Chediak-Higashi syndrome: Lysosomal trafficking regulator domains regulate exocytosis of lytic granules but not cytokine secretion by natural killer cells

Abstract

Background Mutations in LYST cause Chediak-Higashi syndrome (CHS), a rare immunodeficiency with impaired cytotoxic lymphocyte function, mainly that of natural killer (NK) cells. Our understanding of NK cell function deficiency in CHS, and how LYST regulates lytic granule exocytosis is very limited. Objective We sought to delineate cellular defects, associated with LYST mutations, responsible for the impaired NK cell function in CHS. Methods We analyzed NK cells from CHS patients with missense mutations in the LYST ARM/HEAT or BEACH domains. Results CHS NK cells displayed severely reduced cytotoxicity. Mutations in the ARM/HEAT domain led to a reduced number of perforin-containing granules, which were significantly increased in size, but able to polarize to the immunological synapse (IS); however, they were unable to properly fuse with the plasma membrane. Mutations in the BEACH domain resulted in the formation of normal or slightly enlarged granules that had markedly impaired polarization to the immunological synapse, but could be exocytosed upon reaching the IS. Perforin-containing granules in CHS NK cells did not acquire certain lysosomal markers (LAMP1/2), but were positive for markers of transport vesicles (CI-MPR), late endosomes (Rab27a), and to some extent, early endosomes (EEA-1), indicating a lack of integrity in the endo-lysosomal compartments. CHS NK cells had normal cytokine compartments and cytokine secretion. Conclusion LYST is involved in regulation of multiple aspects of NK cell lytic activity ranging from governance of lytic granule size to control of their polarization and exocytosis, as well as the regulation of endo-lysosomal compartment identity. LYST functions in the regulated exocytosis, but not in the constitutive secretion pathway.

Emerging insights into human health and NK cell biology from the study of NK cell deficiencies

“…In particular, several new publications have been focused on the biology of LYST, which when aberrant causes Chediak‐Higashi syndrome. These have demonstrated differences in the severity of disease associated with mutations that affect different domains of LYST . While lytic granules from patients with Chediak‐Higashi syndrome have previously been shown to be unusually large, this was recently advanced further for granules in NK cells from patients with LYST mutations .…”

“…These have demonstrated differences in the severity of disease associated with mutations that affect different domains of LYST . While lytic granules from patients with Chediak‐Higashi syndrome have previously been shown to be unusually large, this was recently advanced further for granules in NK cells from patients with LYST mutations . New studies have demonstrated that the size of lytic granules in Chediak‐Higashi syndrome patient NK cells can be a physical barrier to their directed secretion, as they are unable to transverse the cortical actin network located below the NK cell synaptic membrane .…”

“…In addition to NKD, in which NK cell aberration is the primary, majority, or only clinically relevant immune manifestation, there are other monogenic causes of PIDs that have an effect on NK cell phenotype or function ( shown to be unusually large, 193,194 this was recently advanced further for granules in NK cells from patients with LYST mutations. 144,195 New studies have demonstrated that the size of lytic granules in Chediak-Higashi syndrome patient NK cells can be a physical barrier to their directed secretion, as they are unable to transverse the cortical actin network located below the NK cell synaptic membrane. 195 This network has been shown to regulate granule exocytosis 196 and the fact that large granules cannot find egress is further evidence to support the actin meshwork as a checkpoint that lytic granules must navigate and pass.…”

Modulation of Secretory Lysosomes During NK Cell Education Leads to Accumulation of Granzyme B and Enhanced Functional Potential

“…76 NK cells in CHS patients are hyperresponsive and hypersecretory but are unable to degranulate. 77,78 Although NK cell activation followed by granule convergence and polarization appears to be normal in LYST-deficient NK cells, the enlarged granules fail to pass through the cortical actin meshwork openings at the immunological synapse. 36 By monitoring granule size and granzyme B density prior to and following degranulation, we observed a selective loss of the pre-converged, large dense-core granules after degranulation.…”

Natural killer cell activity and dysfunction in Hermansky‐Pudlak syndrome

“…Killing of K562 cells is dependent mainly on NKG2D (KLRK1) and LFA1 (ITGAL) receptors, whereas cytotoxicity toward 721.221 cells relies on 2B4 receptor expression by NK cells (Chen et al , 2007). The altered cytotoxicity toward target cells could be due to differences in expression of ligands for NK activating receptors by those target cells (Chen et al , 2006), and/or varied expression levels of activating receptors on NK cells (Gil-Krzewska et al , 2016). Nevertheless, cytotoxicity of HPS-2 NK cells did not improve with increased ratio of NK to target cells (data not shown), indicating a profound impairment of their cytolytic function, in agreement with previous reports (Enders et al , 2006; Jessen et al , 2013).…”