GLUT12 expression and regulation in murine small intestine and human Caco-2 cells.

GLUT12 was cloned from the mammary cancer cell line MCF-7, but its physiological role still needs to be elucidated. To gain more knowledge of GLUT12 function in the intestine, we investigated GLUT12 subcellular localization in the small intestine and its regulation by sugars, hormones, and intracellular mediators in Caco-2 cells and mice. Immunohistochemical methods were used to determine GLUT12 subcellular localization in human and murine small intestine. Brush border membrane vesicles were isolated for western blot analyses. Functional studies were performed in Caco-2 cells by measuring α-methyl-d-glucose (αMG) uptake in the absence of sodium. GLUT12 is located in the apical cytoplasm, below the brush border membrane, and in the perinuclear region of murine and human enterocytes. In Caco-2 cells, GLUT12 translocation to the apical membrane and α-methyl- d-glucose uptake by the transporter are stimulated by protons, glucose, insulin, tumor necrosis factor-α (TNF-α), protein kinase C, and AMP-activated protein kinase. In contrast, hypoxia decreases GLUT12 expression in the apical membrane. Upregulation of TNF-α and hypoxia-inducible factor-1α ( HIF-1α) genes is found in the jejunal mucosa of diet-induced obese mice. In these animals, GLUT12 expression in the brush border membrane is slightly decreased compared with lean animals. Moreover, an intraperitoneal injection of insulin does not induce GLUT12 translocation to the membrane, as it occurs in lean animals. GLUT12 rapid translocation to the enterocytes' apical membrane in response to glucose and insulin could be related to GLUT12 participation in sugar absorption during postprandial periods. In obesity, in which insulin sensitivity is reduced, the contribution of GLUT12 to sugar absorption is affected.

Spatial-temporal protein expression of inhibitor of differentiation-1 (Id1) during fetal embryogenesis and in different mouse and human cancer types.

Inhibitor of differentiation-1 (Id1) plays a role in cell proliferation, acquisition of epithelial to mesenchymal transition (EMT) features and angiogenesis. Id1 was shown to be expressed in some tumor types, mainly in advanced dedifferentiated stages. However, recent studies using a validated and highly specific monoclonal antibody against Id1 have challenged many of the results obtained by immunohistochemistry. The goal of our work was to perform a thorough analysis of Id1 expression in mouse embryos and adult tissues, as well as healthy and malignant mouse and human samples using this validated antibody (Perk et al., 2006). Our results show that Id1 was highly expressed in the oropharyngeal cavity, lung, cartilage and skin of E14 and E15 mouse embryos, but expression was progressively reduced in more developed embryos. Immunostaining only remained in epithelial cells of the gut and uterus of adult mice. Mammary MMTV-Myc and MMTV-Myc/VEGF transgenic mouse tumors, and squamous cell carcinomas of the lung induced by N-nitroso-tris-chloroethylurea (NTCU) were highly positive for Id1, unlike their respective healthy counterparts. Id1 immunostaining in a human tissue microarray (TMA) revealed strong expression in cancers of the oral cavity, bladder and cervix. Some tumor specimens of esophagus, thyroid and breast were also strongly positive. Our results suggest that Id1 is an oncofetal protein highly expressed in particular tumor types that should be reanalyzed in future studies using large cohorts of patients to reassess its diagnostic/prognostic value. Moreover, MMTV-Myc- and NTCU-induced tumors could serve as appropriate mouse models to study Id1 functions in breast and lung cancer, respectively.