Sphingosine suppresses mesothelioma cell proliferation by inhibiting PKC-δ and inducing cell cycle arrest at the G(0)/G(1) phase

Our plain-English summary of Sphingosine suppresses mesothelioma cell proliferation by inhibiting PKC-δ and inducing cell cycle arrest at the G(0)/G(1) phase, by H. Okuwa, T. Kanno, Y. Fujita, et al (Cellular Physiology and Biochemistry, 2012).

The study

• Authors: H. Okuwa, T. Kanno, Y. Fujita, A. Gotoh, C. Tabata, K. Fukuoka, T. Nakano, T. Nishizaki
• Journal: Cellular Physiology and Biochemistry
• Published: 2012;30(4):995-1004
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background/aims: Sphingosine regulates cellular differentiation, cell growth, and apoptosis. The present study aimed at understanding sphingosine-regulated mesothelioma cell proliferation.

Methods: Human malignant mesothelioma cells such as NCI-H28, NCI-H2052, NCI-H2452, and MSTO-211H cells were cultured. The siRNA to silence the protein kinase C (PKC)-δ-targeted gene was constructed and transfected into cells. MTT assay, cell cycle analysis using a flow cytometry, and cell-free PKC-δ assay were carried out.

Results: For all the cell types sphingosine inhibited cell growth in a concentration (1-100 µM)-dependent manner. The sphingosine effect was not prevented by rottlerin, an inhibitor of protein kinase C-δ (PKC-δ); conversely, rottlerin further enhanced the sphingosine effect or rottlerin suppressed mesothelioma cell growth without sphingosine. In the cell-free PKC assay, sphingosine attenuated PKC-δ activity. Knocking-down PKC-δ induced cell cycle arrest at the G0/G1 phase and inhibited cell growth.

Conclusion: The results of the present study show that sphingosine suppressed mesothelioma cell proliferation by inhibiting PKC-δ, to induce cell cycle arrest at the G0/G1 phase.

Copyright © 2012 S. Karger AG, Basel.

In plain English

This was a laboratory study of four human malignant mesothelioma cell lines (NCI-H28, NCI-H2052, NCI-H2452 and MSTO-211H) grown in culture. It did not study people, animals or asbestos exposure. Over 24 to 48 hours, sphingosine reduced living cells in all four lines, more so at higher concentrations (1 to 100 µM). A test for apoptosis, a type of cell death, showed no significant increase. S1P, a related molecule, had little effect on living-cell numbers at 1 to 30 µM. In a cell-free test, activity of the enzyme PKC-δ fell from 2.26 to 0.76 pmol/min with sphingosine. Rottlerin, a drug that blocks PKC-δ, reduced cell numbers on its own, and adding it to sphingosine reduced them further than sphingosine alone. Silencing the PKC-δ gene also slowed growth and left more cells held at an early cell-cycle stage (G0/G1). That cell-cycle test used gene-silenced cells, not sphingosine-treated cells. The authors concluded that sphingosine suppresses mesothelioma cell proliferation by inhibiting PKC-δ. They stated that the signaling pathways behind this sphingosine and PKC-δ dependent inhibition were not yet known.

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) experiment on cultured human cancer cell lines
• Who was studied: Four commercially obtained human malignant mesothelioma cell lines: NCI-H28, NCI-H2052, NCI-H2452 and MSTO-211H. No human participants or animals.
• Exposure: No asbestos exposure was studied. Cells were treated with sphingosine (1-100 µM), S1P (1-30 µM) or the PKC-δ inhibitor rottlerin (0.1-10 µM), or had the PKC-δ gene silenced with siRNA.
• Main results:
  • In all four cell lines, sphingosine for 24-48 h reduced the number of living cells, with larger reductions at higher concentrations from 1 to 100 µM.
  • Sphingosine did not significantly increase apoptotic (TUNEL-positive) cells in any of the cell lines. The data were not shown.
  • S1P at 1 to 30 µM for 24-48 h had little effect on living-cell numbers in all four cell lines.
  • Sphingosine did not increase production of SDK, a fragment of PKC-δ, in any of the cell lines.
  • Rottlerin (10 µM) did not block the effect of sphingosine. With sphingosine it further reduced living cells (P<0.001 compared with sphingosine alone, all cell lines).
  • Rottlerin alone, at 0.1-10 µM, reduced living-cell numbers in all four cell lines, with larger reductions at higher concentrations.
  • In the cell-free test, PKC-δ activity was 2.26 ± 0.32 pmol/min without sphingosine and 0.76 ± 0.06 pmol/min with sphingosine (100 µM), a significant reduction (n=4).
  • Silencing PKC-δ significantly slowed cell growth. The effect was strongest in NCI-H2052 and MSTO-211H, then NCI-H2452, and much weaker in NCI-H28.
  • In all four cell lines, silencing PKC-δ (not sphingosine treatment) increased the share of cells in the G0/G1 phase and decreased the share in the G2/M phase.
• The authors' conclusion: The authors concluded that sphingosine inhibits PKC-δ, causing cell cycle arrest at the G0/G1 phase and so suppressing mesothelioma cell proliferation.
• Limitations the authors state:
  • The authors stated that the signaling pathways underlying the sphingosine and PKC-δ dependent inhibition of proliferation in mesothelioma cells are not yet known.

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, Apoptosis, Malignant Mesothelioma.

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