Expansion of peritoneal B1a cells in NZM2410 lupus-prone mice is regulated by the cell cycle regulator gene Cdkn2c (47.3)

Abstract

Abstract Here, we identified the cyclin-dependent kinase inhibitor Cdkn2c (p18) gene in the Sle2c1 NZM2410-derived lupus susceptibility locus by the combination of genetic mapping and candidate gene analysis, that is responsible for an expansion of the B1a cell compartment. A novel -74 T/C SNP in the p18 promoter is associated with a significantly reduced p18 expression in the splenic B cells and peritoneal cavity (Pc) B1a cells from Sle2c1-carrying mice, as evidenced by micro array, RT-PCR and immunoblot analysis. Compared to B6 controls, this reduced p18 expression leads to a defective G1 cell cycle arrest in splenic B cells that impairs plasma cell function, and to an increased proliferation of Pc B1a cells which results to an age-dependent expansion of the B1a cell compartment. To determine the function of the -74 T/C SNP in p18 expression, we have cloned and characterized the proximal promoter region of the mouse p18 gene in reporter vector. Functional analysis of the 5' flanking region by sequential deletions revealed crucial elements between -300 and +1, confirming the in silico prediction, that two conserved YY-1 sites located in the Sle2c1 allele negatively regulates the p18 expression in SLE prone mouse. EMSAs and ChIP analysis demonstrated that YY-1 interacts in vitro and in vivo with the p18 promoter. These results provide evidence that p18 plays a critical role in B1a cell self-renewal, and its impaired expression leads to high autoreactive accumulation of B1a cells.