KATP channels contribute to NK cell cytotoxicity.

Abstract

ATP-sensitive K+ (KATP) channels regulate diverse processes (e.g. insulin secretion from the pancreas and blood flow) but they may also have a role in immunity. Knockout of Kcnj8 (Kir6.1) in mice leads to an exaggerated susceptibility to lipopolysaccharide (LPS). Moreover, a random mutagenesis screen in mice identified the mayday mutation (both Kcnj8 exons deleted) with a profound susceptibility to infection by mouse cytomegalovirus (MCMV) and a ∼20,000-fold sensitization to LPS, poly(I.C) and CpG DNA. Natural killer (NK) cells are effector lymphocytes of the innate immune system that mediate anti-tumor and microbial responses. Despite having key role in immune defenses, their complement of ion channels and how these channels regulate their function are largely uncharacterized compared to other immune cells. We postulated that KATP channels affect NK cell function. Analysis of microarray and RNA-seq mouse ImmGen datasets shows that, compared to other immune cells, Kcnj8 mRNA is expressed selectively and at high levels in natural killer (NK) cells and in CD8+ effector memory T cells after viral infection. We confirmed that Kir6.1 protein is expressed in isolated mouse splenic NK cells. Expansion of mouse splenic NK cells with IL-15 and IL-2 leads to elevated levels of the cytotoxic granzyme and perforin proteins, which is further increased in the presence of the KATP channel opener pinacidil (30 µM). Co-culture of mouse lymphoma YAC-1 cells with mouse splenic NK cells leads to apoptosis progression of the target cells, as well as increased degranulation of NK cells assessed by surface expression of CD107a assessed by flow cytometry. Apoptosis progression and NK cell degranulation were both significantly enhanced by pinacidil (1-30 µM). These data are consistent with a role for KATP channels in NK cell cytotoxicity, possibly by contributing to the release of cytotoxic proteins from NK cells.