Abstract

Recent findings have implicated glycosphingolipids as modulators of insulin receptor activity. Studies with C57BL/6J ob/ob mice have shown that insulin sensitivity is enhanced by the synthetic hydrophobic iminosugar N-(5-adamantane-1-yl-methoxy-pentyl)-deoxynojirimycin (AMP-DNM) that inhibits glucosylceramide synthase. Here, we treated the liver hepatoma cell line HepG2 with AMP-DNM, resulting in a 70% reduction of glycosphingolipids, and we analyzed the effect on gene expression. Using whole human genome 44K oligonucleotide arrays, we identified 89 genes that were significantly (p < 0.01) up- or down-regulated by AMP-DNM treatment. Of the 56 up-regulated genes, 17 were direct target genes for transcription factors sterol regulatory element-binding protein (SREBP) 1 or SREBP2, which activate genes in the sterol biosynthesis pathway. An increase in cholesterol production rate confirmed that the induction of SREBP target genes seen at the mRNA level resulted in activation of the cholesterol biosynthesis pathway. It is interesting to note that the cholesterol content of the cells did not increase. It is noteworthy that no effects were found on expression of genes related to cell receptor signaling pathways, neither on toxicity nor cell growth. Our findings indicate that inhibition of glucosylceramide synthase with AMP-DNM leads to activation of SREBP target genes and synthesis of cholesterol in HepG2 cells.