Scott Gary K, Marx Corina, Berger Crystal E, Saunders Laura R, Verdin Eric, Schäfer Stefan, Jung Manfred, Benz Christopher C
Buck Institute for Age Research, Novato, CA 94945, USA.
Mol Cancer Res. 2008 Jul;6(7):1250-8. doi: 10.1158/1541-7786.MCR-07-2110.
In addition to repressing ERBB2 promoter function, histone deacetylase (HDAC) inhibitors induce the accelerated decay of mature ERBB2 transcripts; the mechanism mediating this transcript destabilization is unknown but depends on the 3' untranslated region (UTR) of ERBB2 mRNA. Using ERBB2-overexpressing human breast cancer cells (SKBR3), the mRNA stability factor HuR was shown to support ERBB2 transcript integrity, bind and endogenously associate with a conserved U-rich element within the ERBB2 transcript 3' UTR, coimmunoprecipitate with RNA-associated HDAC activity, and colocalize with HDAC6. HDAC6 also coimmunoprecipitates with HuR in an RNA-dependent manner and within 6 hours of exposure to a pan-HDAC inhibitor dose, that does not significantly alter cytosolic HuR levels or HuR binding to ERBB2 mRNA. Cellular ERBB2 transcript levels decline while remaining physically associated with HDAC6. Knockdown of HDAC6 protein by small interfering RNA partially suppressed the ERBB2 transcript decay induced by either pan-HDAC or HDAC6-selective enzymatic inhibitors. Three novel hydroxamates, ST71, ST17, and ST80 were synthesized and shown to inhibit HDAC6 with 14-fold to 31-fold greater selectivity over their binding and inhibition of HDAC1. Unlike more potent pan-HDAC inhibitors, these HDAC6-selective inhibitors produced dose-dependent growth arrest of ERBB2-overexpressing breast cancer cells by accelerating the decay of mature ERBB2 mRNA without repressing ERBB2 promoter function. In sum, these findings point to the therapeutic potential of HuR and HDAC6-selective inhibitors, contrasting ERBB2 stability effects induced by HDAC6 enzymatic inhibition and HDAC6 protein knockdown, and show that ERBB2 transcript stability mechanisms include exploitable targets for the development of novel anticancer therapies.
除了抑制ERBB2启动子功能外，组蛋白去乙酰化酶（HDAC）抑制剂还能诱导成熟ERBB2转录本加速降解；介导这种转录本不稳定的机制尚不清楚，但依赖于ERBB2 mRNA的3'非翻译区（UTR）。利用过表达ERBB2的人乳腺癌细胞（SKBR3），研究发现mRNA稳定性因子HuR可维持ERBB2转录本的完整性，与ERBB2转录本3'UTR内一个保守的富含U元件结合并在体内相互作用，与RNA相关的HDAC活性进行共免疫沉淀，并与HDAC6共定位。HDAC6也以RNA依赖的方式与HuR共免疫沉淀，在暴露于泛HDAC抑制剂剂量的6小时内，这并不会显著改变细胞质中HuR的水平或HuR与ERBB2 mRNA的结合。细胞内ERBB2转录本水平下降，同时仍与HDAC6存在物理关联。通过小干扰RNA敲低HDAC6蛋白可部分抑制泛HDAC或HDAC6选择性酶抑制剂诱导的ERBB2转录本降解。合成了三种新型异羟肟酸酯ST71、ST17和ST80，它们对HDAC6的抑制作用比对HDAC1的结合和抑制作用具有14至31倍的更高选择性。与更强效的泛HDAC抑制剂不同，这些HDAC6选择性抑制剂通过加速成熟ERBB2 mRNA的降解而不抑制ERBB2启动子功能，从而对过表达ERBB2的乳腺癌细胞产生剂量依赖性的生长停滞。总之，这些发现指出了HuR和HDAC6选择性抑制剂的治疗潜力，对比了HDAC6酶抑制和HDAC6蛋白敲低对ERBB2稳定性的影响，并表明ERBB2转录本稳定性机制包括可用于开发新型抗癌疗法的可利用靶点。
