CD98-mediated links between amino acid transport and beta 1 integrin distribution in polarized columnar epithelia.
In non-polarized cells, CD98 has been shown to both influence beta(1) integrins and heterodimerize with LAT-2, which confers amino acid transport capability on the LAT-2/CD98 heterodimer. Since LAT-2 is most heavily expressed in intestine and CD98 associates with the beta(1) integrin splice form selectively found in such epithelia, we investigated the relationship and polarity of these proteins using the intestinal epithelial model Caco2-BBE. CD98 was found to selectively coimmunoprecipitate with both LAT-2 and beta(1) integrin, and, logically, all three proteins were polarized to the same (basolateral) domain. Furthermore, expression of CD98 in polarized epithelia lacking human CD98 (MDCK cells) disrupted beta(1) integrin surface distribution and cytoskeletal architecture, suggesting that CD98 can influence integrin function. Expression of a CD98 mutant lacking the specific residues conferring LAT-2 binding similarly affected cells, confirming that the latter effect was not due to LAT-2 sequestration. Use of CD98 truncation mutants suggest that a 10-amino acid domain located at the putative cytoplasmic tail/transmembrane domain interface was necessary and sufficient to induce the phenotype change. We conclude that the CD98/LAT-2 amino acid transporter is polarized to the same domain on which beta(1) integrin resides. CD98 appears to associate with beta(1) integrin and, in doing so, may influence its function as revealed by disruption of the outside-in signaling that confers cytoskeletal organization. Furthermore, such findings suggest a link between classic transport events and a critical element of barrier function: integrin-mediated influences on cytoskeletal organization.
Merlin
D
D
Epithelial Pathology Unit, Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA. dmerlin@emory.edu
Sitaraman
S
S
Liu
X
X
Eastburn
K
K
Sun
J
J
Kucharzik
T
T
Lewis
B
B
Madara
J L
JL
D027182:Amino Acid Transport System y+; D000818:Animals; D001692:Biological Transport; D019921:Biotinylation; D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D005434:Flow Cytometry; D027301:Fusion Regulatory Protein 1, Light Chains / Q000737:chemistry / Q000378:metabolism; D027261:Fusion Regulatory Protein-1 / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D019012:Integrin beta1 / Q000378:metabolism*; D016023:Integrins / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009154:Mutation; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D014162:Transfection
D027182:Amino Acid Transport System y+; D027301:Fusion Regulatory Protein 1, Light Chains; D027261:Fusion Regulatory Protein-1; D019012:Integrin beta1; D016023:Integrins; D012333:RNA, Messenger; C420646:SLC7A8 protein, human