Alternative titles; symbolsDROSHA, DROSOPHILA, HOMOLOG OF; DROSHARNASE3LRN3HGNC Approved Gene Symbol: DROSHACytogenetic location: 5p13.3 Genomic coordinates ...
Alternative titles; symbols
HGNC Approved Gene Symbol: DROSHA
Cytogenetic location: 5p13.3 Genomic coordinates (GRCh38): 5:31,400,493-31,532,141 (from NCBI)
Members of the ribonuclease III superfamily of double-stranded (ds) RNA-specific endoribonucleases participate in diverse RNA maturation and decay pathways in eukaryotic and prokaryotic cells (Fortin et al., 2002). The RNase III Drosha is the core nuclease that executes the initiation step of microRNA (miRNA) processing in the nucleus (Lee et al., 2003).
▼ Cloning and Expression
By database searching and screening of a human liver cDNA library, Wu et al. (2000) cloned a 1374-amino acid, 160-kD protein. Multiple domains included N-terminal proline-rich and serine-/arginine-rich domains and a C-terminal RNase III domain that was well conserved with RNase III of C. elegans, S. cerevisiae, S. pombe, and E. coli. Both the human RNase III domain and C. elegans RNase III contain 2 RNase III signature sequences. Wu et al. (2000) found that the expressed purified RNase III domain cleaves double-stranded, but not single-stranded, RNA. They observed that the gene was ubiquitously expressed in human tissues and cell lines and that the protein is localized in the cell nucleus. Levels of transcription and translation of the RNase III protein did not change during different phases of the cell cycle. However, a significant fraction of the protein in the nucleus was translocated to the nucleolus during the S phase of the cell cycle. Wu et al. (2000) found that inhibition of human RNase III expression caused cell death, suggesting an essential role for human RNase III in the cell.
Filippov et al. (2000) isolated a Drosophila Drosha cDNA sequence and found homologous sequences in C. elegans and human.
Fortin et al. (2002) mapped the human RNASEN gene to chromosome 5p14-p13 by FISH. The mouse homolog maps to chromosome 15, region B, a region syntenic with the location in human.
▼ Gene Function
Lee et al. (2003) noted that Drosha is a class II RNase III enzyme containing tandem RNase III domains and 1 double-stranded RNA-binding domain, as well as extended amino-terminal proline- and arginine-/serine-rich domains. Because of its localization to the nucleus, Lee et al. (2003) examined the possibility that Drosha may act as a nuclear processing factor for miRNAs. In immunoprecipitation experiments using FLAG-tagged Drosha transiently transfected into human embryonic kidney cells, treatment of the primary precursors with Drosha immunoprecipitate yielded fragments of 60 to 70 nucleotides, which correspond to pre-miRNAs. Drosha, therefore, can catalyze the initiation step of miRNA processing in vitro. Lee et al. (2003) found that all tested miRNAs significantly decreased after Drosha RNA inhibition, suggesting that Drosha may be widely used for the maturation of most, if not all, miRNAs. As Drosha homologs are found in C. elegans, Drosophila, mice, and humans, Lee et al. (2003) suggested that the stepwise processing of miRNAs mediated by Drosha and Dicer is likely to be conserved, at least in animals.
By mutation analysis, Han et al. (2004) showed that the N-terminal RNase III domain (RIIIDa) and the C-terminal RNase III domain (RIIIDb) of Drosha formed an intramolecular dimer. The 2 domains independently cleaved double-stranded primary mRNA (pri-mRNA) and released hairpin-shaped pre-miRNAs. RIIIDa cleaved the strand containing the 3-prime hydroxyl group, and RIIIDb cut the strand containing the 5-prime phosphate. By immunoprecipitation of human embryonic kidney cell nuclear extracts, Han et al. (2004) found that Drosha interacted with DGCR8 (609030), and the 2 proteins were present within a complex of about 650 kD. Both DGCR8 and Drosha could homodimerize in the absence of single-stranded RNA (ssRNA) in addition to interacting with each other. Han et al. (2004) found that DGCR8 was critical for pri-miRNA processing.
Gregory et al. (2004) demonstrated that human Drosha is a component of 2 multiprotein complexes. The larger complex contains multiple classes of RNA-associated proteins including RNA helicases, proteins that bind double-stranded RNA, novel heterogeneous nuclear ribonucleoproteins, and the Ewing sarcoma family of proteins. The smaller complex is composed of Drosha and the double-stranded-RNA-binding protein DGCR8, the product of a gene deleted in DiGeorge syndrome (188400). In vivo knockdown and in vitro reconstitution studies revealed that both components of this smaller complex, termed Microprocessor, are necessary and sufficient in mediating the genesis of miRNAs from the primary miRNA transcript.
Han et al. (2006) used computational and biochemical analyses to elucidate the molecular basis for pri-miRNA processing by Drosha-DGCR8. A typical metazoan pri-miRNA consists of an approximately 33-bp stem, with a terminal loop and basal ssRNA segments. Han et al. (2006) found that the basal ssRNA segments were essential for processing, whereas the terminal loop was dispensable. The cleavage site was determined mainly by the distance (about 11 bp) from the stem-ssRNA junction. DGCR8, but not Drosha, interacted with pri-miRNAs directly and specifically, and the basal ssRNA segments were critical for this interaction. Han et al. (2006) proposed that DGCR8 may function as the molecular anchor that measures the distance from the stem-ssRNA junction.
