Hypomethylating agents increase L1 retroelement expression without inducing novel insertions in myeloid malignancies

Area of Science:

• Genomics
• Epigenetics
• Cancer Biology

Background:

• Human genome contains retroelements, silenced by DNA methylation to prevent mutations.
• Retroelement deregulation is observed in tumors, but its role in leukemia remains unclear.
• Hypomethylating agents are used to treat myelodysplastic syndromes and acute myeloid leukemia.

Purpose of the Study:

• To investigate if hypomethylating agents increase retroelement activity and somatic retrotranspositions in leukemia.
• To assess the impact of long-term hypomethylating agent therapy on retroelement dynamics in myeloid malignancies.

Main Methods:

• Induction of ORF1p protein expression using hypomethylating agents in myeloid cell lines (DAMI, HL-60).
• Analysis of cell lines treated for 4 weeks.
• Next-generation sequencing (NGS)-based analysis of sequential samples from 17 myelodysplastic syndrome patients undergoing hypomethylating agent therapy.

Main Results:

• Hypomethylating agents successfully induced LINE-1-encoded protein (ORF1p) expression in myeloid cell lines.
• No de novo somatic retrotransposition events were detected in either cell lines or patient samples after long-term hypomethylating agent exposure.
• Sensitive NGS methods confirmed the absence of retroelement activity.

Conclusions:

• While hypomethylating agents activate retroelement protein expression in myeloid cells, they do not appear to induce new somatic retrotransposition events.
• Long-term exposure to hypomethylating agents in leukemia does not lead to increased retroelement activity.
• These findings suggest retroelement activity may not be a significant factor in disease progression during hypomethylating agent treatment for myeloid cancers.