Basal level of autophagy and MAP1LC3B-II as potential biomarkers for DHA-induced cytotoxicity in colorectal cancer cells.

The omega-3 fatty acid docosahexaenoic acid (DHA) is known as an anticancer agent. Colorectal cancer (CRC) cells exhibit different sensitivity toward DHA, but the mechanisms involved are still unclear. Gene expression profiling of 10 CRC cell lines demonstrated a correlation between the level of DHA sensitivity and different biological stress responses, such as endoplasmic reticulum (ER) stress, oxidative stress, and autophagy. The basal level of autophagy and MAP1LC3B-II protein correlated with DHA sensitivity in the cell lines studied. DHA induced oxidative stress, ER stress, and autophagy in DHA-sensitive DLD-1 cells, while the less sensitive LS411N cells were affected to a much lesser extent. Co-treatment with DHA and the autophagy inducer rapamycin reduced DHA sensitivity in DLD-1 and HCT-8 cells, while co-treatment with DHA and the autophagy inhibitors chloroquine and 3-methyladenine increased the DHA sensitivity in LS411N and LS513 cells. Differentially expressed genes correlating with DHA sensitivity and the level of autophagy demonstrated an overlap in biological pathways involved. Results indicate the basal level of autophagy and MAP1LC3B-II protein as potential biomarkers for DHA sensitivity in CRC cells. Protocol and data for gene expression experiments have been submitted to ArrayExpress with accession number E-MTAB-5750.