Naturally existing isoforms of miR-222 have distinct functions

Area of Science:

• Molecular Biology
• Genomics
• Biochemistry

Background:

• MicroRNAs (miRNAs) are key regulators of gene expression.
• Endogenously expressed miRNAs exhibit sequence heterogeneity, known as isomiRs.
• 3'-end variations are a common type of isomiR, particularly in human samples.

Purpose of the Study:

• To investigate the functional consequences of 3'-end microRNA isomiR variation.
• To determine the impact of specific isomiRs, such as elongated miR-222 isoforms, on cellular phenotype.
• To explore the molecular mechanisms underlying isomiR-mediated gene regulation.

Main Methods:

• Deep sequencing of small RNAs associated with Argonaute protein.
• Transfection of distinct miR-222 isomiR isoforms into human cell lines.
• Phenotypic analysis of transfected cells, including apoptosis assays.
• Assessment of gene expression changes, focusing on the PI3K-AKT pathway.

Main Results:

• Extensive 3'-isomiR variation was observed for endogenous miRNAs, including miR-222.
• Longer miR-222 isomiRs induced apoptosis in a size-dependent manner, independent of 3' sequence.
• Transfection of longer miR-222 isomiRs downregulated components of the pro-survival PI3K-AKT pathway, including PIK3R3.
• Knockdown of PIK3R3 mimicked the apoptotic and gene-downregulating effects of longer miR-222 isoforms.

Conclusions:

• 3'-end isomiR sequence variation can mediate distinct biological functions.
• The size of 3'-extended miR-222 isoforms is critical for their apoptotic effects.
• IsomiR-mediated regulation of the PI3K-AKT pathway plays a significant role in cellular processes.
• Further investigation into the functional significance of 3'-isomiR prevalence is warranted.