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Triggering of p73-dependent apoptosis in osteosarcoma is under the control of E2Fs-pRb2/p130 complexes
Dario La Sala1, Marcella Macaluso, Carmela Trimarchi
1ITOI-CNR, Unit of Bologna, c/o IOR, 40136 Bologna, Italy.
Abstract:
Mechanisms underlying multidrug resistance (MDR), one of the major causes of cancer treatment failure, are still poorly understood. We selected the osteosarcoma MDR HosDXR150 cell line by culturing Hos cells in the presence of increasing doxorubicin doses and showed that it is crossresistant to vinblastine. Similarly to the Hos parental cell line, HosDXR150 cells present mutated p53, functionally inactivated pRb/p105 and wild-type pRb2/p130. Owing to p53 mutation, MDR-1 gene, codifying for P-glycoprotein, is upregulated. Evasion of apoptosis in HosDXR150 cells is only partially explained by drug extrusion because of P-glycoprotein overexpression. Analysis of gene expression level profiles showed that parental cell line undergoes apoptosis through an E2F1/p73-dependent pathway while its resistant variant evades it. This result can be explained by the presence of distinct E2Fs-pRb2/p130 complexes on the p73 promoter. Namely, in Hos p73 transcription is activated by E2F1-Rb2/p130-p300 complexes, while in HosDXR150 it is kept repressed by E2F4-Rb2/p130-HDAC1 complexes.
Insights
Multidrug resistance (MDR) in osteosarcoma is poorly understood. This study reveals that altered E2F-pRb2/p130 complexes on the p73 promoter contribute to apoptosis evasion in resistant cells.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Biology
Background:
- Multidrug resistance (MDR) is a significant obstacle in cancer chemotherapy, leading to treatment failure.
- The precise molecular mechanisms driving MDR, particularly in osteosarcoma, remain incompletely elucidated.
- Understanding MDR is crucial for developing more effective cancer therapies.
Purpose of the Study:
- To investigate the mechanisms of multidrug resistance (MDR) in an osteosarcoma cell line.
- To identify the molecular players involved in apoptosis evasion in drug-resistant cancer cells.
- To explore the role of transcription factors and their complexes in regulating apoptosis in MDR.
Main Methods:
- Development of a doxorubicin-resistant osteosarcoma cell line (HosDXR150) through stepwise drug selection.
- Comparative analysis of gene expression profiles between parental (Hos) and resistant (HosDXR150) cell lines.
- Investigation of cell cycle regulators (p53, pRb/p105, pRb2/p130) and transcription factor complexes (E2Fs, p73, p300, HDAC1) using gene expression analysis.
Main Results:
- The HosDXR150 cell line exhibited cross-resistance to vinblastine, indicating a broad MDR phenotype.
- Both cell lines possessed mutated p53 and inactivated pRb/p105, but wild-type pRb2/p130.
- Overexpression of the MDR-1 gene (encoding P-glycoprotein) was observed in HosDXR150 cells, contributing partially to drug extrusion.
- Apoptosis evasion in HosDXR150 cells was linked to distinct E2F-pRb2/p130 complexes on the p73 promoter, with repressed transcription in resistant cells.
Conclusions:
- The study elucidates novel mechanisms of apoptosis evasion in osteosarcoma multidrug resistance.
- Differential regulation of p73 transcription by distinct E2F-pRb2/p130 complexes plays a critical role in MDR.
- Targeting these specific transcription factor complexes may offer new therapeutic strategies for overcoming drug resistance in cancer.