Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

RNAP II is frequently paused near gene promoters in mammals, and its transition to productive elongation requires active recruitment of P-TEFb, a cyclin-dependent kinase for RNAP II and other key transcription elongation factors. A fraction of P-TEFb is sequestered in an inhibitory complex containing the 7SK noncoding RNA, but it has been unclear how P-TEFb is switched from the 7SK complex to RNAP II during transcription activation. We report that SRSF2 (also known as SC35, an SR-splicing factor) is part of the 7SK complex assembled at gene promoters and plays a direct role in transcription pause release. We demonstrate RNA-dependent, coordinated release of SRSF2 and P-TEFb from the 7SK complex and transcription activation via SRSF2 binding to promoter-associated nascent RNA. These findings reveal an unanticipated SR protein function, a role for promoter-proximal nascent RNA in gene activation, and an analogous mechanism to HIV Tat/TAR for activating cellular genes.
 ...
PMID:SR proteins collaborate with 7SK and promoter-associated nascent RNA to release paused polymerase. 2366 83

Phosphorylation-dependent cell communication requires enzymes that specifically recognize key proteins in a sea of similar, competing substrates. The protein kinases achieve this goal by utilizing docking grooves in the kinase domain or heterologous protein adaptors to reduce 'off pathway' targeting. We now provide evidence that the nuclear protein kinase CLK1 (cell division cycle2-like kinase 1) important for splicing regulation departs from these classic paradigms by using a novel self-association mechanism. The disordered N-terminus of CLK1 induces oligomerization, a necessary event for targeting its physiological substrates the SR protein (splicing factor containing a C-terminal RS domain) family of splicing factors. Increasing the CLK1 concentration enhances phosphorylation of the splicing regulator SRSF1 (SR protein splicing factor 1) compared with the general substrate myelin basic protein (MBP). In contrast, removal of the N-terminus or dilution of CLK1 induces monomer formation and reverses this specificity. CLK1 self-association also occurs in the nucleus, is induced by the N-terminus and is important for localization of the kinase in sub-nuclear compartments known as speckles. These findings present a new picture of substrate recognition for a protein kinase in which an intrinsically disordered domain is used to capture physiological targets with similar disordered domains in a large oligomeric complex while discriminating against non-physiological targets.
...
PMID:Nuclear protein kinase CLK1 uses a non-traditional docking mechanism to select physiological substrates. 2644 64

Phosphorylation has been generally thought to activate the SR family of splicing factors for efficient splice-site recognition, but this idea is incompatible with an early observation that overexpression of an SR protein kinase, such as the CDC2-like kinase 1 (CLK1), weakens splice-site selection. Here, we report that CLK1 binds SR proteins but lacks the mechanism to release phosphorylated SR proteins, thus functionally inactivating the splicing factors. Interestingly, CLK1 overcomes this dilemma through a symbiotic relationship with the serine-arginine protein kinase 1 (SRPK1). We show that SRPK1 interacts with an RS-like domain in the N terminus of CLK1 to facilitate the release of phosphorylated SR proteins, which then promotes efficient splice-site recognition and subsequent spliceosome assembly. These findings reveal an unprecedented signaling mechanism by which two protein kinases fulfill separate catalytic features that are normally encoded in single kinases to institute phosphorylation control of pre-mRNA splicing in the nucleus.
 ...
PMID:Release of SR Proteins from CLK1 by SRPK1: A Symbiotic Kinase System for Phosphorylation Control of Pre-mRNA Splicing. 2739 83

The versatile functions of SR (serine/arginine-rich) proteins in pre-mRNA splicing and processing are modulated by reversible phosphorylation. Previous studies showed that FgPrp4, the only protein kinase among spliceosome components, is important for intron splicing and the FgSrp1 SR protein is phosphorylated at five conserved sites in Fusarium graminearum. In this study, we showed that the Fgsrp1 deletion mutant rarely produced conidia and caused only limited symptoms on wheat heads and corn silks. Deletion of FgSRP1 also reduced ascospore ejection and deoxynivalenol (DON) production. Interestingly, FgSRP1 had two transcript isoforms due to alternative splicing and both of them were required for its normal functions in growth and DON biosynthesis. FgSrp1 localized to the nucleus and interacted with FgPrp4 in vivo. Deletion of all four conserved phosphorylation sites but not individual ones affected the FgSRP1 function, suggesting their overlapping functions. RNA-seq analysis showed that the expression of over thousands of genes and splicing efficiency in over 140 introns were affected. Taken together, FgSRP1 is important for conidiation, and pathogenesis and alternative splicing is important for its normal functions. The FgSrp1 SR protein is likely important for pre-mRNA processing or splicing of various genes in different developmental and infection processes.
 ...
PMID:The FgSRP1 SR-protein gene is important for plant infection and pre-mRNA processing in Fusarium graminearum. 2865 15

