Studies on signal processing by multisite phosphorylation pathways of the S. cerevisiae cyclin-dependent kinase inhibitor Sic1
Kuupäev
2018-08-21
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Rakkude jagunemine käivitatakse DNA-sünteesi algatamisega. See toimub aga alles siis, kui rakud on valmis kogu järgneva raku jagunemise tsükli peatumata läbi tegema. Rakkude jagunemise käivitavad ja kogu edasist protsessi juhivad tsükliinsõltuvad kinaasid (Tsk). Need on valgud, mis kontrollivad teiste valkude asukohta, eluiga või aktiivsust neile foforhappejääke lisades. Rakutsükli etapid käivitatakse erinevate kindla spetsiifikaga Tsk komplekside poolt.
Rakkude jagunemist kontrolliva mehhanismi uurimiseks kasutatakse laialdaselt mudelorganismina pagaripärmi S. cerevisiae, mille jagunemise tsükli üldine ülesehitus meenutab lihtsustatult inimese rakkudes toimuvat. Pärmirakkude kasvufaasi (G1) käigus rakud akumuleerivad mitmeid Tsk´se. Osad TSK´d on koheselt aktiivsed ning asuvad oma sihtmärke fosforüülima, valmistades rakku S-faasiks ette. Osad Tsk´d, mille aktiivust läheb tarvis alles S-faasi käivitamiseks ja läbiviimiseks, toodetakse inhibeeritud olekus. Nende aktiivsus on blokeeritud valgu Sic1 poolt. Kogu S-faasi käivitamiseks vajalik Tsk toodetakse kasvufaasis tihedalt kompleksis Sic1 valguga, et vältida juhuslikku S-faasi käivitava aktiivsuse lekkimist enne õiget aega.
S-faasi käivitamiseks tuleb Sic1 lagundada, mis vabastab S-faasi spetsiifilise Tsk aktiivsuse. Sic1 ise on Tsk´de sihtmärk ja sisaldab palju fosforüülimiseks sobivaid aminohappeid. Nende fosforüülimine suunab Sic1 lagundamisele, mis määrab S-faasi käivitamise ajastuse ja dünaamika ning on üheks keskseks osaks rakutsükli reguleerimise mehhanismis.
Varasemalt ei olnud teada, millised kinaasid millise dünaamikaga Sic1 fosforüülivad ning seetõttu puudus detailne mudel, kuidas seeläbi saavutatakse kontroll raku jagunemise käivitamise üle. Käesoleva uurimistöö käigus selgitati välja, mis kinaasid ja millise dünaamikaga Sic1 valku fosforüülivad. Sellega avastastasid uurimistöö autorid kvantitatiivse S-faasi käivitamise kontrollmehhanismi, mis reguleerib minutilise täpsusega rakkude jagunemise algust ja tagab selle käivitamiseks piisava koguse Tsk aktiivsust. Selle mehhanismi keskne osa – mitmiksfosforüülitav valk Sic1 – toimib mikrokiibina, mis salvestab kasvufaasis olevas rakus jagunemist toetavad ja takistavad signaalid. Neid signaale tõlgendatakse S-faasi käivitamise ajaks ja dünaamikaks S-faasi käivitava Tsk poolt Sic1 sidumise käigus.
The cell division cycle is initiated with the onset of S-phase where cells replicate their DNA. The DNA-replication is triggered only when cells are sufficiently prepared to conduct following events of cellular division without stopping. The cell division is triggered and following events conducted by cyclin-dependent kinase holoenzymes (Cdk). These multi-component proteins that phosphorylate others to control the localization, lifespan or activity of target proteins. For proper initiation of each cell cycle phase specific Cdk holoenzyme complex is activated. To study the control mechanism of the cell cycle the S. cerevisiae is widely used as a model due to its simplicity and similarity to human cells. During the growth phase (G1) of yeast cells they accumulate different Cdk´s. Some of them are instantly active and begin to phosphorylate their targets preparing cell for the S-phase. Others Cdks necessary to trigger and conduct upcoming S-phase are accumulated in inhibited form. The activity is inhibited by Sic1 protein. All the Cdk necessary for S-phase initiation is accumulated in tight complex with Sic1 protein to avoid early leakage of S-phase kinase activity. To initiate S-phase the Sic1 protein must be degraded that in turn release S-phase specific Cdk activity. Sic1 itself is a Cdk target and contains multiple phosphorylation sites. For Sic1 destruction its phosphorylation from multiple sites is necessary. The phosphorylation of Sic1 determines the timing and dynamics of S-phase onset and has therefore central importance in cell cycle regulating mechanism. Limited knowledge about phosphorylation dynamics of Sic1 shielded quantitative regulatory mechanism of S-phase initiation and left the question of how is the onset of S-phase controlled unsolved. This study unveiled missing details of Sic1 phosphorylation inputs and their quantitative dynamics. Authors discovered a regulatory mechanism, how yeast cells regulate the timing and dynamics of S-phase onset. The central part of this discovery is that Sic1 works as a microprocessor that records growth phase signals and enables these to be transformed to S-phase initiation parameters via S-phase Cdks.
The cell division cycle is initiated with the onset of S-phase where cells replicate their DNA. The DNA-replication is triggered only when cells are sufficiently prepared to conduct following events of cellular division without stopping. The cell division is triggered and following events conducted by cyclin-dependent kinase holoenzymes (Cdk). These multi-component proteins that phosphorylate others to control the localization, lifespan or activity of target proteins. For proper initiation of each cell cycle phase specific Cdk holoenzyme complex is activated. To study the control mechanism of the cell cycle the S. cerevisiae is widely used as a model due to its simplicity and similarity to human cells. During the growth phase (G1) of yeast cells they accumulate different Cdk´s. Some of them are instantly active and begin to phosphorylate their targets preparing cell for the S-phase. Others Cdks necessary to trigger and conduct upcoming S-phase are accumulated in inhibited form. The activity is inhibited by Sic1 protein. All the Cdk necessary for S-phase initiation is accumulated in tight complex with Sic1 protein to avoid early leakage of S-phase kinase activity. To initiate S-phase the Sic1 protein must be degraded that in turn release S-phase specific Cdk activity. Sic1 itself is a Cdk target and contains multiple phosphorylation sites. For Sic1 destruction its phosphorylation from multiple sites is necessary. The phosphorylation of Sic1 determines the timing and dynamics of S-phase onset and has therefore central importance in cell cycle regulating mechanism. Limited knowledge about phosphorylation dynamics of Sic1 shielded quantitative regulatory mechanism of S-phase initiation and left the question of how is the onset of S-phase controlled unsolved. This study unveiled missing details of Sic1 phosphorylation inputs and their quantitative dynamics. Authors discovered a regulatory mechanism, how yeast cells regulate the timing and dynamics of S-phase onset. The central part of this discovery is that Sic1 works as a microprocessor that records growth phase signals and enables these to be transformed to S-phase initiation parameters via S-phase Cdks.
Kirjeldus
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Märksõnad
cell division, protein kinases, CDK, phosphorylation, inhibition