E2F4 and ribonucleotide reductase mediate S-phase arrest in colon cancer cells treated with chlorophyllin.
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.
Chimploy
Korakod
K
Linus Pauling Institute, Oregon State University, Corvallis, OR 97331-6512, USA.
Díaz
G Dario
GD
Li
Qingjie
Q
Carter
Orianna
O
Dashwood
Wan-Mohaiza
WM
Mathews
Christopher K
CK
Williams
David E
DE
Bailey
George S
GS
Dashwood
Roderick H
RH
D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002735:Chlorophyllides / Q000494:pharmacology*; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000473:pathology*; D004247:DNA / Q000378:metabolism; D050687:E2F1 Transcription Factor / Q000032:analysis / Q000378:metabolism; D050704:E2F4 Transcription Factor / Q000032:analysis / Q000502:physiology*; D006801:Humans; D012264:Ribonucleotide Reductases / Q000037:antagonists & inhibitors / Q000502:physiology*; D016196:S Phase / Q000187:drug effects*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology
D016588:Anticarcinogenic Agents; D002735:Chlorophyllides; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D016159:Tumor Suppressor Protein p53; D004247:DNA; D012264:Ribonucleotide Reductases; C007020:chlorophyllin