Green tea polyphenols-induced apoptosis in human osteosarcoma SAOS-2 cells involves a caspase-dependent mechanism with downregulation of nuclear factor-kappaB.
Development of chemotherapy resistance and evasion from apoptosis in osteosarcoma, a primary malignant bone tumor, is often correlated with constitutive nuclear factor-kappaB (NF-kappaB) activation. Here, we investigated the ability of a polyphenolic fraction of green tea (GTP) that has been shown to have antitumor effects on various malignant cell lines to inhibit growth and induce apoptosis in human osteosarcoma SAOS-2 cells. Treatment of SAOS-2 cells with GTP (20-60 microg/ml) resulted in reduced cell proliferation and induction of apoptosis, which correlated with decreased nuclear DNA binding of NF-kappaB/p65 and lowering of NF-kappaB/p65 and p50 levels in the cytoplasm and nucleus. GTP treatment of cells reduced IkappaB-alpha phosphorylation but had no effect on its protein expression. Furthermore, GTP treatment resulted in the inhibition of IKK-alpha and IKK-beta, the upstream kinases that phosphorylate IkappaB-alpha. The increase in apoptosis in SAOS-2 cells was accompanied with decrease in the protein expression of Bcl-2 and concomitant increase in the levels of Bax. GTP treatment of SAOS-2 cells also resulted in significant activation of caspases as was evident by increased levels of cleaved caspase-3 and caspase-8 in these cells. Treatment of SAOS-2 cells with a specific caspase-3 inhibitor Ac-Asp-Glu-Val-Asp-CHO (Ac-DEVD-CHO) and general caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp (OMe)-fluoromethyl ketone (Z-VAD-FMK) rescued SAOS-2 cells from GTP-induced apoptosis. Taken together, these results indicate that GTP is a candidate therapeutic for osteosarcoma that mediates its antiproliferative and apoptotic effects via activation of caspases and inhibition of NF-kappaB.
Hafeez
Bilal Bin
BB
Division of Rheumatic Diseases, Department of Medicine, Case Western Reserve University, 2109 Adelbert Road, BRB-319, Cleveland, OH 44106-4946, USA.
Ahmed
Salahuddin
S
Wang
Naizhen
N
Gupta
Sanjay
S
Zhang
Ailin
A
Haqqi
Tariq M
TM
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D024202:Electrophoretic Mobility Shift Assay; D005419:Flavonoids / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D051550:I-kappa B Kinase / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D020672:I-kappa B Proteins / Q000378:metabolism; D015151:Immunoblotting; D000072000:NF-KappaB Inhibitor alpha; D052002:NF-kappa B p50 Subunit / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology; D012516:Osteosarcoma / Q000378:metabolism / Q000473:pathology; D010636:Phenols / Q000737:chemistry / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D059808:Polyphenols; D013662:Tea / Q000737:chemistry*; D051996:Transcription Factor RelA / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D004268:DNA-Binding Proteins; D005419:Flavonoids; D020672:I-kappa B Proteins; D052002:NF-kappa B p50 Subunit; C000606204:NFKBIA protein, human; D009842:Oligopeptides; D010636:Phenols; D059808:Polyphenols; D013662:Tea; D051996:Transcription Factor RelA; C099158:acetyl-aspartyl-glutamyl-valyl-aspartal; D051028:bcl-2-Associated X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D000072000:NF-KappaB Inhibitor alpha; D011065:Poly(ADP-ribose) Polymerases; D051550:I-kappa B Kinase; D020169:Caspases