against viral infections and tumor growth. Although the actin–myosin (actomyosin) cytoskeleton is crucial for a variety of cellular processes, the role ...of mechanotransduction, the conversion of actomyosin mechanical forces into signaling cascades, was never explored in NK cells. Here, we demonstrate that actomyosin retrograde flow (ARF) controls the immune response of primary human NK cells through a novel interaction between β‐actin and the SH2‐domain‐containing protein tyrosine phosphatase‐1 (SHP‐1), converting its conformation state, and thereby regulating NK cell cytotoxicity. Our results identify ARF as a master regulator of the NK cell immune response. Since actin dynamics occur in multiple cellular processes, this mechanism might also regulate the activity of SHP‐1 in additional cellular systems.
Synopsis
SHP‐1 is crucial for suppressing natural killer (NK) cell activation. Actin retrograde flow regulates SHP‐1 conformation and enzymatic activity upon inhibitory receptor engagement, thereby controlling NK cell mediated cytotoxicity towards cancer cells.
The velocity of the actin retrograde flow is slower at the inhibitory versus the activating NK immunological synapse.
Slower actin retrograde flow enables the interaction of SHP‐1 with β‐actin.
Interaction with β‐actin regulates SHP‐1 conformation and induces its activation.
Blocking actin dynamics during the NK inhibitory response results in “closed” SHP‐1 conformation and reduced SHP‐1 activity.
The reduced enzymatic activity of SHP‐1 following actin retrograde flow arrest results in SHP‐1 substrate activation and NK cell cytotoxicity.
Interaction with β‐actin activates SHP‐1 phosphatase at the inhibitory immunological synapse to suppress natural killer cell cytotoxicity.
The emergence of immunotherapy for cancer treatment bears considerable clinical promise. Nevertheless, many patients remain unresponsive, acquire resistance, or suffer dose-limiting toxicities. ...Immune-editing of tumors assists their escape from the immune system, and the tumor microenvironment (TME) induces immune suppression through multiple mechanisms. Immunotherapy aims to bolster the activity of immune cells against cancer by targeting these suppressive immunomodulatory processes. Natural Killer (NK) cells are a heterogeneous subset of immune cells, which express a diverse array of activating and inhibitory germline-encoded receptors, and are thus capable of directly targeting and killing cancer cells without the need for MHC specificity. Furthermore, they play a critical role in triggering the adaptive immune response. Enhancing the function of NK cells in the context of cancer is therefore a promising avenue for immunotherapy. Different NK-based therapies have been evaluated in clinical trials, and some have demonstrated clinical benefits, especially in the context of hematological malignancies. Solid tumors remain much more difficult to treat, and the time point and means of intervention of current NK-based treatments still require optimization to achieve long term effects. Here, we review recently described mechanisms of cancer evasion from NK cell immune surveillance, and the therapeutic approaches that aim to potentiate NK function. Specific focus is placed on the use of specialized monoclonal antibodies against moieties on the cancer cell, or on both the tumor and the NK cell. In addition, we highlight newly identified mechanisms that inhibit NK cell activity in the TME, and describe how biochemical modifications of the TME can synergize with current treatments and increase susceptibility to NK cell activity.
Cancer-associated fibroblasts (CAFs) are central players in the microenvironment of solid tumors, affecting cancer progression and metastasis. CAFs have diverse phenotypes, origins and functions and ...consist of distinct subpopulations. Recent progress in single-cell RNA-sequencing technologies has enabled detailed characterization of the complexity and heterogeneity of CAF subpopulations in multiple tumor types. In this Review, we discuss the current understanding of CAF subsets and functions as elucidated by single-cell technologies, their functional plasticity, and their emergent shared and organ-specific features that could potentially be harnessed to design better therapeutic strategies for cancer.
Natural killer (NK) cells provide a powerful weapon mediating immune defense against viral infections, tumor growth, and metastatic spread. NK cells demonstrate great potential for cancer ...immunotherapy; they can rapidly and directly kill cancer cells in the absence of MHC‐dependent antigen presentation and can initiate a robust immune response in the tumor microenvironment (TME). Nevertheless, current NK cell‐based immunotherapies have several drawbacks, such as the requirement for ex vivo expansion of modified NK cells, and low transduction efficiency. Furthermore, to date, no clinical trial has demonstrated a significant benefit for NK‐based therapies in patients with advanced solid tumors, mainly due to the suppressive TME. To overcome current obstacles in NK cell‐based immunotherapies, we describe here a non‐viral lipid nanoparticle‐based delivery system that encapsulates small interfering RNAs (siRNAs) to gene silence the key intrinsic inhibitory NK cell molecules, SHP‐1, Cbl‐b, and c‐Cbl. The nanoparticles (NPs) target NK cells in vivo, silence inhibitory checkpoint signaling molecules, and unleash NK cell activity to eliminate tumors. Thus, the novel NP‐based system developed here may serve as a powerful tool for future NK cell‐based therapeutic approaches.
Synopsis
Natural Killer (NK) cells serve as a first line of immune defense against tumor growth and viral infections. This study demonstrates a nanobiology‐based drug delivery system to enhance NK cytotoxicity by suppressing intracellular inhibitory checkpoints in the tumor microenvironment (TME).
NK cytotoxicity was enhanced by nano‐carriers encapsulating siRNAs that target the negative regulatory genes SHP‐1 and Cbls.
Tumor growth was suppressed by these molecularly modified NK cells in‐vivo.
Natural Killer (NK) cells serve as a first line of immune defense against tumor growth and viral infections. This study demonstrates a nanobiology‐based drug delivery system to enhance NK cytotoxicity by suppressing intracellular inhibitory checkpoints in the tumor microenvironment (TME).
