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Drug-resistant breast cancer cells frequently retain expression of a functional wild-type p53 protein
1Division of Cancer Treatment, National Cancer Institute, Bethesda, MD 20892, USA.
Abstract:
Abnormalities in the p53 tumor suppressor gene have been shown to affect cellular processes related to cell cycle control and gene amplification. In this study we compare the status and function of wild-type p53 in MCF-7 breast cancer cells with sublines selected for resistance to chemotherapeutic agents having different mechanisms of action. Sublines that were resistant to melphalan, pyrazafurin, mitoxantrone, etoposide and PALA all retained expression of wild-type p53. Methotrexate-resistant MCF-7 cells were unusual heterozygotes that expressed a wild-type and dominant, in-frame p53 deletion mutant and the doxorubicin-resistant cells expressed only mutant p53. Analysis of the G1 checkpoint after treatment with ionizing radiation revealed that the pyrazafurin-, melphalan- and mitoxantrone-resistant cells arrested strongly in G1. The etoposide- and PALA-resistant cells had an intermediate G1 arrest phenotype and the methotrexate- and doxorubicin-resistant cells had a minimal G1 arrest phenotype. mRNA and protein analyses of downstream effector genes, including P21CIP1/Waf1, mdm2, Gadd 45 and the retinoblastoma protein, did not entirely differentiate sublines having a strong versus intermediate G1 arrest phenotype. Neither the p53 status nor the strength of the G1 arrest could be correlated with cell survival after ionizing radiation. When drug-sensitive MCF-7 cells were treated with the same chemotherapeutic agents, p53 and p21CIP1/Waf1 levels increased between 2- and 14-fold. Together these data suggest that other cellular factors likely play a role in overcoming the inhibitory effects of ionizing radiation on p53 in drug-resistant breast cancer cells.
Insights
Drug-resistant breast cancer cells retain wild-type p53, but show varied G1 checkpoint arrests. Other cellular factors, not p53 status, may influence radiation resistance.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- The p53 tumor suppressor gene is crucial for cell cycle control and preventing gene amplification.
- Abnormalities in p53 are common in various cancers, impacting cellular responses to stress.
- Understanding p53 function in drug-resistant cancer cells is vital for developing effective therapies.
Purpose of the Study:
- To investigate the status and function of wild-type p53 in MCF-7 breast cancer cells with acquired resistance to diverse chemotherapeutic agents.
- To correlate p53 status and G1 checkpoint function with cellular response to ionizing radiation in drug-resistant cells.
Main Methods:
- MCF-7 breast cancer cell lines were selected for resistance to melphalan, pyrazafurin, mitoxantrone, etoposide, PALA, methotrexate, and doxorubicin.
- p53 gene status (wild-type vs. mutant) and protein expression were analyzed.
- G1 cell cycle checkpoint function was assessed after ionizing radiation treatment.
- Expression of downstream p53 target genes (P21CIP1/Waf1, mdm2, Gadd 45) and retinoblastoma protein was evaluated.
Main Results:
- Most drug-resistant sublines retained wild-type p53, except for methotrexate-resistant (heterozygous wild-type/mutant) and doxorubicin-resistant (mutant only) cells.
- G1 arrest strength varied: strong in melphalan-, pyrazafurin-, and mitoxantrone-resistant cells; intermediate in etoposide- and PALA-resistant cells; minimal in methotrexate- and doxorubicin-resistant cells.
- p53 status and G1 arrest strength did not correlate with cell survival after ionizing radiation.
- Drug-sensitive MCF-7 cells showed increased p53 and p21CIP1/Waf1 levels upon chemotherapeutic agent treatment.
Conclusions:
- Wild-type p53 is generally maintained in MCF-7 cells resistant to various chemotherapeutic agents.
- The G1 checkpoint response to ionizing radiation is heterogeneous among drug-resistant sublines and not solely dependent on p53 status.
- Factors beyond p53 and G1 arrest likely contribute to overcoming radiation inhibition in drug-resistant breast cancer cells.