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Epigenetic inactivation of the candidate 3p21.3 suppressor gene BLU in human cancers
Angelo Agathanggelou1, Ashraf Dallol, Sabine Zöchbauer-Müller
1Section of Medical and Molecular Genetics, Department of Paediatrics and Child Health, university of Birmingham, The Medical School, Edgbaston, Birmingham B15 2TT, UK.
Abstract:
Many distinct regions of 3p show frequent allelic losses in a wide range of tumour types. Previously, the BLU candidate tumour suppressor gene (TSG) encoded by a gene-rich critical deleted region in 3p21.3 was found to be inactivated rarely in lung cancer, although expression was downregulated in a subset of lung tumour cell lines. To elucidate the role of BLU in tumorigenesis, we analysed BLU promoter methylation status in tumour cell lines and detected promoter region hypermethylation in 39% lung, 42% breast, 50% kidney, 86% neuroblastoma and 80% nasopharyngeal (NPC) tumour cell lines. Methylation of the BLU promoter region correlated with the downregulation of BLU transcript expression in tumour cell lines. Expression was recovered in tumour cell lines treated with 5-aza 2-deoxycytidine. Exogenous expression of BLU in neuroblastoma (SK-N-SH) and NSCLC (NCI-H1299) resulted in reduced colony formation efficiency, in vitro. Furthermore, methylation of the BLU promoter region was detected in primary sporadic SCLC (14%), NSCLC (19%) and neuroblastoma (41%). As frequent methylation of the RASSF1A 3p21.3 TSG has also been reported in these tumour types, we investigated whether BLU and RASSF1A methylation were independent or related events. No correlation was found between hypermethylation of RASSF1A and BLU promoter region CpG islands in SCLC or neuroblastoma. However, there was association between RASSF1A and BLU methylation in NSCLC (P=0.0031). Our data suggest that in SCLC and neuroblastoma, RASSF1A and BLU methylations are unrelated events and not a manifestation of a regional alteration in epigenetic status, while in NSCLC there may be a regional methylation effect. Together, these data suggest a significant role for epigenetic inactivation of BLU in the pathogenesis of common human cancers and that methylation inactivation of BLU occurs independent of RASSF1A in SCLC and neuroblastoma tumours.
Insights
Epigenetic silencing of the BLU tumor suppressor gene through promoter hypermethylation is common in various cancers, including lung, breast, kidney, neuroblastoma, and nasopharyngeal carcinoma. This inactivation impacts tumor suppressor activity and may be linked to RASSF1A methylation in non-small cell lung cancer.
Area of Science:
- Cancer Biology
- Epigenetics
- Tumorigenesis
Background:
- Allelic losses in the 3p region are frequent across diverse tumor types.
- The BLU (Genie) tumor suppressor gene (TSG) located in 3p21.3 is a critical deleted region.
- Previous studies showed rare BLU inactivation but downregulated expression in some lung cancer cell lines.
Purpose of the Study:
- To investigate the role of BLU in tumorigenesis by analyzing its promoter methylation status.
- To determine the correlation between BLU promoter methylation and its transcript expression.
- To assess the functional consequence of BLU expression in cancer cell lines and the relationship between BLU and RASSF1A methylation.
Main Methods:
- Analysis of BLU promoter methylation status in various tumor cell lines and primary tumors.
- Treatment of tumor cell lines with 5-aza-2'-deoxycytidine to assess methylation reversibility.
- Exogenous expression of BLU in neuroblastoma and non-small cell lung cancer (NSCLC) cell lines.
- Investigation of the correlation between BLU and RASSF1A methylation in different tumor types.
Main Results:
- BLU promoter hypermethylation was detected in 39% of lung, 42% of breast, 50% of kidney, 86% of neuroblastoma, and 80% of nasopharyngeal carcinoma (NPC) cell lines.
- BLU promoter methylation correlated with downregulated BLU transcript expression, which was reversible with 5-aza-2'-deoxycytidine treatment.
- Exogenous BLU expression reduced colony formation efficiency in neuroblastoma and NSCLC cell lines.
- BLU promoter methylation was found in 14% of SCLC, 19% of NSCLC, and 41% of neuroblastoma primary tumors.
- BLU and RASSF1A methylation were independent in SCLC and neuroblastoma but associated in NSCLC.
Conclusions:
- Epigenetic inactivation of BLU via promoter methylation plays a significant role in the pathogenesis of common human cancers.
- BLU methylation-induced inactivation is independent of RASSF1A methylation in SCLC and neuroblastoma.
- A potential regional methylation effect involving RASSF1A and BLU exists in NSCLC.
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