title: The PBX1 lupus susceptibility gene regulates CD44 expression.
abstract: 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.
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL, 32610-0275, USA.
authors.forename: Yuxin
authors.initials: Y
authors.lastname: Niu
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL, 32610-0275, USA.
authors.forename: Mayami
authors.initials: M
authors.lastname: Sengupta
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL, 32610-0275, USA.
authors.forename: Anton A
authors.initials: AA
authors.lastname: Titov
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL, 32610-0275, USA.
authors.forename: Seung-Chul
authors.initials: SC
authors.lastname: Choi
authors.affiliation: Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL, 32610-0275, USA. Electronic address: morel@ufl.edu.
authors.forename: Laurence
authors.initials: L
authors.lastname: Morel
mesh_terms: D015153:Blotting, Western; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D047369:Chromatin Immunoprecipitation; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000235:genetics; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D018960:Hyaluronan Receptors / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D047468:Immunoprecipitation; D019169:Jurkat Cells; D008180:Lupus Erythematosus, Systemic / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D008213:Lymphocyte Activation / Q000235:genetics* / Q000276:immunology; D016297:Mutagenesis, Site-Directed; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D020033:Protein Isoforms / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction
chemical_list: C497483:CD44 protein, human; D004268:DNA-Binding Proteins; D018960:Hyaluronan Receptors; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; C083400:PBX1 protein, human
keywords: CD44; Lupus; PBX1; T cells