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Koutras N, Morfos V, Konnaris K, Kouvela A, Shaukat AN, Stathopoulos C, Stamatopoulou V, Nika K. Integrated signaling and transcriptome analysis reveals Src family kinase individualities and novel pathways controlled by their constitutive activity. Front Immunol 2023; 14:1224520. [PMID: 37680627 PMCID: PMC10482094 DOI: 10.3389/fimmu.2023.1224520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Accepted: 08/07/2023] [Indexed: 09/09/2023] Open
Abstract
The Src family kinases (SFKs) Lck and Lyn are crucial for lymphocyte development and function. Albeit tissue-restricted expression patterns the two kinases share common functions; the most pronounced one being the phosphorylation of ITAM motifs in the cytoplasmic tails of antigenic receptors. Lck is predominantly expressed in T lymphocytes; however, it can be ectopically found in B-1 cell subsets and numerous pathologies including acute and chronic B-cell leukemias. The exact impact of Lck on the B-cell signaling apparatus remains enigmatic and is followed by the long-lasting question of mechanisms granting selectivity among SFK members. In this work we sought to investigate the mechanistic basis of ectopic Lck function in B-cells and compare it to events elicited by the predominant B-cell SFK, Lyn. Our results reveal substrate promiscuity displayed by the two SFKs, which however, is buffered by their differential susceptibility toward regulatory mechanisms, revealing a so far unappreciated aspect of SFK member-specific fine-tuning. Furthermore, we show that Lck- and Lyn-generated signals suffice to induce transcriptome alterations, reminiscent of B-cell activation, in the absence of receptor/co-receptor engagement. Finally, our analyses revealed a yet unrecognized role of SFKs in tipping the balance of cellular stress responses, by promoting the onset of ER-phagy, an as yet completely uncharacterized process in B lymphocytes.
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Affiliation(s)
| | | | | | | | | | | | | | - Konstantina Nika
- Department of Biochemistry, School of Medicine, University of Patras, Patras, Greece
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Shaukat AN, Kaliatsi EG, Skeparnias I, Stathopoulos C. The Dynamic Network of RNP RNase P Subunits. Int J Mol Sci 2021; 22:ijms221910307. [PMID: 34638646 PMCID: PMC8509007 DOI: 10.3390/ijms221910307] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Revised: 09/22/2021] [Accepted: 09/23/2021] [Indexed: 11/17/2022] Open
Abstract
Ribonuclease P (RNase P) is an important ribonucleoprotein (RNP), responsible for the maturation of the 5′ end of precursor tRNAs (pre-tRNAs). In all organisms, the cleavage activity of a single phosphodiester bond adjacent to the first nucleotide of the acceptor stem is indispensable for cell viability and lies within an essential catalytic RNA subunit. Although RNase P is a ribozyme, its kinetic efficiency in vivo, as well as its structural variability and complexity throughout evolution, requires the presence of one protein subunit in bacteria to several protein partners in archaea and eukaryotes. Moreover, the existence of protein-only RNase P (PRORP) enzymes in several organisms and organelles suggests a more complex evolutionary timeline than previously thought. Recent detailed structures of bacterial, archaeal, human and mitochondrial RNase P complexes suggest that, although apparently dissimilar enzymes, they all recognize pre-tRNAs through conserved interactions. Interestingly, individual protein subunits of the human nuclear and mitochondrial holoenzymes have additional functions and contribute to a dynamic network of elaborate interactions and cellular processes. Herein, we summarize the role of each RNase P subunit with a focus on the human nuclear RNP and its putative role in flawless gene expression in light of recent structural studies.
