Adipose PancreasAorta MuscleHeart Liver LungKidney Testis Spleen Brian 18S p55 γ p55 α Figure S1 Tissue distribution of p55 . (A) Representative RT-PCR showing that p55  is expressed in aorta. (B) Representative RT-PCR showing the expression of p55  mRNA is dominant in aorta and VSMCs rather than p55 . A. B. 18Sp55 γ p55 α Aorta VSMCs Supplementary Figures

p53  -actin Scrambled p53 siRNA1 p53 siRNA Figure S2 Representative western blots and averaged data showing the knockdown of p53 in cultured VSMCs infected with scrambled or two sets of p53 siRNA (p53 siRNA1 and p53 siRNA2; n = 6; **P <0.01 versus scrambled).

p53 MG Ad-p55  Ad-GFP + β- actin Figure S3 The regulation of p53 by p55  with or without proteasome inhibitor MG132. Cells were treated with MG132 (20  M) for 4 hours before harvesting. For all panels, HCT116 p53 +/+ cells were infected with Ad-GFP or Ad- p55  (100 m.o.i., 48 hours). n = 6; **P <0.01 versus Ad-GFP; †P <0.05 versus Ad-p55 . †

Figure S4 p55  reverses MDM2-induced p53 reduction. HCT116 p53 +/+ cells were infected with Ad-GFP or Ad-p55  (100 m.o.i., 48 hours), and cotransfected with MDM2 expressing vector as indicated. n = 5; *P <0.05, **P <0.01 versus Ad-GFP; †P <0.05 versus Ad-GFP/MDM Ad-p55 γ MDM Ad-GFP p53 GAPDH Flag (p55 γ) Flag (MDM2) 90 kDa 55 kDa GFP †

Ad-GFP Ad-p55  Hoechst staining A. B.C. Figure S5 Overexpression of p55  does not affect cell survival. (A) Representative image of Hoechst staining in VSMCs transfected with Ad-GFP or Ad-p55  (n = 5; 100 m.o.i. for 48 hours). (B and C) Overexpression of p55  does not affect PDGF-BB-induced Akt and ERK phosphorylation. Representative western blot and averaged data showing the total or phosphorylated Akt (B) and ERK (C) protein level in the VSMCs transfected with Ad-GFP or Ad-p55  (n = 6). p-ERK t-ERK Ad-GFP Ad-p55  PDGF-BB p-Akt t-Akt Ad-GFP Ad-p55  PDGF-BB

Figure S6 Overexpression of p55  and knockdown of p55  does not affect PI3K activity. (A) PI3K activity in VSMCs transfected with Ad-GFP or Ad-p55  (n = 5; 100 m.o.i. for 48 hours). (B) PI3K activity in VSMCs transfected with Ad- scrambled or Ad-p55  -shRNA1 or Ad-p55  -shRNA2 (n = 5; 100 m.o.i. for 48 hours). A.B. Ad-GFP Ad-p55  Ad-scrambled Ad-p55  -shRNA1 Ad-p55  -shRNA

Table S1 Identify p53 as one of the p55  associated proteins by mass spectrum SequenceDescriptiveConf% IPI K.KKPLDGEYFTLQIR.GTP53 Isoform 1 of Cellular tumor antigen p % IPI accession number Three independent experiments were performed for p55  interacting proteins totally. Cells without infection of Ad-p55  -flag served as control. The p53 protein was identified in two independent experiments.