Apical trafficking in epithelial cells: signals, clusters and motors

OA Weisz, E Rodriguez-Boulan - Journal of cell science, 2009 - journals.biologists.com
Journal of cell science, 2009journals.biologists.com
In the early days of epithelial cell biology, researchers working with kidney and/or intestinal
epithelial cell lines and with hepatocytes described the biosynthetic and recycling routes
followed by apical and basolateral plasma membrane (PM) proteins. They identified the
trans-Golgi network and recycling endosomes as the compartments that carried out apical-
basolateral sorting. They described complex apical sorting signals that promoted
association with lipid rafts, and simpler basolateral sorting signals resembling clathrin …
In the early days of epithelial cell biology, researchers working with kidney and/or intestinal epithelial cell lines and with hepatocytes described the biosynthetic and recycling routes followed by apical and basolateral plasma membrane (PM) proteins. They identified the trans-Golgi network and recycling endosomes as the compartments that carried out apical-basolateral sorting. They described complex apical sorting signals that promoted association with lipid rafts, and simpler basolateral sorting signals resembling clathrin-coated-pit endocytic motifs. They also noticed that different epithelial cell types routed their apical PM proteins very differently, using either a vectorial (direct) route or a transcytotic (indirect) route. Although these original observations have generally held up, recent studies have revealed interesting complexities in the routes taken by apically destined proteins and have extended our understanding of the machinery required to sustain these elaborate sorting pathways. Here, we critically review the current status of apical trafficking mechanisms and discuss a model in which clustering is required to recruit apical trafficking machineries. Uncovering the mechanisms responsible for polarized trafficking and their epithelial-specific variations will help understand how epithelial functional diversity is generated and the pathogenesis of many human diseases.
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