title: The ribonucleotide reductase subunit M2B subcellular localization and functional importance for DNA replication in physiological growth of KB cells.
abstract: Ribonucleoside diphosphate reductase (EC 1.17.4.1) (RR) is a potential target for antineoplastic agents due to its crucial role in DNA replication and repair. The expression and activity of RR subunits are highly regulated to maintain an optimal dNTP pool, which is required to maintain genetic fidelity. The human RR small subunit M2B (p53R2) is thought to contribute to DNA repair in response to DNA damage. However, it is not clear whether M2B is involved in providing dNTPs for DNA replication under physiological growth conditions. Serum starvation synchronized studies showed that a rapid increase of M2B was associated with cyclin E, which is responsible for regulation of G(1)/S-phase transition. A living cell sorting study that used KB cells in normal growth, further confirmed that M2B increased to maximum levels at the G(1)/S-phase transition, and decreased with DNA synthesis. Confocal studies revealed that M2B redistributed from the cytoplasm to the nucleus earlier than hRRM2 in response to DNA replication. Nuclear accumulation of M2B is associated with dynamic changes in dNTP at early periods of serum addition. By using M2B-shRNA expression vectors, inhibition of M2B may result in growth retardation in KB cells. We conclude that M2B may translocate from the cytoplasm into the nucleus and allow dNTPs to initiate DNA synthesis in KB cells under physiological conditions. Thus, our findings suggested that M2B might play an important role for initiating DNA replication of KB cells in normal growth.
authors.affiliation: Department of Medical Oncology and Therapeutic Research, City of Hope National Medical Center, 1500 E. Duarte Road, Duarte, CA 91010-3000, USA.
authors.forename: Xiyong
authors.initials: X
authors.lastname: Liu
authors.forename: Bingsen
authors.initials: B
authors.lastname: Zhou
authors.forename: Lijun
authors.initials: L
authors.lastname: Xue
authors.forename: Jennifer
authors.initials: J
authors.lastname: Shih
authors.forename: Karen
authors.initials: K
authors.lastname: Tye
authors.forename: Christina
authors.initials: C
authors.lastname: Qi
authors.forename: Yun
authors.initials: Y
authors.lastname: Yen
mesh_terms: D018797:Cell Cycle Proteins / Q000032:analysis / Q000502:physiology*; D049109:Cell Proliferation; D019925:Cyclin A / Q000032:analysis; D019926:Cyclin B / Q000032:analysis; D056744:Cyclin B1; D019927:Cyclin E / Q000032:analysis; D004261:DNA Replication; D016193:G1 Phase; D006801:Humans; D007624:KB Cells; D021381:Protein Transport; D012264:Ribonucleotide Reductases / Q000032:analysis / Q000502:physiology*; D016196:S Phase
chemical_list: C534699:CCNB1 protein, human; D018797:Cell Cycle Proteins; D019925:Cyclin A; D019926:Cyclin B; D056744:Cyclin B1; D019927:Cyclin E; C405947:RRM2B protein, human; D012264:Ribonucleotide Reductases