Newly Synthesized Transferrin Receptors Can Be Detected in the Endosome before They Appear on the Cell Surface (*)
- From the Medical Research Council Laboratory for Molecular Cell Biology and Department of Biology, University College London, Gordon Street, London WC1E 6BQ, United Kingdom
- § To whom correspondence should be addressed: MRC Laboratory for Molecular Cell Biology, University College London, Gordon St., London WC1E 6BQ, United Kingdom. Tel.: 071-380-7806; Fax: 071-380-7805.
Abstract
It is well established that a proportion of newly synthesized lysosomal enzymes and class II major histocompatibility complex antigens are delivered directly to the endocytic pathway from the Golgi complex. Here we show that a significant proportion of newly synthesized transferrin receptors can be detected in endosomes before reaching the cell surface. These newly synthesized transferrin receptors are delivered to the endosome more efficiently than either constitutively secreted soluble proteins or glycophosphatidylinositol-anchored plasma membrane proteins suggesting that their transfer to the endosome is signal-dependent. Identification of a signal-dependent transfer step for proteins like the transferrin receptor operating on the exocytic pathway has important implications for membrane biogenesis, especially in the establishment of cell surface polarity.
Footnotes
-
↵* 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:
- TGN
-
trans-Golgi network
- ALP
-
alk aline phosphatase
- GPI
-
glycophosphatidylinositol
- Tfn-R
-
transferrin receptor
- DMEM
-
Dulbecco's modified Eagle's medium
- FCS
-
fetal calf serum.
-
- Received January 24, 1995.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