Davis et al. (2008) found that the processing of primary transcripts of miR21 (611020) (pri-miR21) into precursor miR21 (pre-miR21) by the Drosha complex is promoted by TGF-beta (190180) and bone morphogenetic protein (BMP; see 112264) signaling, which promote a rapid increase in expression of mature miR21 through a posttranscriptional step. miR21 downregulates PDCD4 (608610), which in turn acts as a negative regulator of smooth muscle contractile genes. TGF-beta and BMP-specific SMAD signal transducers SMAD1 (601595), SMAD2 (601366), SMAD3 (603109), and SMAD5 (603110) are recruited to pri-miR21 in a complex with the RNA helicase p68 (DDX5: 180630), a component of the Drosha microprocessor complex. The shared cofactor SMAD4 (600993) is not required for this process. Thus, Davis et al. (2008) concluded that regulation of microRNA biogenesis by ligand-specific SMAD proteins is critical for control of the vascular smooth muscle cell phenotype and potentially for SMAD4-independent responses mediated by the TGF-beta and BMP signaling pathways.
Merritt et al. (2008) observed decreased mRNA and protein expression of the RNAse III enzymes DICER1 (606241) and DROSHA in 60 and 51%, respectively, of 111 invasive epithelial ovarian cancer (167000) specimens. Low DICER1 expression was significantly associated with advanced tumor stage (p = 0.007), and low DROSHA expression with suboptimal surgical cytoreduction (p = 0.02). Cancer specimens with both high DICER1 expression and high DROSHA expression were associated with increased median survival. Although rare missense variants were found in both genes, the presence or absence did not correlate with the level of expression. The findings implicated a component of the RNA-interference machinery, which regulates gene expression, in the pathogenesis of ovarian cancer. Merritt et al. (2009) noted that 109 of the 111 samples used in the 2008 study had serous histologic features, of which 93 were high-grade and 16 were low-grade tumors.
In mice, Ago2 (EIF2C2; 606229) is uniquely required for viability, and only this Argonaute family member retains catalytic competence. To investigate the evolutionary pressure to conserve Argonaute enzymatic activity, Cheloufi et al. (2010) engineered a mouse with catalytically inactive Ago2 alleles. Homozygous mutants died shortly after birth with an obvious anemia. Examination of microRNAs and their potential targets revealed a loss of miR451 (612071), a small RNA important for erythropoiesis. Though this microRNA is processed by Drosha, its maturation does not require Dicer. Instead, the pre-miRNA becomes loaded into Ago and is cleaved by the Ago catalytic center to generate an intermediate 3-prime end, which is then further trimmed. Cheloufi et al. (2010) concluded that their findings linked the conservation of Argonaute catalysis to a conserved mechanism of microRNA biogenesis that is important for vertebrate development.
Francia et al. (2012) demonstrated in human, mouse, and zebrafish that DICER and DROSHA, but not downstream elements of the RNAi pathway, are necessary to activate the DNA damage response (DDR) upon exogenous DNA damage and oncogene-induced genotoxic stress, as studied by DDR foci formation and by checkpoint assays. DDR foci are sensitive to RNase A treatment, and DICER- and DROSHA-dependent RNA products are required to restore DDR foci in RNase-A-treated cells. Through RNA deep sequencing and the study of DDR activation at a single inducible DNA double-strand break, Francia et al. (2012) demonstrated that DDR foci formation requires site-specific DICER- and DROSHA-dependent small RNAs, named DDRNAs, which act in a MRE11-RAD50-NBS1-complex (see 602667)-dependent manner. DDRNAs, either chemically synthesized or in vitro generated by DICER cleavage, are sufficient to restore the DDR in RNase-A-treated cells, also in the absence of other cellular RNAs.
▼ Molecular Genetics
Rakheja et al. (2014) reported the whole-exome sequencing of 44 Wilms tumors (see WT1, 194070), identifying missense mutations in the microRNA (miRNA)-processing enzymes DROSHA and DICER1, and novel mutations in MYCN (164840), SMARCA4 (603254), and ARID1A (603024). Examination of tumor miRNA expression, in vitro processing assays, and genomic editing in human cells demonstrated that DICER1 and DROSHA mutations influence miRNA processing through distinct mechanisms. DICER1 RNase IIIB mutations preferentially impair processing of miRNAs deriving from the 5-prime arm of pre-miRNA hairpins, while DROSHA RNase IIIB mutations globally inhibit miRNA biogenesis through a dominant-negative mechanism. Both DROSHA and DICER1 mutations impair expression of tumor-suppressing miRNAs, including the LET7 family (see 605386), which are important regulators of MYCN, LIN28 (see 611043), and other Wilms tumor oncogenes. Rakheja et al. (2014) concluded that these results provided insights into the mechanisms through which mutations in miRNA biogenesis components reprogram miRNA expression in human cancer and suggested that these defects define a distinct subclass of Wilms tumors.