Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD 21224, USA.
Nucleic Acids Res. 2009 Dec;37(22):7623-37. doi: 10.1093/nar/gkp755.
The X chromosome-linked inhibitor of apoptosis protein (XIAP) is the most potent intrinsic caspase inhibitor and plays an important role in the maintenance of intestinal epithelial integrity. The RNA binding protein, HuR, regulates the stability and translation of many target transcripts. Here, we report that HuR associated with both the 3'-untranslated region and coding sequence of the mRNA encoding XIAP, stabilized the XIAP transcript and elevated its expression in intestinal epithelial cells. Ectopic HuR overexpression or elevated cytoplasmic levels of endogenous HuR by decreasing cellular polyamines increased [HuR/XIAP mRNA] complexes, in turn promoting XIAP mRNA stability and increasing XIAP protein abundance. Conversely, HuR silencing in normal and polyamine-deficient cells rendered the XIAP mRNA unstable, thus reducing the steady state levels of XIAP. Inhibition of XIAP expression by XIAP silencing or by HuR silencing reversed the resistance of polyamine-deficient cells to apoptosis. Our findings demonstrate that HuR regulates XIAP expression by stabilizing its mRNA and implicates HuR-mediated XIAP in the control of intestinal epithelial apoptosis.
X 染色体连锁的凋亡蛋白抑制剂（XIAP）是最有效的内源性半胱天冬酶抑制剂，在维持肠道上皮细胞完整性方面发挥着重要作用。RNA 结合蛋白 HuR 调节许多靶转录本的稳定性和翻译。在这里，我们报告 HuR 与编码 XIAP 的 mRNA 的 3'-非翻译区和编码序列都结合，稳定了 XIAP 转录本，并在肠道上皮细胞中升高其表达。通过减少细胞多胺来过表达外源性 HuR 或升高内源性 HuR 的细胞质水平，增加 [HuR/XIAP mRNA] 复合物，进而促进 XIAP mRNA 的稳定性并增加 XIAP 蛋白丰度。相反，在正常和多胺缺乏细胞中沉默 HuR 使 XIAP mRNA 不稳定，从而降低 XIAP 的稳态水平。通过 XIAP 沉默或 HuR 沉默抑制 XIAP 表达，逆转了多胺缺乏细胞对细胞凋亡的抵抗。我们的研究结果表明，HuR 通过稳定其 mRNA 来调节 XIAP 的表达，并表明 HuR 介导的 XIAP 参与了对肠道上皮细胞凋亡的控制。
