Regulatory Pathways of SR Protein Kinases

描述（由申请人提供）：剪接是一种共转录过程，单个基因可以转化为多个独特的mRNA片段，以增强蛋白质多样性。虽然剪接是复杂生物体正常细胞功能的组成部分，但剪接选择中的错误可能是极其有害的。事实上，剪接错误与许多人类疾病有关，包括肌肉萎缩症、阿尔茨海默病、帕金森病、代谢紊乱、共济失调和癌症。剪接发生在剪接体上，剪接体是一种包含RNA和蛋白质的大分子复合物。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重要剪接因子。SR蛋白含有富含精氨酸-丝氨酸重复序列的c端结构域，其多磷酸化控制着剪接位点的选择。SRPK蛋白激酶家族磷酸化这些RS结构域，引导SR蛋白进入细胞核进行剪接活性。虽然SRPKs通常定位于细胞质中发挥这一功能，但在某些条件下，它们可以进入细胞核，进一步影响SR蛋白的磷酸化水平和选择性基因剪接。尽管磷酸化对剪接位点的选择至关重要，但对残基特异性的了解甚少

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.