Regulatory Pathways of SR Protein Kinases

描述(申请人提供)：剪接是一种共转录过程，通过该过程，单个基因可以转化为多个独特的信使核糖核酸片段，以增强蛋白质多样性。虽然剪接对于复杂生物体的正常细胞功能是不可或缺的，但错误的剪接选择可能是极其有害的。事实上，拼接错误与许多人类疾病有关，包括肌肉营养不良、阿尔茨海默病、帕金森氏症、代谢紊乱、共济失调和癌症。剪接发生在剪接体，这是一种既包括RNA又包括蛋白质的大分子复合体。在后一组中，SR蛋白是控制剪接体在前体mRNA上组装的位置和方式的基本剪接因子。SR蛋白含有富含精氨酸-丝氨酸重复序列的C末端结构域，其多聚磷酸化控制着剪接位点的选择。SRPK蛋白激酶家族将这些RS结构域磷酸化，引导SR蛋白进入细胞核进行剪接活动。虽然SRPKs通常定位于细胞质中以实现这一功能，但它们在某些条件下可以进入细胞核，进一步影响SR蛋白的磷酸化水平和选择性基因剪接。虽然磷酸化对剪接位点的选择至关重要，但人们对残基的特异性知之甚少 SR蛋白的磷酸化控制着基因的选择性剪接。显然，了解SRPKs在细胞中是如何调控的，以及它们如何识别和磷酸化SR蛋白，对于理解基因剪接和与错误剪接相关的疾病病理是至关重要的。我们发现SRPKs和磷酸酶以相反的方向工作，将磷酸盐集中到RS结构域的C末端。我们现在将探索这种被称为“磷酸盐偏向”的独特磷酸盐分布如何影响SR蛋白的功能。我们最近发现，SRPK1的催化活性依赖于一个核苷酸释放因子，该因子由一个大的插入结构域和一个N末端延伸的序列元件组成。我们认为这种保守的释放因子是细胞内SRPK调节的枢纽。我们将演示磷酸化和蛋白质-蛋白质相互作用如何调节该因子，并调节SR蛋白的磷酸化水平和基因剪接。

DESCRIPTION (provided by applicant): Splicing is a co-transcriptional process whereby a single gene can be converted into multiple unique mRNA fragments for enhanced protein diversity. While splicing is integral for normal cellular function in complex organisms, mistakes i splice-selection can be extremely deleterious. In fact, splicing errors are associated with numerous human diseases including muscular dystrophy, Alzheimer's disease, parkinsonism, metabolic disorders, ataxias and cancers. Splicing occurs at the spliceosome, a macromolecular complex that includes both RNA and proteins. In the latter group, SR proteins are essential splicing factors that control where and how the spliceosome assembles on precursor mRNA. SR proteins contain C-terminal domains rich in arginine-serine repeats whose polyphosphorylation controls splice-site selection. The SRPK family of protein kinases phosphorylates these RS domains directing SR proteins into the nucleus for splicing activity. While SRPKs are normally localized to the cytoplasm for this function, they can enter the nucleus under certain conditions further affecting SR protein phosphorylation levels and alternative gene splicing. Although phosphorylation is critical for splice-site choice, very little is known about how residue-specific phosphorylation of SR proteins controls alternative gene splicing. Clearly, knowing how the SRPKs are regulated in the cell and how they recognize and phosphorylate SR proteins is essential for an understanding of gene splicing and disease pathologies related to mis-splicing. We showed that SRPKs and phosphatases work in opposite directions concentrating phosphates toward the C-terminal end of RS domains. We will now explore how this unique phosphate distribution termed "phosphate biasing" affects SR protein function. We recently showed that the catalytic activity of SRPK1 is dependent on a nucleotide release factor composed of sequence elements from a large insert domain and an N-terminal extension. We propose that this conserved release factor is a hub for SRPK regulation in the cell. We will demonstrate how phosphorylation and protein-protein interactions modulate this factor and regulate SR protein phosphorylation levels and gene splicing.