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

• Published in: Cancer research (Chicago, Ill.) Ill.), 1999-09, Vol.59 (18), p.4610-4617
• Main Authors: CHUNG, J. Y, CHUANSHU HUANG, XIAOFENG MENG, ZIGANG DONG, YANG, C. S
• Format: Article
• Language: English
• Subjects: Animals; Antioxidants - pharmacology; Biflavonoids; Biological and medical sciences; black tea; Carcinogenesis, carcinogens and anticarcinogens; Catechin - analogs & derivatives; Catechin - pharmacology; Cell Division - drug effects; Cell Line, Transformed; Cell Transformation, Neoplastic; Dose-Response Relationship, Drug; Flavonoids; Foods and miscellaneous; Genes, ras; green tea; H-ras gene; Medical sciences; Mice; Phenols - pharmacology; Polymers - pharmacology; polyphenols; Structure-Activity Relationship; Tea; Transcription Factor AP-1 - drug effects; Transfection; Tumors
• ISSN: 0008-5472; 1538-7445

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.