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Suramin increases p53 protein levels but does not activate the p53-dependent G1 checkpoint
S P Howard1, S J Park, L Hughes-Davies
1Stress Protein Group, Joint Center for Radiation Therapy, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
Abstract:
Suramin is an antineoplastic agent which has a cytostatic effect on both normal and tumor-derived cells. We have investigated whether the induction of growth arrest by suramin requires the p53 protein, a tumor suppressor gene product involved in the initiation of growth arrest following DNA damage. Activation of the p53 protein by genotoxic agents causes increased p53 protein levels and p53-dependent transcription of the p21 gene. The p21 protein then inhibits cyclin-dependent kinases, initiating G1 arrest. Exposure of NIH-3T3 cells to suramin caused a rapid (1-2 h) increase in the level of p53-DNA-binding activity. Flow cytometric analysis indicated that suramin arrested NIH-3T3 cells in G0-G1. However, suramin did not increase the p53-dependent transcription of the p21 gene or inhibit cyclin-dependent kinase 2 kinase activity. If NIH-3T3 cells were exposed to radiation or suramin plus radiation, p21 mRNA levels were increased and cyclin-dependent kinase 2 kinase activity was inhibited, indicating that suramin does not block the cells' ability to increase p21 levels. To determine whether the G0-G1 arrest induced by suramin required p53, NIH-3T3 cells transfected with a dominant negative mutant p53 gene to eliminate wild-type p53 function (NMP cells) were exposed to suramin. NMP cells still exhibited G0-G1 arrest after suramin treatment. Suramin increases p53 protein levels, but fails to increase p21 mRNA levels or to activate the G1 checkpoint. These data suggest that suramin induces growth arrest in NIH-3T3 cells by a mechanism that is independent of cellular p53 status.
Insights
Suramin, an antineoplastic agent, induces cell growth arrest independently of the p53 protein. This study shows suramin increases p53 levels but does not activate the p21 gene or G1 checkpoint.
Area of Science:
- Cell biology
- Molecular oncology
- Cancer research
Background:
- Suramin is an antineoplastic agent with cytostatic effects on normal and tumor cells.
- The p53 protein, a tumor suppressor, is crucial for initiating growth arrest after DNA damage.
- p53 activation leads to increased p53 levels, p21 gene transcription, and G1 arrest via cyclin-dependent kinase inhibition.
Purpose of the Study:
- To investigate if suramin-induced growth arrest requires the p53 protein.
- To determine the mechanism by which suramin affects cell cycle progression.
- To clarify the role of p53 and p21 in suramin's cytostatic effects.
Main Methods:
- Exposure of NIH-3T3 cells to suramin.
- Analysis of p53-DNA-binding activity and p53-dependent transcription of the p21 gene.
- Flow cytometry for cell cycle analysis (G0-G1 arrest).
- Assessment of cyclin-dependent kinase 2 activity.
- Experiments using NIH-3T3 cells with a dominant-negative p53 mutant (NMP cells).
Main Results:
- Suramin treatment rapidly increased p53-DNA-binding activity in NIH-3T3 cells.
- Suramin induced G0-G1 arrest in NIH-3T3 cells.
- Suramin did not increase p21 gene transcription or inhibit cyclin-dependent kinase 2 activity.
- Suramin did not block the cells' ability to increase p21 levels when combined with radiation.
- NMP cells, lacking functional p53, still exhibited G0-G1 arrest upon suramin exposure.
- Suramin increases p53 protein levels but not p21 mRNA or G1 checkpoint activation.
Conclusions:
- Suramin induces G0-G1 cell cycle arrest in NIH-3T3 cells.
- The growth arrest mechanism induced by suramin is independent of the p53 protein's status.
- Suramin's effects on cell cycle progression do not rely on the canonical p53-p21 pathway.