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Basolateral sorting signals differ in their ability to redirect apical proteins to the basolateral cell surface
The Journal of Biological Chemistry
|March 29, 2000
Summary
Cellular protein sorting relies on specific signals. This study reveals that the number of signals, not just their type, significantly influences whether proteins end up on the apical or basolateral side of epithelial cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Polarized sorting of membrane proteins is crucial for epithelial cell function.
- Both cytoplasmic (basolateral) and transmembrane/exoplasmic (apical) signals direct protein localization.
- Basolateral signals have been considered dominant over apical determinants.
Purpose of the Study:
- To investigate the role of cytoplasmic signals in polarized sorting.
- To determine if basolateral signals are always dominant over apical signals.
- To explore the influence of protein oligomerization state on sorting efficiency.
Main Methods:
- Construction of chimeric proteins by fusing cytoplasmic domains of basolateral proteins (asialoglycoprotein receptor H1, transferrin receptor) to apical protein segments (aminopeptidase N).
- Analysis of chimeric protein localization in Madin-Darby canine kidney cells.
- Generation of multimeric fusion proteins to assess the effect of signal valence.
Main Results:
- Both transferrin receptor and H1 cytoplasmic domains induced endocytosis.
- Only the transferrin receptor cytoplasmic domain mediated stable basolateral expression.
- The H1 fusion protein initially localized basolaterally but was later resorted to the apical surface.
- Signal valence (number of signals) influenced the sorting outcome, with a tetrameric fusion protein showing functional H1 signaling.
Conclusions:
- Basolateral signals are not inherently dominant over apical determinants for steady-state polarity.
- The valence of sorting signals plays a critical role in the polarized sorting of membrane proteins.
- Protein oligomerization state significantly impacts the efficiency and outcome of polarized sorting.
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