Abstract
Caco-2, a human cell line, displays several biochemical and morphological characteristics of differentiated enterocytes. Among these is the ability to transport zinc from the apical to the basal compartment. This process was enhanced following exposure by the apical compartment to increasing concentrations of the metal. High pressure liquid chromatography fractionation of the media obtained from cells labeled with radioactive zinc showed that metallothioneins (MTs), small metal-binding, cysteine-rich proteins), were present in the apical and basal media of controls as well as in cells grown in the presence of high concentrations of zinc. Following exposure to the metal, the levels of Zn-MTs in the apical medium increased, while in the basal compartment the greatest part of zinc appeared in a free form with minor changes in the levels of basal MTs. Metabolic labeling experiments with radioactive cysteine confirmed the apical secretion of MTs. A stable transfectant clone of Caco-2 cells (CL11) was selected for its ability to express constitutively high levels of the mouse metallothionein I protein. This cell line showed an enhanced transport of the metal following exposure to high concentrations of zinc and a constitutive secretion of the mouse metallothionein I protein in the apical compartment. Together, these findings strongly support the hypothesis of a functional role between the biosynthesis and secretion of MTs and the transport of zinc in intestinal cells.
Highlights
Zinc is an element essential for growth, present in all eukaryotic organisms, where is found as cofactor in many enzymes and proteins [1, 2]
Data in this paper describe the transport of zinc in polarized Caco-2 cells, an in vitro model of enterocyte differentiation [19], and provide evidence of its role in the synthesis and secretion of MTs
In Caco-2 Cells, Transport of Zinc Is Dependent on Concentrations of the Metal in the Apical Medium—Experiments of zinc transport were performed on Caco-2 cells grown on permeable filters between 16 and 21 days to reach a fully differentiated status
Summary
Zinc is an element essential for growth, present in all eukaryotic organisms, where is found as cofactor in many enzymes and proteins [1, 2]. Previous studies with radioactive isotopes have established that the synthesis of MTs is induced within the enterocyte by parenteral or oral administration of zinc (14 –16), while in rats and humans the secretion of zinc in the gastrointestinal tract is regulated by the dietary status of the metal [17, 18]. Data in this paper describe the transport of zinc in polarized Caco-2 cells, an in vitro model of enterocyte differentiation [19], and provide evidence of its role in the synthesis and secretion of MTs. zinc transport was found to be affected both by its concentration in the medium as well as by the expression of MT proteins, suggesting a cooperative relationship in the regulation of zinc transport in enterocyte cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
