A novel type of detergent-resistant membranes may contribute to an early protein sorting event in epithelial cells.
One sorting mechanism of apical and basolateral proteins in epithelial cells is based on their solubility profiles with Triton X-100. Nevertheless, apical proteins themselves are also segregated beyond the trans-Golgi network by virtue of their association or nonassociation with cholesterol/sphingolipid-rich microdomains (Jacob, R., and Naim, H. Y. (2001) Curr. Biol. 11, 1444-1450). Therefore, extractability with Triton X-100 does not constitute an absolute criterion of protein sorting. Here, we investigate the solubility patterns of apical and basolateral proteins with other detergents and demonstrate that the mild detergent Tween 20 is adequate to discriminate between apical and basolateral proteins during early stages in their biosynthesis. Although the mannose-rich forms of the apical proteins sucrase-isomaltase, lactase-phlorizin hydrolase, aminopeptidase N, and dipeptidylpeptidase IV reveal similar solubility profiles comprising soluble and nonsoluble fractions, the basolateral proteins, vesicular stomatitis virus G protein, major histocompatibility complex class I, and CD46 are entirely soluble with this detergent. The insoluble Tween 20 membranes are enriched in phosphatidylinositol and phosphatidylglycerol compatible with their synthesis in the endoplasmic reticulum and the existence of a novel class of detergent-resistant membranes. The association of the mannose-rich biosynthetic forms of the apical proteins, sucraseisomaltase, lactase-phlorizin hydrolase, aminopeptidase N, and dipeptidylpeptidase IV with the Tween 20-resistant membranes suggests an early polarized sorting mechanism prior to maturation in the Golgi apparatus.
Alfalah
Marwan
M
Department of Physiological Chemistry, School of Veterinary Medicine, D-30559 Hannover, Germany.
Wetzel
Gabi
G
Fischer
Ina
I
Busche
Roger
R
Sterchi
Erwin E
EE
Zimmer
Klaus-Peter
KP
Sallmann
Hans-Peter
HP
Naim
Hassan Y
HY
D000243:Adenosine Deaminase / Q000737:chemistry; D000818:Animals; D018826:CD13 Antigens / Q000494:pharmacology; D019556:COS Cells; D018938:Caco-2 Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002522:Chlorocebus aethiops; D002784:Cholesterol / Q000378:metabolism; D003902:Detergents / Q000494:pharmacology*; D018819:Dipeptidyl Peptidase 4 / Q000737:chemistry; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology* / Q000473:pathology; D006023:Glycoproteins / Q000737:chemistry; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D006825:Hybridomas / Q000378:metabolism; D047468:Immunoprecipitation; D007700:Kinetics; D043322:Lactase / Q000737:chemistry; D010694:Lactase-Phlorizin Hydrolase / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008358:Mannose / Q000737:chemistry; D051916:Membrane Cofactor Protein / Q000096:biosynthesis; D021962:Membrane Microdomains / Q000737:chemistry; D051379:Mice; D017830:Octoxynol / Q000494:pharmacology; D009834:Oligo-1,6-Glucosidase / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D010716:Phosphatidylinositols / Q000737:chemistry; D011136:Polysorbates / Q000494:pharmacology; D021381:Protein Transport; D013107:Sphingolipids / Q000378:metabolism; D013393:Sucrase / Q000737:chemistry; D013395:Sucrose / Q000494:pharmacology; D014162:Transfection; D021601:trans-Golgi Network / Q000378:metabolism
D003902:Detergents; D006023:Glycoproteins; D008055:Lipids; D051916:Membrane Cofactor Protein; D010715:Phosphatidylglycerols; D010716:Phosphatidylinositols; D011136:Polysorbates; D013107:Sphingolipids; D013395:Sucrose; D017830:Octoxynol; D002784:Cholesterol; D009834:Oligo-1,6-Glucosidase; D043322:Lactase; D013393:Sucrase; D010694:Lactase-Phlorizin Hydrolase; D018826:CD13 Antigens; C042807:DPP4 protein, human; D018819:Dipeptidyl Peptidase 4; D000243:Adenosine Deaminase; D008358:Mannose