Mazroui Rachid, Di Marco Sergio, Clair Eveline, von Roretz Christopher, Tenenbaum Scott A, Keene Jack D, Saleh Maya, Gallouzi Imed-Eddine
Department of Biochemistry, McGill University Health Center, McGill University, Montreal, Quebec H3G 146, Canada.
J Cell Biol. 2008 Jan 14;180(1):113-27. doi: 10.1083/jcb.200709030. Epub 2008 Jan 7.
The RNA-binding protein HuR affects cell fate by regulating the stability and/or the translation of messenger RNAs that encode cell stress response proteins. In this study, we delineate a novel regulatory mechanism by which HuR contributes to stress-induced cell death. Upon lethal stress, HuR translocates into the cytoplasm by a mechanism involving its association with the apoptosome activator pp32/PHAP-I. Depleting the expression of pp32/PHAP-I by RNA interference reduces both HuR cytoplasmic accumulation and the efficiency of caspase activation. In the cytoplasm, HuR undergoes caspase-mediated cleavage at aspartate 226. This cleavage activity is significantly reduced in the absence of pp32/PHAP-I. Substituting aspartate 226 with an alanine creates a noncleavable isoform of HuR that, when overexpressed, maintains its association with pp32/PHAP-I and delays the apoptotic response. Thus, we propose a model in which HuR association with pp32/PHAP-I and its caspase-mediated cleavage constitutes a regulatory step that contributes to an amplified apoptotic response.
RNA 结合蛋白 HuR 通过调节编码细胞应激反应蛋白的信使核糖核酸的稳定性和/或翻译来影响细胞命运。在本研究中，我们阐明了一种新的调节机制，通过该机制 HuR 促成应激诱导的细胞死亡。在致死性应激下，HuR 通过一种涉及其与凋亡小体激活剂 pp32/PHAP-I 结合的机制转位至细胞质中。通过 RNA 干扰降低 pp32/PHAP-I 的表达，可减少 HuR 在细胞质中的积累以及半胱天冬酶激活的效率。在细胞质中，HuR 在天冬氨酸 226 处发生半胱天冬酶介导的切割。在没有 pp32/PHAP-I 的情况下，这种切割活性显著降低。用丙氨酸替代天冬氨酸 226 可产生一种不可切割的 HuR 异构体，当该异构体过表达时，它会维持其与 pp32/PHAP-I 的结合并延迟凋亡反应。因此，我们提出了一个模型，其中 HuR 与 pp32/PHAP-I 的结合及其半胱天冬酶介导的切割构成了一个调节步骤，有助于增强凋亡反应。
