Nuclear RNR-α antagonizes cell proliferation by directly inhibiting ZRANB3

Abstract

Since the origins of DNA-based life, the enzyme ribonucleotide reductase (RNR) has spurred proliferation because of its rate-limiting role in de novo deoxynucleoside-triphosphate (dNTP) biosynthesis. Paradoxically, the large subunit, RNR-α, of this obligatory two-component complex in mammals plays a context-specific antiproliferative role. There is little explanation for this dichotomy. Here, we show that RNR-α has a previously unrecognized DNA-replication inhibition function, leading to growth retardation. This underappreciated biological activity functions in the nucleus, where RNR-α interacts with ZRANB3. This process suppresses ZRANB3's function in unstressed cells, which we show to promote DNA synthesis. This nonreductase function of RNR-α is promoted by RNR-α hexamerization-induced by a natural and synthetic nucleotide of dA/ClF/CLA/FLU-which elicits rapid RNR-α nuclear import. The newly discovered nuclear signaling axis is a primary defense against elevated or imbalanced dNTP pools that can exert mutagenic effects irrespective of the cell cycle.

Breaking the Fourth Wall: Modulating Quaternary Associations for Protein Regulation and Drug Discovery

“…Thus, we defined a PPI‐mediated downregulation of DNA synthesis that requires RNR‐α hexamerization‐promoted partial nuclear import. Consistent with the multiple gain‐of‐function concept, we found that RNR‐α nuclear translocation was suppressed by IRBIT, a known negative regulator of RNR in mammals, which also interacted selectively with hexameric RNR‐α (Figure ) …”

“…[77] However,o ur genetic and biochemical data established that hexameric RNR-a partially translocated into the nucleust hrough association with importin. [76] This study also found that ZRANB3 was ap ositive regulator of DNA synthesis, and RNR-a in the nucleusdirectly bound and inhibited ZRANB3, leading to suppression of DNA synthesis. Thus, we defined aP PI-mediatedd ownregulation of DNA synthesis that requires RNR-a hexamerization-promoted partial nuclear import.…”

“…The nuclear localization of ZRANB3 was intriguing because RNR‐α is almost exclusively cytosolic . However, our genetic and biochemical data established that hexameric RNR‐α partially translocated into the nucleus through association with importin . This study also found that ZRANB3 was a positive regulator of DNA synthesis, and RNR‐α in the nucleus directly bound and inhibited ZRANB3, leading to suppression of DNA synthesis.…”

“… Structure of small molecules relevant to this Minireview. A) Classical inhibitors (ClF, FlU, ClA have PPI‐modulatory roles that may contribute to their clinical efficacies …”

“…Scheme1.Structure of small molecules relevant to this Minireview.A)Classicalinhibitors (ClF, FlU,ClA havePPI-modulatory roles that maycontribute to their clinical efficacies. [72,73,76,77] )B)PPI blockers.C )PPI stabilizers. D) PPIstabilizers that induce gain-of-function (e.g.,PROTACs) or amplificationo ffunction following post-translational modifications (PTMs;e.g.,H NEylation [83] ).…”