A basolateral sorting motif in the MICA cytoplasmic tail.
The MHC class I chain-related MICA molecule is a stress-induced, highly polymorphic, epithelia-specific, membrane-bound glycoprotein interacting with the activating NK cell receptor NKG2D and/or gut-enriched Vdelta1-bearing gammadelta T cells. We have previously reported the presence of a MICA transmembrane-encoded short-tandem repeat harboring a peculiar allele, A5.1, characterized by a frame shift mutation leading to a premature intradomain stop codon, thus denying the molecule of its 42-aa cytoplasmic tail. Given that this is the most common population-wide MICA allele found, we set out to analyze the functional consequences of cytoplasmic tail deletion. Here, we show native expression of MICA at the basolateral surface of human intestinal epithelium, the site of putative interaction with intraepithelial T and NK lymphocytes. We then demonstrate, in polarized epithelial cells, that although the full-length MICA protein is sorted to the basolateral membrane, the cytoplasmic tail-deleted construct as well as the naturally occurring A5.1 allele are aberrantly transported to the apical surface. Site-directed mutagenesis identified the cytoplasmic tail-encoded leucine-valine dihydrophobic tandem as the basolateral sorting signal. Hence, the physiological location of MICA within epithelial cells is governed by its cytoplasmic tail, implying impairment in A5.1 homozygous individuals, perhaps relevant to the immunological surveillance exerted by NK and T lymphocytes on epithelial malignancies.
Suemizu
Hiroshi
H
Department of Genetic Information, Tokai University School of Medicine, Bohseidai, Isehara 259-1193, Japan.
Radosavljevic
Mirjana
M
Kimura
Minoru
M
Sadahiro
Sotaro
S
Yoshimura
Shinichi
S
Bahram
Seiamak
S
Inoko
Hidetoshi
H
D000483:Alleles; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D003062:Codon; D003593:Cytoplasm / Q000378:metabolism; D004285:Dogs; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D015870:Gene Expression; D049452:Green Fluorescent Proteins; D015395:Histocompatibility Antigens Class I / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism; D007424:Intracellular Fluid / Q000378:metabolism; D007930:Leucine; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014633:Valine
D003062:Codon; D015395:Histocompatibility Antigens Class I; D008164:Luminescent Proteins; C099187:MHC class I-related chain A; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D007930:Leucine; D014633:Valine