Polarized Distribution and Delivery of Plasma Membrane Proteins in Thyroid Follicular Epithelial Cells

doi:10.1074/jbc.270.6.2478

Polarized Distribution and Delivery of Plasma Membrane Proteins in Thyroid Follicular Epithelial Cells (*)

From the (1)Division of Endocrinology, Beth Israel Hospital, Harvard Medical School and
the (2)Program in Biological and Biomedical Sciences, Harvard Medical School, Boston, Massachusetts 02215 and
the (3)Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142

^§ To whom correspondence should be addressed. Tel.: 617-735-4280; Fax: 617-735-2927.

Abstract

Thyroid follicular cells coordinate several oppositely located surface enzyme activities. Recent studies have raised questions about the basic mechanisms used to achieve thyroid surface polarity. We investigated these mechanisms in primary thyroid epithelial monolayers cultured on porous filters. In the steady state, most Na/K-ATPase and aminopeptidase N were available for surface biotinylation, and these proteins exhibited physiological distributions (basolateral and apical, respectively). Glycosylphosphatidylinositol-anchored proteins were also apically distributed. By pulse-chase, newly synthesized transmembrane proteins exhibited polarized surface delivery that was oriented similarly to that observed at steady state. Little time elapsed between acquisition of Golgi-specific processing and cell surface arrival. Interestingly, when either newly synthesized or steady state-labeled thyroid peroxidase was similarly analyzed, only 30% of the enzyme was ever detected at the cell surface. Of this, the majority was localized apically. The data suggest that most thyroid peroxidase remains intracellular in these monolayers, consistent with the possibility of intracellular iodination activity in addition to apical extracellular iodination. Nevertheless, in filter-polarized thyrocytes, most newly synthesized plasma membrane proteins appear to be sorted in the Golgi complex for direct delivery to apical and basolateral domains.

Footnotes

↵* This work was supported by National Institutes of Health Grant DK 40344 (to P. A.), FIRST Award GM 50443 and the Whitehead Fellow's Program (to M. P. L.), as well as National Institutes of Health Training Grants DK07516 and AG08812 (to R. K.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

FRT

Fischer rat thyroid

APN

aminopeptidase N

NKA

Na/K-ATPase

TPO

thyroid peroxidase

TSH

thyrotropin

PAGE

polyacrylamide gel electrophoresis

GPI

glycosylphosphatidylinositol

PI-PLC

phosphatidylinositol-specific phospholipase C.
↵² As has been observed by others (Gottardi and Caplan, 1993), the NKA β-subunit was biotinylated far more efficiently than the α-subunit.
↵³ M. P. Lisanti, R. Kuliawat, and P. Arvan, unpublished data.
- Received September 22, 1994.
- Revision received November 2, 1994.