Involvement of annexin A8 in the properties of pancreatic cancer.

Although Annexin A8 (ANXA8), a member of a superfamily of calcium and phospholipid binding proteins, is physiologically expressed in a tissue-specific manner, recent microarray studies reported that ANXA8 was also ectopically expressed in pancreatic cancers. We investigated the molecular mechanism of expression of ANXA8 in cancer cells and its functional role in pancreatic cancer cells. ANXA8 was diversely expressed in human cancer cell lines. Expression was enhanced by treatment with 5-aza-dC and butyrate, and correlated with methylation status at CpG in the promoter-exon 1 region. Inhibition of ANXA8 using siRNA in BxPC-3 cells which express ANXA8 at a high level elevated caspase-3 and -7 activities. In in vitro invasion assay, inhibition of ANXA8 using siRNA in BxPC-3 reduced the numbers of migrating cells, and down-regulated HIF-1α mRNA transcription. Overexpression of ANXA8 increased the number of viable cells and BrdU incorporation in PANC-1 cells, which express ANXA8 at a low level. Expression of ANXA8 was induced under conditions of nutrient deprivation, and overexpression of ANXA8 showed resistance against serum starvation in PANC-1 cells. In a promoter assay, co-transfection with the expression vector of ANXA8 and the vector of a reporter gene containing the promoter of HIF-1α enhanced HIF-1α promoter activity. In contrast, this effect of ANXA8 was inhibited by administration of BAPTA-AM, an intracellular Ca²⁺ chelator. These results suggest that ectopic ANXA8 expression in cancer cells might involve an epigenetic mechanism. ANXA8 might play an important role in calcium fluctuation-mediated HIF-1α transcriptional activation and cell viability.