Abstract
CD81 is a widely expressed tetraspanin that associates in B cells with CD19 in the CD19-CD21-CD81 signaling complex. CD81 is necessary for normal CD19 expression; cd81(-/-) B cells express lower levels of CD19, especially cd81(-/-) small pre-BII cells, which are almost devoid of surface CD19. The dependence of CD19 expression on CD81 is specific to this particular tetraspanin since cd9(-/-) B cells express normal levels of CD19. Furthermore, expression of human CD81 in mouse cd81(-/-) B cells restored surface CD19 to normal levels. Quantitative analysis of CD19 mRNA demonstrated normal levels, even in cd81(-/-) pre-BII cells. Analysis of CD19 at the protein level identified two CD19 glycoforms in both wild-type and cd81(-/-) B cells. The higher M(r) glycoform is significantly reduced in cd81(-/-) B cells and is endoglycosidase H (endo-H) resistant. In contrast, the low M(r) glycoform is comparably expressed in cd81(-/-) and in wild-type B cells and is endo-H sensitive. Because endo-H sensitivity is tightly correlated with endoplasmic reticulum localization, we suggest that the dependency of CD19 expression on CD81 occurs in a postendoplasmic reticulum compartment where CD81 is necessary for normal trafficking or for surface membrane stability of CD19.
Publication types
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Comparative Study
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Animals
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Antigens, CD / biosynthesis
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Antigens, CD / genetics
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Antigens, CD / physiology*
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Antigens, CD19 / analysis
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Antigens, CD19 / biosynthesis*
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Antigens, CD19 / metabolism
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B-Lymphocyte Subsets / chemistry
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B-Lymphocyte Subsets / cytology*
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B-Lymphocyte Subsets / immunology*
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B-Lymphocyte Subsets / metabolism
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Bone Marrow Cells / chemistry
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Bone Marrow Cells / cytology
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Bone Marrow Cells / immunology
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Bone Marrow Cells / metabolism
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Cell Differentiation / genetics
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Cell Differentiation / immunology
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Cell Line
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Cell Membrane / immunology
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Cell Membrane / metabolism
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Cells, Cultured
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Endoplasmic Reticulum / chemistry
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Endoplasmic Reticulum / immunology*
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Endoplasmic Reticulum / metabolism*
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Female
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Hematopoietic Stem Cells / chemistry
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Hematopoietic Stem Cells / cytology
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Hematopoietic Stem Cells / immunology
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Hematopoietic Stem Cells / metabolism
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Hexosaminidases
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Humans
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Male
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Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase
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Membrane Glycoproteins / physiology
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Membrane Proteins / biosynthesis
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Membrane Proteins / deficiency
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Membrane Proteins / genetics
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Membrane Proteins / physiology*
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Mice
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Mice, Inbred BALB C
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Mice, Inbred C3H
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Mice, Inbred C57BL
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Mice, Knockout
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Protein Isoforms / analysis
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Protein Isoforms / biosynthesis
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Protein Isoforms / metabolism
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RNA, Messenger / biosynthesis
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Tetraspanin 28
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Tetraspanin 29
Substances
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Antigens, CD
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Antigens, CD19
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CD81 protein, human
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CD9 protein, human
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Cd81 protein, mouse
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Cd9 protein, mouse
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Membrane Glycoproteins
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Membrane Proteins
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Protein Isoforms
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RNA, Messenger
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Tetraspanin 28
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Tetraspanin 29
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Hexosaminidases
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Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase