Suppressor of IKK epsilon (SIKE) acts as a bridge between innate immune signalling pathway and cytoskeletal rearrangements

Abstract

Innate immunity coordinates the first line of defense against invading pathogens. This involves the recruitment and subsequent migration of nearby immune cells to the site of infection, allowing the pathogen to be consumed via phagocytosis to sequester the infection. These processes require the rapid disassembly, rearrangement, and repolymerization of the network of structural proteins known as the cytoskeleton. Migration and phagocytosis are one of the functional consequences of innate immune receptor triggered signaling pathways. Signals coalesce at catalytic hubs, such as kinases, which serve to amplify and regulate the signal. In the anti‐viral response, TANK binding kinase 1 (TBK1) functions as a catalytic hub. Suppressor of IKK epsilon (SIKE) acts as a high affinity, alternate TBK1 substrate, although SIKE's downstream function is not yet defined. The primary goal of this work was to assess the effect of SIKE on cytoskeletal rearrangements in migration and phagocytosis. For these studies, a CRISPR knockout cell line was derived, SIKE‐CR, from chronic myelogenous leukemia (CML) cell line KBM‐7 named HAP1. Wound healing assays of HAP1 parental cells and SIKE‐CR illustrated that the absence of SIKE significantly decreased cell migration. In the mouse macrophage RAW 264.7 cell line, SIKE expression was knocked down via lentiviral delivery of shRNA targeting SIKE. Phagocytosis was assessed in WT and SIKE knockdown cells via uptake of latex beads labeled with IgG‐FITC. Reduced SIKE expression increased phagocytic uptake. To determine SIKE interactions with cytoskeletal proteins, co‐immunoprecipitations (cIP), in vitro precipitation (IVP) reactions, and enzyme‐linked immunosorbent assays (ELISA) were completed and demonstrated SIKE:tubulin and SIKE:α‐actinin complexes. Together, these studies establish an interaction between SIKE and cytoskeletal proteins and suggest that SIKE functions in cytoskeletal rearrangement associated with migration and phagocytosis.Support or Funding InformationWork supported by NIH grant R21AI107447 and USD SURE.