The PBX1 lupus susceptibility gene regulates CD44 expression

• Published in: Molecular immunology Vol. 85; pp. 148 - 154
• Main Authors: Niu, Yuxin, Sengupta, Mayami, Titov, Anton A., Choi, Seung-Chul, Morel, Laurence
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.05.2017
• Subjects: animal models; binding sites; Blotting, Western; CD4-positive T-lymphocytes; CD4-Positive T-Lymphocytes - immunology; CD44; Chromatin Immunoprecipitation; DNA; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Flow Cytometry; Gene Expression Regulation - genetics; genes; Genetic Predisposition to Disease - genetics; homeostasis; Humans; Hyaluronan Receptors - biosynthesis; Hyaluronan Receptors - genetics; Hyaluronan Receptors - immunology; Immunoprecipitation; Jurkat Cells; leukemia; Lupus; lupus erythematosus; Lupus Erythematosus, Systemic - genetics; Lupus Erythematosus, Systemic - immunology; Lupus Erythematosus, Systemic - metabolism; Lymphocyte Activation - genetics; Lymphocyte Activation - immunology; memory; microRNA; Mutagenesis, Site-Directed; mutation; PBX1; Pre-B-Cell Leukemia Transcription Factor 1; Protein Isoforms - genetics; Protein Isoforms - immunology; Protein Isoforms - metabolism; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Real-Time Polymerase Chain Reaction; T cells; Lupus; T cells; PBX1; CD44
• ISSN: 0161-5890; 1872-9142
• DOI: 10.1016/j.molimm.2017.02.016

•PBX1-d is novel splice isoform of PBX1 that is expressed in lupus CD4+ T cells.•PBX1 binds to the CD44 promoter and directly regulates its expression.•PBX1-d enhances CD44 expression relative to PBX1-b, the normal PBX1 isoform.•PBX1-d and PBX1-b have different DNA binding and co-factor recruitment requirement. PBX1-d is novel splice isoform of pre-B-cell leukemia homeobox 1 (PBX1) that lacks its DNA-binding and Hox-binding domains, and functions as a dominant negative. We have shown that PBX1-d expression in CD4+ T cells is associated with systemic lupus erythematosus (SLE) in a mouse model as well as in human subjects. More specifically, PBX1-d expression leads to the production of autoreactive activated CD4+ T cells, a reduced frequency and function of Foxp3+ regulatory T (Treg) cells and an expansion of follicular helper T (Tfh) cells. Very little is known about the function of PBX1 in T cells, except that it directly regulates the expression of miRNAs associated with Treg and Tfh homeostasis. In the present study, we show that PBX1 directly regulated the expression of CD44, a marker of T cell activation. Two PBX1 binding sites in the promoter directly regulated CD44 expression, with PBX1-d driving a higher expression than the normal isoform PBX1-b. In addition, mutations in each of the two binding sites had different effects of PBX1-b and PBX1-d. Finally, we showed that an enhanced recruitment of co-factor MEIS by PBX1-d over PBX1-b, while there was no difference for co-factor PREP1 recruitment. Therefore, this study demonstrates that the lupus-associated PBX1-d isoform directly transactivates CD44, a marker of CD44 activation and memory, and that it has different DNA binding and co-factor recruitment relative to the normal isoform. Taken together, these results confirm that PBX1 directly regulates genes related to T cell activation and shows that the lupus-associated isoform PBX1-d has unique molecular functions.