Our knowledge of the evolution and the role of untranslated region (UTR) in SARS-CoV-2 pathogenicity is very limited. Leader sequence, originated from UTR, is found at the 5′ ends of all encoded SARS-CoV-2 transcripts, highlighting its importance. Here, evolution of leader sequence was compared between human pathogenic and non-pathogenic coronaviruses. Then, profiling of microRNAs that can inactivate the key UTR regions of coronaviruses was carried out. A distinguished pattern of evolution in leader sequence of SARS-CoV-2 was found. Mining all available microRNA families against leader sequences of coronaviruses resulted in discovery of 39 microRNAs with a stable thermodynamic binding energy. Notably, SARS-CoV-2 had a lower binding stability against microRNAs. hsa-MIR-5004-3p was the only human microRNA able to target the leader sequence of SARS and to a lesser extent, also SARS-CoV-2. However, its binding stability decreased remarkably in SARS-COV-2. We found some plant microRNAs with low and stable binding energy against SARS-COV-2. Meta-analysis documented a significant (p < 0.01) decline in the expression of MIR-5004-3p after SARS-COV-2 infection in trachea, lung biopsy, and bronchial organoids as well as lung-derived Calu-3 and A549 cells. The paucity of the innate human inhibitory microRNAs to bind to leader sequence of SARS-CoV-2 can contribute to its high replication in infected human cells.

DNA damage usually happens in all cell types, which may originate from endogenous sources (i.e., DNA replication errors) or be emanated from radiations or chemicals. These damages range from changes in few nucleotides to significant structural abnormalities on chromosomes and, if not repaired, could disturb the cellular homeostasis or cause cell death. As the most significant response to DNA damage, DNA repair provides biological pathways by which DNA damages are corrected and returned into their natural circumstance. However, an aberration in the DNA repair mechanisms may result in genomic and chromosomal instability and the accumulation of mutations. The activation of oncogenes and/or inactivation of tumor suppressor genes is a serious consequence of genomic and chromosomal instability and may bring the cells into a cancerous phenotype. Therefore, genomic and chromosomal instability is usually considered a crucial factor in carcinogenesis and an important hallmark of various human malignancies. In the present study, we review our current understanding of the most updated mechanisms underlying genomic instability in cancer and discuss the potential promises of these mechanisms in finding new targets for the treatment of cancer.

Alternative RNA splicing in stem cells and cancer stem cells: Importance of transcript-based expression analysis