bims-micpro Biomed News
on Discovery and characterization of microproteins
Issue of 2022‒03‒06
five papers selected by
Thomas Farid Martínez
University of California, Irvine

  1. Mol Cell. 2022 Feb 17. pii: S1097-2765(22)00085-5. [Epub ahead of print]
      Synthetic lethality through combinatorial targeting DNA damage response (DDR) pathways provides exciting anticancer therapeutic benefit. Currently, the long noncoding RNAs (lncRNAs) have been implicated in tumor drug resistance; however, their potential significance in DDR is still largely unknown. Here, we report that a human lncRNA, CTD-2256P15.2, encodes a micropeptide, named PAR-amplifying and CtIP-maintaining micropeptide (PACMP), with a dual function to maintain CtIP abundance and promote poly(ADP-ribosyl)ation. PACMP not only prevents CtIP from ubiquitination through inhibiting the CtIP-KLHL15 association but also directly binds DNA damage-induced poly(ADP-ribose) chains to enhance PARP1-dependent poly(ADP-ribosyl)ation. Targeting PACMP alone inhibits tumor growth by causing a synthetic lethal interaction between CtIP and PARP inhibitions and confers sensitivity to PARP/ATR/CDK4/6 inhibitors, ionizing radiation, epirubicin, and camptothecin. Our findings reveal that a lncRNA-derived micropeptide regulates cancer progression and drug resistance by modulating DDR, whose inhibition could be employed to augment the existing anticancer therapeutic strategies.
    Keywords:  CtIP; DNA damage response; DNA double-strand break repair; PARP inhibitor; drug resistance; long noncoding RNA; micropeptide; poly(ADP-ribosyl)ation; synthetic lethal
  2. J Proteome Res. 2022 Feb 28.
      Short open reading frame-encoded peptides (SEPs) are microproteins with less than 100 amino acids that play an essential role in the growth and development of organisms. There are plenty of short open reading frames in Drosophila melanogaster that potentially code polypeptides. We chose 11 time points during the life cycle of Drosophila to investigate microproteins, particularly those related to development. Finally, we identified a total of 410 microproteins, of which 27 were noncoding RNA-encoded proteins. Of the 410 microproteins, 74 were expressed in all stages from embryo to adults, whereas 300 microproteins were only found in one or two time points. Approximately, one-third of the microproteins were not reported previously and 44 were obtained from de novo sequencing, validated by synthetic peptides. These microproteins are related to the main bioprocesses of growth and development, such as multicellular organism reproduction, postmating behavior, and oviposition. Over half of the microproteins have predicted functional domains and are conserved across species, suggesting that these microproteins have critical functions in fly development. This work enriches the D. melanogaster proteome and provides a significant data resource for growth and development research.
    Keywords:  Drosophila melanogaster; SEPs; de novo sequencing; microprotein; ncRNA; top-down
  3. Cell Mol Life Sci. 2022 Mar 03. 79(3): 171
      BACKGROUND: Upstream open reading frames (uORFs) represent translational control elements within eukaryotic transcript leader sequences. Recent data showed that uORFs can encode for biologically active proteins and human leukocyte antigen (HLA)-presented peptides in malignant and benign cells suggesting their potential role in cancer cell development and survival. However, the role of uORFs in translational regulation of cancer-associated transcripts as well as in cancer immune surveillance is still incompletely understood.METHODS: We examined the translational regulatory effect of 29 uORFs in 13 cancer-associated genes by dual-luciferase assays. Cellular expression and localization of uORF-encoded peptides (uPeptides) were investigated by immunoblotting and immunofluorescence-based microscopy. Furthermore, we utilized mass spectrometry-based immunopeptidome analyses in an extensive dataset of primary malignant and benign tissue samples for the identification of naturally presented uORF-derived HLA-presented peptides screening for more than 2000 uORFs.
    RESULTS: We provide experimental evidence for similarly effective translational regulation of cancer-associated transcripts through uORFs initiated by either canonical AUG codons or by alternative translation initiation sites (aTISs). We further demonstrate frequent cellular expression and reveal occasional specific cellular localization of uORF-derived peptides, suggesting uPeptide-specific biological implications. Immunopeptidome analyses delineated a set of 125 naturally presented uORF-derived HLA-presented peptides. Comparative immunopeptidome profiling of malignant and benign tissue-derived immunopeptidomes identified several tumor-associated uORF-derived HLA ligands capable to induce multifunctional T cell responses.
    CONCLUSION: Our data provide direct evidence for the frequent expression of uPeptides in benign and malignant human tissues, suggesting a potentially widespread function of uPeptides in cancer biology. These findings may inspire novel approaches in direct molecular as well as immunotherapeutic targeting of cancer-associated uORFs and uPeptides.
    Keywords:  Cancer; Immunopeptidomics; Mass spectrometry; Translational control; uORF
  4. Front Oncol. 2022 ;12 781270
      The discovery of circular RNAs and exploration of their biological functions are increasingly attracting attention in cell bio-sciences. Owing to their unique characteristics of being highly conserved, having a relatively longer half-life, and involvement in RNA maturation, transportation, epigenetic regulation, and transcription of genes, it has been accepted that circRNAs play critical roles in the variety of cellular processes. One of the critical importance of these circRNAs is the presence of small open reading frames that enable them to encode peptides/proteins. In particular, these encoded peptides/proteins mediate essential cellular activities such as proliferation, invasion, epithelial-mesenchymal transition, and apoptosis and develop an association with the development and progression of cancers by modulating diverse signaling pathways. In addition, these peptides have potential roles as biomarkers for the prognosis of cancer and are being used as drug targets against tumorigenesis. In the present review, we thoroughly discussed the biogenesis of circRNAs and their functional mechanisms along with a special emphasis on the reported chimeric peptides/proteins encoded by circRNAs. Additionally, this review provides a perspective regarding the opportunities and challenges to the potential use of circRNAs in cancer diagnosis and therapeutic targets in clinics.
    Keywords:  biomarkers; cancer; chimeric peptides/proteins; circRNAs; therapeutic target
  5. Front Microbiol. 2022 ;13 840911
      Viruses play a key role in explaining the pathogenesis of various autoimmune disorders, whose underlying principle is defined by the activation of autoreactive T-cells. In many cases, T-cells escape self-tolerance due to the failure in encountering certain MHC-I self-peptide complexes at substantial levels, whose peptides remain invisible from the immune system. Over the years, contribution of unstable defective ribosomal products (DRiPs) in immunosurveillance has gained prominence. A class of unstable products emerge from non-canonical translation and processing of unannotated mammalian and viral ORFs and their peptides are cryptic in nature. Indeed, high throughput sequencing and proteomics have revealed that a substantial portion of our genomes comprise of non-canonical ORFs, whose generation is significantly modulated during disease. Many of these ORFs comprise short ORFs (sORFs) and upstream ORFs (uORFs) that resemble DRiPs and may hence be preferentially presented. Here, we discuss how such products, normally "hidden" from the immune system, become abundant in viral infections activating autoimmune T-cells, by discussing their emerging role in infection and disease. Finally, we provide a perspective on how these mechanisms can explain several autoimmune disorders in the wake of the COVID-19 pandemic.
    Keywords:  COVID-19; autoimmunity; cryptic peptides; defective ribosomal products; non-canonical translation; viruses