|Coordinate||41,376,146 bp (GRCm38)|
|Base Change||A ⇒ G (forward strand)|
|Gene Name||phosphoinositide-3-kinase adaptor protein 1|
|Chromosomal Location||41,274,218-41,385,070 bp (-)|
|MGI Phenotype||PHENOTYPE: Mice homozygous for disruptions in this gene have abnormalities in B cell maturation. [provided by MGI curators]|
|Amino Acid Change||Tyrosine changed to Histidine|
|Institutional Source||Beutler Lab|
|Gene Model||predicted gene model for protein(s): [ENSMUSP00000052777]|
AA Change: Y45H
|Predicted Effect||probably benign
PolyPhen 2 Score 0.003 (Sensitivity: 0.98; Specificity: 0.44)
|Meta Mutation Damage Score||0.0898|
|Is this an essential gene?||Non Essential (E-score: 0.000)|
|Candidate Explorer Status||CE: excellent candidate; human score: 0; ML prob: 0.446|
Linkage Analysis Data
|Alleles Listed at MGI|
|Mode of Inheritance||Unknown|
|Last Updated||2019-09-04 9:32 PM by Anne Murray|
|Record Created||2019-01-10 7:19 PM by Bruce Beutler|
The Pintail phenotype was identified among G3 mice of the pedigree R6515, some of which showed reduced frequencies of B1 cells in the peripheral blood (Figure 1).
|Nature of Mutation|
Whole exome HiSeq sequencing of the G1 grandsire identified 44 mutations. The diminished B1 cell frequency phenotype was linked to a mutation in Pik3ap1: a T to C transition at base pair 41,376,146 (v38) on chromosome 19, or base pair 8,925 in the GenBank genomic region NC_000085 encoding Pik3ap1. Linkage was found with a dominant model of inheritance, wherein eight variant homozygotes and 36 heterozygous mice departed phenotypically from 35 homozygous reference mice with a P value of 4.565 x 10-12 (Figure 2).
The mutation corresponds to residue 303 in the NM_031376 mRNA sequence in exon 2 of 17 total exons.
The mutated nucleotide is indicated in red. The mutation results in a tyrosine to histidine substitution at position 45 (Y45H) in the B cell adaptor protein (BCAP) protein, and is strongly predicted by PolyPhen-2 to be benign (score = 0.003).
BCAP shares several structural features with other adaptor proteins including BANK (B-cell scaffold protein with ankyrin repeats), an adaptor for CD40, a protein present on antigen presenting cells (see walla, a mutation in CD40 ligand) and with the Drosophila protein Dof (Downstream of FGF receptor), an adaptor that is essential in FGF-mediated signaling (1;2). The domains of BCAP include: an ankyrin repeat-like sequence (aa 333-401), a predicted coiled-coil forming sequence (aa 636-669), proline-rich sequences (3 in mouse; aa 530-552, 760-808) and a region designated the Dof/BCAP/BANK (DBB) domain (aa 182-318) (3-6) (Figure 3). The proline-rich region at the C-terminus of BCAP facilitates interaction between BCAP and the N-terminal SH3 domains of Src protein tyrosine kinases (PTKs), PLC-γ, and Grb2 (7). Tyrosine motifs (YxNx, YxxV, and YxxM) facilitate the binding of BCAP to Grb2, SHP-2 and BTK/Syk, respectively. Following B cell activation, BCAP is phosphorylated at four tyrosine residues (Y264, Y420, Y445 and Y460) within 4 respective YxxM motifs by BTK and Syk activation (3;8;9).
The Pintail mutation results in a tyrosine to histidine substitution at position 45 (Y45H) in the BCAP protein; Tyr45 is within an undefined region of BCAP.
For more information about Pik3ap1, please see the record for sothe.
In B cell receptor (BCR)-mediated signaling, either transmembrane (i.e. CD19) or cytosolic adaptors (i.e. TC21, Cbl, Gab, B-cell linker (BLNK (see busy) or SLP-65), and BCAP are tyrosine phosphorylated on their YxxM motifs by protein tyrosine kinases (i.e. Btk, Syk and/or Lyn) and subsequently associate with PI3K to amplify and integrate several signaling pathways (6;7;10-13). Upon activation of BCR-mediated signaling, Syk initiates BCAP phosphorylation, while Btk sustains it. Lyn negatively regulates BCAP phosphorylation by initiating the phosphorylation of immunoreceptor tyrosine-based inhibition motifs (ITIMS) on inhibitory receptor proteins CD22 and PIRB (7;14). BCAP and CD19 have a complementary role in P13K activation: upon BCAP binding to PI3K, there is an upregulation in PI3K activity and PI3K translocates to CD19-bearing lipid rafts rich in PI(4,5)P2 (15;16). Upon an induction of BCR-mediated signaling, there is a concomitant stimulation of growth arrest and apoptosis in immature B cells with a promotion of survival and proliferation of mature B cells (13). Phosphorylated PI3K-associated adaptor proteins, including BCAP, recruit enzymes such as phospholipase C-gamma 2 (PLC-γ2) (see queen) and PI3K to facilitate B-cell proliferation, differentiation and activation via the PI3K pathway (6;7;12;17). It has been proposed that BCAP can mediate PI3K activation in two ways: (i) PI3K-BCAP binding upregulates PI3K enzymatic activity, or (ii) BCAP is associated with a CD19-mediated translocation of PI3K (9). This study also suggested that there is another unidentified molecule that can assist in the translocation of PI3K upon BCR activation (9). BCAP deficient mature splenic B cells undergo activation-induced apoptosis more readily than cells that express BCAP (5;9;10;13). After B cell receptor engagement in the BCAP deficient B cells, expression of cell survival molecules (i.e. Bcl-xL) was not induced (5). Furthermore, maturation and/or survival of a B cell subset (peritoneal B1) was not promoted; marginal zone (MZ) B cell numbers were similar to wild-type (6).
