Phosphatidylinositol Induces Caspase-Independent Apoptosis of Malignant Pleural Mesothelioma Cells by Accumulating AIF in the Nucleus

Our plain-English summary of Phosphatidylinositol Induces Caspase-Independent Apoptosis of Malignant Pleural Mesothelioma Cells by Accumulating AIF in the Nucleus, by S. Kanemura, A. Tsuchiya, T. Kanno, et al (Cellular Physiology and Biochemistry, 2015).

The study

• Authors: S. Kanemura, A. Tsuchiya, T. Kanno, T. Nakano, T. Nishizaki
• Journal: Cellular Physiology and Biochemistry
• Published: 2015;36(3):1037-48
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background/aims: Phosphatidylinositol (PI) regulates a variety of cell processes. The present study investigated the antitumor action of 1,2-dioleoyl-sn-glycero-3-phospho-(1'-myo-inositol)(DOPI) and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-myo-inositol)(DPPI) on human malignant pleural mesothelioma (MPM) cell lines such as NCI-H28, NCI-H2052, NCI-H2452, and MSTO-211H cells.

Methods: MTT assay, TUNEL staining, flow cytometry using propidium iodide (PI) and annexin V (AV), enzymatic caspase assay, and nuclear staining using DAPI were carried out, and mitochondrial membrane potentials and intracellular distribution of apoptosis-inducing factor (AIF) were monitored in cells with and without the siRNA silencing the Bid-targeted gene.

Results: Both DOPI and DPPI reduced cell viability for all the investigated MPM cell lines in a concentration (0.01-100 µM)-dependent manner. DOPI and DPPI significantly increased TUNEL-positive cells and the population of PI-negative/AV-positive and PI-positive/AV-positive cells, corresponding to early apoptosis and late apoptosis/secondary necrosis, respectively. DOPI and DPPI perturbed mitochondrial membrane potentials in MSTO-211H cells, but no significant activation of caspase-3, -4, -8, and -9 was obtained. DOPI and DPPI upregulated expression of Bid in MSTO-211H cells. DOPI and DPPI significantly increased nuclear localization of AIF without affecting expression of the mRNAs and proteins in MSTO-211H cells, which was inhibited by knocking-down Bid. In the DAPI staining, nuclear fragmentation and condensation were found.

Conclusion: The results of the present study indicate that DOPI and DPPI facilitate Bid-mediated AIF release from the mitochondria, to accumulate AIF in the nucleus and induce caspase-independent apoptosis of MPM cells.

© 2015 S. Karger AG, Basel.

In plain English

This was a laboratory study of human malignant pleural mesothelioma cells grown in culture. It did not study people or asbestos exposure. The authors tested two forms of a natural cell-membrane fat called phosphatidylinositol, named DOPI and DPPI, on four mesothelioma cell lines. Both reduced cell survival in all four lines as the concentration rose from 0.01 to 100 micromolar, with a sharp drop above 10 micromolar. Later tests used one line, MSTO-211H. In these cells, both substances increased signs of programmed cell death (apoptosis) and disturbed the cells' mitochondria. The authors said the results also suggested necrosis. The substances did not activate caspase-3, -4, -8 or -9, enzymes that drive the usual form of apoptosis. Both raised mRNA levels of a gene called Bid and increased the amount of a protein called AIF in the cell nucleus. Reducing Bid levels with a gene-silencing tool (siRNA) inhibited this increase. The authors concluded that DOPI and DPPI cause caspase-independent apoptosis of mesothelioma cells by building up AIF in the nucleus. They said this raises the possibility of phosphatidylinositol as a target for drug design.

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 human mesothelioma cell lines grown in culture
• Who was studied: Four commercially obtained human malignant pleural mesothelioma cell lines (NCI-H28, NCI-H2052, NCI-H2452, MSTO-211H). All four were used for cell-viability tests, and MSTO-211H alone was used for all later experiments. No human subjects.
• Exposure: Two phosphatidylinositols, DOPI and DPPI, tested at 0.01 to 100 micromolar in viability tests and at 10 micromolar in most other experiments. Asbestos exposure was not studied.
• Main results:
  • In all four mesothelioma cell lines, DOPI and DPPI reduced cell viability in a concentration-dependent way (0.01 to 100 micromolar), with a sharp reduction above 10 micromolar. The two substances did not differ in effect.
  • In MSTO-211H cells, DOPI and DPPI significantly increased TUNEL-positive cells (a marker of apoptosis) compared with untreated cells.
  • Flow cytometry of MSTO-211H cells showed increases in cells classed as primary necrosis, early apoptosis and late apoptosis/secondary necrosis. The authors said this suggests the substances also induce necrosis.
  • DOPI and DPPI perturbed mitochondrial membrane potentials in MSTO-211H cells.
  • DOPI increased cytochrome c in the cell fluid of MSTO-211H cells after 12 hours of treatment. DPPI had no such effect.
  • DOPI and DPPI did not activate caspase-3 or caspase-9 in MSTO-211H cells.
  • DOPI and DPPI did not activate caspase-4 or caspase-8.
  • Both substances increased Bid mRNA in MSTO-211H cells. mRNA for Bad, Bax, Puma, Hrk and Noxa was not affected.
  • DOPI and DPPI significantly increased the amount of AIF protein in the nucleus. The distribution of AMID protein was not affected.
  • Nuclear fragmentation and condensation were seen more clearly in treated cells than in untreated control cells.
  • In cells given the Bid siRNA, Bid protein was clearly suppressed compared with cells given the control siRNA.
  • Knocking down Bid inhibited the increase in nuclear AIF caused by DOPI and DPPI.
• The authors' conclusion: The authors concluded that DOPI and DPPI induce caspase-independent apoptosis of mesothelioma cells by accumulating AIF in the nucleus. They said this raises the possibility that phosphatidylinositol is a target for drug design for treating mesothelioma.

Topics

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

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