MicroRNAs (miRNAs) are small RNAs of approximately 22 nucleotides, which function as regulators of gene expression in eukaryotes. miRNAs are initially expressed in the nucleus as part of long primary transcripts called primary miRNAs (pri-miRNAs). Inside the nucleus, pri-miRNAs are partially digested by the enzyme Drosha, to form -70 nucleotide-long hairpin precursor miRNA (pre-miRNA) that is exported to the cytoplasm for further processing by into shorter, and mature miRNAs.
During both normal development and pathological states, there is sometimes a disparity between the expression levels of pri-miRNAs and the presence of the corresponding mature miRNAs. The initiation of pri-miRNA processing by Drosha represents a fundamental regulatory step in miRNA processing. Dr. Hammond and colleagues have determined that that blocking Drosha activity can suppress miRNA production in cancer cells.
"The alterations in miRNA expression that are observed in cancer are dramatic. Our studies raise the possibility that a single regulatory event could be the cause of this widespread miRNA mis-regulation. Understanding this regulatory step will provide important information about the molecular events in carcinogenesis, and may lead to novel therapeutic strategies."