Short RNAs repress translation after initiation in mammalian cells

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• MicroRNAs (miRNAs) are key regulators of gene expression, predicted to target a significant portion of mammalian genes.
• Understanding the precise mechanisms of miRNA-mediated translational repression is crucial for deciphering gene regulation.

Purpose of the Study:

• To investigate the molecular mechanism underlying miRNA-mediated translational repression in human cells.
• To determine whether repression occurs during translation initiation or elongation.

Main Methods:

• Utilized partially complementary small interfering RNAs (siRNAs) to mimic miRNA activity.
• Assessed mRNA association with polyribosomes and puromycin sensitivity to evaluate translation elongation.
• Examined cap-independent translation (HCV IRES, CrPV IRES) and metabolic labeling to pinpoint the stage of repression.
• Analyzed translational readthrough and ribosome dissociation rates after initiation blockade.

Main Results:

• Repressed mRNAs remained associated with actively elongating polyribosomes.
• Inhibition of translation occurred post-initiation, affecting cap-independent translation.
• Silencing occurred before nascent polypeptide chain completion.
• Short RNAs reduced translational readthrough and accelerated ribosome dissociation from repressed mRNAs.

Conclusions:

• Short RNAs, likely including microRNAs (miRNAs), primarily repress gene translation through ribosome drop-off during the elongation phase.
• This mechanism provides new insights into post-transcriptional gene silencing and regulation.