Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
Neoplasia. 2012 Oct;14(10):986-93. doi: 10.1593/neo.121218.
AT-rich interactive domain 1A (ARID1A) has emerged as a new tumor suppressor in which frequent somatic mutations have been identified in several types of human cancers. Although most ARID1A somatic mutations are frame-shift or nonsense mutations that contribute to mRNA decay and loss of protein expression, 5% of ARID1A mutations are in-frame insertions or deletions (indels) that involve only a small stretch of peptides. Naturally occurring in-frame indel mutations provide unique and useful models to explore the biology and regulatory role of ARID1A. In this study, we analyzed indel mutations identified in gynecological cancers to determine how these mutations affect the tumor suppressor function of ARID1A. Our results demonstrate that all in-frame mutants analyzed lost their ability to inhibit cellular proliferation or activate transcription of CDKN1A, which encodes p21, a downstream effector of ARID1A. We also showed that ARID1A is a nucleocytoplasmic protein whose stability depends on its subcellular localization. Nuclear ARID1A is less stable than cytoplasmic ARID1A because ARID1A is rapidly degraded by the ubiquitin-proteasome system in the nucleus. In-frame deletions affecting the consensus nuclear export signal reduce steady-state protein levels of ARID1A. This defect in nuclear exportation leads to nuclear retention and subsequent degradation. Our findings delineate a mechanism underlying the regulation of ARID1A subcellular distribution and protein stability and suggest that targeting the nuclear ubiquitin-proteasome system can increase the amount of the ARID1A protein in the nucleus and restore its tumor suppressor functions.
富含 AT 的相互作用结构域蛋白 1A（ARID1A）是一种新的肿瘤抑制因子，在多种人类癌症中频繁发现其体细胞突变。尽管大多数 ARID1A 体细胞突变是导致 mRNA 降解和蛋白表达缺失的移码或无义突变，但 5%的 ARID1A 突变是框内插入或缺失（indels），仅涉及一小段肽。天然存在的框内插入缺失突变提供了独特而有用的模型，可用于探索 ARID1A 的生物学和调节作用。在这项研究中，我们分析了妇科癌症中鉴定的插入缺失突变，以确定这些突变如何影响 ARID1A 的肿瘤抑制功能。我们的结果表明，分析的所有框内突变体均丧失了抑制细胞增殖或激活 CDKN1A 转录的能力，CDKN1A 编码 ARID1A 的下游效应物 p21。我们还表明，ARID1A 是一种核质蛋白，其稳定性取决于其亚细胞定位。核内 ARID1A 不如细胞质 ARID1A 稳定，因为 ARID1A 在核内迅速被泛素-蛋白酶体系统降解。影响共识核输出信号的框内缺失会降低 ARID1A 的稳态蛋白水平。这种核输出缺陷导致核内保留和随后的降解。我们的发现描绘了 ARID1A 亚细胞分布和蛋白稳定性调节的机制，并表明靶向核内泛素-蛋白酶体系统可以增加核内 ARID1A 蛋白的数量，并恢复其肿瘤抑制功能。
