Defective nuclear translocation of nuclear factor of activated T cells and extracellular signal-regulated kinase underlies deficient IL-2 gene expression in Wiskott-Aldrich syndrome

Abstract

Proliferation and IL-2 production in response to T-cell receptor ligation are impaired in patients with Wiskott-Aldrich syndrome (WAS). The transcription factors nuclear factor-kappaB (NF-kappaB), nuclear factor of activated T cells (NF-AT), and activating protein-1 (AP-1) play a critical role in IL-2 gene expression. To investigate the mechanisms of impaired IL-2 production after T-cell receptor ligation in T cells deficient in WAS protein (WASP). T cells from WASP-/- mice were stimulated with anti-CD3 and anti-CD28. Nuclear NF-kappaB, NF-AT, and AP-1 DNA-binding activity was examined by electroshift mobility assay. NF-ATp dephosphorylation and nuclear localization were examined by Western blot and indirect immunofluorescence. Phosphorylation of the mitogen-activated protein kinases Erk and Jnk, and of their nuclear substrates Elk-1 and c-Jun, was examined by Western blot. Expression of mRNA for IL-2 and the NF-kappaB-dependent gene A20 and of the AP-1 components c-fos and c-Jun was examined by quantitative RT-PCR. Nuclear translocation and activity of NF-kappaB were normal in T cells from WASP-/- mice. In contrast, NF-ATp dephosphorylation and nuclear localization, nuclear AP-1 binding activity, and expression of c-fos, but not c-Jun, were all impaired. Phosphorylation of Jnk, c-Jun, and Erk were normal. However, nuclear translocation of phosphorylated Erk and phosphorylation of its nuclear substrate Elk1, which activates the c-fos promoter, were impaired. These results suggest that WASP is essential for NF-ATp activation, and for nuclear translocation of p-Erk, Elk1 phosphorylation, and c-fos gene expression in T cells. These defects underlie defective IL-2 expression and T-cell proliferation in WAS.