Serine-arginine (SR) proteins are essential splicing factors containing a canonical RNA recognition motif (RRM), sometimes followed by a pseudo-RRM, and a C-terminal arginine/serine-rich (RS) domain that undergoes multisite phosphorylation. Phosphorylation regulates the localization and activity of SR proteins, and thus may provide insight into their differential biological roles. The phosphorylation mechanism of the prototypic SRSF1 by serine-arginine protein kinase 1 (SRPK1) has been well-studied, but little is known about the phosphorylation of other SR protein members. In the present study, interaction and kinetic assays unveiled how SRSF1 and the single RRM-containing SRSF3 are phosphorylated by SRPK2, another member of the SRPK family. We showed that a conserved SRPK-specific substrate-docking groove in SRPK2 impacts the binding and phosphorylation of both SR proteins, and the localization of SRSF3. We identified a nonconserved residue within the groove that affects the kinase processivity. We demonstrated that, in contrast to SRSF1, for which SRPK-mediated phosphorylation is confined to the N-terminal region of the RS domain, SRSF3 phosphorylation sites are spread throughout its entire RS domain in vitro Despite this, SRSF3 appears to be hypophosphorylated in cells at steady state. Our results suggest that the absence of a pseudo-RRM renders the single RRM-containing SRSF3 more susceptible to dephosphorylation by phosphatase. These findings suggest that the single RRM- and two RRM-containing SR proteins represent two subclasses of phosphoproteins in which phosphorylation statuses are maintained by unique mechanisms, and pose new directions to explore the distinct roles of SR proteins in vivo.
 ...
PMID:Distinct mechanisms govern the phosphorylation of different SR protein splicing factors. 3047 76

Serine-arginine (SR) protein kinase 1 (SRPK1) catalyzes the phosphorylation of SR proteins, which are a conserved family of splicing factors that contain a domain rich in arginine and serine repeats. SR proteins play important roles in constitutive pre-mRNA splicing and are also important regulators of alternative splicing. During herpes simplex virus infection, SRPK1 is inactivated and its cellular distribution is markedly altered by interaction with the viral protein ICP27, resulting in hypophosphorylation of SR proteins. Mutational analysis previously showed that the RGG box motif of ICP27 is required for interaction with SRPK1; however, the mechanism for the inhibition and the exact role of the RGG box was unknown. Here, we used solution nuclear magnetic resonance (NMR) spectroscopy and isothermal titration calorimetry (ITC) to demonstrate that the isolated peptide comprising the RGG box of ICP27 binds to SRPK1 with high affinity, competing with a native substrate, the SR repeat region of SR protein SRSF1. We determined the crystal structure of the complex between SRPK1 and an RGG box peptide, which revealed that the viral peptide binds to the substrate docking groove, mimicking the interactions of SR repeats. Site-directed mutagenesis within the RGG box further confirmed the importance of selected arginine residues for interaction, relocalization, and inhibition of SRPK1 in vivo Together these data reveal the molecular mechanism of the competitive inhibition of cellular SRPK1 by viral ICP27, which modulates SRPK1 activity.IMPORTANCE Serine arginine (SR) proteins are a family of mRNA regulatory proteins that can modulate spliceosome association with different splice sites and therefore regulate alternative splicing. Phosphorylation within SR proteins is necessary for splice-site recognition, and this is catalyzed by SR protein kinase 1 (SRPK1). The herpes simplex virus (HSV-1) protein ICP27 has been shown previously to interact with and downregulate SRPK1 activity in vivo; however, the molecular mechanism for this interaction and inhibition was unknown. Here, we demonstrate that the isolated peptide fragment of ICP27 containing RGG box binds to SRPK1 with high affinity, and competes with a native cellular substrate. Elucidation of the SRPK1-RGG box crystal structure further showed that a short palindromic RGRRRGR sequence binds in the substrate docking groove of SRPK1, mimicking the binding of SR repeats of substrates. These data reveal how the viral protein ICP27 inactivates SRPK1, promoting hypophosphorylation of proteins regulating splicing.
 ...
PMID:Molecular Mechanism of SR Protein Kinase 1 Inhibition by the Herpes Virus Protein ICP27. 3164 Oct 93

As the ortholog of human SR protein kinase 1 in fission yeast Schizosaccharomyces pombe, Dsk1 specifically phosphorylates SR proteins (serine/arginine-rich proteins) and promotes splicing of nonconsensus introns. The SRPK (SR protein-specific kinase) family performs highly conserved functions in eukaryotic cells including cell proliferation, differentiation, development, and apoptosis. Although Dsk1 was originally identified as a mitotic regulator, its specific targets involved in cell cycle have yet been unexplored. In this study, using a phosphoproteomics approach, we examined differential protein phosphorylation between wild-type cells and dsk1-deletion mutants. We found reduced phosphorylation of 149 peptides corresponding to 133 proteins in the dsk1-null cells. These proteins are involved in various cellular processes, including cytoskeleton organization and signal transduction, and specifically enriched in multiple steps of cell cycle control. Further, targeted MS analyses and in vitro biochemical assays established Cdr2 protein kinase and kinesin motor Klp9 as novel substrates of Dsk1, which function in cell size control for mitotic entry and in chromosome segregation for mitotic exit, respectively. The phosphoprotein networks mediated by Dsk1 reveal, for the first time, the molecular links connecting Dsk1 to mitotic phase transition, sister-chromatid segregation, and cytokinesis, providing further evidence of Dsk1's diverse influence on cell cycle progression and regulation.
 ...
PMID:Phosphoproteomics Reveals Novel Targets and Phosphoprotein Networks in Cell Cycle Mediated by Dsk1 Kinase. 3206 75


<< Previous 1 2 3 4 5