Involvement of the oncogenic small nucleolar RNA SNORA24 in regulation of p53 stability in colorectal cancer

Colorectal cancer (CRC) is a common malignant cancer worldwide. Although the molecular mechanism of CRC carcinogenesis has been studied extensively, the details remain unclear. Small nucleolar RNAs (snoRNAs) have recently been reported to have essential functions in carcinogenesis, although their roles in CRC pathogenesis are largely unknown. In this study, we found that the H/ACA snoRNA SNORA24 was upregulated in various cancers, including CRC. SNORA24 expression was significantly associated with age and history of colon polyps in CRC patient cohorts, with high expression associated with a decreased 5-year overall survival. Our results indicated that the oncogenic function of SNORA24 is mediated by promoting G1/S phase transformation, cell proliferation, colony formation, and growth of xenograft tumors. Furthermore, SNORA24 knockdown induced massive apoptosis. RNA-sequencing and gene ontology (GO) enrichment analyses were performed to explore its downstream targets. Finally, we confirmed that SNORA24 regulates p53 protein stability in a proteasomal degradation pathway. Our study clarifies the oncogenic role of SNORA24 in CRC and advance the current model of the role of the p53 pathway in this process.

[Detection and functions of viral RNA modifications: perspectives in biology and medicine]

Viral RNAs (either derived from DNA viruses and genomic/mRNAs of RNA viruses) produced and replicated in eukaryotic cells are exposed to the activity of host cell RNA modification machinery. Moreover, some complex viruses encode their own RNA modification enzymes, generally cap-related m⁷G-and 2'-O-methyltransferases whose expression allows specific modification of viral transcripts and modulation of viral RNA recognition by host restriction systems. Here we review current achievements in the detection of viral RNA modifications by liquid chromatography coupled to mass spectrometry (LC-MS) and deep sequencing-based approaches. The presence, origin and characterized functions of RNA modifications in viral RNAs are discussed.

Pseudouridine as a novel biomarker in prostate cancer

Epitranscriptomic analysis has recently led to the profiling of modified nucleosides in cancer cell biological matrices, helping to elucidate their functional roles in cancer and reigniting interest in exploring their use as potential markers of cancer development and progression. Pseudouridine, one of the most well-known and the most abundant of the RNA nucleotide modifications, is the C5-glycoside isomer of uridine and its distinctive physiochemical properties allows it to perform many essential functions. Pseudouridine functionally (a) confers rigidity to local RNA structure by enhancing RNA stacking, engaging in a cooperative effect on neighboring nucleosides that overall contributes to RNA stabilization (b) refines the structure of tRNAs, which influences their decoding activity (c) facilitates the accuracy of decoding and proofreading during translation and efficiency of peptide bond formation, thus collectively improving the fidelity of protein biosynthesis and (e) dynamically regulates mRNA coding and translation. Biochemical synthesis of pseudouridine is carried out by pseudouridine synthases. In this review we discuss the evidence supporting an association between elevated pseudouridine levels with the incidence and progression of human prostate cancer and the translational significance of the value of this modified nucleotide as a novel biomarker in prostate cancer progression to advanced disease.

Base-pairing interactions between substrate RNA and H/ACA guide RNA modulate the kinetics of pseudouridylation, but not the affinity of substrate binding by H/ACA small nucleolar ribonucleoproteins

H/ACA small nucleolar ribonucleoproteins (snoRNPs) pseudouridylate RNA in eukaryotes and archaea. They target many RNAs site-specifically through base-pairing interactions between H/ACA guide and substrate RNA. Besides ribosomal RNA (rRNA) and small nuclear RNA (snRNA), H/ACA snoRNPs are thought to also modify messenger RNA (mRNA) with potential impacts on gene expression. However, the base pairing between known target RNAs and H/ACA guide RNAs varies widely in nature, and therefore the rules governing substrate RNA selection are still not fully understood. To provide quantitative insight into substrate RNA recognition, we systematically altered the sequence of a substrate RNA target by the Saccharomyces cerevisiae H/ACA guide RNA snR34. Time courses measuring pseudouridine formation revealed a gradual decrease in the initial velocity of pseudouridylation upon reducing the number of base pairs between substrate and guide RNA. Changing or inserting nucleotides close to the target uridine severely impairs pseudouridine formation. Interestingly, filter binding experiments show that all substrate RNA variants bind to H/ACA snoRNPs with nanomolar affinity. Next, we showed that binding of inactive, near-cognate RNAs to H/ACA snoRNPs does not inhibit their activity for cognate RNAs, presumably because near-cognate RNAs dissociate rapidly. We discuss that the modulation of initial velocities by the base-pairing strength might affect the order and efficiency of pseudouridylation in rRNA during ribosome biogenesis. Moreover, the binding of H/ACA snoRNPs to near-cognate RNAs may be a mechanism to search for cognate target sites. Together, our data provide critical information to aid in the prediction of productive H/ACA guide-substrate RNA pairs.

Predictive value of pseudouridine in prostate cancer

BACKGROUND

Recent studies have shown that certain small nucleolar RNAs (H/ACA snoRNAs) and the protein dyskerin (DKC1) are upregulated in prostate cancer and are thought to contribute to progression of disease. These components convert uridine to pseudouridine (abbreviated ψ), a type of post-transcriptional modification of RNA. Given the increased abundance of H/ACA snoRNAs and expression of DKC1 in prostate carcinomas, and because whole-body turnover of RNA increases in support of rapidly-growing cancer cells, we examined the value of pseudouridine as a biomarker for prostate cancer.

METHODS

Using a monoclonal antibody against pseudouridine, we tested its ability to distinguish between two 25-base RNA oligonucleotide sequences that differed by only one ψ-substitution, and subsequently measured ψ in RNA isolated from several prostate cancer cell lines representing different stages of disease using dot blot assays and pseudouridinylated RNA linked immunosorbent assay (PURLISA). We also performed immunohistochemistry on a tissue micro array (12 cases/24 cores) containing prostate adenocarcinomas and normal adjacent tissue (NAT).

RESULTS

High levels of pseudouridine were detected in androgen-independent cell lines (PC3 and Du145) compared to androgen-sensitive (LNCaP) and immortalized human prostate (RWPE) cells. Immunohistochemistry of a tissue micro array (TMA) containing normal adjacent and cancerous prostate tissue revealed a significant difference in immunoreactivity between normal and malignant tissue (P ≤ 0.0001).

CONCLUSION

Our results provide new information on the relationship between pseudouridine expression and clinical progression of prostate cancer.