cis-9,trans-11-conjugated linoleic acid down-regulates phorbol ester-induced NF-kappaB activation and subsequent COX-2 expression in hairless mouse skin by targeting IkappaB kinase and PI3K-Akt.
Conjugated linoleic acid (CLA) has been reported to inhibit mouse skin carcinogenesis, particularly in the promotion stage, but underlying molecular mechanisms remain poorly understood. Since persistent induction of cyclooxygenase-2 (COX-2) is frequently implicated in carcinogenesis, we investigated the effect of cis-9,trans-11-CLA (9Z,11E-CLA) on the tumor promoter-induced COX-2 expression in HR-1 hairless mouse skin in vivo. Topical application of 9Z,11E-CLA caused significant inhibition of COX-2 expression at 6 h induced by 10 nmol 12-O-tetradecanoylphorbol-13-acetate (TPA) in HR-1 mouse skin. Since NF-kappaB is known to regulate COX-2 gene expression, we determined the effect of 9Z,11E-CLA on TPA-induced activation of this transcription factor. Treatment of mouse skin with 9Z,11E-CLA reduced TPA-induced DNA binding as well as nuclear translocation of NF-kappaB by blocking phosphorylation and subsequent degradation of IkappaBalpha. In addition, 9Z,11E-CLA attenuated TPA-induced phosphorylation of extracellular signal-regulated protein kinase, p38 mitogen-activated protein kinase and Akt. To further elucidate the molecular mechanism underlying the inactivation of NF-kappaB by 9Z,11E-CLA, we investigated its effect on TPA-induced activation of IkappaB kinase (IKK), an upstream kinase that regulates NF-kappaB via phosphorylation and degradation of IkappaBalpha. 9Z,11E-CLA treatment down-regulated phosphorylation and catalytic activities of IKKalpha/beta in TPA-treated mouse skin. Co-treatment of mouse skin with the IKKbeta-specific inhibitor SC-514 (1 micromol) attenuated TPA-induced activation of Akt and NF-kappaB, and also the expression of COX-2 in hairless mouse skin. Taken together, 9Z,11E-CLA inhibits NF-kappaB driven-COX-2 expression by blocking the IKK and PI3K-Akt signaling in TPA-treated hairless mouse skin in vivo, which may account for its previously reported anti-tumor promoting effects.
Hwang
Dal-Mi
DM
National Research Laboratory of Molecular Carcinogenesis and Chemoprevention, College of Pharmacy, Seoul 151-742, South Korea.
Kundu
Joydeb Kumar
JK
Shin
Jun-Wan
JW
Lee
Jung-Chul
JC
Lee
Hyong Joo
HJ
Surh
Young-Joon
YJ
D000818:Animals; D001483:Base Sequence; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D017931:DNA Primers; D004789:Enzyme Activation; D051550:I-kappa B Kinase / Q000378:metabolism*; D044243:Linoleic Acids, Conjugated / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008812:Mice, Hairless; D016328:NF-kappa B / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012867:Skin / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D017931:DNA Primers; D044243:Linoleic Acids, Conjugated; D016328:NF-kappa B; C503589:cis-9, trans-11-conjugated linoleic acid; D051546:Cyclooxygenase 2; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D051550:I-kappa B Kinase; D013755:Tetradecanoylphorbol Acetate