Potentiation by vitamin D analogs of TNFα and ceramide-induced apoptosis in MCF-7 cells is associated with activation of cytosolic phospholipase A2

Abstract

Synthetic analogs of vitamin D induce apoptosis in cultured breast cancer cells and cause regression of experimentallyinduced rat mammary tumors. To further elucidate the mechanisms involved, we have examined interactions between two vitamin D analogs (CB1093 and EB1089) and known mediators of apoptosis, TNFa and ceramide. Pretreatment of MCF-7 breast cancer cells with CB1093 and EB1089 substantially potentiated cytotoxic effects of TNFa as assessed by cell viability assay, DNA fragmentation and videomicroscopy. No significant changes in the levels of TNFa or TNF-RI transcripts were detected. CB1093 primed cells demonstrated enhanced responsiveness to cell permeable C 2 -ceramide in terms of increased DNA fragmentation and loss of cell viability. Activation of cytosolic phospholipase A 2 (cPLA 2 ) has been implicated in TNFa-mediated apoptosis. As assessed by [ 3 H]-arachidonic acid release, cells primed for 48 h with CB1093 (50 nM) showed enhanced cPLA 2 activation in response to TNFa or ceramide. CB1093 treatment alone led to cPLA 2 activation and loss of cell viability which was inhibited by the specific inhibitor AACOCF 3 . These results suggest that TNFa and vitamin D analogs share a common pathway leading to apoptosis involving cPLA 2 activation and/ or ceramide generation.

Calcium and Calpain as Key Mediators of Apoptosis-like Death Induced by Vitamin D Compounds in Breast Cancer Cells

“…The use of combinations of therapeutical agents that trigger cell death by independent pathways may circumvent resistance problems. Promising in vitro data showing synergistic apoptosis-inducing effects of combination treatments employing vitamin D analogs with agents triggering other death pathways strongly support this idea (11,48,56).…”

“…Why calpain does not activate caspases in vitamin D-treated MCF-7 cells is as yet unclear. It is, however, unlikely to be the result of any dominant caspase inhibitor induced by vitamin D compounds because pretreatment of MCF-7 cells with 1,25(OH) 2 D 3 does not inhibit but, in fact, enhances TNF-induced caspase activation (11,56). Furthermore, it is not because of the lack of caspase-3 expression in MCF-7 cells.…”

BEX2 Is Overexpressed in a Subset of Primary Breast Cancers and Mediates Nerve Growth Factor/Nuclear Factor-κB Inhibition of Apoptosis in Breast Cancer Cell Lines

“…This provided us with a clue about a possible mechanism for involvement of the BEX gene family in breast cancer in light of the published data showing that NGF inhibits the apoptotic response to C2 in cell lines through p75NTR and NF-nB. C2 is a ceramide analogue that induces massive apoptosis of breast cancer cells (45,46). For these studies, we analyzed BEX2 because BEX1 is not expressed in the breast cancer cell lines used.…”

1α,25-Dihydroxyvitamin D3 (calcitriol) and its analogue, 19-nor-1α,25(OH)2D2, potentiate the effects of ionising radiation on human prostate cancer cells

“…Observations that support combining 1,25(OH) 2 D 3 with ionising radiation include the following: (a) both IR and 1,25(OH) 2 D 3 induce apoptosis in prostate carcinoma cells by apparently distinct pathways (Welsh et al, 1995;Billis et al, 1998;James et al, 1998;Pirianov et al, 1999;Ding and Fisher, 2001;McGuire et al, 2001;Sheard, 2001;Liu et al, 2002); (b) other agents that induce cellular differentiation, for example, phenylacetate, platelet-derived growth factor and retinoic acid, are known to enhance the cytotoxic effects of IR (Bill et al, 1992b;Miller et al, 1997;Hoffmann et al, 1999); (c) EB 1089 has been shown to enhance the radiation sensitivity of breast carcinoma cells (Sundaram and Gewirtz, 1999). These findings strongly suggest that 1,25(OH) 2 D 3 may enhance the cytotoxic effects of IR on prostate cancer cells.…”