IIAEK Targets Intestinal Alkaline Phosphatase (IAP) to Improve Cholesterol Metabolism with a Specific Activation of IAP and Downregulation of ABCA1

• Main Authors: Asahi Takeuchi, Kentaro Hisamatsu, Natsuki Okumura, Yuki Sugimitsu, Emiko Yanase, Yoshihito Ueno, Satoshi Nagaoka
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: Nutrients
• Subjects: IIAEK; alkaline phosphatase; photoaffinity labeling; Caco-2 cells; cholesterol; ABCA1
• Online Access: https://www.mdpi.com/2072-6643/12/9/2859

IIAEK (Ile-Ile-Ala-Glu-Lys, lactostatin) is a novel cholesterol-lowering pentapeptide derived from bovine milk β-lactoglobulin. However, the molecular mechanisms underlying the IIAEK-mediated suppression of intestinal cholesterol absorption are unknown. Therefore, we evaluated the effects of IIAEK on intestinal cholesterol metabolism in a human intestinal model using Caco-2 cells. We found that IIAEK significantly reduced the expression of intestinal cholesterol metabolism-associated genes, particularly that of the ATP-binding cassette transporter A1 (ABCA1). Subsequently, we chemically synthesized a novel molecular probe, IIXEK, which can visualize a complex of target proteins interacting with photoaffinity-labeled IIAEK by fluorescent substances. Through photoaffinity labeling and MS analysis with IIXEK for the rat small intestinal mucosa and intestinal lipid raft fractions of Caco-2 cells, we identified intestinal alkaline phosphatase (IAP) as a specific molecule interacting with IIAEK and discovered the common IIAEK-binding amino acid sequence, GFYLFVEGGR. IIAEK significantly increased IAP mRNA and protein levels while decreasing ABCA1 mRNA and protein levels in Caco-2 cells. In conclusion, we found that IIAEK targets IAP to improve cholesterol metabolism via a novel signaling pathway involving the specific activation of IAP and downregulation of intestinal ABCA1.