The process of mechanotransduction, that is, conversion of physical forces into biochemical signaling cascades, has attracted interest as a potential mechanism for regulating immune cell activation. ...The cytoskeleton serves a critical role in a variety of lymphocyte functions, from cellular activation, proliferation, adhesion, and migration, to creation of stable immune synapses, and execution of functions such as directed cytotoxicity. Though traditionally considered a scaffold that enables formation of signaling complexes that maintain stable immune synapses, the cytoskeleton was additionally shown to play a dynamic role in lymphocyte signaling cascades by sensing physical cues such as substrate rigidity, and transducing these mechanical features into chemical signals that ultimately influence lymphocyte effector functions. It is thus becoming clear that cytoskeletal dynamics are essential for the lymphocyte response, beyond the role of the cytoskeleton as a stationary framework. Here, we describe the transduction of extracellular forces to activate signaling pathways and effector functions mediated through the cytoskeleton in lymphocytes. We also highlight recent discoveries of cytoskeleton‐mediated mechanotransduction on intracellular signaling pathways in NK cells.
Review of how mechanical forces mediate lymphocyte effector functions through regulation of cytoskeletal dynamics.
Abstract
Cancer cells depend on actin cytoskeleton rearrangement to carry out hallmark malignant functions including activation, proliferation, migration and invasiveness. Wiskott–Aldrich Syndrome ...protein (WASp) is an actin nucleation-promoting factor and is a key regulator of actin polymerization in hematopoietic cells. The involvement of WASp in malignancies is incompletely understood. Since WASp is exclusively expressed in hematopoietic cells, we performed
in silico
screening to identify small molecule compounds (SMCs) that bind WASp and promote its degradation. We describe here one such identified molecule; this WASp-targeting SMC inhibits key WASp-dependent actin processes in several types of hematopoietic malignancies in vitro and in vivo without affecting naïve healthy cells. This small molecule demonstrates limited toxicity and immunogenic effects, and thus, might serve as an effective strategy to treat specific hematopoietic malignancies in a safe and precisely targeted manner.
Natural killer (NK) cells play a crucial role in immunity, killing virally infected and cancerous cells. The balance of signals initiated upon engagement of activating and inhibitory NK receptors ...with cognate ligands determines killing or tolerance. Nevertheless, the molecular mechanisms regulating rapid NK cell discrimination between healthy and malignant cells in a heterogeneous tissue environment are incompletely understood. The SHP-1 tyrosine phosphatase is the central negative NK cell regulator that dephosphorylates key activating signaling proteins. Though the mechanism by which SHP-1 mediates NK cell inhibition has been partially elucidated, the pathways by which SHP-1 is itself regulated remain unclear. Here, we show that phosphorylation of SHP-1 in NK cells on the S591 residue by PKC-θ promotes the inhibited SHP-1 'folded' state. Silencing PKC-θ maintains SHP-1 in the active conformation, reduces NK cell activation and cytotoxicity, and promotes tumor progression in vivo. This study reveals a molecular pathway that sustains the NK cell activation threshold through suppression of SHP-1 activity.
Tumors initiate by mutations in cancer cells, and progress through interactions of the cancer cells with non-malignant cells of the tumor microenvironment. Major players in the tumor microenvironment ...are cancer-associated fibroblasts (CAFs), which support tumor malignancy, and comprise up to 90% of the tumor mass in pancreatic cancer. CAFs are transcriptionally rewired by cancer cells. Whether this rewiring is differentially affected by different mutations in cancer cells is largely unknown. Here we address this question by dissecting the stromal landscape of BRCA-mutated and BRCA Wild-type pancreatic ductal adenocarcinoma. We comprehensively analyze pancreatic cancer samples from 42 patients, revealing different CAF subtype compositions in germline BRCA-mutated vs. BRCA Wild-type tumors. In particular, we detect an increase in a subset of immune-regulatory clusterin-positive CAFs in BRCA-mutated tumors. Using cancer organoids and mouse models we show that this process is mediated through activation of heat-shock factor 1, the transcriptional regulator of clusterin. Our findings unravel a dimension of stromal heterogeneity influenced by germline mutations in cancer cells, with direct implications for clinical research.
Natural killer (NK) cells are innate lymphoid cells, which play key roles in elimination of virally infected and malignant cells. The balance between activating and inhibitory signals derived from NK ...surface receptors govern the NK cell immune response. The cytoskeleton facilitates most NK cell effector functions, such as motility, infiltration, conjugation with target cells, immunological synapse assembly, and cytotoxicity. Though many studies have characterized signaling pathways that promote actin reorganization in immune cells, it is not completely clear how particular cytoskeletal architectures at the immunological synapse promote effector functions, and how cytoskeletal dynamics impact downstream signaling pathways and activation. Moreover, pioneering studies employing advanced imaging techniques have only begun to uncover the architectural complexity dictating the NK cell activation threshold; it is becoming clear that a distinct organization of the cytoskeleton and signaling receptors at the NK immunological synapse plays a decisive role in activation and tolerance. Here, we review the roles of the actin cytoskeleton in NK cells. We focus on how actin dynamics impact cytolytic granule secretion, NK cell motility, and NK cell infiltration through tissues into inflammatory sites. We will also describe the additional cytoskeletal components, non-muscle Myosin II and microtubules that play pivotal roles in NK cell activity. Furthermore, special emphasis will be placed on the role of the cytoskeleton in assembly of immunological synapses, and how mutations or downregulation of cytoskeletal accessory proteins impact NK cell function in health and disease.
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