Differential recognition of tyrosine-based basolateral signals by AP-1B subunit mu1B in polarized epithelial cells.
To investigate the importance of tyrosine recognition by the AP-1B clathrin adaptor subunit mu1B for basolateral sorting of integral membrane proteins in polarized epithelial cells, we have produced and characterized a mutant form of mu1B. The mutant (M-mu1B) contains alanine substitutions of each of the four conserved residues, which in the AP-2 adaptor subunit micro2 are critical for interacting with tyrosine-based endocytosis signals. We show M-mu1B is defective for tyrosine binding in vitro, but is nevertheless incorporated into AP-1 complexes in transfected cells. Using LLC-PK1 cells expressing either wild type or M-mu1B, we find that there is inefficient basolateral expression of membrane proteins whose basolateral targeting signals share critical tyrosines with signals for endocytosis. In contrast, membrane proteins whose basolateral targeting signals are distinct from their endocytosis signals (transferrin and low-density lipoprotein receptors) accumulate at the basolateral domain normally, although in a manner that is strictly dependent on mu1B or M-mu1B expression. Our results suggest that mu1B interacts with different classes of basolateral targeting signals in distinct ways.
Division of Molecular Membrane Biology, Cancer Research Institute, Kanazawa University Graduate School of Medical Science, Kanazawa, Ishikawa 920-0934, Japan.
Hisashi
H
Sugimoto
Masayuki
M
Sugahara
Heike
H
Fölsch
Yasuhiro
Y
Koide
Fubito
F
Nakatsu
Naotaka
N
Tanaka
Toshiro
T
Nishimura
Mitsuru
M
Furukawa
Chris
C
Mullins
Nobuhiro
N
Nakamura
Ira
I
Mellman
Hiroshi
H
Ohno
D033983:Adaptor Protein Complex mu Subunits / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites; D001692:Biological Transport / Q000502:physiology*; D002460:Cell Line; D016764:Cell Polarity; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D046911:Macromolecular Substances; D011485:Protein Binding; D021382:Protein Sorting Signals; D011973:Receptors, LDL / Q000378:metabolism; D011990:Receptors, Transferrin / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D020798:Two-Hybrid System Techniques; D014443:Tyrosine / Q000378:metabolism*
D033983:Adaptor Protein Complex mu Subunits; D046911:Macromolecular Substances; D021382:Protein Sorting Signals; D011973:Receptors, LDL; D011990:Receptors, Transferrin; D014443:Tyrosine