Effects of Docosahexaenoic Acid and Eicosapentaenoic Acid on the Differential Protein Expression in Human Hepatocellular Carcinoma Cells

Abstract

Hepatocellular carcinoma (HCC) plays a leading role in causing cancer death due to its high metastatic potential and frequent tumor recurrence rate after treatment. Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are two important omega 3-polyunsaturated fatty acids (ˆ3-PUFAs) which have been shown to be able to inhibit the growth of hepatocarcinoma in animal models; however, the mechanisms are not fully understood. Adopting a proteomic approach, we investigated the effects of DHA and EPA on the expression of proteins in the human hepatocellular carcinoma cell line PLC with no metastatic potential. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) was employed for protein separation in the subcellular fractions prior to fluorescent protein staining by SyproRuby protein gel stain. Comparison of differential protein expression between control and fatty acid treatments and between DHA and EPA treatments was enabled by image analysis and protein spots were identified by mass spectrometry (MALDI-TOF/TOF). Results indicate that DHA (200 ÌM) was more effective at causing PLC cell death than EPA (200 ÌM). DHA down-regulated the expression of annexin A2, a protein which is closely associated with angiogenesis and metastasis, and placental anticoagulant protein II (PP4-X), which is involved in the morphological diversification and dissemination of human carcinoma. The N-myc downstream regulated gene 1, a metastasis suppressor gene, is up-regulated in EPA-treated cancer cells whereas the ubiquinol-cytochrome c reductase core protein I (UQCRC1) is down-regulated. UQCRC1 is involved in mitochondria-to-nucleus retrograde response in human cancer and is highly expressed in breast and ovarian tumors. These data not only facilitate the identification of differentially expressed proteins that are involved in hepatocellular carcinogenesis, but may also provide candidate biomarkers for the development of therapeutic tools with dietary fatty acids.