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Shaukat AN, Kaliatsi EG, Stamatopoulou V, Stathopoulos C. Mitochondrial tRNA-Derived Fragments and Their Contribution to Gene Expression Regulation. Front Physiol 2021; 12:729452. [PMID: 34539450 PMCID: PMC8446549 DOI: 10.3389/fphys.2021.729452] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Accepted: 08/09/2021] [Indexed: 01/14/2023] Open
Abstract
Mutations in human mitochondrial tRNAs (mt-tRNAs) are responsible for several and sometimes severe clinical phenotypes, classified among mitochondrial diseases. In addition, post-transcriptional modifications of mt-tRNAs in correlation with several stress signals can affect their stability similarly to what has been described for their nuclear-encoded counterparts. Many of the perturbations related to either point mutations or aberrant modifications of mt-tRNAs can lead to specific cleavage and the production of mitochondrial tRNA-derived fragments (mt-tRFs). Although mt-tRFs have been detected in several studies, the exact biogenesis steps and biological role remain, to a great extent, unexplored. Several mt-tRFs are produced because of the excessive oxidative stress which predominantly affects mitochondrial DNA integrity. In addition, mt-tRFs have been detected in various diseases with possible detrimental consequences, but also their production may represent a response mechanism to external stimuli, including infections from pathogens. Finally, specific point mutations on mt-tRNAs have been reported to impact the pool of the produced mt-tRFs and there is growing evidence suggesting that mt-tRFs can be exported and act in the cytoplasm. In this review, we summarize current knowledge on mitochondrial tRNA-deriving fragments and their possible contribution to gene expression regulation.
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Affiliation(s)
| | - Eleni G Kaliatsi
- Department of Biochemistry, School of Medicine, University of Patras, Patras, Greece
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Kaliatsi EG, Argyriou AI, Bouras G, Apostolidi M, Konstantinidou P, Shaukat AN, Spyroulias GA, Stathopoulos C. Functional and Structural Aspects of La Protein Overexpression in Lung Cancer. J Mol Biol 2020; 432:166712. [PMID: 33197462 DOI: 10.1016/j.jmb.2020.11.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 11/09/2020] [Accepted: 11/09/2020] [Indexed: 10/23/2022]
Abstract
La is an abundant phosphoprotein that protects polymerase III transcripts from 3'-5' exonucleolytic degradation and facilitates their folding. Consisting of the evolutionary conserved La motif (LAM) and two consecutive RNA Recognition Motifs (RRMs), La was also found to bind additional RNA transcripts or RNA domains like internal ribosome entry site (IRES), through sequence-independent binding modes which are poorly understood. Although it has been reported overexpressed in certain cancer types and depletion of its expression sensitizes cancer cells to certain chemotherapeutic agents, its role in cancer remains essentially uncharacterized. Herein, we study the effects of La overexpression in A549 lung adenocarcinoma cells, which leads to increased cell proliferation and motility. Expression profiling of several transcription and translation factors indicated that La overexpression leads to downregulation of global translation through hypophosphorylation of 4E-BPs and upregulation of IRES-mediated translation. Moreover, analysis of La localization after nutrition deprivation of the transfected cells showed a normal distribution in the nucleus and nucleoli. Although the RNA binding capacity of La has been primarily linked to the synergy between the conserved LAM and RRM1 domains which act as a module, we show that recombinant stand-alone LAM can specifically bind a pre-tRNA ligand, based on binding experiments combined with NMR analysis. We propose that LAM RNA binding properties could support the expanding and diverse RNA ligand repertoire of La, thus promoting its modulatory role, both under normal and pathogenic conditions like cancer.
