The NF90-NF45 complex functions as a negative regulator in the microRNA processing pathway

Area of Science:

• Molecular Biology
• Gene Regulation
• Biochemistry

Background:

• The positive regulation of microRNA (miRNA) processing is understood, but negative regulatory mechanisms remain largely unexplored.
• Identifying factors that control miRNA biogenesis is crucial for understanding gene expression and cellular function.

Purpose of the Study:

• To investigate the role of nuclear factor 90 (NF90) and NF45 proteins in the negative regulation of miRNA biogenesis.
• To elucidate the mechanism by which NF90-NF45 impacts miRNA processing and mature miRNA levels.

Main Methods:

• Overexpression of NF90 and NF45 proteins in cells.
• Treatment with an RNA polymerase II inhibitor (alpha-amanitin).
• Analysis of pri-miRNA and pre-miRNA levels.
• Investigation of protein-RNA interactions using binding assays.
• Depletion of NF90 using specific inhibitors.

Main Results:

• Overexpression of NF90-NF45 led to pri-miRNA accumulation, independent of transcriptional activation.
• The NF90-NF45 complex directly binds to pri-miRNAs, with higher affinity for pri-let-7a than pri-miR-21.
• NF90-NF45 does not interact with the Microprocessor complex but inhibits pri-miRNA processing.
• Depletion of NF90 reduced pri-let-7a, increased mature let-7a, and suppressed transformed cell growth.

Conclusions:

• The NF90-NF45 complex acts as a negative regulator of miRNA biogenesis by binding pri-miRNAs.
• This binding event sterically hinders the Microprocessor complex, reducing mature miRNA production.
• NF90-NF45 inhibition of let-7a miRNA production contributes to transformed cell proliferation, suggesting therapeutic potential.