B-cell linker

B-cell linker
Identifiers
Symbols	BLNK ; AGM4; BASH; BLNK-S; LY57; SLP-65; SLP65; bca
External IDs	OMIM: 604515 MGI: 96878 HomoloGene: 32038 GeneCards: BLNK Gene
Gene ontology Molecular function • transmembrane receptor protein tyrosine kinase adaptor activity • SH3/SH2 adaptor activity • protein binding Cellular component • intracellular • cytoplasm • cytosol • plasma membrane Biological process • inflammatory response • humoral immune response • transmembrane receptor protein tyrosine kinase signaling pathway • positive regulation of signal transduction • B cell differentiation • intracellular signal transduction Sources: Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	29760	17060
Ensembl	ENSG00000095585	ENSMUSG00000061132
UniProt	Q8WV28	Q9QUN3
RefSeq (mRNA)	NM_001114094	NM_008528
RefSeq (protein)	NP_001107566	NP_032554
Location (UCSC)	Chr 10: 96.19 – 96.27 Mb	Chr 19: 40.93 – 40.99 Mb
PubMed search

The B-cell linker protein is encoded by the BLNK gene^[1][2] and is an adaptor protein also known as SLP-65,^[3] BASH,^[4] and BCA.^[5] BLNK is expressed in B cells and macrophages and plays a large role in B cell receptor signalling, in a fashion analogous to the role its paralogue SLP-76 plays in T cell receptor signalling.^[6] As it has no known intrinsic enzymatic activity, the function of BLNK is to temporally and spatially coordinate and regulate signalling effectors downstream of the B cell receptor.

Function

The function of BLNK was first illustrated in BLNK deficient DT40 cells, a chicken B-cell line, which exhibited an abrogated intracellular calcium mobilisation response and impaired activation of MAP kinases p38, JNK, and to a lesser degree ERK upon B-cell receptor (BCR) activation as compared to wild type DT40 cells.^[7] In knockout mice, BLNK deficiency results in a partial block in B-cell development,^[8][9] and in humans BLNK deficiency results in a much more profound block in B-cell development.^[10]

Linker or adaptor proteins provide mechanisms by which receptors can amplify and regulate downstream effector proteins. The B-cell linker protein is essential for normal B-cell development.[supplied by OMIM]^[2]

Structure

BLNK consists of a N-terminal leucine zipper motif followed by an "acidic" region, a proline-rich region, and a C-terminal SH2 domain. The leucine zipper motif allows BLNK to localise to the plasma membrane, presumably by coiled-coil interactions with a membrane protein.^[11] This leucine zipper motif distinguishes BLNK from its paralogue SLP-76 which, although having an N-terminal heptad-like organisation of leucine and isoleucine residues, has not been experimentally shown to have this motif. Recruitment of BLNK to the plasma membrane is also achieved by binding of the SH2 domain of BLNK to a non-ITAM phospho-tyrosine on Igα, a part of the B cell receptor complex.^[12][13][14]

The acidic region of BLNK contains several inducibly phosphorylated tyrosine residues, at least five in humans, that mediate protein-protein interactions between BLNK and PLCγ2, Btk, Vav, and Nck.^[15] A more recent mass spectrometry study of BLNK in DT40 cells found that at least 41 unique serine, threonine, and tyrosine residues are phosphorylated on BLNK.^[16]

Interactions

B-cell linker has been shown to interact with Grb2,^{[1][3][12][17]} SH3KBP1,<ref name=pmid"11071869">Watanabe, S.; Take, H.; Takeda, K.; Yu, Z. X.; Iwata, N.; Kajigaya, S. (2000). "Characterization of the CIN85 Adaptor Protein and Identification of Components Involved in CIN85 Complexes". Biochemical and Biophysical Research Communications 278 (1): 167–174. doi:10.1006/bbrc.2000.3760. PMID 11071869.</ref> CD79A,^[12][13] MAP4K1^[18] and Bruton's tyrosine kinase.^[19][20]

