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.

Superoxide anion and proteasomal dysfunction contribute to curcumin-induced paraptosis of malignant breast cancer cells

“…Given that mitochondrial and ER enlargement was recently reported to be a characteristic of paraptosis [11,14,15], we next examined whether curcumin-induced cell death in malignant breast cancer cells shared other features of paraptosis. Pretreatment of MDA-MB-435S cells with CHX effectively blocked curcumin-induced cell death (Fig.…”

“…Paraptosis is characterized by a process of vacuolation that begins with physical enlargement of mitochondria and the endoplasmic reticulum (ER) [11,14,15]. This form of cell death does not involve the apoptotic characteristics of pyknosis, DNA fragmentation, or caspase activation [11].…”

Glioma Big Potassium Channel Expression in Human Cancers and Possible T Cell Epitopes for Their Immunotherapy

“…Earlier, we showed that prolonged activation of BK channels of T9 or U251 gliomas in vitro causes cell swelling and eventually leads to paraptosis (7,8). When paraptotic BK channel-activated/killed T9 cells were used as the immunogen, T9-specific tumor immunity toward the T9 glioma cells was generated within naive rats (8).…”

“…Both chloride channel-1 and aquaporins are also overexpressed in glioma (41)(42)(43). BK channel activation leads to cell swelling, whereas CLIC1 activation leads to cell shrinkage (7,8,44). Both of these functions, swelling and shrinking, are needed for cell volume regulation and motility.…”

“…Human U251 (7) and rat T9 gliomas (8) immediately swelled upon activation of the big potassium (BK) channels using a BK ionophore; paraptosis ultimately occurred within 18-24 h. Functional membrane BK channels were detected on the human and rat glioma cells by using patch-clamping techniques. Additionally, BK channels were found on the ER and the mitochondria (7,8), providing a plausible rationale for why these organelles are specifically targeted in paraptosis. These ion channels are also called Maxi-K, hSlo, mSlo, KCNMA1, calcium-dependent, large conductance-, or voltage-activated channels (9)(10)(11)(12)(13)(14)(15)(16)(17).…”