Only 10%–20% of colorectal cancer (CRC) patients observe effective responses to 5-fluorouracil (5-FU) based chemo-treatment. We used real-time PCR array and Western blot analysis to examine the expression alteration of acetyltransferases and deacetylases in 5-FU resistant CRC cell lines as compared to their respective parental CRC cell lines. Unlike other acetyltransferases and deacetylases, we found that the expression of acetyltransferase P300/CBP-associated factor (PCAF) is consistently decreased in three 5-FU resistant CRC cell lines. Similarly, knockdown of PCAF in HCT116 CRC parental cell line also increases the resistance to 5-FU and attenuates 5-FU-induced apoptosis. Mechanistically, we demonstrated that increased binding of trimethylated histone H3K27 in the promoter region of PCAF attenuated its transcription in 5-FU resistant HCT116/5-FU cells. Decreased PCAF impairs the acetylation of p53 and attenuates the p53-dependent transcription of p21, which results in the increased cyclin D1 and phosphorylation of Retinoblastoma 1. Conversely, overexpression of PCAF in CRC cell lines increases p21 and their susceptibility to 5-FU in vitro and in vivo. However, knockdown of p21 abolishes the beneficial effects of PCAF overexpression on increasing the sensitivity of HCT116/5-FU cells to 5-FU. Also, the reduced intensity of PCAF immunostaining was observed in the precancerous lesion, and microarray data from the public database further demonstrated the association between PCAF down-regulation and poor survival outcome. Our data suggest that PCAF-mediated p53 acetylation is an essential regulatory mechanism for increasing the susceptibility of CRC to 5-FU.

只有10％–20％的大肠癌（CRC）患者观察到对基于5-氟尿嘧啶（5-FU）的化学治疗的有效反应。我们使用实时PCR阵列和蛋白质印迹分析来检查5-FU抗性CRC细胞系与其各自的亲代CRC细胞系相比，乙酰转移酶和脱乙酰基酶的表达变化。与其他乙酰转移酶和脱乙酰酶不同，我们发现乙酰转移酶P300 / CBP相关因子（PCAF）的表达在三种5-FU耐药CRC细胞系中持续下降。同样，在HCT116 CRC亲本细胞系中PCAF的敲低也增加了对5-FU的抗性并减弱了5-FU诱导的细胞凋亡。机械上，我们证明PCAF启动子区域中三甲基化组蛋白H3K27的结合增加会减弱其在5-FU耐药HCT116 / 5-FU细胞中的转录。PCAF的减少会损害p53的乙酰化作用，并减弱p21的p53依赖性转录，从而导致细胞周期蛋白D1的增加和视网膜母细胞瘤1的磷酸化。相反，PCAF在CRC细胞系中的过表达会增加p21及其对5-FU的敏感性体外和体内。但是，敲除p21消除了PCAF过表达对增加HCT116 / 5-FU细胞对5-FU敏感性的有益作用。同样，在癌前病变中观察到了PCAF免疫染色强度的降低，并且来自公共数据库的微阵列数据进一步证明了PCAF下调与不良生存结果之间的关联。我们的数据表明，PCAF介导的p53乙酰化是增加CRC对5-FU敏感性的必不可少的调节机制。