Regulation of IL-2 gene expression by Siva and FOXP3 in human T cells

<p>Abstract</p> <p>Background</p> <p>Severe autoinflammatory diseases are associated with mutations in the <it>Foxp3 </it>locus in both mice and humans. <it>Foxp3 </it>is required for the development, function, and maintenance of regulatory T cells (T_regs), a subset of CD4 cells that suppress T cell activation and inflammatory processes. <it>Siva </it>is a pro-apoptotic gene that is expressed across a range of tissues, including CD4 T cells. Siva interacts with three tumor necrosis factor receptor (TNFR) family members that are constitutively expressed on T_regcells: CD27, GITR, and OX40.</p> <p>Results</p> <p>Here we report a biophysical interaction between FOXP3 and Siva. We mapped the interaction domains to Siva's C-terminus and to a central region of FOXP3. We showed that <it>Siva </it>repressed IL-2 induction by suppressing <it>IL-2 </it>promoter activity during T cell activation. Siva-1's repressive effect on <it>IL-2 </it>gene expression appears to be mediated by inhibition of NFkappaB, whereas FOXP3 repressed both NFkappaB and NFAT activity.</p> <p>Conclusions</p> <p>In summary, our data suggest that both <it>FOXP3 </it>and <it>Siva </it>function as negative regulators of IL-2 gene expression in T_regcells, via suppression of NFAT by <it>FOXP3 </it>and of NFkappaB by both <it>FOXP3 </it>and <it>Siva</it>. Our work contributes evidence for <it>Siva's </it>role as a T cell signalling mediator in addition to its known pro-apoptotic function. Though further investigations are needed, evidence for the biophysical interaction between FOXP3 and Siva invites the possibility that Siva may be important for proper T_regcell function.</p

FoxP3 interacts with linker histone H1.5 to modulate gene expression and program Treg cell activity

The forkhead box transcription factor FoxP3 controls the development and function of CD4+CD25+ regulatory T (Treg) cell. FoxP3 modulates gene expression in Treg cells by multiple epigenetic mechanisms that are not clearly defined. We identified FoxP3 interacting proteins in human T cells by co-IP/MS. We discovered that FoxP3 interacted with linker histone H1.5 via the leucine zipper (LZ) domain. Two independent IPEX patient-derived single residue mutations in the LZ of FoxP3 both abrogated its interaction with H1.5. Functionally, FoxP3 and H1.5 cooperatively repressed IL-2 expression in human T cells; and silencing of H1.5 expression inhibited the ability of FoxP3 to suppress IL-2 expression. We show that FoxP3 specifically enhanced H1.5 association at the IL-2 promoter, but reduce its association at the CTLA4 promoter, correlated with higher or lower histone acetylation of the respective promoters. Finally, silencing of H1.5 expression in human Treg cells impaired the Treg function to suppress target T cells. We conclude that FoxP3 interacts with H1.5 to alter its binding to target genes to modulate their expression and to program Treg function