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Qualitative regulation of B cell antigen receptor signaling by CD19: selective requirement for PI3-kinase activation, inositol-1,4,5-trisphosphate production and Ca2+ mobilization.

Buhl AM, Pleiman CM, Rickert RC, Cambier JC - J. Exp. Med. (1997)

Bottom Line: PI3-Kinase activation is dependent on phosphorylation of CD19 Y484 and Y515.Antigen-induced CD19-dependent PI3-kinase activation is required for normal phosphoinositide hydrolysis and Ca2+ mobilization responses.Thus, CD19 functions as a B cell antigen receptor accessory molecule that modifies antigen receptor signaling in a qualitative manner.

View Article: PubMed Central - PubMed

Affiliation: Division of Basic Sciences, Department of Pediatrics, National Jewish Medical and Research Center, 1400 Jackson Street, Denver, Colorado 80206, USA.

ABSTRACT
Genetic ablation of the B cell surface glycoprotein CD19 severely impairs the humoral immune response. This requirement is thought to reflect a critical role of CD19 in signal transduction that occurs upon antigen C3dg coligation of antigen receptors with CD19 containing type 2 complement receptors (CR2). Here we show that CD19 plays a key accessory role in B cell antigen receptor signaling independent of CR2 coligation and define molecular circuitry by which this function is mediated. While CD19 is not required for antigen-mediated activation of receptor proximal tyrosines kinases, it is critical for activation of phosphatidylinositol 3-kinase (PI3-kinase). PI3-Kinase activation is dependent on phosphorylation of CD19 Y484 and Y515. Antigen-induced CD19-dependent PI3-kinase activation is required for normal phosphoinositide hydrolysis and Ca2+ mobilization responses. Thus, CD19 functions as a B cell antigen receptor accessory molecule that modifies antigen receptor signaling in a qualitative manner.

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Expression levels of  surface markers on the plasmacytoma cell lines. Flow cytometric  analysis was performed on the  J558Lμm3CD45+ (dotted lines),  J558Lμm3CD45+CD19+ (thick  lines), and J558L μm3CD45+  CD19+ (Y484F,Y515F) (thin lines)  cell lines. Shown is staining with  secondary alone (A), biotinylated  b-7-6 anti-IgM (B), biotinylated  I32.5 anti-CD45 (C), or biotinylated HD37 anti-hCD19 (D) followed by PE-conjugated streptavidin.
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Figure 1: Expression levels of surface markers on the plasmacytoma cell lines. Flow cytometric analysis was performed on the J558Lμm3CD45+ (dotted lines), J558Lμm3CD45+CD19+ (thick lines), and J558L μm3CD45+ CD19+ (Y484F,Y515F) (thin lines) cell lines. Shown is staining with secondary alone (A), biotinylated b-7-6 anti-IgM (B), biotinylated I32.5 anti-CD45 (C), or biotinylated HD37 anti-hCD19 (D) followed by PE-conjugated streptavidin.

Mentions: Although tyrosine phosphorylation of CD19 after BCR ligation is well documented, the contribution of CD19 to BCR signaling is not defined. To study the role of CD19 in antigen-induced signal transduction we generated a wild-type CD19-positive and Y484/Y515 to F CD19-positive variant of the J558Lμm3CD45+ plasmacytoma. The parent clone expresses a NP-specific BCR and CD45, but does not express CD19 (28, 32). Human CD19 (hCD19) was introduced into this clone by retroviral infection, and lines (polyclonal populations) were isolated by G418 selection and fluorescence activated cell sorting of cells. Flow cytometric analysis revealed similar expression levels of sIgM, CD45 and CD19 in the plasmacytoma cell lines (Fig. 1). Human CD19 was utilized since antibodies to mouse CD19 were not available at the time the studies were undertaken, and human and mouse CD19 are highly homologous (79% in nucleotide sequence, 75% in amino acid sequence) particularly in the cytoplasmic domain (3, 33). Recent studies indicate that human CD19 complements B cell function in CD19−/− mice (34). In addition, using a recently generated rat mAb, 1D3, specific for murine CD19 (35), Krop et al. (22) have demonstrated that murine CD19 shares with human CD19 an association with complement receptor CD21 and CD81, tyrosine phosphorylation, binding of PI3-kinase, and synergistic signaling with membrane IgM.


