Leupaxin negatively regulates B cell receptor signaling.
The role of the paxillin superfamily of adaptor proteins in B cell antigen receptor (BCR) signaling has not been studied previously. We show here that leupaxin (LPXN), a member of this family, was tyrosine-phosphorylated and recruited to the plasma membrane of human BJAB lymphoma cells upon BCR stimulation and that it interacted with Lyn (a critical Src family tyrosine kinase in BCR signaling) in a BCR-induced manner. LPXN contains four leucine-rich sequences termed LD motifs, and serial truncation and specific domain deletion of LPXN indicated that its LD3 domain is involved in the binding of Lyn. Of a total of 11 tyrosine sites in LPXN, we mutated Tyr(22), Tyr(72), Tyr(198), and Tyr(257) to phenylalanine and demonstrated that LPXN was phosphorylated by Lyn only at Tyr(72) and that this tyrosine site is proximal to the LD3 domain. The overexpression of LPXN in mouse A20 B lymphoma cells led to the suppression of BCR-induced activation of JNK, p38 MAPK, and, to a lesser extent, Akt, but not ERK and NFkappaB, suggesting that LPXN can selectively repress BCR signaling. We further show that LPXN suppressed the secretion of interleukin-2 by BCR-activated A20 B cells and that this inhibition was abrogated in the Y72F LPXN mutant, indicating that the phosphorylation of Tyr(72) is critical for the biological function of LPXN. Thus, LPXN plays an inhibitory role in BCR signaling and B cell function.
Chew
Valerie
V
Laboratory of Immune Regulation, Biomedical Sciences Institutes, Agency for Science, Technology and Research and Singapore Immunology Network, Singapore 138673, Singapore.
Lam
Kong-Peng
KP
Laboratory of Immune Regulation, Biomedical Sciences Institutes, Agency for Science, Technology and Research and Singapore Immunology Network, Singapore 138673, Singapore. Electronic address: lam_kong_peng@immunol.a-star.edu.sg.
D000818:Animals; D001402:B-Lymphocytes / Q000502:physiology; D015815:Cell Adhesion Molecules / Q000502:physiology*; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D051379:Mice; D010750:Phosphoproteins / Q000502:physiology*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D019061:src-Family Kinases / Q000502:physiology
D015815:Cell Adhesion Molecules; D007376:Interleukin-2; C112251:LPXN protein, human; D010750:Phosphoproteins; D011947:Receptors, Antigen, B-Cell; D014443:Tyrosine; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D051057:Proto-Oncogene Proteins c-akt; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases