Talk on Saturday 09:06-09:06am submitted by Jonathan Dinman
Ribosomal frameshifting in the CCR5 mRNA is regulated by miRNAs and NMD.
Ashton T Belew (University of Maryland), Arturas Meskauskas (University of Maryland), Sharmishtha Musalgaonkar (University of Maryland), Vivek M Advani (University of Maryland), Jonathan D Dinman (University of Maryland)
Programmed -1 ribosomal frameshift (-1 PRF) signals redirect translating ribosomes to slip back one base on mRNAs. While well characterized in viruses, how this may regulate cellular gene expression is not understood. Here, we describe a -1 PRF signal in the human mRNA encoding CCR5. CCR5 encodes a cytokine receptor which is also utilized by HIV-1 as a co-receptor for entry into CD4+ T-cells. CCR5 mRNA-mediated -1 PRF is directed by a structurally dynamic mRNA pseudoknot. Sequence-specific stimulation of CCR5-mediated -1 PRF is promoted by at least two miRNAs. Mapping the mRNA/miRNA interaction suggests that formation of a triplex RNA structure stimulates -1 PRF by stabilizing the frameshift-promoting mRNA pseudoknot. A -1 PRF event on the CCR5 mRNA directs translating ribosomes to a premature termination codon, destabilizing it through the nonsense-mediated mRNA decay (NMD) pathway. At least one additional mRNA decay pathway is also implicated. The native CCR5 mRNA is shown to be a substrate for NMD, and siRNA knockdown of NMD results in increased expression of CCR5p. Conversely, stimulation of -1 PRF by specific miRNAs results in decreases steady-state abundance of the CCR5 mRNA, and decreased CCR5p expression. Functional -1 PRF signals that appear to be regulated by miRNAs are also demonstrated in mRNAs encoding six other cytokine receptors suggesting a novel mode through which immune responses may be fine-tuned in mammalian cells.
Keywords: Frameshifting, Pseudoknot, miRNA