MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate gene expression. Recent studies show that miRNAs can be exported from mammalian cells into the extracellular environment, suggesting they may play a role in cell-to-cell communication. This study demonstrates that after serum deprivation, several human cell lines export significant amounts of miRNAs into the culture medium. The export process is energy-dependent and miRNAs are found both inside and outside of known cell-derived vesicles such as microvesicles and exosomes. The researchers identified some candidate proteins involved in this system, including nucleophosmin 1 (NPM1), which may protect extracellular miRNAs from degradation. These findings suggest a previously unrecognized miRNA trafficking system in mammalian cells that could facilitate cell-to-cell communication. The study also shows that miRNAs can remain stable outside the cell for extended periods, indicating they may serve as signaling molecules. The export of miRNAs is influenced by cellular energy levels and the presence of specific RNA-binding proteins. The results support the hypothesis that miRNAs can be exported from cells and may function in intercellular communication. The study highlights the complexity of miRNA export and the potential for miRNAs to act as biomarkers or signaling molecules in various biological processes.MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate gene expression. Recent studies show that miRNAs can be exported from mammalian cells into the extracellular environment, suggesting they may play a role in cell-to-cell communication. This study demonstrates that after serum deprivation, several human cell lines export significant amounts of miRNAs into the culture medium. The export process is energy-dependent and miRNAs are found both inside and outside of known cell-derived vesicles such as microvesicles and exosomes. The researchers identified some candidate proteins involved in this system, including nucleophosmin 1 (NPM1), which may protect extracellular miRNAs from degradation. These findings suggest a previously unrecognized miRNA trafficking system in mammalian cells that could facilitate cell-to-cell communication. The study also shows that miRNAs can remain stable outside the cell for extended periods, indicating they may serve as signaling molecules. The export of miRNAs is influenced by cellular energy levels and the presence of specific RNA-binding proteins. The results support the hypothesis that miRNAs can be exported from cells and may function in intercellular communication. The study highlights the complexity of miRNA export and the potential for miRNAs to act as biomarkers or signaling molecules in various biological processes.