Identification of a novel interaction partner of serine-arginine protein kinase 2 and studies on their roles in transcriptional regulation.

SR蛋白在前體信使核糖核酸(pre-mRNA)的組成性剪接和選擇性剪接中扮演者重要的角色，在這個過程中它需要被SR蛋白激酶(SRPK) 燐酸化才能正常行使功能。經典的SR蛋白是由N端一到二個RNA識別基序(RRM) 以及C端一串精氨酸－絲氨酸(RS) 二肽所構成。SR蛋白的燐酸化調控它的亞細胞定位以及生理功能。此外，SR 蛋白激酶1(SRPK1) 和SR蛋白原型ASF/SF2的復合物結構顯示底物的結合需要第二個非標準的RRM結構域以及在N端可以被燐酸化的RS結構域，但是，第一個標準的RRM結構域對於SR 蛋白激酶1的結合卻是可以或缺的。在這裡，我們展示了SR蛋白激酶2(SRPK2) 結合並且燐酸化SRp20的RS結構域，SRp20是另外一個只包含一個RNA識別基序(RRM) 的SR蛋白。與ASF/SF2相似的是，SRp20中的標準RNA識別基序對於SRPK2的結合並不是必要的。與此同時，我們發現錨定槽對於底物的識別作用在SRPK2中也是保守的，因為，錨定槽中四個關鍵氨基酸的突變會削弱它對SRp20的結合。此外，現在認為SRPK2的功能已經不限於對前體信使核糖核酸(pre-mRNA) 的剪接調控。最近發現，SRPK2也可以燐酸化Tau蛋白並且介導阿爾茨海默疾病中的認知性缺陷。組成性的激活是SR蛋白激酶中的一個固有特性，然而人們對於它的調控機制還不是很清楚。因此, 為了更好的瞭解SRPK2，我們采用酵母雙雜交的方法並且最終發現一個新的SRPK2相互作用蛋白: ZNF187。ZNF187是一個可以結合血清反應元件(SRE) 的轉綠因子。我們的研究發現，它可以正向調控SRE的轉錄激活。然而，SRPK2在EGF的刺激下卻起着抑制的效果，其中EGF的刺激會促使SRPK2進入細胞核。進一步證實，通過RNAi干擾的方法敲掉SRPK2可以增加ZNF187誘導的SRE活性。在共轉染實驗中，SRPK2可以把ZNF187誘導的SRE活性逆轉到本底水平。對於可以和EGF刺激的SRPK2有着相似細胞定位的缺失或者突變研究發現，它們都可以產生相一致的抑制現象。於此相反，對於和SRPK2有着不同細胞定位的突變，它卻不能產生抑制效果。因此，我們認為在EGF的刺激下，SRPK2進入細胞核並且負向的調控ZNF187激活的SRE。令人驚訝的是，如果細胞在FBS的刺激下，SRPK2卻上調SRE活性，並且它可以協同增加ZNF187對於SRE的誘導。這些結果表明SRPK2對於ZNF187誘導的SRE轉綠調控是刺激物依賴的。SR proteins are critical players in regulating both constitutive and alternative pre-mRNA splicing, during which the phosphorylation by SR Protein Kinases (SRPKs) is required. Classical SR proteins contain one or two RNA Recognition Motifs (RRM) in their N terminus and a stretch of Arginine-Serine (RS) dipeptides in C terminus. Phosphorylation status of SR proteins regulates their subcellular localization as well as physiological function. In addition, complex structure of SRPK1 with ASF/SF2, a prototype of SR protein, shows that substrate binding requires non-canonicalRRM2 domain and RS domain, which can be extensivelyphosphorylated. However, the canonical RRM1 domain is dispensable for such interaction.Here we show that SRPK2 binds and phosphorylates SRp20, a classical single RRM domain-containing SR protein, at its RS domain. Similarly with ASF/SF2, the canonical RRM domain of SRp20 is dispensable for interacting with SRPK2. Meanwhile, we also find that a docking groove that iscritical for substrate binding in SRPK1 is also conserved in SRPK2, since mutations on four key residues in docking groove impair its binding affinity with SRp20.In addition, SRPK2 is now known to function more then regulating mRNA splicing, such as cell proliferation and cell apoptosis. Recently, SRPK2 is also shown to be a kinase phosphorylating Tau and mediate the cognitive defects in Alzheimer’s disease (AD). Besides, an intrinsic character of SRPKs lies in that they are constitutively active, but the regulation mechanism is not well understood. Therefore, in order to obtain a better recognition about SRPK2, we applied yeast two-hybrid assay and eventually anew interaction partner called ZNF187 was identified.ZNF187 is a transcriptional factor that binds with Serum Response Element (SRE). Our studies showed that it isa positive regulator of SRE activity. However, SRPK2 showed inhibiting effect on SRE activation with the treatment of EGF, which could induce its nucleus entry, when co-transfected, it reversed the stimulating effect on SRE by ZNF187 to basal level. Furthermore, knockdown of SRPK2 by RNAi would enhance ZNF187-stimuated SRE activation. Studies on truncation and mutations that have the similar effect with EGF-induced subcellular localization of SRPK2 also generated the same inhibiting phenomenon. In contrast, mutant that has distinct localization with SRPK2 wild type failed to exert suppression. Therefore, we conclude that with the treatment of EGF, SRPK2 moves into nucleus and negatively regulates ZNF187-stimulated transactivation of SRE. Surprisingly, when cells were treated with FBS, SRPK2 showed stimulation on SRE activity and it synergized ZNF187-stimulated effect on SRE, indicating that transcriptional regulation of SRPK2 on ZNF187-stimulated SRE activity is stimuli-dependent.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Shang, Yong.Thesis (Ph.D.) Chinese University of Hong Kong, 2014.Includes bibliographical references (leaves 113-137).Abstracts also in Chinese