| Stress-Dependent Regulation of the Cell Cycle
James A. Borowiec Ph.D.
Professor
Department of Biochemistry |
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| Research Summary |
Ionizing radiation (IR) and other DNA damaging agents can lead to instability of the genetic information and cellular transformation. To lessen the deleterious effects of such stress, eukaryotic cells have evolved various checkpoint mechanisms that halt the progression of the cell cycle at the G1/S and G2/M boundaries, and within S phase. Cells thus have the opportunity to repair the damage or, if the cell judges the damage too severe, to undergo apoptosis. My laboratory has been studying the intra-S phase checkpoint, a poorly understood control mechanism that serves to inhibit DNA replication at the level of origin firing after various types of cell stress.
We have found that nucleolin, a key factor in ribosome biogenesis, also acts to repress origin firing following stress. Stresses such as IR cause a dramatic redistribution of nucleolin from the nucleolus to the nucleoplasm. Nucleolin relocalization requires complex formation with the tumor suppressor p53 protein, and this interaction can also regulate p53 activity. The relocalization of nucleolin then leads to a great increase in complex formation with RPA, the eukaryotic single-stranded DNA-binding protein. Nucleolin significantly inhibits the ability of RPA to support origin firing by sequestering RPA away from chromosomal DNA replication foci. Among other experimental goals, we are defining the signal transduction pathways that regulate the nucleolin-p53 and nucleolin-RPA interactions, and examining the effects of nucleolin on p53 and RPA activity. |
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| Related Documents |
| Replication Protein A (RPA) phosphorylation prevents RPA association with replication centers |
(view pdf) | We find that RPA phosphorylation prevents RPA association with replication centers in vivo and potentially serves as a marker for sites of DNA damage. |
| Nucleolin-p53 interaction |
(view pdf) | We find a novel p53-dependent mechanism in which genotoxic stress mobilizes nucleolin for transient replication inhibition and DNA repair. |
| Formation of a complex between nucleolin and replication protein A after cell stress prevents initiation of DNA replication |
(view pdf) | A biochemical screen was used to identify nucleolin,
a key factor in ribosome biogenesis, as a high-affinity
binding partner for human replication protein A (hRPA). These findings represent a novel mechanism that represses chromosomal replication after cell stress. | | |
| Related Images |
Image 1 | Model for the regulatory effects on nucleolin on cell-cycle progression. Under stress conditions, nucleolin relocalizes from the nucleolus to the nucleoplasm. Nucleolin relocalization is facilitated by p53 with nucleolin modulating p53 activity. In the nucleoplasm, nucleolin also binds to RPA and sequesters RPA from replication centers, contributing to the inhibition of chromosomal DNA replication. | | |
| Research Information |
Research Interests | Regulation of Eukaryotic DNA Replication | Research Keywords | cell cycle checkpoints, eukaryotic DNA replication, replication protein A (RPA), nucleolin, p53
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