TitleE2F4 and ribonucleotide reductase mediate S-phase arrest in colon cancer cells treated with chlorophyllin.
Publication TypeJournal Article
Year of Publication2009
AuthorsChimploy K, G Díaz D, Li Q, Carter O, Dashwood W-M, Mathews CK, Williams DE, Bailey GS, Dashwood RH
JournalInt J Cancer
Volume125
Issue9
Pagination2086-94
Date Published2009 Nov 01
ISSN1097-0215
KeywordsAnticarcinogenic Agents, Cell Line, Tumor, Chlorophyllides, Colonic Neoplasms, DNA, E2F1 Transcription Factor, E2F4 Transcription Factor, Humans, Ribonucleotide Reductases, S Phase, Tumor Suppressor Protein p53
Abstract

Chlorophyllin (CHL) is a water-soluble derivative of chlorophyll that exhibits cancer chemopreventive properties, but which also has been studied for its possible cancer therapeutic effects. We report here that human colon cancer cells treated with CHL accumulate in S-phase of the cell cycle, and this is associated with reduced expression levels of p53, p21, and other G(1)/S checkpoint controls. At the same time, E2F1 and E2F4 transcription factors become elevated and exhibit increased DNA binding activity. In CHL-treated colon cancer cells, bromodeoxyuridine pulse-chase experiments provided evidence for the inhibition of DNA synthesis. Ribonucleotide reductase (RR), a pivotal enzyme for DNA synthesis and repair, was reduced at the mRNA and protein level after CHL treatment, and the enzymatic activity was inhibited in a concentration-dependent manner both in vitro and in vivo. Immunoblotting revealed that expression levels of RR subunits R1, R2, and p53R2 were reduced by CHL treatment in HCT116 (p53(+/+)) and HCT116 (p53(-/-)) cells, supporting a p53-independent mechanism. Prior studies have shown that reduced levels of RR small subunits can increase the sensitivity of colon cancer cells to clinically used DNA-damaging agents and RR inhibitors. We conclude that by inhibiting R1, R2, and p53R2, CHL has the potential to be effective in the clinical setting, when used alone or in combination with currently available cancer therapeutic agents.

DOI10.1002/ijc.24559
Alternate JournalInt. J. Cancer
PubMed ID19585502
PubMed Central IDPMC2753276
Grant ListCA122959 / CA / NCI NIH HHS / United States
P01 CA090890 / CA / NCI NIH HHS / United States
P30 ES00210 / ES / NIEHS NIH HHS / United States
R29 CA065525 / CA / NCI NIH HHS / United States
CA090890 / CA / NCI NIH HHS / United States
R01 CA065525 / CA / NCI NIH HHS / United States
R01 CA122959 / CA / NCI NIH HHS / United States
CA65525 / CA / NCI NIH HHS / United States
P01 CA090890-01A29001 / CA / NCI NIH HHS / United States
P30 ES000210 / ES / NIEHS NIH HHS / United States