MicroRNA miR-128 represses LINE-1 (L1) retrotransposition by down-regulating the nuclear import factor TNPO1.

Area of Science:

• Genomics
• Molecular Biology
• Epigenetics

Background:

• Repetitive elements like LINE-1 (L1) constitute ~50% of the human genome.
• L1 elements can cause genomic instability via retrotransposition.
• Somatic L1 transcription is normally repressed by epigenetic mechanisms like DNA methylation.

Purpose of the Study:

• Investigate if miR-128 controls L1 activity by repressing cellular proteins.
• Identify cellular factors involved in L1 retrotransposition regulated by miR-128.

Main Methods:

• RNA sequencing and bioinformatics analysis to identify miR-128 targets.
• Luciferase reporter assays to validate miR-128 binding to TNPO1 mRNA.
• Cellular assays to manipulate miR-128 and TNPO1 levels and assess L1 retrotransposition.
• Western blotting and immunofluorescence to track L1 protein nuclear import.

Main Results:

• miR-128 directly targets the 3' UTR of transportin 1 (TNPO1) mRNA.
• Modulating TNPO1 levels impacts L1 retrotransposition and nuclear import of L1 complexes.
• TNPO1 facilitates the nuclear import of L1 ribonucleoprotein complexes.
• Overexpression of TNPO1 partially rescues the L1 repressive effect of miR-128.

Conclusions:

• miR-128 employs a dual mechanism to control L1 retrotransposition in somatic cells.
• This involves direct repression of L1 RNA and indirect regulation of TNPO1, a key factor for L1 nuclear import.
• Identified TNPO1 as the first protein factor involved in L1 nuclear import and retrotransposition.