References

1. Fu, C.; Turck, C. W.; Kurosaki, T.; Chan, A. C. (1998). "BLNK: A central linker protein in B cell activation". Immunity 9 (1): 93–103. doi:10.1016/S1074-7613(00)80591-9. PMID 9697839.
2. "Entrez Gene: BLNK B-cell linker".
3. Wienands, J.; Schweikert, J.; Wollscheid, B.; Jumaa, H.; Nielsen, P. J.; Reth, M. (1998). "SLP-65: A new signaling component in B lymphocytes which requires expression of the antigen receptor for phosphorylation". The Journal of Experimental Medicine 188 (4): 791–795. doi:10.1084/jem.188.4.791. PMC 2213353. PMID 9705962.
4. Goitsuka, R.; Fujimura, Y.; Mamada, H.; Umeda, A.; Morimura, T.; Uetsuka, K.; Doi, K.; Tsuji, S.; Kitamura, D. (1998). "BASH, a novel signaling molecule preferentially expressed in B cells of the bursa of Fabricius". Journal of immunology (Baltimore, Md. : 1950) 161 (11): 5804–5808. PMID 9834055.
5. Gangi-Peterson, L.; Peterson, S. N.; Shapiro, L. H.; Golding, A.; Caricchio, R.; Cohen, D. I.; Margulies, D. H.; Cohen, P. L. (1998). "Bca: An activation-related B-cell gene". Molecular immunology 35 (1): 55–63. doi:10.1016/s0161-5890(98)00008-x. PMID 9683264.
6. Koretzky, G. A.; Abtahian, F.; Silverman, M. A. (2006). "SLP76 and SLP65: Complex regulation of signalling in lymphocytes and beyond". Nature Reviews Immunology 6 (1): 67–78. doi:10.1038/nri1750. PMID 16493428.
7. Ishiai, M.; Kurosaki, M.; Pappu, R.; Okawa, K.; Ronko, I.; Fu, C.; Shibata, M.; Iwamatsu, A.; Chan, A. C.; Kurosaki, T. (1999). "BLNK required for coupling Syk to PLC gamma 2 and Rac1-JNK in B cells". Immunity 10 (1): 117–125. doi:10.1016/S1074-7613(00)80012-6. PMID 10023776.
8. Jumaa, H.; Wollscheid, B.; Mitterer, M.; Wienands, J.; Reth, M.; Nielsen, P. J. (1999). "Abnormal development and function of B lymphocytes in mice deficient for the signaling adaptor protein SLP-65". Immunity 11 (5): 547–554. doi:10.1016/S1074-7613(00)80130-2. PMID 10591180.
9. Pappu, R.; Cheng, A. M.; Li, B.; Gong, Q.; Chiu, C.; Griffin, N.; White, M.; Sleckman, B. P.; Chan, A. C. (1999). "Requirement for B cell linker protein (BLNK) in B cell development". Science 286 (5446): 1949–1954. doi:10.1126/science.286.5446.1949. PMID 10583957.
10. Minegishi, Y.; Rohrer, J.; Coustan-Smith, E.; Lederman, H. M.; Pappu, R.; Campana, D.; Chan, A. C.; Conley, M. E. (1999). "An essential role for BLNK in human B cell development". Science 286 (5446): 1954–1957. doi:10.1126/science.286.5446.1954. PMID 10583958.
11. Köhler, F.; Storch, B.; Kulathu, Y.; Herzog, S.; Kuppig, S.; Reth, M.; Jumaa, H. (2005). "A leucine zipper in the N terminus confers membrane association to SLP-65". Nature Immunology 6 (2): 204–210. doi:10.1038/ni1163. PMID 15654340.
12. Engels, N.; Wollscheid, B.; Wienands, J. R. (2001). "Association of SLP-65 / BLNK with the B cell antigen receptor through a non-ITAM tyrosine of Ig-α". European Journal of Immunology 31 (7): 2126–2134. doi:10.1002/1521-4141(200107)31:7<2126::AID-IMMU2126>3.0.CO;2-O. PMID 11449366.
