bims-micpro Biomed News
on Discovery and characterization of microproteins
Issue of 2023‒03‒05
six papers selected by
Thomas Farid Martínez
University of California, Irvine

  1. Nat Commun. 2023 Feb 25. 14(1): 1078
      Protein arginine methyltransferase (PRMT) 5 is over-expressed in a variety of cancers and the master transcription regulator E2F1 is an important methylation target. We have explored the role of PRMT5 and E2F1 in regulating the non-coding genome and report here a striking effect on long non-coding (lnc) RNA gene expression. Moreover, many MHC class I protein-associated peptides were derived from small open reading frames in the lncRNA genes. Pharmacological inhibition of PRMT5 or adjusting E2F1 levels qualitatively altered the repertoire of lncRNA-derived peptide antigens displayed by tumour cells. When presented to the immune system as either ex vivo-loaded dendritic cells or expressed from a viral vector, lncRNA-derived peptides drove a potent antigen-specific CD8 T lymphocyte response, which translated into a significant delay in tumour growth. Thus, lncRNA genes encode immunogenic peptides that can be deployed as a cancer vaccine.
  2. J Clin Invest. 2023 Mar 01. pii: e159940. [Epub ahead of print]133(5):
      Emerging evidence suggests that cryptic translation within long noncoding RNAs (lncRNAs) may produce novel proteins with important developmental/physiological functions. However, the role of this cryptic translation in complex diseases (e.g., cancer) remains elusive. Here, we applied an integrative strategy combining ribosome profiling and CRISPR/Cas9 screening with large-scale analysis of molecular/clinical data for breast cancer (BC) and identified estrogen receptor α-positive (ER+) BC dependency on the cryptic ORFs encoded by lncRNA genes that were upregulated in luminal tumors. We confirmed the in vivo tumor-promoting function of an unannotated protein, GATA3-interacting cryptic protein (GT3-INCP) encoded by LINC00992, the expression of which was associated with poor prognosis in luminal tumors. GTE-INCP was upregulated by estrogen/ER and regulated estrogen-dependent cell growth. Mechanistically, GT3-INCP interacted with GATA3, a master transcription factor key to mammary gland development/BC cell proliferation, and coregulated a gene expression program that involved many BC susceptibility/risk genes and impacted estrogen response/cell proliferation. GT3-INCP/GATA3 bound to common cis regulatory elements and upregulated the expression of the tumor-promoting and estrogen-regulated BC susceptibility/risk genes MYB and PDZK1. Our study indicates that cryptic lncRNA-encoded proteins can be an important integrated component of the master transcriptional regulatory network driving aberrant transcription in cancer, and suggests that the "hidden" lncRNA-encoded proteome might be a new space for therapeutic target discovery.
    Keywords:  Breast cancer; Genetics; Noncoding RNAs; Oncology; Translation
  3. iScience. 2023 Feb 17. 26(2): 105943
      Eukaryotic mRNA has long been considered monocistronic, but nowadays, alternative proteins (AltProts) challenge this tenet. The alternative or ghost proteome has largely been neglected and the involvement of AltProts in biological processes. Here, we used subcellular fractionation to increase the information about AltProts and facilitate the detection of protein-protein interactions by the identification of crosslinked peptides. In total, 112 unique AltProts were identified, and we were able to identify 220 crosslinks without peptide enrichment. Among these, 16 crosslinks between AltProts and Referenced Proteins (RefProts) were identified. We further focused on specific examples such as the interaction between IP_2292176 (AltFAM227B) and HLA-B, in which this protein could be a potential new immunopeptide, and the interactions between HIST1H4F and several AltProts which can play a role in mRNA transcription. Thanks to the study of the interactome and the localization of AltProts, we can reveal more of the importance of the ghost proteome.
    Keywords:  Cell biology; Molecular network; Proteomics
  4. Development. 2023 Feb 27. pii: dev.201177. [Epub ahead of print]
      Gene expression regulation in eukaryotes is a multi-level process, including transcription, mRNA translation, and protein turnover. Many studies have reported the sophisticated transcriptional regulations during neural development, but the global translational dynamics are still ambiguous. Here, we differentiate human embryonic stem cells (ESCs) into neural progenitor cells (NPCs) with high efficiency and perform ribosome sequencing and RNA sequencing on both ESCs and NPCs. Data analysis reveals that translational controls engage in many critical pathways and contribute significantly to neural fate determination regulation. Furthermore, we show that the sequence characteristics in the untranslated region (UTR) might regulate translation efficiency. Specifically, genes with short 5'UTR and intense Kozak sequence are associated with high translation efficiency in human ESCs, while genes with long 3'UTR are related to high translation efficiency in NPCs. In addition, we have identified four biasedly-used codons (GAC, GAT, AGA, and AGG) and dozens of short open reading frames during neural progenitor differentiation. Thus, our study reveals the translational landscape during early human neural differentiation and provides insights into the regulation of cell fate determination at the translational level.
    Keywords:  Embryonic stem cells; Neural differentiation; Short open reading frame; Translational landscape; Translational regulation
  5. J Clin Invest. 2023 Mar 01. pii: e167271. [Epub ahead of print]133(5):
      A majority of the human genome is transcribed into noncoding RNAs, of which long noncoding RNAs (lncRNAs) form a large and heterogeneous fraction. While lncRNAs are mostly noncoding, recent evidence suggests that cryptic translation within some lncRNAs may produce proteins with important regulatory functions. In this issue of the JCI, Zheng, Wei, and colleagues used an integrative functional genomic strategy to systematically identify cryptic lncRNA-encoded ORFs that play a role in estrogen receptor-positive (ER+) breast cancer (BC). They identified 758 cryptic lncRNA-encoded ORFs undergoing active translation, of which 28 had potential functional and clinical relevance in ER+ BC. The LINC00992-encoded polypeptide GT3-INCP was upregulated in ER+ BC and drove tumor growth. GT3-INCP was regulated by estrogen and the ER and acted via the transcription factor GATA3 to regulate BC susceptibility and risk genes. These findings discern a largely unexplored class of molecules and have implications for many pathologies, including cancer.
  6. Nucleic Acids Res. 2023 Mar 03. pii: gkad135. [Epub ahead of print]
      Roughly half of animal mRNAs contain upstream open reading frames (uORFs). These uORFs can represent an impediment to translation of the main ORF since ribosomes usually bind the mRNA cap at the 5' end and then scan for ORFs in a 5'-to-3' fashion. One way for ribosomes to bypass uORFs is via leaky scanning, whereby the ribosome disregards the uORF start codon. Hence leaky scanning is an important instance of post-transcriptional regulation that affects gene expression. Few molecular factors regulating or facilitating this process are known. Here we show that the PRRC2 proteins PRRC2A, PRRC2B and PRRC2C impact translation initiation. We find that they bind eukaryotic translation initiation factors and preinitiation complexes, and are enriched on ribosomes translating mRNAs with uORFs. We find that PRRC2 proteins promote leaky scanning past translation start codons, thereby promoting translation of mRNAs containing uORFs. Since PRRC2 proteins have been associated with cancer, this provides a mechanistic starting point for understanding their physiological and pathophysiological roles.