Aberrant DNA Methylation, Expression, and Occurrence of Transcript Variants of the ABC Transporter

Area of Science:

• Oncology
• Molecular Biology
• Epigenetics

Background:

• ABCA7 (ATP-binding cassette subfamily A member 7) is aberrantly expressed in various cancers, including breast cancer.
• Investigating epigenetic and genetic alterations in ABCA7 is crucial for understanding breast cancer pathogenesis.

Purpose of the Study:

• To identify specific epigenetic, genetic, and alternative splicing alterations of ABCA7 in breast cancer.
• To determine the association between these alterations and ABCA7 expression levels.

Main Methods:

• Analysis of tumor and adjacent tissues from breast cancer patients.
• Quantitative PCR (qPCR) to detect ABCA7 mRNA transcripts, including intron-containing variants.
• DNA methylation analysis of CpG sites.
• Treatment of breast cancer cell lines with doxorubicin and paclitaxel.
• Shotgun proteomics to assess splicing factor expression.

Main Results:

• Aberrant CpG methylation at the exon 5-intron 5 boundary of ABCA7 was observed in a molecular subtype-specific manner, with evidence of epigenetic field cancerization.
• DNA methylation levels in promoter-exon 1, intron 1, and exon 5-intron 5 boundaries did not correlate with ABCA7 mRNA levels.
• Intron-containing ABCA7 mRNA transcripts were identified and were not subtype-specific or directly correlated with DNA methylation.
• Chemotherapy treatment altered ABCA7 intron levels, associated with dysregulation of splicing factors.

Conclusions:

• Epigenetic alterations, specifically DNA methylation at the ABCA7 exon 5-intron 5 boundary, show molecular subtype specificity in breast cancer.
• Intron-containing ABCA7 transcripts are present and their levels are modulated by chemotherapy, suggesting a role in alternative splicing regulation.
• The findings highlight the complex regulation of ABCA7 in breast cancer, involving epigenetic modifications and alternative splicing, particularly in response to therapeutic agents.