13. Kabak, S.; Skaggs, B. J.; Gold, M. R.; Affolter, M.; West, K. L.; Foster, M. S.; Siemasko, K.; Chan, A. C.; Aebersold, R.; Clark, M. R. (2002). "The Direct Recruitment of BLNK to Immunoglobulin α Couples the B-Cell Antigen Receptor to Distal Signaling Pathways". Molecular and Cellular Biology 22 (8): 2524–2535. doi:10.1128/MCB.22.8.2524-2535.2002. PMC 133735. PMID 11909947.
14. Pike, K. A.; Ratcliffe, M. J. (2005). "Dual requirement for the Ig alpha immunoreceptor tyrosine-based activation motif (ITAM) and a conserved non-Ig alpha ITAM tyrosine in supporting Ig alpha beta-mediated B cell development". Journal of immunology (Baltimore, Md. : 1950) 174 (4): 2012–2020. doi:10.4049/jimmunol.174.4.2012. PMID 15699130.
15. Chiu, C. W.; Dalton, M.; Ishiai, M.; Kurosaki, T.; Chan, A. C. (2002). "BLNK: Molecular scaffolding through 'cis'-mediated organization of signaling proteins". The EMBO Journal 21 (23): 6461–6472. doi:10.1093/emboj/cdf658. PMC 136961. PMID 12456653.
16. Oellerich, T.; Gronborg, M.; Neumann, K.; Hsiao, H. -H.; Urlaub, H.; Wienands, J. (2009). "SLP-65 Phosphorylation Dynamics Reveals a Functional Basis for Signal Integration by Receptor-proximal Adaptor Proteins". Molecular & Cellular Proteomics 8 (7): 1738–1750. doi:10.1074/mcp.M800567-MCP200. PMC 2709198. PMID 19372136.
17. Fusaki, N.; Tomita, S.; Wu, Y.; Okamoto, N.; Goitsuka, R.; Kitamura, D.; Hozumi, N. (2000). "BLNK is associated with the CD72 / SHP-1 / Grb2 complex in the WEHI231 cell line after membrane IgM cross-linking". European Journal of Immunology 30 (5): 1326–1330. doi:10.1002/(SICI)1521-4141(200005)30:5<1326::AID-IMMU1326>3.0.CO;2-Q. PMID 10820378.
18. Tsuji, S.; Okamoto, M.; Yamada, K.; Okamoto, N.; Goitsuka, R.; Arnold, R.; Kiefer, F.; Kitamura, D. (2001). "B Cell Adaptor Containing Src Homology 2 Domain (Bash) Links B Cell Receptor Signaling to the Activation of Hematopoietic Progenitor Kinase 1". The Journal of Experimental Medicine 194 (4): 529–539. doi:10.1084/jem.194.4.529. PMC 2193495. PMID 11514608.
19. Yasuda, T.; Tezuka, T.; Maeda, A.; Inazu, T.; Yamanashi, Y.; Gu, H.; Kurosaki, T.; Yamamoto, T. (2002). "Cbl-b Positively Regulates Btk-mediated Activation of Phospholipase C-γ2 in B Cells". The Journal of Experimental Medicine 196 (1): 51–63. doi:10.1084/jem.20020068. PMC 2194016. PMID 12093870.
20. Hashimoto, S.; Iwamatsu, A.; Ishiai, M.; Okawa, K.; Yamadori, T.; Matsushita, M.; Baba, Y.; Kishimoto, T.; Kurosaki, T.; Tsukada, S. (1999). "Identification of the SH2 domain binding protein of Bruton's tyrosine kinase as BLNK--functional significance of Btk-SH2 domain in B-cell antigen receptor-coupled calcium signaling". Blood 94 (7): 2357–2364. PMID 10498607.

