Journal Article

The role of activated MEK-ERK pathway in quercetin-induced growth inhibition and apoptosis in A549 lung cancer cells

T.T.T. Nguyen, E. Tran, T.H. Nguyen, P.T. Do, T.H. Huynh and H. Huynh

in Carcinogenesis

Volume 25, issue 5, pages 647-659
Published in print May 2004 | ISSN: 0143-3334
Published online May 2004 | e-ISSN: 1460-2180 | DOI:
The role of activated MEK-ERK pathway in quercetin-induced growth inhibition and apoptosis in A549 lung cancer cells

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Dietary phytochemicals have been shown to be protective against various types of cancers. However, the precise underlying protective mechanisms are poorly understood. In the present study, we report that treatment of A549 cells with quercetin resulted in a dose-dependent reduction in cell viability and DNA synthesis with the rate of apoptosis equivalent to 1.2 ± 0.8, 6.3 ± 0.9, 16.5 ± 1.5, 36.4 ± 2.6 and 42.5 ± 5.8% on treatment with 0.1% dimethylsulfoxide, 14.5, 29.0, 43.5 and 58.0 µM quercetin, respectively. Concomitantly, quercetin treatments led to a 1.1-, 1.1-, 2.5- and 3.5-fold increase in Bax. Similar elevations were also observed in Bad, which increased 1.1-, 2.1-, 2.2- and 2.3-fold, respectively, as compared with control. While Bcl-2 was decreased by 30%, Bcl-xL was elevated in a dose-dependent fashion. Quercetin also induced the cleavage of caspase-3, caspase-7 and PARP (poly ADP-ribose polymerase). While Akt-1 and phosphorylated Akt-1 were inhibited, the extracellular signal-regulated kinase (ERK) was phosphorylated following quercetin treatment in a dose-dependent fashion. Phosphorylation of ERK and c-Jun occurred at 3 h and was sustained over 14 h. Phosphorylation of MEK1/2 was increased in concordance with ERK activation. Quercetin-induced phosphorylation of c-Jun N-terminal kinase (JNK) and cleavage of caspase-3 occurred 6 h after quercetin exposure and before cleavage of caspase-7 and PARP was detected. Inhibition of MEK1/2 but not PI-3 kinase, p38 kinase or JNK abolished quercetin-induced phosphorylation of c-Jun, cleavage of caspase-3 and -7, cleavage of PARP and apoptosis. Inhibition of caspase activation completely blocked quercetin-induced apoptosis. Expression of constitutively activated MEK1 in A549 cells led to activation of caspase-3 and apoptosis. The results suggest that in addition to inactivation of Akt-1 and alteration in the expression of the Bcl-2 family of proteins, activation of MEK-ERK is required for quercetin-induced apoptosis in A549 lung carcinoma cells.

Keywords: DMSO, dimethylsulfoxide; ERK, extracellular signal-regulated kinase; JNK, c-Jun N-terminal kinase; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; PARP, poly ADP-ribose polymerase; SRF, serum-free RPMI 1640; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling

Journal Article.  8070 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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