Cocoa Procyanidins Suppress Transformation by Inhibiting Mitogen-activated Protein Kinase Kinase

Abstract

Cocoa was shown to inhibit chemically induced carcinogenesis in animals and exert antioxidant activity in humans. However, the molecular mechanisms of the chemopreventive potential of cocoa and its active ingredient(s) remain unknown. Here we report that cocoa procyanidins inhibit neoplastic cell transformation by suppressing the kinase activity of mitogen-activated protein kinase kinase (MEK). A cocoa procyanidin fraction (CPF) and procyanidin B2 at 5 g/ml and 40 M, respectively, inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced neoplastic transformation of JB6 P؉ mouse epidermal (JB6 P؉) cells by 47 and 93%, respectively. The TPAinduced promoter activity and expression of cyclooxygenase-2, which is involved in tumor promotion and inflammation, were dose-dependently inhibited by CPF or procyanidin B2. The activation of activator protein-1 and nuclear factor-B induced by TPA was also attenuated by CPF or procyanidin B2. The TPAinduced phosphorylation of MEK, extracellular signal-regulated kinase, and p90 ribosomal s6 kinase was suppressed by CPF or procyanidin B2. In vitro and ex vivo kinase assay data demonstrated that CPF or procyanidin B2 inhibited the kinase activity of MEK1 and directly bound with MEK1. CPF or procyanidin B2 suppressed JB6 P؉ cell transformation induced by epidermal growth factor or H-Ras, both of which are known to be involved in MEK/ERK signal activation. In contrast, theobromine (up to 80 M) had no effect on TPA-induced transformation, cyclooxygenase-2 expression, the transactivation of activator protein-1 or nuclear factor-B, or MEK. Notably, procyanidin B2 exerted stronger inhibitory effects compared with PD098059 (a well known pharmacological inhibitor of MEK) on MEK1 activity and neoplastic cell transformation.

Lipogenesis Is Decreased by Grape Seed Proanthocyanidins According to Liver Proteomics of Rats Fed a High Fat Diet

“…Other flavonoids have been reported to have an effect on G protein signaling. For example, cocoa procyanidins inhibit the activity of the mitogen-activated protein kinase (85), and isoflavones attenuate vascular contraction, at least in part, through inhibition of the RhoA/Rho kinase signaling pathway (86).…”

Phosphoinositol 3-kinase, a novel target molecule for the inhibitory effects of juglone on TPA-induced cell transformation

“…Cells were maintained in Eagle's minimum essential medium (MEM) supplemented with 5% fetal bovine serum (FBS), 2 mM L-glutamine and 25 µg/ml gentamicin at 37˚C in a 5% CO 2 incubator. The JB6 CI41 cell line was stably transfected with activator protein-1 (AP-1) and cyclooxygenase-2 (COX-2) luciferase reporter plasmids obtained from Dr Zigang Dong (The Hormel Institute, University of Minnesota, Austin, MN) (22).…”

Update on Cancer Prevention Research in the United States and China: The 2009 China—U.S. Forum on Frontiers of Cancer Research

“…Research directed toward elucidating underlying molecular mechanisms of chemoprevention or chemoprotection with edible phytochemicals present in fruits, vegetables, spices, and herbs has recognized distinct redox-sensitive transcription factors and their upstream regulators as potential targets (35). Research findings from The Hormel Institute have shown that blocking certain cellular signals with natural small molecule inhibitors can decrease UV-induced skin carcinogenesis and other cancers (32,33,(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46).…”