RASGRP1 deficiency causes immunodeficiency with impaired cytoskeletal dynamics

Abstract

RASGRP1 is an important guanine nucleotide exchange factor and activator of the RAS-MAPK pathway following T cell antigen receptor (TCR) signaling. The consequences of RASGRP1 mutations in humans are unknown. In a patient with recurrent bacterial and viral infections, born to healthy consanguineous parents, we used homozygosity mapping and exome sequencing to identify a biallelic stop-gain variant in RASGRP1. This variant segregated perfectly with the disease and has not been reported in genetic databases. RASGRP1 deficiency was associated in T cells and B cells with decreased phosphorylation of the extracellular-signal-regulated serine kinase ERK, which was restored following expression of wild-type RASGRP1. RASGRP1 deficiency also resulted in defective proliferation, activation and motility of T cells and B cells. RASGRP1-deficient natural killer (NK) cells exhibited impaired cytotoxicity with defective granule convergence and actin accumulation. Interaction proteomics identified the dynein light chain DYNLL1 as interacting with RASGRP1, which links RASGRP1 to cytoskeletal dynamics. RASGRP1-deficient cells showed decreased activation of the GTPase RhoA. Treatment with lenalidomide increased RhoA activity and reversed the migration and activation defects of RASGRP1-deficient lymphocytes.

Combined immunodeficiency with EBV positive B cell lymphoma and epidermodysplasia verruciformis due to a novel homozygous mutation in RASGRP1

“…While vaccine titers were not available for our patient, she developed hypogammaglobulinemia requiring IVIG. The previously reported patient with RASGRP1 deficiency displayed reduced in vitro proliferation and class switching of primary B cells and reduced ERK phosphorylation in EBV-immortalized B cells following IgM stimulation [5]. These findings are all consistent with an intrinsic defect in RASGRP1-deficient B cells.…”

“…This led to complete loss of protein expression, suggesting that protein expression may have also been abolished in our patient. Due to the patient’s death, we could not examine her cells for RAS dependent phosphorylation of ERK, which was impaired in the previously reported case of RASGRP1 deficiency [5]. Our patient and the previously reported patient with RASGRP1 deficiency shared markedly similar features that include recurrent infections, CD4 + T cell lymphopenia, poor T cell proliferation to mitogens, defective NK function, and EBV-associated lymphoma.…”

“…Activated RAS initiates a MAP-kinase cascade, which leads to cytoskeletal reorganization and transcription of effector molecules [4, 5]. Studies of murine models have shown that RASGRP1 signaling is essential for thymocyte development and function, as well as B cell tolerance [1, 6].…”

“…Studies of murine models have shown that RASGRP1 signaling is essential for thymocyte development and function, as well as B cell tolerance [1, 6]. Only a single case of human RASGRP1 deficiency has been reported in the literature, in a patient with recurrent pneumonias, severe failure to thrive, herpetic lesions, and EBV-associated lymphoma [5]. Laboratory findings were notable for CD4 + T cell lymphopenia, poor T cell proliferation to mitogens, and defective NK function.…”

“…Laboratory findings were notable for CD4 + T cell lymphopenia, poor T cell proliferation to mitogens, and defective NK function. IgG levels were normal, though antibody responses to hepatitis B and pneumococcal vaccines were poor [5]. We report a second case of RASGRP1 deficiency due to a novel nonsense mutation in RASGRP1 .…”