The open conformation of WASP regulates its nuclear localization and gene transcription in myeloid cells.

Mutations in the gene encoding the Wiskott-Aldrich syndrome protein (WASP) are responsible for Wiskott-Aldrich syndrome and WASP is a major actin regulator in the cytoplasm. Although rare gain-of-function mutations in the WASP gene are known to result in X-linked neutropenia (XLN), the molecular pathogenesis of XLN is not fully understood. In this study, we showed that all reported constitutively activating mutants (L270P, S272P and I294T) of WASP were hyperphosphorylated by Src family tyrosine kinases and demonstrated higher actin polymerization activities compared with wild-type (WT) WASP. Further analysis showed a tendency of activating WASP mutants to localize in the nucleus compared with WT or the Y291F mutant of WASP. In addition, we found that WASP could form a complex with nuclear RNA-binding protein, 54 kDa (p54nrb) and RNA polymerase II (RNAP II). ChIP assays revealed that WASP associated with DNA, although the affinity was relatively weaker than RNAP II. To determine whether gene transcription was affected by WASP mutation in myeloid cells, we performed microarray analysis and found different expression profiles between WT and L270P WASP-transfected K562 cells. Among the genes affected, granulocyte colony-stimulating factor receptor, Runx1, and protein tyrosine phosphatase receptor c were included. ChIP on chip analysis of genomic DNA showed WT and L270P WASP had a highly similar DNA-binding pattern but differed in binding affinity at the same locus. Therefore, our results suggest that the open conformation of WASP regulates its nuclear localization and plays requisite roles in regulating gene transcription that would contribute to the outcome in the nucleus of myeloid cells.

Characterization of a novel nonsense mutation in the interleukin-7 receptor alpha gene in a Korean patient with severe combined immunodeficiency.

Although it has been suggested that defective interleukin 7 receptor (IL-7R) signaling is one of the principal causes of severe combined immunodeficiency disease (SCID) in mice and humans, little is known about the molecular and clinical characteristics of human IL-7Ralpha mutations. We report a novel mutation of the IL-7Ralpha gene in a Korean SCID patient with a greatly diminished T-cell count but normal numbers of B-cells and natural killer (NK) cells. Using direct sequencing and restriction fragment length polymorphism analysis, we identified a C-->T nucleotide change at position 638. This change resulted in a nonsense mutation (R206stop) in this patient. Both parents were heterozygous for C/T at this site. The results of this study emphasize the importance of characterization of IL-7Ralpha mutations in SCID patients with diminished T-cell numbers but normal numbers of B-cells and NK cells.