beta1B integrin subunit contains a double lysine motif that can cause accumulation within the endoplasmic reticulum.
Human epidermal keratinocytes are one of the few cell types that express the beta1B splice variant of the beta1 integrin subunit. Although in transfection experiments beta1B acts as a dominant negative inhibitor of cell adhesion, we found that beta1B was expressed at very low levels in keratinocytes, both in vivo and in culture, and had a predominantly cytoplasmic distribution, concentrated within the endoplasmic reticulum. To examine why beta1B accumulated in the cytoplasm, we prepared chimeras between CD8alpha and the beta1A and beta1B integrin cytoplasmic domains. In transfected HeLa cells, both constructs reached the cell surface but the rate of maturation of the beta1B chimera was considerably retarded relative to beta1A. The beta1B cytoplasmic domain contains two lysine residues that resemble the double lysine motif characteristic of many proteins that are resident within the endoplasmic reticulum. Mutation of each lysine individually to serine had no effect on CD8beta1B maturation, but when both residues were mutated the rate of CD8beta1B maturation increased to that of CD8beta1A. Further analysis of beta1B function in keratinocytes must, therefore, take into account the low abundance of the isoform relative to beta1A and the potential for beta1B to accumulate in the endoplasmic reticulum.
Kee
W J
WJ
Keratinocyte Laboratory, Imperial Cancer Research Fund, London, WC2A 3PX, United Kingdom.
Li
E R
ER
Watt
F M
FM
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D014644:Genetic Variation; D006367:HeLa Cells; D006801:Humans; D007231:Infant, Newborn; D019012:Integrin beta1 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism*; D008239:Lysine; D046911:Macromolecular Substances; D008297:Male; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012867:Skin / Q000166:cytology / Q000378:metabolism
D019012:Integrin beta1; D046911:Macromolecular Substances; D020033:Protein Isoforms; D008239:Lysine