Abstracts for the "World Conference of Stress" meeting in Budapest, August 2007:
THE APOPTOTIC EFFECT OF N-3 FATTY ACIDS ON THE LEUKEMIA CELL LINE HL60 IS LIKELY TO BE MEDIATED THROUGH ER STRESS.
J. E. Slagsvold, S. A. Schonberg.
Background - Numerous studies indicate an inverse relationship between dietary intake of n-3 polyunsaturated fatty acids (PUFAs) and cancer. Cell culture studies show that n-3 PUFAs inhibit cell proliferation and induce programmed cell death, apoptosis. However, the molecular mechanisms behind these effects are complex and unclear. Aim – To investigate signaling pathways involved in EPA-induced growth arrest/apoptosis in HL-60 cells. Materials and methods – Gene expression profiling of HL60 cells treated with EPA was performed by Affymetrix GeneChip System and key markers of relevant pathways verified at protein level by Western blotting. Results - Several transcripts involved in ER homeostasis, cell cycle and apoptosis were affected. Transcripts involved in the unfolded protein response (UPR) pathway, chaperones, folding proteins and transcripts involved in apoptosis, were upregulated, whereas cyclin D1 and cellcycle/progression transcripts were downregulated. Proteins in the UPR like eIF2a -P, ATF4, SQSTM-1 and cyclin D1 were verified by western blotting. Conclusion - The data clearly show that the n-3 PUFA EPA induces apoptosis in HL 60 cells and that the mechanism may be mediated through ER stress.
Stress protein activation by the omega-3 fatty acid docosahexaenoic acid in human colon cancer cells
Hilde Bremseth, Anne Goril Lundemo, Caroline Hild Jakobsen, Gro Leite Størvold Hans Einar Krokan and Svanhild Arentz Schonberg
Docosahexaenoic acid (commonly known as DHA; 22:6 n-3) is an omega-3 essential fatty acid. We have earlier shown that DHA affects the proliferation and survival of colon cancer cells. In order to evaluate the molecular mechanisms involved in the anti-cancer action of this fatty acid, gene expression analysis were performed at several time points. The results showed activation of a stress response after treatment of the cells with DHA. Heat shock protein 70 (HSP70) and the Nrf2-dependent stress protein heme oxygenase-1 (HO-1) were both found to be highly up-regulated at the protein level. These results suggest that stress proteins are key mediators or modulators of the effects of DHA. Genes encoding redox enzymes were also found to be up-regulated after DHA treatment. The work presented here will try to answer if the observed stress protein activation in colon cancer cells treated with DHA is related to changes in the cellular redox state and involves modification of redox-sensitive transcription factors.
DHA induces disturbance in cholesterol homeostasis, ER stress and cell cycle arrest in colon cancer cells
GL Storvold, CH Jakobsen, H Bremseth, SA Schonberg
Epidemiological, animal and cell culture studies indicate an inverse association between long chain omega-3 fatty acids and growth of cancers such as breast, prostate and colon. We have previously shown that docosahexaenoic acid (DHA) induces growth arrest in different colon cancer cell lines, but little information regarding the molecular mechanisms exists. Microarray analysis has revealed that DHA induces cellular stress, and that activation of the endoplasmic reticulum (ER) stress pathway may be one mechanism leading to growth arrest. The main functions of ER are regulation of calcium homeostasis, protein folding and processing, and lipid synthesis. Disturbances in any of these functions may lead to ER stress. We have observed an accumulation of cholesteryl esters in our cell lines after DHA treatment, but only slight increases in total cholesterol levels. In addition we observe increased protein levels of HMG-CoA reductase, the rate limiting enzyme in cholesterol biosynthesis, and nSREBP2, the main regulator of genes involved in cholesterol synthesis and uptake. This indicates a cellular demand for cholesterol. Previously we have observed that treatment with DHA leads to an accumulation of cells in G2/M phase of the cell cycle. Progression through G2/M phase is cholesterol-dependent and cholesterol depletion will lead to inactivation of CDK1, downregulation of cyclin B1, and G2/M arrest. In addition activation of ER stress may lead to cell cycle arrest by depletion of cyclin D1. The aim of this study is to investigate the mechanisms by which DHA affects cholesterol homeostasis, induces cell cycle arrest and ER stress, and the possible link between these events.
