Human monocytes kill M-CSF-expressing glioma cells by BK channel activation.

Abstract

In this study, human monocytes/macrophages were observed to kill human U251 glioma cells expressing membrane macrophage colony-stimulating factor (mM-CSF) via a swelling and vacuolization process called paraptosis. Human monocytes responded to the mM-CSF-transduced U251 glioma cells, but not to viral vector control U251 glioma cells (U251-VV), by producing a respiratory burst within 20 min. Using patch clamp techniques, functional big potassium (BK) channels were observed on the membrane of the U251 glioma cell. It has been previously reported that oxygen indirectly regulates BK channel function. In this study, it was demonstrated that prolonged BK channel activation in response to the respiratory burst induced by monocytes initiates paraptosis in selected glioma cells. Forced BK channel opening within the glioma cells by BK channel activators (phloretin or pimaric acid) induced U251 glioma cell swelling and vacuolization occurred within 30 min. U251 glioma cell cytotoxicity, induced by using BK channel activators, required between 8 and 12 h. Swelling and vacuolization induced by phloretin and pimaric acid was prevented by iberiotoxin, a specific BK channel inhibitor. Confocal fluorescence microscopy demonstrated BK channels co-localized with the endoplasmic reticulum and mitochondria, the two targeted organelles affected in paraptosis. Iberiotoxin prevented monocytes from producing death in mM-CSF-expressing U251glioma cells in a 24 h assay. This study demonstrates a novel mechanism whereby monocytes can induce paraptosis via the disruption of internal potassium ion homeostasis.

• Authors: Neil T Hoa, Jian Gang Zhang, Christina L Delgado, Michael P Myers, Linda L Callahan, Gerald Vandeusen, Patric M Schiltz, H Terry Wepsic, Martin R Jadus
• Journal: Laboratory investigation; a journal of technical methods and pathology (Lab Invest) Vol. 87 Issue 2 Pg. 115-29 (Feb 2007) ISSN: 0023-6837 [Print] United States
• PMID: 17318194 (Publication Type: Comparative Study, Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• DNA Primers
• Diterpenes
• Large-Conductance Calcium-Activated Potassium Channels
• Peptides
• iberiotoxin
• Macrophage Colony-Stimulating Factor
• pimaric acid
• Potassium
• Phloretin

Topics

• Cell Death (immunology)
• Cell Line, Tumor
• DNA Primers
• Diterpenes (pharmacology)
• Electrophysiology
• Glioma (immunology)
• Homeostasis (immunology)
• Humans
• Large-Conductance Calcium-Activated Potassium Channels (antagonists & inhibitors, metabolism)
• Macrophage Activation (immunology)
• Macrophage Colony-Stimulating Factor (metabolism)
• Microscopy, Fluorescence
• Models, Biological
• Monocytes (drug effects, immunology, metabolism)
• Peptides (pharmacology)
• Phloretin (pharmacology)
• Potassium (metabolism)
• RNA Interference
• Respiratory Burst (immunology)
• Reverse Transcriptase Polymerase Chain Reaction
• Time Factors