PCBP2 Regulates p16^INK4a-Dependent Cellular Senescence in Response to Iron

Recently, we have identified rs1333046 as one of the candidate functional single nucleotide polymorphisms (fSNPs) on the atherosclerosis-associated CDKN2A/B locus. However, how rs1333046 influences the pathogenesis of and susceptibility to atherosclerosis is unknown. In this work, we demonstrate that rs1333046 is part of a cis-regulatory element (cis-RE) that regulates p16^INK4a and p16^INK4a-dependent cellular senescence in human endothelial cells (ECs). This is achieved by recruiting poly(rC)-binding protein 2 (PCBP2), a member of the poly-cytosine binding protein family. We also reveal that PCBP2 is an upstream regulator of CD40, which regulates the expression of senescence-associated secretory phenotype (SASP) genes through NF-κB signaling. Moreover, consistent with PCBP2 being an iron chaperone, we discover that iron can induce cellular senescence by regulating both p16^INK4a and CD40-mediated SASP gene expression through PCBP2. Notably, iron dynamically regulates p16^INK4a expression by altering the binding of PCBP2 to rs1333046. In addition, reducing intracellular labile iron by overexpressing both iron storage protein ferritin light chain (FTL) and iron exporter ferroportin 1 (FPN1) in ECs suppresses cellular senescence, and overexpression of PCBP2 in both FTL- and FPN1-overexpressing cells restores cellular senescence. Thus, our studies suggest that iron could be a potential environmental factor regulating atherosclerosis-associated cellular senescence, and this is achieved by modulating PCBP2-dependent p16^INK4a and CD40 expression. This study shows the mechanism by which iron affects the pathology of atherosclerosis.