Involvement of activator protein-1 (AP-1) in induction of apoptosis by vitamin E succinate in human breast cancer cells

Abstract

The purpose of this study was to document induction of apoptosis by vitamin E succinate (VES; RRR-alpha-tocopheryl succinate) in human breast cancer cells in culture and to characterize potential c-jun involvement. VES at 18.8 microM (10 micrograms/mL) induced DNA synthesis arrest, reduced total cell numbers, and induced apoptosis in estrogen receptor-positive and estrogen-responsive MCF-7 human breast cancer cells. VES at 10 micrograms/mL induced apoptosis in greater than 60% of cells within 3 d of treatment. Apoptosis was documented by detection of fragmented or condensed nuclei in 4',6-diamindino-2-phenylindole-stained cells, detection of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeled DNA, and DNA laddering. Analyses of mRNA and protein levels of candidate molecules involved in apoptosis showed that MCF-7 cells treated with VES exhibited elevated and persistent expression of c-jun. MCF-7 cells stably transfected with a dominant-negative interfering mutant c-jun, TAM-67, and expressing high levels of mutant jun exhibited approximately 50% blockage of VES-mediated apoptosis. In addition to increased c-jun expression after VES treatment, VES-treated MCF-7 cells exhibited elevated activator protein-1 (AP-1) binding activity. Comparisons of AP-1 binding factors by super-shift analyses with jun-specific antibodies in cells sensitive to VES-induced apoptosis (empty-vector control 7-1 cells) and cells resistant to VES-induced apoptosis (TAM-67-containing TAM-9 cells) showed that the sensitive cells expressed c-jun and jun D and the resistant cells TAM-67 AP-1 binding proteins after VES treatment. These studies suggested that c-jun may be involved in the apoptotic process initiated by VES treatment of human MCF-7 breast cancer cells.

Dietary L‐carnitine alters gene expression in skeletal muscle of piglets

“…The observed down‐regulation of genes encoding members of the AP‐1 family by L ‐carnitine and the association of L ‐carnitine supplementation with decreased DNA binding is in line with recent observations demonstrating that carnitine injection reduces AP‐1 DNA‐binding activity 34, and carnitine deficiency up‐regulates JUN and FOS 35. There is compelling evidence that elevated AP‐1 binding activity and expression of JUN, FOS and activating transcription factor 3 induce apoptosis in various cell types 36, whereas inhibition of AP‐1 signalling has the opposite effect 37. Our findings therefore suggest that L ‐carnitine might have anti‐apoptotic effects in skeletal muscle of piglets.…”

Antiproliferative and Apoptotic Effects of Tocopherols and Tocotrienols on Preneoplastic and Neoplastic Mouse Mammary Epithelial Cells

“…Tocopherols and tocotrienols have been shown to inhibit several mitogenic signaling pathways, including protein kinase C, adenylate cyclase, and cyclic AMP‐dependent protein activation in other cell types, and it is possible that one or more of these effects may be responsible for mediating the inhibitory effects of these compounds on CL‐S1, ‐SA, and +SA mammary epithelial cell proliferation (11, 32–36). Similarly, multiple signaling pathways have been implicated in mediating tocopherol‐ and tocotrienol‐induced apoptosis (13–15). However, the present results do not provide evidence that the antiproliferative and apoptotic effects of these compounds occur through independent intracellular mechanisms.…”

γ‐Tocotrienol Prevents Oxidative Stress‐Induced Telomere Shortening in Human Fibroblasts Derived from Different Aged Individuals

“…The c-fos encodes a nuclear protein that forms heterodimer with jun and binds a common DNA site (AP-1) to regulate various transcriptional activity. Vitamin E treatment also has been shown to induce c-jun expression as well as AP-1 binding activity in human breast cancer cells 34,35. These studies suggest that the protective role of vitamin E against DNA damage induced by H 2 O 2 and UV is in part, mediated by upregulation of c-fos expression and AP-1 binding activity.…”