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Affiliation(s)
- Eleni G Kaliatsi
- Department of Biochemistry, School of Medicine, University of Patras, 26504 Patras, Greece
| | | | - Georgios Bouras
- Department of Pharmacy, University of Patras, 26504 Patras, Greece
| | - Maria Apostolidi
- Department of Biochemistry, School of Medicine, University of Patras, 26504 Patras, Greece
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Skeparnias I, Αnastasakis D, Shaukat AN, Grafanaki K, Stathopoulos C. Expanding the repertoire of deadenylases. RNA Biol 2017; 14:1320-1325. [PMID: 28267419 PMCID: PMC5711463 DOI: 10.1080/15476286.2017.1300222] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Revised: 02/13/2017] [Accepted: 02/23/2017] [Indexed: 12/20/2022] Open
Abstract
Deadenylases belong to an expanding family of exoribonucleases involved mainly in mRNA stability and turnover, with the exception of PARN which has additional roles in the biogenesis of several important non-coding RNAs, including miRNAs and piRNAs. Recently, PARN in C. elegans and its homolog PNLDC1 in B. mori were reported as the elusive trimmers mediating piRNA biogenesis. In addition, characterization of mammalian PNLDC1 in comparison to PARN, showed that is specifically expressed in embryonic stem and germ cells, as well as during early embryo development. Moreover, its expression is correlated with epigenetic events mediated by the de novo DNMT3b methyltransferase and knockdown in stem cells upregulates important genes that regulate multipotency. The recent data suggest that at least some new deadenylases may have expanded roles in cell metabolism as regulators of gene expression, through mRNA deadenylation, ncRNAs biogenesis and ncRNA-mediated mRNA targeting, linking essential mechanisms that regulate epigenetic control and transition events during differentiation. The possible roles of mammalian PNLDC1 along those dynamic networks are discussed in the light of new extremely important findings.
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Affiliation(s)
- Ilias Skeparnias
- Department of Biochemistry, School of Medicine, University of Patras, Greece
| | | | | | - Katerina Grafanaki
- Department of Biochemistry, School of Medicine, University of Patras, Greece
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Anastasakis D, Skeparnias I, Shaukat AN, Grafanaki K, Kanellou A, Taraviras S, Papachristou DJ, Papakyriakou A, Stathopoulos C. Mammalian PNLDC1 is a novel poly(A) specific exonuclease with discrete expression during early development. Nucleic Acids Res 2016; 44:8908-8920. [PMID: 27515512 PMCID: PMC5062988 DOI: 10.1093/nar/gkw709] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 08/02/2016] [Indexed: 12/28/2022] Open
Abstract
PNLDC1 is a homologue of poly(A) specific ribonuclease (PARN), a known deadenylase with additional role in processing of non-coding RNAs. Both enzymes were reported recently to participate in piRNA biogenesis in silkworm and C. elegans, respectively. To get insights on the role of mammalian PNLDC1, we characterized the human and mouse enzymes. PNLDC1 shows limited conservation compared to PARN and represents an evolutionary related but distinct group of enzymes. It is expressed specifically in mouse embryonic stem cells, human and mouse testes and during early mouse embryo development, while it fades during differentiation. Its expression in differentiated cells, is suppressed through methylation of its promoter by the de novo methyltransferase DNMT3B. Both enzymes are localized mainly in the ER and exhibit in vitro specificity restricted solely to 3′ RNA or DNA polyadenylates. Knockdown of Pnldc1 in mESCs and subsequent NGS analysis showed that although the expression of the remaining deadenylases remains unaffected, it affects genes involved mainly in reprogramming, cell cycle and translational regulation. Mammalian PNLDC1 is a novel deadenylase expressed specifically in cell types which share regulatory mechanisms required for multipotency maintenance. Moreover, it could be involved both in posttranscriptional regulation through deadenylation and genome surveillance during early development.
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Affiliation(s)
- Dimitrios Anastasakis
- Department of Biochemistry, School of Medicine, University of Patras, 26504 Rio Achaia, Greece
| | - Ilias Skeparnias
- Department of Biochemistry, School of Medicine, University of Patras, 26504 Rio Achaia, Greece
| | | | - Katerina Grafanaki
- Department of Biochemistry, School of Medicine, University of Patras, 26504 Rio Achaia, Greece
| | - Alexandra Kanellou
- Department of Physiology, School of Medicine, University of Patras, 26504 Rio Achaia, Greece
| | - Stavros Taraviras
- Department of Physiology, School of Medicine, University of Patras, 26504 Rio Achaia, Greece
| | - Dionysios J Papachristou
- Department of Anatomy, Histology and Embryology, School of Medicine, University of Patras, 26504 Rio Achaia, Greece
| | - Athanasios Papakyriakou
- Laboratory of Chemical Biology, National Centre for Scientific Research 'Demokritos', 15341 Athens, Greece
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