A polyphenol mixture from cinnamon targets p38 MAP kinase-regulatedsignaling pathways to produce G2/M arrestNorberta W. Schoene?, Meghan A. Kelly, Marilyn M. Polansky, Richard A. AndersonDiet, Genomics, and Immunology Laboratory, Beltsville Human Nutrition Research Center, ARS, USDA, Beltsville, MD 20705-2350, USAReceived 4 March 2008; received in revised form 3 June 2008; accepted 9 June 2008AbstractWe recently demonstrated that treatment of three leukemic cell lines with an aqueous extract of cinnamon (CE) for 24 h produced dose-dependent arrests in the G2/M phase of the cell cycle. To accomplish the goal of understanding underlying mechanisms, we selected the cellline most responsive to the CE treatment to study the effects of the extract on signaling molecules regulating cell cycle progression. Cell cycleanalyses were conducted on treated versus nontreated cells from 0–6 h. The percentages of cells in G2/M in CE-treated cells increasedsignificantly from 11.0±1.0 to 23.6±1.4 after 6 h, while the percentage for nontreated cells remained unchanged (12.3±0.8). Multiparametricflow cytometric analyses were used to associate activation of p38 mitogen-activated protein kinase (MAPK) with cells arrested in G2/M, thesize of these cells, and the presence or absence of cyclin B1. After 4 h, there was a 26% increase in the activated phosphorylated form of p38MAPK in CE-treated cells compared with the nontreated control cells, with larger cells showing the greater increases. Although theproportion of CE-treated cells in G2/M was higher than controls, this population was shown to be less positive for cyclin B1 than the controlG2/M population. Our results demonstrate that CE significantly modulated two signaling proteins, p38 MAPK and cyclin B, that regulateprogression through G2/M. Overall, the data provide evidence that CE affects proliferation in a leukemic cell line by disrupting criticalphosphorylating/dephosphorylating signaling events that propel cells through the G2/M phase.© 2009 Elsevier Inc. All rights reserved.Keywords: Cinnamon; Polyphenols; G2/M; p38 MAPK; Cyclin B11. IntroductionChemopreventive properties have long been attributed topolyphenolic compounds present in the human diet [1,2].These natural substances are of interest as they are potentialsources of anticancer compounds with minimal debilitatingside effects and toxicity. Investigations at molecular andcellular levels have revealed multiple mechanisms to explainthe chemoprotective action of these dietary constituents [3].We recently demonstrated that a mixture of polyphenolsfrom an aqueous extract of cinnamon (CE) possessedanticancer properties by blocking cell cycle progression ofleukemic cell lines at the G2/M phase [4]. Progressionthrough the phases of the cell cycle is controlled by amultiplicity of signaling networks linked by appropriatelytimed actions of kinases, phosphatases, and formation ofregulatory protein complexes [5]. In addition to the G2/Marrest with CE, we also demonstrated that the extract reducedtotal phosphatase activity in the cell lines [4]. Thisobservation is in accord with work in our laboratorycharacterizing both insulin mimetic and phosphatase-inhibi-tory properties of CE in insulin responsive cells [6]. Byinhibiting phosphatase activity, CE contributes to a shift inthe balance of kinases/phosphatases with the end result of anincreased sensitivity to the action of insulin in both cells andin human subjects [7,8].To further understand how CE affects signaling toproduce the G2/M block, we have extended our investiga-tions to look at consequences of short term CE treatment oncell cycle progression in a CD45 negative Jurkat clone [alsoknown as the Wurzburg cell line (W)]. We have shown thatW demonstrated an enhanced sensitivity to the CE-inducedG2/M compared to the other cell lines used in our initialstudy [4]. Taking advantage of this characteristic, weAvailable online at www.sciencedirect.comJournal of Nutritional Biochemistry 20 (2009) 614–620?Corresponding author. Tel.: +1 301 504 8388; fax: +1 301 504 9062.E-mail address: norberta.schoene@ars.usda.gov (N.W. Schoene).0955-2863/$ – see front matter © 2009 Elsevier Inc. All rights reserved.doi:10.1016/j.jnutbio.2008.06.006
