Function and Regulation of Yeast Ribonucleotide Reductase: Cell Cycle, Genotoxic Stress, and Iron Bioavailability

Abstract

Ribonucleotide reductases (RNRs) are essential enzymes that catalyze the reduction of ribonucleotides to desoxyribonucleotides, thereby providing the building blocks required for de novo DNA biosynthesis. The RNR function is tightly regulated because an unbalanced or excessive supply of deoxyribonucleoside triphosphates (dNTPs) dramatically increases the mutation rates during DNA replication and repair that can lead to cell death or genetic anomalies. In this review, we focus on Saccharomyces cerevisiae class Ia RNR as a model to understand the different mechanisms controlling RNR function and regulation in eukaryotes. Many studies have contributed to our current understanding of RNR allosteric regulation and, more recently, to its link to RNR oligomerization. Cells have developed additional mechanisms that restrict RNR activity to particular periods when dNTPs are necessary, such as the S phase or upon genotoxic stress. These regulatory strategies include the transcriptional control of the RNR gene expression, inhibition of RNR catalytic activity, and the subcellular redistribution of RNR subunits. Despite class Ia RNRs requiring iron as an essential cofactor for catalysis, little is known about RNR function regulation depending on iron bioavailability. Recent studies into yeast have deciphered novel strategies for the delivery of iron to RNR and for its regulation in response to iron deficiency. Taken together, these studies open up new possibilities to explore in order to limit uncontrolled tumor cell proliferation via RNR.

Quantitative proteomics of the yeast Hsp70/Hsp90 interactomes during DNA damage reveal chaperone-dependent regulation of ribonucleotide reductase

“…In this study, only one interactor, the ribonucleotide-diphosphate reductase (RNR) small subunit protein Rnr4, fulfilled this criterion. Rnr4 is particularly biologically interesting, due to its key role in cell cycle progression and DNA damage resistance [4, 5, 52]. To validate the chaperone-Rnr4 interactions detected by mass spectrometry, we performed IMAC bead pull-downs from lysates of cells expressing HA-tagged Rnr4 and untagged or HIS 6 -tagged Ssa1 or Hsp82.…”

“…dNTP synthesis is blocked upon inhibition of the key enzyme in dNTP formation, ribonucleotide reductase (RNR) [4]. RNR constitutes a complex of pairs of large (R1) and small (R2) subunits.…”

“…HU and other agents, including the nucleoside analog gemcitabine (Gemzar), remain important agents in cancer chemotherapy. These agents are commonly combined with radiotherapy and/or genotoxic chemotherapy, which potentiate RNR inhibitors via exposing the requirement for dNTPs in DNA repair [4, 7]. It would be highly desirable to identify agents that can enhance the therapeutic benefit of RNR inhibitors without incurring additional toxicity.…”

Essential functions of iron-requiring proteins in DNA replication, repair and cell cycle control

“…In plants, the expressions of R1 and R2 are also S phase specific and dependent on the E2F-like motifs in their promoters (Chaboute et al, 2002). In budding yeast, the transcriptions of RNR genes ( RNR1 , RNR2 and RNR4 ) peak at the beginning of the S phase by regulating the transcription factor pairs Mbp1/Swi6 and Swi4/Swi6, which can bind to the Mlul cell cycle box (Sanvisens et al, 2013). However, no cell cycle regulation has been observed in RNR3 transcription (Lee and Elledge, 2006; Sanvisens et al, 2013).…”

Ribonucleotide reductase metallocofactor: assembly, maintenance and inhibition

“…In addition, RRM2 is also subjected to ubiquitin mediated pioteasomal degradation once cells completed DNA replication and/or repair, through two E3 ubiquitin ligase complexes, the Skp1/Cullin/F-box (SCF) and the anaphase-promoting complex (APC) (Chabes et al, 2003b; D’Angiolella et al, 2012). In budding yeast, transcription of the RNR genes peaks at the beginning of the S phase through regulation of the transcription factor pairs Mbp1/Swi6 and Swi4/Swi6 (Elledge et al, 1993; Sanvisens et al, 2013). In response to DNA damage, mammalian cells increase transcription of p53R2 (RRM2B) to facilitate DNA repair (Nakano et al, 2000; Tanaka et al, 2000) via activation of the ATM/ATR-CHK checkpoint pathway (Harper and Elledge, 2007).…”