Trans-10,cis-12, not cis-9,trans-11, conjugated linoleic acid inhibits G1-S progression in HT-29 human colon cancer cells.
Commercial preparations of conjugated linoleic acid (CLA) contain both positional and geometric isomers of octadecadienoic acid, with cis-9,trans-11 CLA (c9t11) and trans-10,cis-12 CLA (t10c12) as the principal isomers. We showed previously that CLA reduced the incidence of colon tumors in rats treated with 1,2-dimethylhydrazine. In addition, our previous in vitro studies showed that t10c12 inhibited the growth of HT-29 and Caco-2 human colon cancer cells, whereas c9t11 had no effect on cell growth. In the present study, to examine the effects of the CLA isomers on cell cycle and cell cycle regulatory proteins, we treated HT-29 cells with various concentrations (0-4 micromol/L) of the individual CLA isomers. A DNA flow cytometric analysis revealed that t10c12 induced a G1 arrest, whereas c9t11 had no effect on the cell cycle. Western blot analysis of total cell lysates revealed no alteration in the protein expression of cyclin A, cyclin D, cyclin E, cyclin-dependent kinase (CDK) 2, or CDK4 due to t10c12 treatment. However, t10c12 substantially increased the protein expression and mRNA accumulation of the CDK inhibitor p21(CIP1/WAF1). The t10c12 isomer increased the association of p21(CIP1/WAF1) with CDK2 and proliferating cell nuclear antigen, but decreased the levels of phosphorylated retinoblastoma protein (Rb), with an increase in the levels of hypophosphorylated Rb protein. An in vitro kinase assay using histone H1 as a substrate showed that the activities of CDK2 were significantly decreased by t10c12. These results indicate that t10c12 exerts its growth inhibitory effects in colon cancer cells through the induction of G1 cell cycle arrest. The induction of p21(CIP1/WAF1) may be one of the mechanisms by which t10c12 inhibits cell cycle progression in HT-29 cells.
Department of Food Science and Nutrition, Hallym University, Chuncheon, 200-702, Korea.
Han Jin
HJ
Cho
Eun Ji
EJ
Kim
Soon Sung
SS
Lim
Mi Kyung
MK
Kim
Mi-Kyung
MK
Sung
Jong-Sang
JS
Kim
Jung Han Yoon
JH
Park
D051357:Cyclin-Dependent Kinase 2 / Q000032:analysis / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4 / Q000032:analysis / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D016193:G1 Phase / Q000187:drug effects*; D015870:Gene Expression / Q000187:drug effects; D019073:HT29 Cells; D006801:Humans; D044243:Linoleic Acids, Conjugated / Q000494:pharmacology*; D010766:Phosphorylation; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D016160:Retinoblastoma Protein / Q000378:metabolism; D016196:S Phase / Q000187:drug effects*
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D044243:Linoleic Acids, Conjugated; D018809:Proliferating Cell Nuclear Antigen; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; C503589:cis-9, trans-11-conjugated linoleic acid; C496197:trans-10,cis-12-conjugated linoleic acid; C495894:CDK2 protein, human; C495900:CDK4 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4