Vitamin K₂ selectively induced apoptosis in ovarian TYK-nu and pancreatic MIA PaCa-2 cells out of eight solid tumor cell lines through a mechanism different from geranylgeraniol

Abstract

Purpose. In this study, we examined the effects of vitamin K₂ (menaquinone 4), which has a geranylgeranyl side chain, on various lines of cells derived from human solid tumors and compared them with the effects of geranylgeraniol (GGO).

Methods. Cell proliferation was determined with 3′-[1-[(phenylamino)carbonyl]-3,4-tetrazolium-bis (4-methoxy-6-nitro) benzene-sulfonic acid hydrate (XTT), and the induction of apoptosis was analyzed by TUNEL staining and flow cytometry as well as by measurement of DNA fragmentation, released nucleosomes and caspase-3 activity. Levels of Bcl-2, Bax and cytochrome c were determined by immunoblotting.

Results. GGO inhibited the growth of all eight cell lines derived from solid tumors, while vitamin K₂ selectively inhibited the proliferation of ovarian TYK-nu and pancreatic MIA PaCa-2 cancer cells, inducing apoptosis in both cell lines. Far more time was required for the induction of apoptosis in these two cell lines by vitamin K₂ than by GGO. Apoptotic signals induced in TYK-nu cells during the first 2 days that followed the addition of vitamin K₂ to the culture medium were reversible, but these signals became irreversible after 3 days of treatment with vitamin K₂. The induction of apoptosis in TYK-nu cells by vitamin K₂ was inhibited by cycloheximide and also by starvation at a low concentration of serum. Neither cycloheximide nor starvation had any effect on the induction of apoptosis by GGO. Cytochrome c was released simultaneously with the initiation of apoptosis on treatment of TYK-nu cells with vitamin K₂ or GGO. However, GGO induced the release of cytochrome c from isolated mitochondria, while vitamin K₂ did not. The amount of Bcl-2 in TYK-nu cells was reduced by vitamin K₂, but not by GGO.

Conclusions. In contrast to GGO, vitamin K₂ induced apoptosis selectively in pancreatic MIA-PaCa 2 and ovarian TYK-nu cancer cells. It is suggested that de novo protein synthesis might be necessary for induction of apoptosis by vitamin K₂ but not by GGO, and thus, that vitamin K₂ and GGO might induce apoptosis by different mechanisms.