6mer Seed Toxicity in Viral microRNAs

Area of Science:

• Molecular Biology
• Virology
• Genetics

Background:

• MicroRNAs (miRNAs) are small noncoding RNAs regulating gene expression via RNA interference.
• miRNA targeting relies on the seed sequence (nucleotides 2-7/8).
• A G-rich six-nucleotide seed sequence can be highly toxic to cells.

Purpose of the Study:

• To investigate if viral miRNAs (v-miRNAs) utilize toxic seed sequences to induce cell death.
• To determine the prevalence of noncanonical toxic 6mer seeds in v-miRNAs compared to cellular miRNAs.

Main Methods:

• Screening of 215 v-miRNAs from 17 human pathogenic viruses.
• Analysis of seed sequences for G-rich motifs and noncanonical positioning.
• Functional validation of toxic 6mer seed activity using specific v-miRNAs.

Main Results:

• A subset of v-miRNAs was found to possess toxic G-rich 6mer seed sequences.
• miR-K12-6-5p from Kaposi sarcoma-associated herpesvirus demonstrated noncanonical toxic 6mer seed activity.
• v-miRNAs are statistically more likely than cellular miRNAs to employ noncanonical 6mer seeds.

Conclusions:

• Viruses have evolved to incorporate toxic 6mer seed sequences within their miRNAs to induce cell death.
• This mechanism represents a potential viral strategy for host cell manipulation and survival.
• The findings highlight a novel aspect of v-miRNA function and viral evolution.