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A comparative study of P53/MDM2 genes alterations and P53/MDM2 proteins immunoreactivity in soft-tissue sarcomas
P Rieske1, J K Bartkowiak, A M Szadowska
1Dept. of Molecular Biology, Medical University of Lodz, Poland.
Abstract:
In the present study, the expression of P53 and MDM2 proteins were examined in 94 soft-tissue sarcomas (35 malignant fibrohistiocytomas, 15 neurosarcomas, 14 liposarcomas, 13 leiomyosarcomas, 11 fibrosarcomas and 6 dermatofibrosarcomas) by immunohistochemistry. The immunohistochemical findings were correlated with P53 mutation analysis using PCR-SSCP, PCR-HDF and direct sequencing, and MDM2 amplification studies by differential PCR. P53 immunopositivity was found in 25 out of 94 (26.6%) cases. Alterations of the P53 gene were detected in 12 (12.8%) tumors; eight of these tumors revealed P53 immunoreactivity. A high number of P53 positive and P53 mutated tumors were histologically defined as poorly differentiated G3 (64.0% and 75.0%, respectively). MDM2 immunopositivity was revealed in 36 out of 94 (38.3%) cases. MDM2 amplification occurred in 17 tumors (18.1%); only nine of these tumors exhibited MDM2 immunoreactivity. Overall, MDM2 positivity was not associated with MDM2 amplification in 27 out of 94 tumors (28.7%). There was no significant correlation between MDM2 overexpression and histological grade. However, when the samples were stratified by immunophenotype, the majority of tumors (52.5%) with isolated MDM2 overexpression (dissociated from P53 positivity) were defined histologically as low grade (G1 + G2). These results support the notion that besides P53 alterations, MDM2 gene deregulation seems to be an important event in sarcomas evolution. Additionally, the mechanism of MDM2-mediated degradation of P53 protein, without involving stabilization and inactivation of P53 gene, should be considered for better understanding of all features of tumor progression processes.
Insights
TP53 gene alterations and MDM2 deregulation are key events in soft-tissue sarcoma development. MDM2 overexpression, particularly without TP53 involvement, is linked to low-grade tumors, suggesting complex roles in sarcoma progression.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Soft-tissue sarcomas (STS) are a heterogeneous group of malignancies.
- The tumor suppressor protein P53 and its regulator MDM2 play critical roles in cell cycle control and apoptosis.
- Dysregulation of the P53-MDM2 pathway is implicated in various cancers, including STS.
Purpose of the Study:
- To investigate the expression and correlation of P53 and MDM2 proteins and their genetic alterations in a cohort of STS.
- To determine the relationship between P53/MDM2 status and histological grade in different STS subtypes.
Main Methods:
- Immunohistochemistry was used to assess P53 and MDM2 protein expression in 94 STS samples.
- P53 gene mutations were analyzed using PCR-SSCP, PCR-HDF, and direct sequencing.
- MDM2 amplification was studied by differential PCR.
Main Results:
- P53 immunopositivity was observed in 26.6% of cases, with mutations detected in 12.8%. Poorly differentiated G3 tumors showed higher rates of P53 positivity and mutation.
- MDM2 immunopositivity was found in 38.3% of cases, while MDM2 amplification occurred in 18.1%.
- MDM2 positivity was not consistently associated with MDM2 amplification. Isolated MDM2 overexpression (without P53 positivity) was more frequent in low-grade tumors (G1+G2).
Conclusions:
- Both P53 alterations and MDM2 gene deregulation are significant events in STS evolution.
- The MDM2-mediated degradation of P53, independent of P53 gene stabilization, is a crucial mechanism to consider in understanding STS progression.
- These findings highlight the complex interplay of the P53-MDM2 axis in the pathogenesis of soft-tissue sarcomas.