Translation-dependent and -independent mRNA decay occur through mutually exclusive pathways defined by ribosome density during T cell activation.

mRNA translation and decay are tightly interconnected processes both in the context of mRNA quality-control pathways and for the degradation of functional mRNAs. Cotranslational mRNA degradation through codon usage, ribosome collisions, and the recruitment of specific proteins to ribosomes is an important determinant of mRNA turnover. However, the extent to which translation-dependent mRNA decay (TDD) and translation-independent mRNA decay (TID) pathways participate in the degradation of mRNAs has not been studied yet. Here we describe a comprehensive analysis of basal and signal-induced TDD and TID in mouse primary CD4+ T cells. Our results indicate that most cellular transcripts are decayed to some extent in a translation-dependent manner. Our analysis further identifies the length of untranslated regions, the density of ribosomes, and GC3 content as important determinants of TDD magnitude. Consistently, all transcripts that undergo changes in ribosome density within their coding sequence upon T cell activation display a corresponding change in their TDD level. Moreover, we reveal a dynamic modulation in the relationship between GC3 content and TDD upon T cell activation, with a reversal in the impact of GC3- and AU3-rich codons. Altogether, our data show a strong and dynamic interconnection between mRNA translation and decay in mammalian primary cells.

Treatment selection and real-world analysis of immunotherapy with or without chemotherapy in PD-L1-high metastatic non-small cell lung cancer.

BACKGROUND: Lung cancer is the leading cause of cancer death in Australia. Immunotherapy has improved outcomes in patients with metastatic non-small cell lung cancer (NSCLC). Pembrolizumab is approved in first-line treatment as single-agent immunotherapy (SAI) or combination chemoimmunotherapy (CIT). In metastatic NSCLC programmed death-ligand 1 (PD-L1) ≥50% either regimen may be used. AIMS: We aim to identify patient and tumour characteristics that influence treatment selection. METHODS: This is a retrospective observational study. Pharmacy records identified patients with metastatic/recurrent NSCLC receiving pembrolizumab at two metropolitan centres in Victoria, Australia, since 2018. Demographics, tumour characteristics, Charlson Comorbidity Index (CCI) and treatment data were collected. Descriptive and multivariate analyses were performed. RESULTS: Sixty-one patients had metastatic NSCLC PD-L1 ≥50% and received pembrolizumab with median age of 65.6 years, Eastern Cooperative Oncology Group 0-1 in 82%. CIT was administered to 23% (14) with no difference in rate of delivery between centres (P = 0.808). CCI mean score differed (3.38 SAI vs 2.36 CIT, P = 0.042). Patients with high CCI score (≥2) were less likely to receive CIT (OR = 0.15, P = 0.003, 95% confidence interval (CI) 0.04-0.57). Primary tumours over 5 cm were more likely to receive CIT (OR = 3.74, P = 0.043, 95% CI = 1.04-13.42). Site-specific metastases of liver, brain and pericardial effusion were not associated with CIT. CONCLUSIONS: Patients with higher comorbidity score were less likely to receive CIT, suggesting chemotherapy avoidance in comorbid patients. Larger tumours are associated with CIT use, indicating that oncologists may use tumour size as a surrogate of disease burden. Limitations include small sample size and data cut-off. Future prospective studies could incorporate comorbid status and a validated disease burden score to stratify patients.

Estimating cancers attributable to physical inactivity in Australia.

OBJECTIVES: It was previously estimated that 1814 (1.6 % of incident cancers) were attributable to physical inactivity in Australia in 2010, when only three sites were considered. We estimated the burden of cancer due to physical inactivity in Australia for 13 sites. DESIGN: The population attributable fraction estimated site-specific cancer cases attributable to physical inactivity for 13 cancers. The potential impact fraction was used to estimate cancers that could have been prevented in 2015 if Australian adults had increased their physical activity by a modest amount in 2004-05. METHODS: We used 2004-05 national physical activity prevalence data, 2015 national cancer incidence data, and contemporary relative-risk estimates for physical inactivity and cancer. We assumed a 10-year latency period. RESULTS: An estimated 6361 of the cancers observed in 2015 were attributable to physical inactivity, representing 4.8 % of all cancers diagnosed. If Australian adults had increased their physical activity by one category in 2004-05, 2564 cases (1.9 % of all cancers) could have been prevented in 2015. CONCLUSIONS: More than three times as many cancers are attributable to physical inactivity than previously reported. Physical activity promotion should be a central component of cancer prevention programmes in Australia.

Attenuating ribosome load improves protein output from mRNA by limiting translation-dependent mRNA decay.

Developing an effective mRNA therapeutic often requires maximizing protein output per delivered mRNA molecule. We previously found that coding sequence (CDS) design can substantially affect protein output, with mRNA variants containing more optimal codons and higher secondary structure yielding the highest protein outputs due to their slow rates of mRNA decay. Here, we demonstrate that CDS-dependent differences in translation initiation and elongation rates lead to differences in translation- and deadenylation-dependent mRNA decay rates, thus explaining the effect of CDS on mRNA half-life. Surprisingly, the most stable and highest-expressing mRNAs in our test set have modest initiation/elongation rates and ribosome loads, leading to minimal translation-dependent mRNA decay. These findings are of potential interest for optimization of protein output from therapeutic mRNAs, which may be achieved by attenuating rather than maximizing ribosome load.