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© The Rockefeller University Press, 0021-9525/1997//319 $5.00
The Journal of Cell Biology, Volume 136, Number 2, , 1997 319-330

Article

Targeting of an Intestinal Apical Endosomal Protein to Endosomes in Nonpolarized Cells



Jean M. Wilson and Tamara L. Colton

Department of Cell Biology and Anatomy and Department of Pediatrics, Steele Memorial Children's Research Center, University of Arizona, Tucson, Arizona 85724

Polarized cells such as epithelial cells and neurons have distinct endosomal compartments associated with different plasma membrane domains. The endosomes of the neuronal cell body and the basolateral cytoplasm of epithelial cells are thought to perform cellular "housekeeping" functions such as the uptake of nutrients and metabolites, while the endosomes in the apical cytoplasm or axons are thought to be specialized for the sorting and transcytosis of cell type–specific ligands and receptors. However, it is not known if nonpolarized cells such as fibroblasts contain a specialized endosomal compartment analogous to the specialized endosomes found in neurons and epithelia. We have expressed a protein that is normally found in the apical early endosomes of developing intestinal epithelial cells in normal rat kidney fibroblasts. This apical endosomal marker, called endotubin, is targeted to early endosomes in transfected fibroblasts, and is present in peripheral as well as perinuclear endosomes. The peripheral endosomes that contain endotubin appear to exclude transferrin, fluid phase markers, and the mannose-6-phosphate receptor, although in the perinuclear region colocalization of endotubin and these markers is present. In addition, endotubin positive structures do not tubulate in response to brefeldin A and instead redistribute to a diffuse perinuclear location. Since this endosomal compartment has many of the characteristics of an apical or axonal endosomal compartment, our results indicate that nonpolarized cells also contain a specialized early endosomal compartment.

Abbreviations used in this paper: BFA, brefeldin A; lgp, lysosomal glycoprotein; M6PR, mannose-6-phosphate receptor; NRK, normal rat kidney.

This manuscript is dedicated to the memory of Dr. Barry King.


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