Pre-B cell leukemia homeobox protein Pbx1 is associated with lupus susceptibility in mice and humans

Sle1a.1 is part of the Sle1a lupus susceptibility locus which results in the production of activated and autoreactive CD4+ T cells as well as a reduction in the peripheral regulatory T cell (Treg) pool. Sle1a.1 CD4+ T cells showed a defective response to retinoic acid (RA) expansion of TGFβ-induced Tregs. At the molecular level, Sle1a.1 corresponds to an increased expression of a novel splice isoform of Pbx1, Pbx1-d. Pbx1-d over-expression is sufficient to induce an activated/inflammatory phenotype in Jurkat T cells, and to decrease their apoptotic response to RA. PBX1-d is expressed more frequently in lupus patients than in healthy controls, and its presence correlates with an increased memory T cell population. These findings indicate that Pbx1 is a novel lupus susceptibility gene that regulates T cell activation and tolerance. Total RNA from CD4+ T cells from C57BL/6 (B6) and B6.Sle1a.1 (Sle) mice was isolated, with 4 biological replicates each. Gene expression data from C57BL/6 mice were compared with data from B6.Sle2c1 mice.