Actin Retrograde Flow Regulated by the Wiskott–Aldrich Syndrome Protein Drives the Natural Killer Cell Response

SIMPLE SUMMARY: Immune cells sense mechanical stimuli from their microenvironment by transducing them into biochemical signals through mechanosensors, in a process called mechanotransduction. The cytoskeleton mediates mechanotransduction in response to local environmental changes. The cytoskeletal component, actin, provides the structural basis for the NK cell immunological synapse (NKIS) and polarization of the signaling complex and secretory apparatus. Actin-mediated mechanotransduction is essential to adjust and to improve the natural killer (NK) cell response to changes induced by the microenvironment. Wiskott–Aldrich Syndrome protein (WASp), another key cytoskeletal component, plays a role in actin filament nucleation, and hence it’s branching toward the membrane. Here, we found that WASp regulates mechanotransduction by controlling F-actin movement thereby modulating NK cell signaling and the equilibrium between activation versus inhibition. WASp regulation of the actin retrograde flow (ARF) provides a novel mechanism to modulate the functional outcome of NK cells in response to their environment. ABSTRACT: Understanding the crosstalk between natural killer (NK) cells and the tumor microenvironment (TME) has enhanced the potential of exploiting the interplay between activation and inhibition of NK cells for immunotherapy. This interaction is crucial for understanding how tumor cells escape NK cell immune surveillance. NK cell dysfunction is regulated by two molecular mechanisms, downregulated activating receptor ligand expression on the tumor cells, and upregulated inhibitory signals delivered to NK cells. Recent studies demonstrated the role of mechanotransduction in modulating NK cell responses in the TME. The immunological synapse represents a functional interface between the NK cell and its target, regulated by Actin Retrograde Flow (ARF), which drives the adhesion molecules and receptors toward the central zone of the immunological synapse (IS). Here, we further characterize the role of ARF in controlling the immune response of NK cells, using CRISPR/cas9-mediated Wiskott–Aldrich Syndrome protein (WASp) gene silencing of NK cells. We demonstrate that WASp regulates ARF velocity, affecting the conformation and function of the key NK inhibitory regulator, SH2-domain containing protein tyrosine phosphatase-1 (SHP-1), and consequently, the NK cell response. Our results demonstrate the potential of modulating the biophysical and intracellular regulation of NK activation as a promising approach for improving immunotherapy.