Rationale: Disturbed flow occurring in arterial branches and curvatures induces vascular endothelial cell (EC) dysfunction and atherosclerosis. We postulated that disturbed flow plays important role in modulating phosphoprotein expression profiles to regulate endothelial functions and atherogenesis. Objective: The goal of this study is to discover novel site-specific phosphorylation alterations induced by disturbed flow in ECs to contribute to atherosclerosis. Methods and Results: Quantitative phosphoproteomics analysis of ECs exposed to disturbed flow with low and oscillatory shear stress (0.5±4 dynes/cm 2 ) versus pulsatile shear stress (12±4 dynes/cm 2 ) revealed that oscillatory shear stress induces phospho-YY1 S118 (serine [S]118 phosphorylation of Yin Yang 1) in ECs. Elevated phospho-YY1 S118 level in ECs was further confirmed to be present in the disturbed flow regions in experimental animals and human atherosclerotic arteries. This disturbed flow-induced EC phospho-YY1 S118 is mediated by CK2α (casein kinase 2α) through its direct interaction with YY1. Yeast 2-hybrid library screening and in situ proximity ligation assays demonstrate that phospho-YY1 S118 directly binds ZKSCAN4 (zinc finger with KRAB [krüppel-associated box] and SCAN [SRE-ZBP, CTfin51, AW-1 and Number 18 cDNA] domains 4) to induce promoter activity and gene expression of HDM2 (human double minute 2), which consequently induces EC proliferation through downregulation of p53 and p21 CIP1 . Administration of apoE-deficient ( ApoE −/− ) mice with CK2-specific inhibitor tetrabromocinnamic acid or atorvastatin inhibits atherosclerosis formation through downregulations of EC phospho-YY1 S118 and HDM2. Generation of novel transgenic mice bearing EC-specific overexpression of S118-nonphosphorylatable mutant of YY1 in ApoE −/− mice confirms the critical role of phospho-YY1 S118 in promoting atherosclerosis through EC HDM2. Conclusions: Our findings provide new insights into the mechanisms by which disturbed flow induces endothelial phospho-YY1 S118 to promote atherosclerosis, thus indicating phospho-YY1 S118 as a potential molecular target for atherosclerosis treatment.