Qualitative regulation of B cell antigen receptor signaling by CD19: selective requirement for PI3-kinase activation, inositol-1,4,5-trisphosphate production and Ca2+ mobilization.

Buhl AM, Pleiman CM, Rickert RC, Cambier JC - J. Exp. Med. (1997)

Expression levels of  surface markers on the plasmacytoma cell lines. Flow cytometric  analysis was performed on the  J558Lμm3CD45+ (dotted lines),  J558Lμm3CD45+CD19+ (thick  lines), and J558L μm3CD45+  CD19+ (Y484F,Y515F) (thin lines)  cell lines. Shown is staining with  secondary alone (A), biotinylated  b-7-6 anti-IgM (B), biotinylated  I32.5 anti-CD45 (C), or biotinylated HD37 anti-hCD19 (D) followed by PE-conjugated streptavidin.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199152&req=5

Figure 1: Expression levels of surface markers on the plasmacytoma cell lines. Flow cytometric analysis was performed on the J558Lμm3CD45+ (dotted lines), J558Lμm3CD45+CD19+ (thick lines), and J558L μm3CD45+ CD19+ (Y484F,Y515F) (thin lines) cell lines. Shown is staining with secondary alone (A), biotinylated b-7-6 anti-IgM (B), biotinylated I32.5 anti-CD45 (C), or biotinylated HD37 anti-hCD19 (D) followed by PE-conjugated streptavidin.
Mentions: Although tyrosine phosphorylation of CD19 after BCR ligation is well documented, the contribution of CD19 to BCR signaling is not defined. To study the role of CD19 in antigen-induced signal transduction we generated a wild-type CD19-positive and Y484/Y515 to F CD19-positive variant of the J558Lμm3CD45+ plasmacytoma. The parent clone expresses a NP-specific BCR and CD45, but does not express CD19 (28, 32). Human CD19 (hCD19) was introduced into this clone by retroviral infection, and lines (polyclonal populations) were isolated by G418 selection and fluorescence activated cell sorting of cells. Flow cytometric analysis revealed similar expression levels of sIgM, CD45 and CD19 in the plasmacytoma cell lines (Fig. 1). Human CD19 was utilized since antibodies to mouse CD19 were not available at the time the studies were undertaken, and human and mouse CD19 are highly homologous (79% in nucleotide sequence, 75% in amino acid sequence) particularly in the cytoplasmic domain (3, 33). Recent studies indicate that human CD19 complements B cell function in CD19−/− mice (34). In addition, using a recently generated rat mAb, 1D3, specific for murine CD19 (35), Krop et al. (22) have demonstrated that murine CD19 shares with human CD19 an association with complement receptor CD21 and CD81, tyrosine phosphorylation, binding of PI3-kinase, and synergistic signaling with membrane IgM.

Bottom Line: PI3-Kinase activation is dependent on phosphorylation of CD19 Y484 and Y515.Antigen-induced CD19-dependent PI3-kinase activation is required for normal phosphoinositide hydrolysis and Ca2+ mobilization responses.Thus, CD19 functions as a B cell antigen receptor accessory molecule that modifies antigen receptor signaling in a qualitative manner.

View Article: PubMed Central - PubMed

Affiliation: Division of Basic Sciences, Department of Pediatrics, National Jewish Medical and Research Center, 1400 Jackson Street, Denver, Colorado 80206, USA.

ABSTRACT
Genetic ablation of the B cell surface glycoprotein CD19 severely impairs the humoral immune response. This requirement is thought to reflect a critical role of CD19 in signal transduction that occurs upon antigen C3dg coligation of antigen receptors with CD19 containing type 2 complement receptors (CR2). Here we show that CD19 plays a key accessory role in B cell antigen receptor signaling independent of CR2 coligation and define molecular circuitry by which this function is mediated. While CD19 is not required for antigen-mediated activation of receptor proximal tyrosines kinases, it is critical for activation of phosphatidylinositol 3-kinase (PI3-kinase). PI3-Kinase activation is dependent on phosphorylation of CD19 Y484 and Y515. Antigen-induced CD19-dependent PI3-kinase activation is required for normal phosphoinositide hydrolysis and Ca2+ mobilization responses. Thus, CD19 functions as a B cell antigen receptor accessory molecule that modifies antigen receptor signaling in a qualitative manner.

Show MeSH
Related in: MedlinePlus