Submitted on June 6, 2006
Accepted on August 2, 2006
Induction of Cell Cycle Arrest and Apoptosis in HT-29 Human Colon Cancer Cells by the Dietary Compound Luteolin
Do Y. Lim1, Yoonhwa Jeong2, Angela Tyner3, and Jung H Y Park4*
1 Food Science and Nutrition, Hallym University, Chuncheon, Gangwon, Korea, Republic of
2 Food and Science, Dankook University, Seoul, Korea, Republic of
3 University of illinois, United States; Biochemistry and Molecular Genetics, University of illinois, United States
4 Food Science and Nutrition, Hallym University, Chunchon, Gangwon, Korea, Republic of; Division of Life Sciences, Hallym University, 1 Okchon Dong, Chunchon, 200-702, Korea, Republic of
* To whom correspondence should be addressed. E-mail: jyoon{at}hallym.ac.kr.
Luteolin is 3',4',5,7-tetrahydroxyflavone found in celery, green pepper and perilla leaf that inhibits tumorigenesis in animal models. We examined luteolin-mediated regulation of cell cycle progression and apoptosis in the HT-29 human colon cancer cell line. Luteolin decreased DNA synthesis and viable HT-29 cell numbers in a concentration-dependent manner. It inhibited cyclin-dependent kinase (CDK)4 and 2 activity, resulting in G1 arrest with a concomitant decrease of phosphorylation of retinoblastoma protein. Activities of CDK4 and CDK2 decreased within 2 h after luteolin treatment, with a 38% decrease in CDK2 activity (P < 0.05) observed in cells treated with 40 µmol/L luteolin. Luteolin inhibited CDK2 activity in a cell-free system, suggesting that it directly inhibits CDK2. Cyclin D1 levels decreased after luteolin treatment, although no changes in expression of cyclin A, cyclin E, CDK4 or CDK2 were detected. Luteolin also promoted G2/M arrest at 24 h post treatment by downregulating cyclin B1 expression and inhibiting cell division cycle (CDC)2 activity. Luteolin promoted apoptosis with increased activation of caspases 3, 7, and 9 and enhanced poly(ADP-ribose) polymerase cleavage and decreased expression of p21CIP1/WAF1, survivin, Mcl-1, Bcl-xL, and Mdm-2. Decreased expression of these key anti-apoptotic proteins could contribute to the increase in p53-independent apoptosis that was observed in HT-29 cells. We demonstrate that luteolin promotes both cell cycle arrest and apoptosis in the HT-29 colon cancer cell line, providing insight about the mechanisms underlying its anti-tumorigenic activities.
