Intectin, a Novel Small Intestine-specific Glycosylphosphatidylinositol-anchored Protein, Accelerates Apoptosis of Intestinal Epithelial Cells

Abstract

Intestinal epithelial cells undergo rapid turnover and exfoliation especially at the villus tips. This process is modulated by various nutrients especially fat. Apoptosis is one of the important regulatory mechanisms of this turnover. Therefore, identification of the factors that control epithelial cell apoptosis should help us understand the mechanism of intestinal mucosal turnover. Here, we report the identification of a novel small intestine-specific member of the Ly-6 family, intectin, by signal sequence trap method. Intectin mRNA expression was exclusively identified in the intestine and localized at the villus tips of intestinal mucosa, which is known to undergo apoptosis. Intectin mRNA expression was modulated by nutrition. Intestinal epithelial cells expressing intectin were more sensitive to palmitate-induced apoptosis, compared with control intestinal epithelial cells, and such effect was accompanied by increased activity of caspase-3. Intectin expression also reduced cell-cell adhesion of intestinal epithelial cells.Intestinal epithelial cells originate from stem cells at the base of the crypt and migrate along the crypt-villus axis toward the intestinal lumen. When intestinal epithelial cells reach the luminal surface at the villus tips, they finally exfoliate into the lumen, and their cell cycle is terminated with a life span of only 3-5 days (1, 2). This constant and rapid turnover of intestinal mucosa is essential for maximal nutrient absorption, adaptation to changes in diet, and repair of mucosal injury (3).Apoptosis plays an important role in maintaining the physiological integrity of many tissues. In the intestine, apoptosis is a key regulator for the turnover of intestinal mucosa, and apoptotic intestinal epithelial cells have been detected at the villus tips of the small intestine and the colonic luminal surface (4 -6). However, the one or more underlying mechanisms of this process have not been elucidated. In this regard, it is important to identify the factors that control intestinal epithelial cell apoptosis to understand the mechanism of intestinal mucosal turnover.The present study was designed to identify a small intestinederived protein or secretory protein modulated nutritionally that is involved in the control of intestinal epithelial cell apoptosis. Using the efficient signal sequence trap (SST) 1 method (7), we identified a novel small intestine-specific GPI-anchored protein, intectin, which showed distinct localization at the villus tips of intestinal mucosa and accelerated fatty acid-induced apoptosis of intestinal epithelial cells. EXPERIMENTAL PROCEDURESCloning of Intectin cDNA-Poly(A) ϩ RNAs were extracted from the small intestinal epithelium of C57BL/6J mice under three feeding conditions; ad libitum, 24-h fasting, and 24-h fasting followed by 24-h feeding, and from the small intestinal epithelium of ad libitum-fed db/db mice. Equal amount of poly(A) ϩ RNA from each group was pooled and used as the template to synthesize complementary DNA (cDNA). To selectively clone the gen...

Pancreatic α-Amylase Controls Glucose Assimilation by Duodenal Retrieval through N-Glycan-specific Binding, Endocytosis, and Degradation

“…One further possibility is that pancreatic ␣-amylase serves as a source of amino acids for the proliferation of small intestine epithelial cells. It is known that epithelial cells require a large supply of amino acids to maintain their turnover rate, which is the most rapid of any tissue in the body (31)(32)(33). Amino acids are produced by constant proteolysis, which breaks down both dietary and endogenous proteins for reuse in protein synthesis (34).…”

Non-Invasive Exploration of Neonatal Gastric Epithelium by Using Exfoliated Epithelial Cells

“…Exfoliation has been described as an active biochemical process, highly context-dependent and linked to epithelium homeostasis [1], [2], [3], [4]. It is believed that epithelial cells, loosing contact with companion cells as well as extracellular matrix, enter anoikis [5].…”

Survival of Exfoliated Epithelial Cells: A Delicate Balance between Anoikis and Apoptosis

“…On lactating rat pups, we obtained similar results by fastening the pups for 5 hours and allowed them to be reunited with their mother for one hour before sacrifice [43]. By contrast, on adult laboratory mice, fatty acids (like palmitate) are inducers of intectin, a protein implicated in the exfoliation of apoptotic cells at the top of the villus of the small intestine within an hour after meal [3]. These models of nutritional manipulations to induce exfoliation on small intestine of mice [3] or gastric mucosa of rats [5] indicate that the mechanism of exfoliation is highly context dependent, but they also open the possibility to develop in vivo studies of anoikis and autophagy in relation with the functioning of peripheral circadian clocks.…”

“…By contrast, on adult laboratory mice, fatty acids (like palmitate) are inducers of intectin, a protein implicated in the exfoliation of apoptotic cells at the top of the villus of the small intestine within an hour after meal [3]. These models of nutritional manipulations to induce exfoliation on small intestine of mice [3] or gastric mucosa of rats [5] indicate that the mechanism of exfoliation is highly context dependent, but they also open the possibility to develop in vivo studies of anoikis and autophagy in relation with the functioning of peripheral circadian clocks. The disponibility of laboratory rodent models is of paramount importance to develop in vivo studies on anoikis and its connection with molecular circadian clocks to evaluate the stability of chronobiological molecular information in exfoliated cells.…”

“…Exfoliated epithelial cells can be used as surrogate for tissue biopsies in predicting changes in gene expression, DNA methylation, DNA damage, protein expression, and accumulation of dietary components [1, 2]. Exfoliation has also been described as an active biochemical process linked to the homeostasis of gut epithelium [3–6]. It is believed that epithelial cells, loosing contact with companion cells (like fibroblasts) as well as extracellular matrix, enter anoikis [7].…”