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Dominant activating RAC2 mutation with lymphopenia, immunodeficiency and cytoskeletal defects

Amy P. Hsu, Agnes Donkó, Megan E. Arrington, Muthulekha Swamydas, Danielle Fink, Arundhoti Das, Omar Escobedo, Vincent Bonagura, Paul Szabolcs, Harry N. Steinberg, Jenna Bergerson, Amanda Skoskiewicz, Melanie Makhija, Joie Davis, Ladan Foruraghi, Cindy Palmer, Ramsay L. Fuleihan, Joseph A. Church, Avinash Bhandoola, Michail S. Lionakis, Sharon Campbell, Thomas L. Leto, Douglas Kuhns and Steven M. Holland

Key points

  • E62K is a dominant, activating mutation of the small GTPase, RAC2; patients with RAC2[E62K] have lymphoid and myeloid defects.

  • Rac2+/E62K mice phenocopy the T- and B-cell lymphopenia, increased neutrophil F-actin and excessive superoxide production seen in patients.

Abstract

RAC2, through interactions with NADPH component p67phox, activates neutrophil superoxide production, while interactions with p21-activated kinase (PAK1) are necessary for fMLF-induced actin remodeling. We identified three patients with de novo RAC2[E62K] mutations resulting in severe T- and B-cell lymphopenia, myeloid dysfunction and recurrent respiratory infections. Neutrophils from RAC2[E62K] patients exhibited excessive superoxide production, impaired fMLF-directed chemotaxis, and abnormal macropinocytosis. Cell lines transfected with RAC2[E62K] displayed characteristics of active GTP-bound RAC2 including enhanced superoxide production and increased membrane ruffling. Biochemical studies demonstrated that RAC2[E62K] retains intrinsic GTP hydrolysis, however GTPase-activating protein (GAP) failed to accelerate hydrolysis resulting in prolonged active GTP-bound RAC2. Rac2+/E62K mice phenocopy the T- and B-cell lymphopenia, increased neutrophil F-actin and excessive superoxide production seen in patients. This gain of function mutation highlights a specific, non-redundant role for RAC2 in hematopoietic cells that discriminates RAC2 from the related, ubiquitous RAC1.

  • Submitted November 15, 2018.
  • Accepted January 29, 2019.