Polarized targeting of epithelial cell proteins in thyrocytes and MDCK cells

Daniel Prabakaran, Rexford S. Ahima, John W. Harney, Marla J. Berry, P. Reed Larsen, Peter Arvan

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


Polarized trafficking signals may be interpreted differently in different cell types. In this study, we have compared the polarized trafficking of different proteins expressed endogenously in primary porcine thyroid epithelial cells to similar proteins expressed in MDCK cells. As in MDCK cells, NH4Cl treatment of filter-grown thyrocytes caused mis-sorted soluble proteins to exhibit enhanced secretion to the apical medium. In independent studies, thrombospondin 1 (a thyroid basolaterally secreted protein) was secreted basolaterally from MDCK cells. Likewise, the 5'-deiodinase (a thyroid basolateral membrane protein) encoded by the DI01 gene was also distributed basolaterally in transfected MDCK cells. Consistent with previous reports, when the secretion of human growth hormone (an unglycosylated regulated secretory protein) was examined from transfected MDCK cells, the release was nonpolarized. However, transfected thyrocytes secreted growth hormone apically in a manner dependent upon zinc addition. Moreover, two additional regulated secretory proteins expressed in thyrocytes, thyroglobulin (the major endogenous glycoprotein) and parathyroid hormone (an unglycosylated protein expressed transiently), were secreted apically even in the absence of zinc. We hypothesize that while cellular mechanisms for interpreting polarity signals are generally similar between thyrocytes and MDCK cells, thyrocytes allow for specialized packaging of regulated secretory proteins for apical delivery, which does not require glycosylation but may involve availability of certain ions as well as appropriate intracellular compartmentation.

Original languageEnglish (US)
Pages (from-to)1247-1256
Number of pages10
JournalJournal of cell science
Issue number8
StatePublished - 1999
Externally publishedYes


  • Apical sorting
  • MDCK cell
  • Regulated secretory pathway
  • Storage granule
  • Thyrocyte

ASJC Scopus subject areas

  • Cell Biology


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