Laboratory of Genomic Physiology, State Key Laboratory of Medical Neurobiology, Institutes of Brain Science, School of Basic Medical Sciences, Shanghai Medical College, Fudan University, Shanghai, 200032 China.
J Biol Chem. 2013 Mar 29;288(13):8898-909. doi: 10.1074/jbc.M113.456715. Epub 2013 Feb 8.
The serine/arginine-rich (SR) proteins are one type of major actors in regulation of pre-mRNA splicing. Their functions are closely related to the intracellular spatial organization. The RS domain and phosphorylation status of SR proteins are two critical factors in determining the subcellular distribution. Mammalian Transformer-2β (Tra2β) protein, a member of SR proteins, is known to play multiple important roles in development and diseases. In the present study, we characterized the subcellular and subnuclear localization of Tra2β protein and its related mechanisms. The results demonstrated that in the brain the nuclear and cytoplasmic localization of Tra2β were correlated with its phosphorylation status. Using deletional mutation analysis, we showed that the nuclear localization of Tra2β was determined by multiple nuclear localization signals (NLSs) in the RS domains. The point-mutation analysis disclosed that phosphorylation of serine residues in the NLSs inhibited the function of NLS in directing Tra2β to the nucleus. In addition, we identified at least two nuclear speckle localization signals within the RS1 domain, but not in the RS2 domain. The nuclear speckle localization signals determined the localization of RS1 domain-contained proteins to the nuclear speckle. The function of the signals did not depend on the presence of serine residues. The results provide new insight into the mechanisms by which the subcellular and subnuclear localization of Tra2β proteins are regulated.
丝氨酸/精氨酸丰富（SR）蛋白是调节前体 mRNA 剪接的主要因子之一。它们的功能与细胞内的空间组织密切相关。RS 结构域和 SR 蛋白的磷酸化状态是决定亚细胞分布的两个关键因素。哺乳动物转录因子-2β（Tra2β）蛋白是 SR 蛋白家族的一员，已知在发育和疾病中发挥多种重要作用。在本研究中，我们对 Tra2β 蛋白的亚细胞和亚核定位及其相关机制进行了表征。结果表明，在大脑中，Tra2β 的核内和细胞质定位与其磷酸化状态相关。通过缺失突变分析，我们表明 Tra2β 的核定位由 RS 结构域中的多个核定位信号（NLS）决定。点突变分析表明，NLS 中丝氨酸残基的磷酸化抑制了 NLS 指导 Tra2β进入细胞核的功能。此外，我们在 RS1 结构域内鉴定出至少两个核斑点定位信号，但在 RS2 结构域内没有。核斑点定位信号决定了包含 RS1 结构域的蛋白质在核斑点中的定位。信号的功能不依赖于丝氨酸残基的存在。这些结果为 Tra2β 蛋白亚细胞和亚核定位的调节机制提供了新的见解。
