Drosha knockdown in human cells reduces viability but does not affect snRNA or rRNA synthesis or processing

We asked whether the human drosha protein, an RNase III homolog known to process microRNAs (miRNAs), might also be a small nuclear RNA (snRNA) 3' processing factor. Using retroviral siRNA silencing constructs, we stably knocked down drosha protein to nearly undetectable levels. Knockdown cells exhibited reduced growth rates and viability compared to controls, but no accumulation of unprocessed U2 snRNA precursors. In fungi, RNase III homologs process rRNA precursors and certain mRNAs. Although rRNA processing appears to be normal in the drosha knockdown cells, expression microarray analysis revealed misregulation of several mRNAs involved in cell growth and proliferation. Curiously, drosha knockdown appeared to downregulate the predicted mRNA targets of several miRNAs

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