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Inactivation of the RASSF1A in osteosarcoma
Sungjig Lim1, Moon Ho Yang, Jae Hoon Park
1Department of Pathology, School of Medicine, Inje University, Sanggye Paik Hospital, Kanazawa, Japan.
Abstract:
We investigated the expression and mutation of three isoforms of the Ras effector RASSF1 in 10 primary osteosarcomas and 6 osteosarcoma cell lines. RASSF1A was not expressed in 40% (4/10) of the primary osteosarcomas and 83.3% (5/6) of the osteosarcoma cell lines. RASSF1B and RASSF1C expression was absent in 30% (3/10) and 0% (0/10) of primary tumors, and 100% (6/6) and 0% (0/6) of osteosarcoma cell lines, respectively. Treatment of these cell lines with the DNA methylation inhibitor 5-aza-2'-deoxycytidine reactivated the transcription of RASSF1A, but not that of RASSF1B or RASSF1C. No somatic mutations were noted in RASSF1 in either the primary tumors or cell lines. Our data indicate that epigenetic inactivation of RASSF1A by hypermethylation of its promoter region is a frequent event, and may play an important role in the tumorigenesis of osteosarcomas.
Insights
Epigenetic silencing of RASSF1A, a Ras effector, is frequent in osteosarcoma. DNA methylation inhibitor 5-aza-2'-deoxycytidine reactivated RASSF1A transcription, suggesting its role in tumor development.
Area of Science:
- Oncology
- Molecular Biology
- Epigenetics
Background:
- The Ras effector RASSF1 gene family plays a crucial role in tumor suppression.
- Dysregulation of RASSF1 isoforms may contribute to various cancers, including osteosarcoma.
Purpose of the Study:
- To investigate the expression and mutation status of RASSF1 isoforms (RASSF1A, RASSF1B, RASSF1C) in osteosarcoma.
- To determine the role of epigenetic modifications, specifically DNA methylation, in RASSF1 regulation in osteosarcoma.
Main Methods:
- Analysis of RASSF1 isoform expression in 10 primary osteosarcomas and 6 osteosarcoma cell lines.
- Treatment of osteosarcoma cell lines with the DNA methylation inhibitor 5-aza-2 acut;-deoxycytidine to assess transcriptional reactivation.
- Mutation analysis of RASSF1 in primary tumors and cell lines.
Main Results:
- RASSF1A expression was absent in 40% of primary tumors and 83.3% of cell lines.
- RASSF1B and RASSF1C expression was also reduced or absent in a significant proportion of samples.
- DNA methylation inhibitor reactivated RASSF1A transcription, but not RASSF1B or RASSF1C.
- No somatic mutations were detected in RASSF1.
Conclusions:
- Epigenetic inactivation of RASSF1A through promoter hypermethylation is a common event in osteosarcoma.
- This epigenetic silencing of RASSF1A likely contributes to osteosarcoma tumorigenesis.
- RASSF1A, rather than RASSF1B or RASSF1C, appears to be the primary target of epigenetic inactivation in this cancer.