Sphingosine kinase 1 is required for mesothelioma cell proliferation: role of histone acetylation

Our plain-English summary of Sphingosine kinase 1 is required for mesothelioma cell proliferation: role of histone acetylation, by S. Kalari, N. Moolky, S. Pendyala, et al (PloS One, 2012).

The study

• Authors: S. Kalari, N. Moolky, S. Pendyala, E.V. Berdyshev, C. Rolle, R. Kanteti, A. Kanteti, W. Ma, D. He, A.N. Husain, H.L. Kindler, P. Kanteti, R. Salgia, V. Natarajan
• Journal: PloS One
• Published: 2012;7(9):e45330
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Malignant pleural mesothelioma (MPM) is a devastating disease with an overall poor prognosis. Despite the recent advances in targeted molecular therapies, there is a clear and urgent need for the identification of novel mesothelioma targets for the development of highly efficacious therapeutics.

Methodology/principal Findings: In this study, we report that the expression of Sphingosine Kinase 1 (SphK1) protein was preferentially elevated in MPM tumor tissues (49 epithelioid and 13 sarcomatoid) compared to normal tissue (n = 13). In addition, we also observed significantly elevated levels of SphK1 and SphK2 mRNA and SphK1 protein expression in MPM cell lines such as H2691, H513 and H2461 compared to the non-malignant mesothelial Met5 cells. The underlying mechanism appears to be mediated by SphK1 induced upregulation of select gene transcription programs such as that of CBP/p300 and PCAF, two histone acetyl transferases (HAT), and the down regulation of cell cycle dependent kinase inhibitor genes such as p27Kip1 and p21Cip1. In addition, using immunoprecipitates of anti-acetylated histone antibody from SphK inhibitor, SphK-I2 treated Met5A and H2691 cell lysates, we also showed activation of other cell proliferation related genes, such as Top2A (DNA replication), AKB (chromosome remodeling and mitotic spindle formation), and suppression of p21 CIP1 and p27KIP1. The CDK2, HAT1 and MYST2 were, however, unaffected in the above study. Using SphK inhibitor and specific siRNA targeting either SphK1 or SphK2, we also unequivocally established that SphK1, but not SphK2, promotes H2691 mesothelioma cell proliferation. Using a multi-walled carbon nanotubes induced peritoneal mesothelioma mouse model, we showed that the SphK1-/- null mice exhibited significantly less inflammation and granulamatous nodules compared to their wild type counterparts.

Conclusions/significance: The lipid kinase SphK1 plays a positive and essential role in the growth and development of malignant mesothelioma and is therefore a likely therapeutic target.

In plain English

This was a laboratory study of an enzyme called sphingosine kinase 1 (SphK1) in malignant pleural mesothelioma. It did not study asbestos exposure. The authors stained tumor tissue from 62 patients (49 epithelioid and 13 sarcomatoid) and 13 normal tissue samples, and reported significantly higher SphK1 in the tumors. In three mesothelioma cell lines, SphK1 messenger RNA was about 4 to 5 fold higher, and SphK2 2 to 2.5 fold higher, than in a non-malignant mesothelial cell line, Met5A. SphK2 protein, however, was lower in the mesothelioma lines. A chemical inhibitor of SphK cut serum-driven growth of mesothelioma cells by about 40 to 50% without affecting Met5A cells. Silencing SphK1, but not SphK2, reduced growth of the H2691 cell line. The inhibitor also reduced histone acetylation, a chemical tagging of DNA-packaging proteins, in H2691 cells. Mice were injected in the abdomen with multi-walled carbon nanotubes and examined for inflammation, not tumors. Mice lacking SphK1 had smaller areas of granulomatous inflammation on the diaphragm than normal mice. The authors proposed SphK1 as a treatment target and said a role for SphK2 could not be excluded.

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 study: immunostaining of a human tumor tissue microarray, experiments on human cell lines, and an animal experiment in mice
• Who was studied: Archival tissue from 62 malignant pleural mesothelioma patients (49 epithelioid, 13 sarcomatoid) and 13 normal tissue samples. Mesothelioma cell lines (H2691, H2461, H513 and others) and the non-malignant mesothelial cell line Met5A. Male wild-type and SphK1-deficient C57BL/6 mice (n = 6 per group).
• Exposure: No asbestos exposure was studied. Cells were treated with a SphK inhibitor (SphK-I2) or with siRNA silencing SphK1 or SphK2. Mice received a single intraperitoneal injection of multi-walled carbon nanotubes at two doses, printed as '50 mg' and '3 mg' (units appear garbled).
• Main results:
  • SphK1 staining was significantly higher in epithelioid and sarcomatoid mesothelioma tumors than in normal tissue (fold figure printed with a garbled symbol, about 4 fold).
  • In mesothelioma cell lines (H2691, H2461, H513) compared with Met5A, SphK1 transcripts rose about 4 to 5 fold and SphK2 transcripts 2 to 2.5 fold.
  • Despite higher SphK2 transcripts, SphK2 protein was much lower in the mesothelioma cell lines than in Met5A.
  • Pretreatment with the SphK inhibitor SphK-I2 reduced serum-induced proliferation of mesothelioma cells by about 40 to 50%. Met5A control cells were insensitive at the concentration tested.
  • Silencing SphK1 reduced serum-dependent proliferation of H2691 cells (reported as 100 vs. 40%). Silencing SphK2 had no effect on H2691 proliferation.
  • In H2691 cells but not Met5A, SphK-I2 increased mRNA expression of p21Cip1 (about 7 fold) and p27Kip1 (about 3 fold).
  • SphK-I2 reduced serum-induced H3 and H4 histone acetylation in H2691 cells but not in Met5A control cells.
  • Relative granuloma area on the diaphragm was 0 (sham), 19055 (lower dose) and 38197 (higher dose) in wild-type mice. In SphK1-deficient mice it was 0 (sham), 4483 (lower dose) and 15988 (higher dose). Units are printed as mm2.
• The authors' conclusion: The authors proposed that SphK1 is an ideal target candidate for developing mesothelioma treatments. They concluded that SphK1, but not SphK2, regulates mesothelioma cell proliferation through histone acetylation.
• Limitations the authors state:
  • Because of background staining problems, SphK2 levels could not be determined in the archival tumor tissue.
  • The rise in p21Cip1 and p27Kip1 mRNA caused by the SphK inhibitor did not translate into higher protein levels. The authors said this questions the importance of these CDK inhibitors in the pathway.
  • The results do not exclude a role for SphK2 in mesothelioma, and further studies are needed.
  • There is a lack of a proper mouse model of mesothelioma. Carbon-nanotube-induced granulomatous inflammation was used instead.

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, Pleural Mesothelioma, Prognosis, Epithelioid, Sarcomatoid, Peritoneal Mesothelioma, Inflammation, Malignant Mesothelioma.

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