Analysis of mRNA Translation by Polysome Profiling

RNA G-quadruplexes control mitochondria-localized mRNA translation and energy metabolism

Cancer cells rely on mitochondria for their bioenergetic supply and macromolecule synthesis. Central to mitochondrial function is the regulation of mitochondrial protein synthesis, which primarily depends on the cytoplasmic translation of nuclear-encoded mitochondrial mRNAs whose protein products are imported into mitochondria. Despite the growing evidence that mitochondrial protein synthesis contributes to the onset and progression of cancer, and can thus offer new opportunities for cancer therapy, knowledge of the underlying molecular mechanisms remains limited. Here, we show that RNA G-quadruplexes (RG4s) regulate mitochondrial function by modulating cytoplasmic mRNA translation of nuclear-encoded mitochondrial proteins. Our data support a model whereby the RG4 folding dynamics, under the control of oncogenic signaling and modulated by small molecule ligands or RG4-binding proteins, modifies mitochondria-localized cytoplasmic protein synthesis. Ultimately, this impairs mitochondrial functions, affecting energy metabolism and consequently cancer cell proliferation.

Selective translational control by PABPC1 phase separation regulates blast crisis and therapy resistance in chronic myeloid leukaemia

Tyrosine kinase inhibitors (TKIs) targeting the BCR-ABL1 fusion tyrosine kinase have revolutionized the treatment of chronic myeloid leukaemia (CML). However, the development of TKI resistance and the subsequent transition from the chronic phase (CP) to blast crisis (BC) threaten patients with CML. Accumulating evidence suggests that translational control is crucial for cancer progression. Our high-throughput CRISPR-Cas9 screening identified poly(A) binding protein cytoplasmic 1 (PABPC1) as a driver for CML progression in the BC stage. PABPC1 preferentially improved the translation efficiency of multiple leukaemogenic mRNAs with long and highly structured 5' untranslated regions by forming biomolecular condensates. Inhibiting PABPC1 significantly suppressed CML cell proliferation and attenuated disease progression, with minimal effects on normal haematopoiesis. Moreover, we identified two PABPC1 inhibitors that inhibited BC progression and overcame TKI resistance in murine and human CML. Overall, our work identifies PABPC1 as a selective translation enhancing factor in CML-BC, with its genetic or pharmacological inhibition overcoming TKI resistance and suppressed BC progression.

Assessment of translation rate in leukemic cells and immune cells of the microenvironment by OPP protein synthesis assay

Despite being tightly regulated, messenger RNA (mRNA) translation, a manner in which cells control expression of genes and rapidly respond to stimuli, is highly dysfunctional and plastic in pathologies including cancer. Conversely, the investigation of molecular mechanisms whereby mRNA translation becomes aberrant in cancer, as well as inhibition thereof, become critical in developing novel therapeutic approaches. More specifically, in malignancies such as chronic lymphocytic leukemia in which aberrant global and transcript specific translation has been linked with poorer patient outcomes, targeting translation is a relevant approach, with various translation inhibitors under development. Here we elaborate on a protein synthesis assay by flow cytometry, O-propargyl-puromycin, demonstrating global mRNA translation rate with a variety of different applications including cell lines, primary cells or co-culture systems in vitro. This method provides a comprehensive tool in quantifying the rate of global mRNA translation in cancer cells, as well as that of the tumor microenvironment cells, or in response to inhibitory therapeutic agents while offering the possibility to simultaneously assess other cellular markers.

The regulatory landscape of 5' UTRs in translational control during zebrafish embryogenesis

The 5' UTRs of mRNAs are critical for translation regulation, but their in vivo regulatory features are poorly characterized. Here, we report the regulatory landscape of 5' UTRs during early zebrafish embryogenesis using a massively parallel reporter assay of 18,154 sequences coupled to polysome profiling. We found that the 5' UTR is sufficient to confer temporal dynamics to translation initiation, and identified 86 motifs enriched in 5' UTRs with distinct ribosome recruitment capabilities. A quantitative deep learning model, DaniO5P, revealed a combined role for 5' UTR length, translation initiation site context, upstream AUGs and sequence motifs on in vivo ribosome recruitment. DaniO5P predicts the activities of 5' UTR isoforms and indicates that modulating 5' UTR length and motif grammar contributes to translation initiation dynamics. This study provides a first quantitative model of 5' UTR-based translation regulation in early vertebrate development and lays the foundation for identifying the underlying molecular effectors.