α-Amylase expressed in human small intestinal epithelial cells is essential for cell proliferation and differentiation

alpha-Amylase, which plays an essential role in starch degradation, is expressed mainly in the pancreas and salivary glands. Human alpha-amylase is also detected in other tissues, but it is unclear whether the alpha-amylase is endogenously expressed in each tissue or mixed exogenously with one expressed by the pancreas or salivary glands. Furthermore, the biological significance of these alpha-amylases detected in tissues other than the pancreas and salivary glands has not been elucidated. We discovered that human alpha-amylase is expressed in intestinal epithelial cells and analyzed the effects of suppressing alpha-amylase expression. alpha-Amylase was found to be expressed at the second-highest messenger RNA level in the duodenum in human normal tissues after the pancreas. alpha-Amylase was detected in the cell extract of Caco-2 intestinal epithelial cells but not secreted into the culture medium. The amount of alpha-amylase expressed increased depending on the length of the culture of Caco-2 cells, suggesting that alpha-amylase is expressed in small intestine epithelial cells rather than the colon because the cells differentiate spontaneously upon reaching confluence in culture to exhibit the characteristics of small intestinal epithelial cells rather than colon cells. The alpha-amylase expressed in Caco-2 cells had enzymatic activity and was identified as AMY2B, one of the two isoforms of pancreatic alpha-amylase. The suppression of alpha-amylase expression by small interfering RNA inhibited cell differentiation and proliferation. These results demonstrate for the first time that alpha-amylase is expressed in human intestinal epithelial cells and affects cell proliferation and differentiation. This alpha-amylase may induce the proliferation and differentiation of small intestine epithelial cells, supporting a rapid turnover of cells to maintain a healthy intestinal lumen.