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Selective suppression of growth factor-induced cell cycle gene expression by Na+/H+ antiport inhibitors
G Vairo1, B G Cocks, E J Cragoe
1Department of Medicine, University of Melbourne, Royal Melbourne Hospital, Parkville, Australia.
Abstract:
Activation of Na+/H+ exchange activity is a ubiquitous response to growth factors and has been implicated in the mitogenic response. Little is known of how the antiport influences events in the nucleus which ultimately control the cell cycle. Using potent Na+/H+ exchange inhibitors we show for normal mouse bone marrow-derived macrophages that this activity is required for the colony-stimulating factor-1-induced gene expression of the M1 and M2 subunits of ribonucleotide reductase, an enzyme critical for DNA synthesis. Suppression of M1 and M2 mRNA levels occurred when the inhibitors were added up to 8 h after the growth factor, mirroring their ability to prevent entry into S phase at similar times. Antiport activity was not required for the induction of other genes associated with cell cycle progression including proliferating cell nuclear antigen and the G1 cyclin, CYL1. These results highlight the differential expression of various cell cycle-associated genes and demonstrates that non-coordinate regulation of CYL1 cyclin and DNA synthesis gene expression can occur. The selective dependence of ribonucleotide reductase subunit gene expression on Na+/H+ exchange activity may provide a biochemical basis for the requirement of persistent antiporter activity during G1 for subsequent entry into S phase.
Insights
Sodium-hydrogen exchange (Na+/H+ exchange) activity is crucial for colony-stimulating factor-1-induced gene expression of ribonucleotide reductase subunits, essential for DNA synthesis. This antiporter activity is required for cell cycle progression into S phase.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Na+/H+ exchange activity is a common response to growth factors and is linked to cell proliferation.
- The specific role of Na+/H+ exchange in nuclear events controlling the cell cycle remains largely uncharacterized.
Purpose of the Study:
- To investigate the role of Na+/H+ exchange activity in growth factor-induced cell cycle progression.
- To determine how Na+/H+ exchange influences gene expression critical for DNA synthesis.
Main Methods:
- Utilized potent Na+/H+ exchange inhibitors in normal mouse bone marrow-derived macrophages.
- Assessed the impact of inhibitors on gene expression of ribonucleotide reductase subunits (M1 and M2) and other cell cycle markers (PCNA, CYL1).
- Monitored the timing of inhibitor addition relative to growth factor stimulation and cell cycle entry (S phase).
Main Results:
- Na+/H+ exchange activity is essential for colony-stimulating factor-1-induced expression of M1 and M2 subunits of ribonucleotide reductase.
- Inhibiting Na+/H+ exchange up to 8 hours after growth factor addition prevented M1/M2 mRNA induction and S phase entry.
- Na+/H+ exchange was not required for the induction of proliferating cell nuclear antigen or G1 cyclin (CYL1).
Conclusions:
- Na+/H+ exchange activity is selectively required for the gene expression of ribonucleotide reductase subunits, critical for DNA synthesis.
- Demonstrates non-coordinate regulation between CYL1 cyclin and DNA synthesis gene expression during the cell cycle.
- Persistent Na+/H+ antiporter activity during G1 phase is biochemically linked to subsequent entry into S phase.