The phenotype observed in the Pintail mice indicates loss of BCAP-associated function in B cell survival.
1) 94°C 2:00
The following sequence of 402 nucleotides is amplified (chromosome 19, - strand):
1 tttcagagag cctcctagaa ggagcaggca ttaatgagct tttttttttc tgtgtctctc
Primer binding sites are underlined and the sequencing primers are highlighted; the mutated nucleotide is shown in red.
1. Aiba, Y., Yamazaki, T., Okada, T., Gotoh, K., Sanjo, H., Ogata, M., and Kurosaki, T. (2006) BANK Negatively Regulates Akt Activation and Subsequent B Cell Responses. Immunity. 24, 259-268.
2. Yokoyama, K., Su Ih, I. H., Tezuka, T., Yasuda, T., Mikoshiba, K., Tarakhovsky, A., and Yamamoto, T. (2002) BANK Regulates BCR-Induced Calcium Mobilization by Promoting Tyrosine Phosphorylation of IP(3) Receptor. EMBO J. 21, 83-92.
3. Battersby, A., Csiszar, A., Leptin, M., and Wilson, R. (2003) Isolation of Proteins that Interact with the Signal Transduction Molecule Dof and Identification of a Functional Domain Conserved between Dof and Vertebrate BCAP. J Mol Biol. 329, 479-493.
4. Wilson, R., Battersby, A., Csiszar, A., Vogelsang, E., and Leptin, M. (2004) A Functional Domain of Dof that is Required for Fibroblast Growth Factor Signaling. Mol Cell Biol. 24, 2263-2276.
5. Yamazaki, T., and Kurosaki, T. (2003) Contribution of BCAP to Maintenance of Mature B Cells through c-Rel. Nat Immunol. 4, 780-786.
6. Yamazaki, T., Takeda, K., Gotoh, K., Takeshima, H., Akira, S., and Kurosaki, T. (2002) Essential Immunoregulatory Role for BCAP in B Cell Development and Function. J Exp Med. 195, 535-545.
7. Okada, T., Maeda, A., Iwamatsu, A., Gotoh, K., and Kurosaki, T. (2000) BCAP: The Tyrosine Kinase Substrate that Connects B Cell Receptor to Phosphoinositide 3-Kinase Activation. Immunity. 13, 817-827.
8. Matsumura, T., Oyama, M., Kozuka-Hata, H., Ishikawa, K., Inoue, T., Muta, T., Semba, K., and Inoue, J. (2010) Identification of BCAP-(L) as a Negative Regulator of the TLR Signaling-Induced Production of IL-6 and IL-10 in Macrophages by Tyrosine Phosphoproteomics. Biochem Biophys Res Commun. 400, 265-270.
9. Inabe, K., and Kurosaki, T. (2002) Tyrosine Phosphorylation of B-Cell Adaptor for Phosphoinositide 3-Kinase is Required for Akt Activation in Response to CD19 Engagement. Blood. 99, 584-589.
10. MacFarlane, A. W.,4th, Yamazaki, T., Fang, M., Sigal, L. J., Kurosaki, T., and Campbell, K. S. (2008) Enhanced NK-Cell Development and Function in BCAP-Deficient Mice. Blood. 112, 131-140.
11. Baracho, G. V., Miletic, A. V., Omori, S. A., Cato, M. H., and Rickert, R. C. (2011) Emergence of the PI3-Kinase Pathway as a Central Modulator of Normal and Aberrant B Cell Differentiation. Curr Opin Immunol. 23, 178-183.
12. Qin, S., and Chock, P. B. (2003) Implication of Phosphatidylinositol 3-Kinase Membrane Recruitment in Hydrogen Peroxide-Induced Activation of PI3K and Akt. Biochemistry. 42, 2995-3003.
13. Gupta, N., Delrow, J., Drawid, A., Sengupta, A. M., Fan, G., and Gelinas, C. (2008) Repression of B-Cell Linker (BLNK) and B-Cell Adaptor for Phosphoinositide 3-Kinase (BCAP) is Important for Lymphocyte Transformation by Rel Proteins. Cancer Res. 68, 808-814.
14. Kurosaki, T., and Kurosaki, M. (1997) Transphosphorylation of Bruton's Tyrosine Kinase on Tyrosine 551 is Critical for B Cell Antigen Receptor Function. J Biol Chem. 272, 15595-15598.
15. Aiba, Y., Kameyama, M., Yamazaki, T., Tedder, T. F., and Kurosaki, T. (2008) Regulation of B-Cell Development by BCAP and CD19 through their Binding to Phosphoinositide 3-Kinase. Blood. 111, 1497-1503.
16. Uinuk-Ool, T., Mayer, W. E., Sato, A., Dongak, R., Cooper, M. D., and Klein, J. (2002) Lamprey Lymphocyte-Like Cells Express Homologs of Genes Involved in Immunologically Relevant Activities of Mammalian Lymphocytes. Proc Natl Acad Sci U S A. 99, 14356-14361.
|Science Writers||Anne Murray|
|Illustrators||Diantha La Vine|
|Authors||Jin Huk Choi, Xue Zhong, and Bruce Beutler|