Induction of Apoptosis by Methyl Alcohol Extract of &lt;i&gt;Enteromorpha linza&lt;/i&gt; (Linnaeus) J Agardh in U937 Human Leukemia Cells

E-O Choi,Ja Hwang,B-W Kim,Y Choi,H-S Kim,M-H Han,H-J Hwang,C Park

doi:10.4314/tjpr.v13i6.8

Abstract

Purpose: To investigate the anti-cancer effect of methyl alcohol extract of Enteromorpha linza (Linnaeus) J. Agardh (MEEL) in U937 human leukemia cells.Methods: Cytotoxicity was evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Apoptosis was detected using 4',6-diamidino-2-phenylindole (DAPI) staining, agarose gel electrophoresis, and flow cytometry. Protein levels were determined by Western blot analysis. Caspase activity was measured spectrophotometrically at 405 nm.Results: MEEL inhibited U937 cell proliferation and induced apoptosis through up-regulation of death receptor-related gene expression, caspase-8 activation and truncation of Bid, which was associated with the loss of mitochondrial membrane potential. Subsequently, the levels of anti-apoptotic proteins such as Bcl-2 and Bcl-xL, and IAP family proteins decreased but those of pro-apoptotic proteins including Bax and Bad increased in MEEL-treated U937 cells. MEEL treatment also resulted in activation of caspase-9 and -3 as well as concomitant cleavage of poly(ADP-ribose) polymerase and phopholipase Cγ-1. However, pretreatment of U937 cells with z-VAD-fmk, a pan caspase inhibitor, abrogated chromatin condensation and DNA fragmentation and prevented cell death induced by the MEEL.Conclusion: The findings suggest that MEEL induced apoptosis in U937 cells through a signaling cascade of death-receptor-mediated extrinsic as well as mitochondria-mediated intrinsic pathways, thus raising the possibility that MEEL may be of value in the development of novel therapeutic approaches for treating leukemia.Keywords: Enteromorpha linza, Apoptosis, Caspase, U937 cells

Highlights

Apoptosis is an active process of cellular selfdestruction with distinct morphological and biochemical features [1,2]
Our results show that the MEEL exhibited a potent pro-apoptotic effect on U937 cells and that such apoptosis occurred in a caspase activation-dependent manner
TBid plays an important role leading to the formation of mitochondrial conformational changes, mitochondrial dysfunction through changes in membrane permeability and subsequent loss of membrane potential (MMP) have been implicated as key apoptotic mechanisms in the mitochondrial apoptotic pathway [3,5,22]

Summary

INTRODUCTION

Apoptosis is an active process of cellular selfdestruction with distinct morphological and biochemical features [1,2]. The mitochondrial apoptotic pathway is initiated through the release of signal factors including cytochrome c by mitochondria within the cell, along with caspase-9 activation, which, in turn, activates caspase-3, resulting in degradation of activated caspase-3 substrate proteins [8,9]. These observations indicate that cross talk between the two pathways is mediated by tBid [10,11].

RESULTS

DISCUSSION

CONCLUSION