Mapping the Interactome of the Nuclear Heparan Sulfate Proteoglycan Syndecan-1 in Mesothelioma Cells

Our plain-English summary of Mapping the Interactome of the Nuclear Heparan Sulfate Proteoglycan Syndecan-1 in Mesothelioma Cells, by A. Kumar-Singh, J. Shrinet, M.M. Parniewska, et al (Biomolecules, 2020).

The study

• Authors: A. Kumar-Singh, J. Shrinet, M.M. Parniewska, J. Fuxe, K. Dobra, A. Hjerpe
• Journal: Biomolecules
• Published: 2020;10(7)
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Syndecan-1 (SDC1) is a cell surface heparan sulfate proteoglycan (HSPG), which regulates various signaling pathways controlling the proliferation and migration of malignant mesothelioma and other types of cancer. We have previously shown that SDC1 can translocate to the nucleus in mesothelioma cells through a tubulin-dependent transport mechanism. However, the role of nuclear SDC1 is largely unknown. Here, we performed co-immunoprecipitation (Co-IP) of SDC1 in a mesothelioma cell line to identify SDC1 interacting proteins. The precipitates contained a large number of proteins, indicating the recovery of protein networks. Proteomic analysis with a focus on nuclear proteins revealed an association with pathways related to cell proliferation and RNA synthesis, splicing and transport. In support of this, the top RNA splicing candidates were verified to interact with SDC1 by Co-IP and subsequent Western blot analysis. Further loss- and gain-of-function experiments showed that SDC1 influences RNA levels in mesothelioma cells. The results identify a proteomic map of SDC1 nuclear interactors in a mesothelioma cell line and suggest a previously unknown role for SDC1 in RNA biogenesis. The results should serve as a fundament for further studies to discover the role of nuclear SDC1 in normal and cancer cells of different origin.

In plain English

This was a laboratory study of a single mesothelioma cell line, STAV-AB. It did not study asbestos or any fiber exposure. The authors looked at which proteins associate with syndecan-1 (SDC1), a protein that can move into the cell nucleus. They pulled SDC1 out of cell extracts with antibodies and identified the proteins that came with it. After proteins also found in control samples were removed, 671 proteins remained, and 314 of these (46.8%) were associated with the nucleus. The nuclear proteins were linked to eight pathways, mainly RNA splicing, ribosome and RNA transport, as well as the cell cycle. Two of these proteins, EWSR1 and FUS, were confirmed by a second method. When SDC1 was silenced, total RNA relative to DNA was significantly lower than in control cells (p = 0.0379). When SDC1 was overexpressed, actin RNA was lower (p = 0.0364). The authors concluded that SDC1 may play a role in pathways from cell proliferation to RNA synthesis and transport. They noted that results from one cell line cannot be generalized to other cells.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) cell-line experiment: co-immunoprecipitation with proteomic (mass spectrometry) analysis, followed by SDC1 loss- and gain-of-function experiments
• Who was studied: One human mesothelioma cell line, STAV-AB; no patients or workers were studied
• Exposure: No asbestos or fiber exposure was studied. The experimental manipulation was of SDC1 levels: overexpression of full-length SDC1 (compared with an empty vector control) and silencing of SDC1 with siRNA
• Main results:
  • 750 proteins were found in the SDC1 antibody precipitate and 92 in the non-specific controls. After the 79 shared proteins were removed, 671 proteins remained for analysis
  • Of the 671 interacting proteins, 314 (46.8%) were associated with the nucleus, counting proteins assigned to more than one location
  • Analysis of all interacting proteins found 28 over-represented pathways. Analysis of the nuclear proteins alone found eight
  • The top three pathways, Spliceosome, Ribosome and RNA transport, appeared in both analyses
  • Western blots confirmed that EWSR1 and FUS were precipitated together with SDC1, using both SDC1 antibodies
  • SDC1, EWSR1 and FUS were all present in the nuclei, but microscopy showed little evidence that they sat in the same place (co-localization)
  • In SDC1 knockdown cells, total RNA normalized to DNA content was significantly lower than in control cells (p = 0.0379)
  • In cells overexpressing SDC1, total RNA tended to be lower, but this was not statistically significant (p = 0.0689)
  • Overexpression of SDC1 decreased actin RNA levels compared with controls (p = 0.0364)
  • For SDC1 knockdown, the article reports no significant effect (p = 0.212). The sentence calls this 'total RNA levels' but cites the actin panel, Figure 4b
• The authors' conclusion: The authors concluded that their functional classification indicated a role for SDC1 in various pathways, from cell proliferation to RNA synthesis and transport, in a mesothelioma cell line
• Limitations the authors state:
  • The results come from a single mesothelioma cell line and cannot be generalized to the SDC1 nuclear interactome in other cells
  • The exact mechanism and role of SDC1 in these processes remain unknown and have not been proven in vitro or in vivo

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma.

Related studies

• Syndecan-1 alters heparan sulfate composition and signaling pathways in malignant mesothelioma — G. Heidari-Hamedani, R.R. Vivès, et al. (2015)
• Novel genes and pathways modulated by syndecan-1: implications for the proliferation and cell-cycle regulation of malignant mesothelioma cells — T. Szatmári, F. Mundt, et al. (2012)
• The role of syndecan-1 in cellular signaling and its effects on heparan sulfate biosynthesis in mesenchymal tumors — T. Szatmári, K. Dobra (2013)
• Effect of syndecan-1 overexpression on mesenchymal tumour cell proliferation with focus on different functional domains — F. Zong, E. Fthenou, et al. (2010)
• Oxidative stress alters syndecan-1 distribution in lungs with pulmonary fibrosis — C.R. Kliment, J.M. Englert, et al. (2009)
• Diagnostic and prognostic value of soluble syndecan-1 in pleural malignancies — F. Mundt, G. Heidari-Hamedani, et al. (2014)

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