원문정보
초록
영어
The expression of glycan chains and hydrophobic structures of glycolipids is precisely regulated in a time- and space-dependent manner. We focus our research on two genes, Gsl5 (glycosphingolipid regulatory gene 5) and Des2 (degenerative spermatocyte 2). Gsl5 regulates the expression of GlcNAc 1-6(Gal 1-3)GalNAc containing glycolipids and glycoproteins through controlling the activity of 6GlcNAc transferase in mouse kidney. Des2 encodes a hydroxylase which hydroxylates dihydroceramide:sphinganine at C4 position and is responsible for the expression of glycolipids containing C4 hydroxysphinganine (phytosphingosine) in the small intestine and kidney of mice. We found that Gsl5 locates at about 5.5 kb upstream of exon 1 of 6GlcNAc T1, consists of eight pairs of two GT-repeats, and controls 6GlcNAc T1 mRNA expression in kidney proximal tubular cellspecific manner. 6GlcNAc transferase transfers GlcNAc on the GalNAc of Gal 1-3GalNAc and of glycolipids and glycoproteins, respectively. One of glycoproteins modified by the GlcNAc transferase in the proximal tubular epithelial cells is megalin, which binds and reabsorbs small molecular weight proteins from urine produced by the blood filtration at glomeruli. We purified two types of megalin, one carries Gal 1-4(Fuc 1-3)GlcNAc 1-6(Gal 1- 3)GalNAc 1-Ser/Thr (Lewis X-core 2 structure) and the other the structure without the Gal 1-4(Fuc 1-3)GlcNAc 1-6 branch from mouse kidneys. Ligand binding capacity of the megalin with Lewis Xcore 2 structure was much higher than that without the branch structure. Des2 hydroxylase requires NADH, NADH-dependent cytochrome b5 reductase, and cytochrome b5 for producing the activity. mRNA expression of Des2 is regulated in a tissue-specific manner, highest in the small intestine and high in the kidney. We are in the process of establishing Des2 knock out mice and are going to analyze phenotypes. We consider that C4-hydroxylated sphinganine containing glycolipids play a significant role for maintaining functions of nutrient absorption.