title: Differentiation- and polarization-dependent zinc tolerance in Caco-2 cells.
abstract: OBJECTIVE
  Enterocytes are feasibly confronted with enormous zinc concentrations especially as a result of oral zinc supplementation. In the present study, we investigated the mechanisms underlying the exceptional ability to withstand this usually toxic load using the enterocytic cell line Caco-2.
  
  
  METHODS
  By MTT test analysis, we compared zinc tolerance in undifferentiated Caco-2 cells (udCaco-2) and differentiated Caco-2 cells (dCaco-2). By RT-PCR, we compared the respective baseline expression levels of certain zinc transporters and metallothioneins (MTs) as well as the regulation of these components in response to high zinc concentrations. Moreover, using dCaco-2 cells cultured on porous membranes, we explored zinc tolerance in dependence of the side of zinc administration: apical versus basolateral.
  
  
  RESULTS
  dCaco-2 cells tolerate significantly higher levels of zinc compared to udCaco-2 cells. This adaptation was accompanied by upregulated ZnT-1 and downregulated ZIP1 levels. The expression of metallothioneins MT1A and MT1X was also significantly downregulated during differentiation. Moreover, apparent from profound differences in zinc tolerance between apical and basolateral zinc application, polarization was concluded to have substantial impact on cellular zinc tolerance.
  
  
  CONCLUSIONS
  The profound increase in zinc tolerance we found in differentiated enterocyte-type Caco-2 cells and in particular, the impact of polarization are likely to reflect the physiologically indispensable capability of enterocytes to cope with remarkable concentrations of intestinal zinc.
authors.affiliation: Center for Pathobiochemistry and Genetic, Institute Medical Chemistry, Medical University of Vienna, Austria.
authors.forename: Nina
authors.initials: N
authors.lastname: Zemann
authors.forename: Adolf
authors.initials: A
authors.lastname: Zemann
authors.forename: Petra
authors.initials: P
authors.lastname: Klein
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Elmadfa
authors.forename: Manfred
authors.initials: M
authors.lastname: Huettinger
mesh_terms: D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000378:metabolism; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation; D015536:Down-Regulation; D020895:Enterocytes / Q000166:cytology / Q000187:drug effects*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D008668:Metallothionein / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation; D015032:Zinc / Q000032:analysis / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; C530099:MT1A protein, human; D012333:RNA, Messenger; C498299:SLC30A1 protein, human; C403517:SLC39A1 protein, human; C017800:zinc-binding protein; D008668:Metallothionein; D015032:Zinc