Translational Regulation by Upstream Open Reading Frames and Its Relevance to Human Genetic Disease

Abstract

Abstract Upstream open reading frames (uORFs) are cis ‐acting elements, located before or overlapped with the main coding ORF (mORF), that regulate cap‐dependent translation efficiency in a transcript‐specific manner. More than half of the human transcripts bear at least one uORF. In addition, it has been recently revealed that many of these uORFs initiate at non‐AUG codons, which significantly increases the complexity and diversity of the human translatome. These regulons are considered repressors of downstream translation but, in some biological contexts, they induce mORF expression. There are several the mechanisms by which AUG and non‐AUG uORFs regulate gene expression, allowing the cell to control transcript‐specific translation according to its needs. Also, we describe several examples of uORF genetic variants associated with human genetic diseases. Studying these cases and understanding the resultant abnormal mechanisms of uORF‐mediated translational control is of extreme importance for the development of new therapeutic strategies. Key Concepts Upstream open reading frames (uORFs) are cis ‐acting translational regulatory elements present within the 5′ leader sequence of mRNAs. uORFs can regulate gene expression by repressing or promoting translation of the downstream main ORF (mORF), according to the cellular environment. The number of uORFs, the intercistronic distance, the overlap with the mORF and the context of the initiation codon are the uORF‐related structural features that most influence their translational regulatory capacity. uORF‐mediated repression of mORF translation is usually achieved by ribosome dissociation, ribosome stalling, induction of nonsense‐mediated mRNA decay (NMD) or production of inhibitory peptides. uORF‐mediated induction of mORF translation is usually achieved by ribosome bypass or translation reinitiation. uORFs initiated by non‐AUG codons are more frequent than previously appreciated, having important biological functions. uORF‐altering polymorphisms and mutations, which create, disrupt or change a uORF, can cause human genetic diseases. Studying and understanding the uORF‐mediated mechanisms of gene expression regulation may provide knowledge to develop novel therapies for several human diseases.