RhoG deficiency abrogates cytotoxicity of human lymphocytes and causes hemophagocytic lymphohistiocytosis

Abstract

Exocytosis of cytotoxic granules (CG) by lymphocytes is required for the elimination of infected and malignant cells. Impairments in this process underly a group of diseases with dramatic hyperferritinemic inflammation termed hemophagocytic lymphohistiocytosis (HLH). Although genetic and functional studies of HLH have identified proteins controlling distinct steps of CG exocytosis, the molecular mechanisms that spatiotemporally coordinate CG release remain unclear. We studied a patient exhibiting characteristic clinical features of HLH associated with markedly impaired cytotoxic T lymphocyte (CTL) and natural killer (NK) cell exocytosis functions, who was bearing biallelic deleterious mutations in the gene encoding the small GTPase RhoG. Experimental ablation of RHOG in a model cell line and primary CTLs from healthy individuals uncovered a hitherto unappreciated role of RhoG in retaining CGs in the vicinity of the plasma membrane (PM), a fundamental prerequisite for CG exocytotic release. We discovered that RhoG engages in a protein-protein interaction with Munc13-4, an exocytosis protein essential for CG fusion with the PM. We show that this interaction is critical for docking of Munc13-4-positive CGs to the PM and subsequent membrane fusion and release of CG content. Thus, our study illuminates RhoG as a novel essential regulator of human lymphocyte cytotoxicity, and provides the molecular pathomechanism behind the identified here and previously unreported genetically-determined form of HLH.

Digenic Inheritance: Evidence and Gaps in Hemophagocytic Lymphohistiocytosis

“…Following cell activation and formation of the IS, vesicles containing RAB27A, vesicles containing MUNC13-4, and CGs co-localize at the IS and fuse into a common vesicular structure ( 26 ). While RAB27A mediates the docking of these CGs, MUNC13-4, itself tethered to the membrane via a required protein-protein interaction with the small GTPase RhoG ( 27 ), is required for the final step prior to granule fusion with the plasma membrane. This final process, known as priming, makes these granules competent for exocytosis ( 9 ).…”

Morphological profiling of human T and NK lymphocytes by high-content cell imaging

“…At this stage, we cannot generalize the case of ARPC1B deficiency in establishing a systematic relationship between IS alteration and functional defects. However, it is interesting that multiple IEIs have been found by us and others to be associated with IS defects and functional impairment (Gil-Krzewska et al, 2018;Kalinichenko et al, 2021;Pfajfer et al, 2017;Salzer et al, 2016). Previous reports have also shown that IEIs where the IS is defective fail to eliminate target cells Mizesko et al, 2013;Pfajfer et al, 2017).…”

Molecular Genetics Diversity of Primary Hemophagocytic Lymphohistiocytosis among Polish Pediatric Patients

“…Nevertheless, the list of genes and causative changes identified so far cannot be considered exhaustive. Recently, defects in RC3H1 , associated with immune dysregulation and systemic hyper-inflammation syndrome, and RHOG , associated with defective lymphocyte exocytosis and HLH, have been proposed as additional causes of FHL (Kalinichenko et al 2021 ; Tavernier et al 2019 ).…”