Trans-10, cis-12, not cis-9, trans-11, conjugated linoleic acid decreases ErbB3 expression in HT-29 human colon cancer cells

AIM: To examine whether trans-10, cis-12 CLA (t10c12) or cis-9, trans-11 CLA (c9t11) inhibits heregulin (HRG)-beta-stimulated cell growth and HRG-beta-ErbB3 signaling in HT-29 cells. METHODS: We cultured HT-29 cells in the absence or presence of the CLA isomers and/or the ErbB3 ligand HRG-beta. MTT assay, [H-3]thymidine incorporation, Annexin V staining, RT-PCR, Western blotting, immunoprecipitation, and in vitro kinase assay were performed. RESULTS: HRG-beta increased cell growth, but did not prevent t10c12-induced growth inhibition. T10c12 inhibited DNA synthesis and induced apoptosis of HT-29 cells, whereas c9t11 had no effect. T10c12 decreased the levels of ErbB1, ErbB2, and ErbB3 proteins and transcripts in a dose-dependent manner, whereas c9t11 had no effect. Immunoprecipitation/Western blot studies revealed that t10c12 inhibited HRG-beta-stimulated phosphorylation of ErbB3, recruitment of the p85 subunit of phosphoinositide 3-kinase (PI3K) to ErbB3, ErbB3-associated PI3K activities, and phosphorylation of Akt. However, c9t11 had no effect on phospho Akt levels. Neither t10c12 nor c9t11 had any effect on HRG-beta-induced phosphorylation of ERK-1/2. CONCLUSION: These results indicate that the inhibition of HT-29 cell growth by t10c12 may be induced via its modulation of ErbB3 signaling leading to inhibition of Akt activation. (C) 2005 The WJG Press and Elsevier Inc. All rights reserved.