ARHGEF1 is a RhoA-specific guanine nucleotide exchange factor expressed in hematopoietic cells. We used whole-exome sequencing to identify compound heterozygous mutations in ARHGEF1, resulting in the loss of ARHGEF1 protein expression in 2 primary antibody–deficient siblings presenting with recurrent severe respiratory tract infections and bronchiectasis. Both ARHGEF1-deficient patients showed an abnormal B cell immunophenotype, with a deficiency in marginal zone and memory B cells and an increased frequency of transitional B cells. Furthermore, the patients’ blood contained immature myeloid cells. Analysis of a mediastinal lymph node from one patient highlighted the small size of the germinal centers and an abnormally high plasma cell content. On the molecular level, T and B lymphocytes from both patients displayed low RhoA activity and low steady-state actin polymerization (even after stimulation of lysophospholipid receptors). As a consequence of disturbed regulation of the RhoA downstream target Rho-associated kinase I/II (ROCK), the patients’ lymphocytes failed to efficiently restrain AKT phosphorylation. Enforced ARHGEF1 expression or drug-induced activation of RhoA in the patients’ cells corrected the impaired actin polymerization and AKT regulation. Our results indicate that ARHGEF1 activity in human lymphocytes is involved in controlling actin cytoskeleton dynamics, restraining PI3K/AKT signaling, and confining B lymphocytes and myelocytes within their dedicated functional environment.
Amine Bouafia, Sébastien Lofek, Julie Bruneau, Loïc Chentout, Hicham Lamrini, Amélie Trinquand, Marie-Céline Deau, Lucie Heurtier, Véronique Meignin, Capucine Picard, Elizabeth Macintyre, Olivier Alibeu, Marc Bras, Thierry Jo Molina, Marina Cavazzana, Isabelle André-Schmutz, Anne Durandy, Alain Fischer, Eric Oksenhendler, Sven Kracker
Myelocytosis, an increase in transitional B cells, and the absence of marginal zone and memory B cells are hallmarks of the patients’ phenotype.