Further reading

• Maruyama K, Sugano S (1994). "Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides". Gene 138 (1–2): 171–4. doi:10.1016/0378-1119(94)90802-8. PMID 8125298.
• Fu C, Chan AC (1997). "Identification of two tyrosine phosphoproteins, pp70 and pp68, which interact with phospholipase Cgamma, Grb2, and Vav after B cell antigen receptor activation". J. Biol. Chem. 272 (43): 27362–8. doi:10.1074/jbc.272.43.27362. PMID 9341187.
• Suzuki Y, Yoshitomo-Nakagawa K, Maruyama K, et al. (1997). "Construction and characterization of a full length-enriched and a 5'-end-enriched cDNA library". Gene 200 (1–2): 149–56. doi:10.1016/S0378-1119(97)00411-3. PMID 9373149.
• Wienands J, Schweikert J, Wollscheid B, et al. (1998). "SLP-65: a new signaling component in B lymphocytes that requires expression of the antigen receptor for phosphorylation". J. Exp. Med. 188 (4): 791–5. doi:10.1084/jem.188.4.791. PMC 2213353. PMID 9705962.
• Hashimoto S, Iwamatsu A, Ishiai M, et al. (1999). "Identification of the SH2 domain binding protein of Bruton's tyrosine kinase as BLNK--functional significance of Btk-SH2 domain in B-cell antigen receptor-coupled calcium signaling". Blood 94 (7): 2357–64. PMID 10498607.
• Su YW, Zhang Y, Schweikert J, et al. (1999). "Interaction of SLP adaptors with the SH2 domain of Tec family kinases". Eur. J. Immunol. 29 (11): 3702–11. doi:10.1002/(SICI)1521-4141(199911)29:11<3702::AID-IMMU3702>3.0.CO;2-R. PMID 10556826.
• Fusaki N, Tomita S, Wu Y, et al. (2000). "BLNK is associated with the CD72/SHP-1/Grb2 complex in the WEHI231 cell line after membrane IgM cross-linking". Eur. J. Immunol. 30 (5): 1326–30. doi:10.1002/(SICI)1521-4141(200005)30:5<1326::AID-IMMU1326>3.0.CO;2-Q. PMID 10820378.
• Mizuno K, Tagawa Y, Mitomo K, et al. (2000). "Src homology region 2 (SH2) domain-containing phosphatase-1 dephosphorylates B cell linker protein/SH2 domain leukocyte protein of 65 kDa and selectively regulates c-Jun NH2-terminal kinase activation in B cells". J. Immunol. 165 (3): 1344–51. doi:10.4049/jimmunol.165.3.1344. PMID 10903736.
• Guo B, Kato RM, Garcia-Lloret M, et al. (2000). "Engagement of the human pre-B cell receptor generates a lipid raft-dependent calcium signaling complex". Immunity 13 (2): 243–53. doi:10.1016/S1074-7613(00)00024-8. PMID 10981967.
• Watanabe S, Take H, Takeda K, et al. (2001). "Characterization of the CIN85 adaptor protein and identification of components involved in CIN85 complexes". Biochem. Biophys. Res. Commun. 278 (1): 167–74. doi:10.1006/bbrc.2000.3760. PMID 11071869.
• Tan JE, Wong SC, Gan SK, et al. (2001). "The adaptor protein BLNK is required for b cell antigen receptor-induced activation of nuclear factor-kappa B and cell cycle entry and survival of B lymphocytes". J. Biol. Chem. 276 (23): 20055–63. doi:10.1074/jbc.M010800200. PMID 11274146.
• Adachi T, Wienands J, Wakabayashi C, et al. (2001). "SHP-1 requires inhibitory co-receptors to down-modulate B cell antigen receptor-mediated phosphorylation of cellular substrates". J. Biol. Chem. 276 (28): 26648–55. doi:10.1074/jbc.M100997200. PMID 11356834.
• Engels N, Wollscheid B, Wienands J (2001). "Association of SLP-65/BLNK with the B cell antigen receptor through a non-ITAM tyrosine of Ig-alpha". Eur. J. Immunol. 31 (7): 2126–34. doi:10.1002/1521-4141(200107)31:7<2126::AID-IMMU2126>3.0.CO;2-O. PMID 11449366.
• Sauer K, Liou J, Singh SB, et al. (2002). "Hematopoietic progenitor kinase 1 associates physically and functionally with the adaptor proteins B cell linker protein and SLP-76 in lymphocytes". J. Biol. Chem. 276 (48): 45207–16. doi:10.1074/jbc.M106811200. PMID 11487585.
• Engels N, Merchant M, Pappu R, et al. (2001). "Epstein-Barr virus latent membrane protein 2A (LMP2A) employs the SLP-65 signaling module". J. Exp. Med. 194 (3): 255–64. doi:10.1084/jem.194.3.255. PMC 2193464. PMID 11489945.
• Tsuji S, Okamoto M, Yamada K, et al. (2001). "B cell adaptor containing src homology 2 domain (BASH) links B cell receptor signaling to the activation of hematopoietic progenitor kinase 1". J. Exp. Med. 194 (4): 529–39. doi:10.1084/jem.194.4.529. PMC 2193495. PMID 11514608.
• Kabak S, Skaggs BJ, Gold MR, et al. (2002). "The direct recruitment of BLNK to immunoglobulin alpha couples the B-cell antigen receptor to distal signaling pathways". Mol. Cell. Biol. 22 (8): 2524–35. doi:10.1128/MCB.22.8.2524-2535.2002. PMC 133735. PMID 11909947.
• Yasuda T, Tezuka T, Maeda A, et al. (2002). "Cbl-b positively regulates Btk-mediated activation of phospholipase C-gamma2 in B cells". J. Exp. Med. 196 (1): 51–63. doi:10.1084/jem.20020068. PMC 2194016. PMID 12093870.