Journal articles

The 5'-untranslated region of Bag-1 mRNA contains an internal ribosome entry segment (IRES) and the translation of Bag-1 protein can be initiated by both cap-dependent and cap-independent mechanisms. In general, cellular IRESs require non-canonical trans-acting factors for their activity, however, very few of the proteins that act on cellular IRESs have been identified. Proteins that interact with viral IRESs have also been shown to stimulate the activity of cellular IRESs and therefore the ability of a range of known viral trans-acting factors to stimulate the Bag-1 IRES was tested.

Protein synthesis is a tightly regulated process that enables post-transcriptional control of gene expression. Dysregulation of this process is associated with the development and progression of cancers because components of the translational machinery function at the point of convergence of aberrant cell signaling pathways. Drugs designed to inhibit mRNA translation are currently in preclinical and early clinical development, and are likely to provide effective anticancer strategies in the future.

The majority of mRNAs in eukaryotic cells are translated via a method that is dependent upon the recognition of, and binding to, the methylguanosine cap at the 5' end of the mRNA, by a set of protein factors termed eIFs (eukaryotic initiation factors). However, many of the eIFs involved in this process are modified and become less active under a number of pathophysiological stress conditions, including amino acid starvation, heat shock, hypoxia and apoptosis.

Post-transcriptional control makes a major contribution to the overall regulation of gene expression pathway. Within the cytoplasm this is mediated by a combination of regulatory RNA motifs within the 5' and 3' untranslated regions of mRNAs and their interacting protein/RNA partners. One of the most common regulatory RNA elements in mammalian transcripts (present in approximately 40% of all mRNAs) are upstream open reading frames (uORFs). However, despite the prevalence of these RNA elements how they function is not well understood.

We demonstrate a 10- to 25-fold increase in the amount of c-myc protein in several independent cell lines derived from patients with multiple myeloma (MM). This is not accompanied by a corresponding increase in the overall level of the c-myc mRNA. There is, however, a 3.4-fold increase in the amount of c-myc mRNA associated with the polysomes in these cell lines without any detectable change in either the polysome size or the rate of translation elongation, thus suggesting that there is an increase in the extent of mobilisation of c-myc mRNA to the polysomes in MM.

During apoptosis, there is a reduction in translation initiation caused by caspase cleavage of several of the factors required for the cap-dependent scanning mechanism. Under these circumstances, many proteins that are required for apoptosis are instead translated by the alternative method of internal ribosome entry. This mechanism requires the formation of a complex RNA structural element and in the presence of internal ribosome entry segment (IRES)-trans-acting factors (ITAFs), the ribosome is recruited to the RNA.

Most eukaryotic translation initiation is thought to be dependent on the 5'-cap structure of the mRNA. It is becoming apparent, however, that the mRNAs of many genes contain IRESs (internal ribosome entry segments) within the 5'-UTR (5'-untranslated region) that allow ribosomes to initiate translation independently of the 5'-cap. IRESs can enable the expression of these genes under conditions (such as viral infection, cellular stress and apoptosis) when cap-dependent translation initiation is compromised, and also provide a target for regulation of gene expression.

A new mechanistic link has been identified between the expression of initiator methionine tRNA and cancer progression, whereby elevated levels of this tRNA specifically drive synthesis of secretome components, resulting in a type II collagen-rich matrix that promotes tumour progression.

Efforts to define serological correlates of protection against COVID-19 have been hampered by the lack of a simple, scalable, standardised assay for SARS-CoV-2 infection and antibody neutralisation. Plaque assays remain the gold standard, but are impractical for high-throughput screening. In this study, we show that expression of viral proteases may be used to quantitate infected cells. Our assays exploit the cleavage of specific oligopeptide linkers, leading to the activation of cell-based optical biosensors. First, we characterise these biosensors using recombinant SARS-CoV-2 proteases.

Einstein et al. (2021) uncover a novel role for the RNA-binding protein YTHDF2, one of the m6A reader proteins, in TNBC proliferation and survival. This study demonstrates the clinical potential of targeting a specific reader protein in the treatment of breast cancer.