Effect of enhanced expression of connexin 43 on sunitinib-induced cytotoxicity in mesothelioma cells

Our plain-English summary of Effect of enhanced expression of connexin 43 on sunitinib-induced cytotoxicity in mesothelioma cells, by M. Uzu, H. Sato, R. Yamada, et al (Journal of Pharmacological Sciences, 2015).

The study

• Authors: M. Uzu, H. Sato, R. Yamada, T. Kashiba, Y. Shibata, K. Yamaura, K. Ueno
• Journal: Journal of Pharmacological Sciences
• Published: 2015;128(1):17-26
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Connexin (Cx) makes up a type of intercellular channel called gap junction (GJ). GJ plays a regulatory role in cellular physiology. The Cx expression level is often decreased in cancer cells compared to that in healthy ones, and the restoration of its expression has been shown to exert antiproliferative effects. This work aims to evaluate the effect of the restoration of connexin 43 (Cx43) (the most ubiquitous Cx subtype) expression on sunitinib (SU)-induced cytotoxicity in malignant mesothelioma (MM) cells. Increased Cx43 expression in an MM cell line (H28) improved the ability of SU to inhibit receptor tyrosine kinase (RTK) signaling. Moreover, higher Cx43 expression promoted SU-induced apoptosis. The cell viability test revealed that Cx43 enhanced the cytotoxic effect of SU in a GJ-independent manner. The effect of Cx43 on a proapoptotic factor, Bax, was then investigated. The interaction between Cx43 and Bax was confirmed by immunoprecipitation. Furthermore, higher Cx43 expression increased the production of a cleaved (active) form of Bax during SU-induced apoptosis with no alteration in total Bax expression. These findings indicate that Cx43 most likely increases sensitivity to SU in H28 through direct interaction with Bax. In conclusion, we found that Cx43 overcame the chemoresistance of MM cells.

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In plain English

In this laboratory study, the authors worked with H28, a human malignant mesothelioma cell line. They made a version, called H28-T, carrying the gene for connexin 43 (Cx43), a protein forming channels between cells called gap junctions. They treated both cell types with the cancer drug sunitinib. No asbestos exposure was studied. H28-T cells had about 13-fold more Cx43 mRNA than H28 cells. H28 cells were resistant to sunitinib, with approximately 80% surviving high concentrations, while H28-T cells showed lower viability. The rise in dying (apoptotic) cells after sunitinib was significantly higher in H28-T cells than in H28 cells. Blocking gap junctions did not raise H28-T viability under sunitinib; at the two highest concentrations it fell significantly further than with sunitinib alone. Cx43 was found bound to Bax, a protein that promotes cell death. An active, cut form of Bax appeared only in sunitinib-treated H28-T cells. The authors concluded that Cx43 could overcome the resistance of H28 cells to sunitinib in a way that did not depend on gap junctions. They noted that they used gene-transfected cells and that parts of the mechanism remain unexplained.

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-culture experiment
• Who was studied: One human malignant mesothelioma cell line, H28, obtained from ATCC, and a Cx43-transfected version of it (H28-T); no human subjects
• Exposure: No asbestos or fiber exposure was studied. The cells were treated with the drug sunitinib (a multi-targeted tyrosine kinase inhibitor), with and without increased Cx43 expression produced by gene transfection. A gap-junction inhibitor (18b-glycyrrhetinic acid, GA) was also used.
• Main results:
  • Cx43 mRNA expression in H28-T cells was approximately 13-fold that of H28 cells
  • H28 cells were resistant to sunitinib: approximately 80% of H28 cells survived even at high concentrations
  • H28-T cell viability was lower than that of H28 cells in the presence of sunitinib
  • The increase in the subG1 (apoptotic) cell population after sunitinib was significantly higher in H28-T cells than in H28 cells
  • In H28-T cells, ERK phosphorylation decreased significantly after 24 h of sunitinib treatment. In H28 cells, sunitinib had no effect on total or phosphorylated ERK.
  • In H28 cells treated with sunitinib, the decreases in Akt phosphorylation and total Akt were not significant changes
  • In the gap-junction blocking experiment, which measured cell viability (MTT assay), GA combined with the two highest sunitinib concentrations (6 and 10) significantly decreased H28-T cell viability compared with sunitinib alone
  • Adding GA to sunitinib did not alter H28 cell viability
  • Cx43 and Bax were immunoprecipitated together from H28-T cell lysates. A cleaved (active) Bax band was detected only in sunitinib-treated H28-T cells.
  • Total Bax was slightly higher in H28-T than H28 cells, but the difference was not statistically significant
  • Knocking down Bax reduced the subG1 (apoptotic) population in sunitinib-treated H28-T cells
• The authors' conclusion: The authors concluded that Cx43 could overcome the chemoresistance of H28 cells to sunitinib in a gap-junction-independent manner, possibly by promoting cleavage and activation of Bax through direct interaction
• Limitations the authors state:
  • The study used Cx43-transfected cells rather than raised natural (endogenous) Cx43
  • Which form of Cx43 (phosphorylated or non-phosphorylated) matters for the interaction with Bax was not determined
  • The mechanism by which gap junctions appeared protective at high sunitinib concentrations remains to be explained
  • How Cx43 promotes Bax activation was not established and is left for future study

Topics

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

Medical terms in this study, explained in our Lexicon: Sunitinib (Sutent), Mesothelioma, Malignant Mesothelioma, Apoptosis.

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