FOXP3 is a homo-oligomer and a component of a supramolecular regulatory complex disabled in the human XLAAD/IPEX autoimmune disease - PubMed (original) (raw)

doi: 10.1093/intimm/dxm043. Epub 2007 Jun 22.

Arabinda Samanta, Xiaomin Song, Kathryn T Iacono, Patrick Brennan, Talal A Chatila, Giovanna Roncador, Alison H Banham, James L Riley, Qiang Wang, Yuan Shen, Sandra J Saouaf, Mark I Greene

Affiliations

FOXP3 is a homo-oligomer and a component of a supramolecular regulatory complex disabled in the human XLAAD/IPEX autoimmune disease

Bin Li et al. Int Immunol. 2007 Jul.

Abstract

We have found that FOXP3 is an oligomeric component of a large supramolecular complex. Certain FOXP3 mutants with single amino acid deletions in the leucine zipper domain of FOXP3 are associated with the X-linked autoimmunity-allergic dysregulation (XLAAD) and immunodysregulation, polyendocrinopathy and enteropathy, X-linked (IPEX) syndrome in humans. We report that the single amino acid deletion found in human XLAAD/IPEX patients within the leucine zipper domain of FOXP3 does not disrupt its ability to join the larger protein complex, but eliminates FOXP3 homo-oligomerization as well as heteromerization with FOXP1. We found that the zinc finger-leucine zipper domain region of FOXP3 is sufficient to mediate both homodimerization and homotetramerization. However, the same domain region from XLAAD/IPEX FOXP3 containing an E251 deletion prevents oligomerizaton and the protein remains monomeric. We also found that wild-type FOXP3 directly binds to the human IL-2 promoter, but the E251 deletion in FOXP3 in XLAAD/IPEX patient's T cells disrupts its association with the IL-2 promoter in vivo and in vitro, and limits repression of IL-2 transcription after T-cell activation. Our results suggest that compromising FOXP3 homo-oligomerization and hetero-oligomerization with the FOXP1 protein impairs DNA-binding properties leading to distinct biochemical phenotypes in humans with the XLAAD/IPEX autoimmune syndrome. This study explains some features of the pathogenesis of a disease syndrome that arises as a consequence of specific assembly failure of a transcriptional repressor due to certain mutations within the FOXP3 leucine zipper.

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