Remodeling of secretory lysosomes during education tunes functional potential in NK cells

Abstract

Inhibitory signaling during natural killer (NK) cell education translates into increased responsiveness to activation; however, the intracellular mechanism for functional tuning by inhibitory receptors remains unclear. Secretory lysosomes are part of the acidic lysosomal compartment that mediates intracellular signalling in several cell types. Here we show that educated NK cells expressing self-MHC specific inhibitory killer cell immunoglobulin-like receptors (KIR) accumulate granzyme B in dense-core secretory lysosomes that converge close to the centrosome. This discrete morphological phenotype is independent of transcriptional programs that regulate effector function, metabolism and lysosomal biogenesis. Meanwhile, interference of signaling from acidic Ca2+ stores in primary NK cells reduces target-specific Ca2+-flux, degranulation and cytokine production. Furthermore, inhibition of PI(3,5)P2 synthesis, or genetic silencing of the PI(3,5)P2-regulated lysosomal Ca2+-channel TRPML1, leads to increased granzyme B and enhanced functional potential, thereby mimicking the educated state. These results indicate an intrinsic role for lysosomal remodeling in NK cell education.

Distinctive phenotypes and functions of innate lymphoid cells in human decidua during early pregnancy

“…dNK responses triggered by activating KIR. pbNK granules function as Ca 2+ ion stores that contribute to increased signalling capacity so that cells with larger granules produce more cytokines when an activating receptor is triggered 24 . We next asked whether Lin− CD56+dMCs become more functional as granule content increases with acquisition of KIR (Figs.…”

“…Other evidence suggests that NK cell granules might play a role in cytokine production. In pbNK from healthy individuals, cells with larger granules are not only better killers, but also produce more cytokines 24 . pbNK from patients with Chediak-Higashi syndrome (CHS) possess NK cells with fewer, larger granules that do not polarise towards canonical NK cell target cells compared to normal pbNK 25,26 .…”

NK Cell Metabolism and TGFβ – Implications for Immunotherapy

“…Similarly, Ca2 + channel agonists/antagonists have also been shown to inhibit NK cell degranulation and killing capacity (90). Goodridge et al recently showed that interfering with Ca2 + stores reduces degranulation and IFNγ production in human NK cells (91). It seems likely that an interplay between Ca2 + signaling, metabolism and function exists in NK cells.…”

Feedback Regulation of Cathepsin C by the Propeptide Dipeptides of Granzymes A and B

“…Basically, the enzyme activity is regulated by the endogenous protein inhibitors to prevent a granzyme maturation to the active form. Based on the size of granules, 43 we can estimate that mM concentration is reached by 2000 dipeptide molecules, when granules have diameter of 200 nm. The concentration of the released propeptide dipeptides may be too low to inhibit cathepsin C. However, granzymes and other serine proteases listed in the Figure 6A have similar structure of propeptides.…”