title: Inhibition of activator protein 1 activity and cell growth by purified green tea and black tea polyphenols in H-ras-transformed cells: structure-activity relationship and mechanisms involved.
abstract: ras gene mutation, which perpetually turns on the growth signal transduction pathway, occurs frequently in many cancer types. The mouse epidermal JB6 cell line has been transfected with a mutant H-ras gene to mimic carcinogenesis in vitro. These transformed cells (30.7b Ras 12) are able to grow in soft agar, exhibiting anchorage independence and high endogenous activator protein 1 (AP-1) activity, which can be detected by a stable AP-1 luciferase reporter. The present study investigated the ability of different pure green and black tea polyphenols to inhibit this ras signaling pathway. The major green tea polyphenols (catechins), (-)-epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin, (-)-epicatechin-3-gallate, (-)-epicatechin, and their epimers, and black tea polyphenols, theaflavin, theaflavin-3-gallate, theaflavin-3'-gallate, and theaflavin-3,3'-digallate (TFdiG), were compared with respect to their ability to inhibit the growth of 30.7b Ras 12 cells and AP-1 activity. All of the tea polyphenols except (-)-epicatechin showed strong inhibition of cell growth and AP-1 activity. Among the catechins, both the galloyl structure on the B ring and the gallate moiety contributed to the growth inhibition and AP-1 activity; the galloyl structure appeared to have a stronger effect on the inhibitory action than the gallate moiety. The epimers of the catechins showed similar inhibitory effects on AP-1 activity. The addition of catalase to the incubation of the cells with EGCG or TFdiG did not prevent the inhibitory effect on AP-1 activity, suggesting that H2O2 does not play a significant role in the inhibition by tea polyphenols. Both EGCG and TFdiG inhibited the phosphorylation of p44/42 (extracellular signal-regulated kinase 1 and 2) and c-jun without affecting the levels of phosphorylated-c-jun-NH2-terminal kinase. TFdiG inhibited the phosphorylation of p38, but EGCG did not. EGCG lowered the level of c-jun, whereas TFdiG decreased the level of fra-1. These results suggest that tea polyphenols inhibited AP-1 activity and the mitogen-activated protein kinase pathway, which contributed to the growth inhibition; however, different mechanisms may be involved in the inhibition by catechins and theaflavins.
authors.affiliation: Laboratory for Cancer Research, College of Pharmacy, Rutgers, The State University of New Jersey, Piscataway 08854, USA.
authors.forename: J Y
authors.initials: JY
authors.lastname: Chung
authors.forename: C
authors.initials: C
authors.lastname: Huang
authors.forename: X
authors.initials: X
authors.lastname: Meng
authors.forename: Z
authors.initials: Z
authors.lastname: Dong
authors.forename: C S
authors.initials: CS
authors.lastname: Yang
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D044946:Biflavonoids; D002392:Catechin / Q000031:analogs & derivatives / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects*; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic; D004305:Dose-Response Relationship, Drug; D005419:Flavonoids; D011905:Genes, ras; D051379:Mice; D010636:Phenols / Q000494:pharmacology*; D011108:Polymers / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D013662:Tea; D018808:Transcription Factor AP-1 / Q000187:drug effects*; D014162:Transfection
chemical_list: D000975:Antioxidants; D044946:Biflavonoids; D005419:Flavonoids; D010636:Phenols; D011108:Polymers; D013662:Tea; D018808:Transcription Factor AP-1; C056068:theaflavin; D002392:Catechin