Mck1 defines a key S-phase checkpoint effector in response to various degrees of replication threats

Abstract

The S-phase checkpoint plays an essential role in regulation of the ribonucleotide reductase (RNR) activity to maintain the dNTP pools. How eukaryotic cells respond appropriately to different levels of replication threats remains elusive. Here, we have identified that a conserved GSK-3 kinase Mck1 cooperates with Dun1 in regulating this process. Deleting MCK1 sensitizes dun1 Δ to hydroxyurea (HU) reminiscent of mec1 Δ or rad53 Δ. While Mck1 is downstream of Rad53, it does not participate in the post-translational regulation of RNR as Dun1 does. Mck1 phosphorylates and releases the Crt1 repressor from the promoters of DNA damage-inducible genes as RNR2-4 and HUG1 . Hug1, an Rnr2 inhibitor normally silenced, is induced as a counterweight to excessive RNR. When cells suffer a more severe threat, Mck1 inhibits HUG1 transcription. Consistently, only a combined deletion of HUG1 and CRT1 , confers a dramatic boost of dNTP levels and the survival of mck1 Δ dun1 Δ or mec1 Δ cells assaulted by a lethal dose of HU. These findings reveal the division-of-labor between Mck1 and Dun1 at the S-phase checkpoint pathway to fine-tune dNTP homeostasis.

Mck1 kinase is a new player in the DNA damage checkpoint pathway

“…In this study, Liu and colleagues [12] show that the highly conserved GSK3-related Mck1 kinase is a downstream target of Rad53 and functions in the Dun1-independent RNR activation pathway. The authors suggest that Mck1 and Dun1 kinases cooperate in a nonredundant manner to provide cells with a multilayer response system to deal with various degrees of replicative stress.…”

“…By contrast, Dun1’s only known substrates are involved in the regulation of ribonucleotide levels [11]. Here, Liu and colleagues [12] show that the GSK3-related kinase Mck1 is directly activated by Rad53 and, like Dun1, regulates ribonucleotide biosynthesis, suggesting it too is a checkpoint kinase.…”

“…The authors suggest that Mck1 and Dun1 kinases cooperate in a nonredundant manner to provide cells with a multilayer response system to deal with various degrees of replicative stress. Using a synthetic genetic screen, Liu and colleagues [12] find that deletion of MCK1 and DUN1 (but not other GSK3 paralogs) displays a synergistic sensitivity to replication stress, reminiscent of mec1Δ or rad53Δ . They show that, like Dun1, Mck1 is phosphorylated by Rad53, and genetic experiments suggest that this phosphorylation is activating.…”

Microproteins: from behind the scenes to the spotlight

“…The RNR inhibitory role of Hug1 may function as a rheostat to prevent excessive dNTP production, which increases genome instability as well. When cells suffer the more severe or persistent stress, Mck1 can inhibit the HUG1 transcription in a Crt1-independent manner to further augment the RNR activity and dNTP levels (Li et al, 2019).…”

The Emerging Roles of Fox Family Transcription Factors in Chromosome Replication, Organization, and Genome Stability

“…It usually comprises a homodimer of large subunit, Rnr1, and a heterodimer of two small subunits, Rnr2 and Rnr4. Another large subunit, Rnr3, is only induced through a multi-level surveillance system when cells suffer replication stress or DNA damage [6,7]. Heterozygous deletion of FHL1 reduces transcription of RNR1 and RNR3 (but not RNR2 and RNR4).…”