The structure of the mu/pseudo light chain complex on human pre-B cells is consistent with a function in signal transduction.
Prior to immunoglobulin (Ig) light (L) chain rearrangement, pre-B cells can express mu heavy (H) chains at the cell surface in association with pseudo (psi) L chains. This complex may be essential for B cell development. We have investigated the composition of the mu/psi L chain complex of a human pre-B cell line, in view of its potential role in transmembrane signal transduction. The mu/lambda receptor of a mature B cell line was analyzed in comparison. The mu/psi L chain complex is associated with disulfide-linked molecules that are homologous or identical to the mb-1 and B29 proteins, known to be integral components of membrane Ig receptors on mature B cells. Both receptors contain tyrosine (Tyr) kinase activity. In the mu/lambda receptor, the lyn and lck Tyr kinases could clearly be identified. The mb-1 and B29 proteins in both mu/lambda and mu/psi L chain receptors are substrates for in vitro phosphorylation on Tyr, but also on serine (Ser) and threonine (Thr) residues. The undefined mu-associated Ser/Thr kinase also phosphorylates the src-related kinases in the mu/lambda receptor and a 43-kDa mu-associated protein that is present in both complexes. The 43-kDa protein may be an integral part of both receptor types, or a transiently associated molecule instrumental in the signaling process. We conclude that the mu/psi L receptor on human pre-B cells fulfills the presently known criteria to function as a signal transduction unit.
Brouns
G S
GS
Division of Immunology, The Netherlands Cancer Institute, Amsterdam.
de Vries
E
E
van Noesel
C J
CJ
Mason
D Y
DY
van Lier
R A
RA
Borst
J
J
D000595:Amino Acid Sequence; D015703:Antigens, CD; D001402:B-Lymphocytes / Q000502:physiology*; D051925:CD79 Antigens; D002460:Cell Line; D005455:Fluorescent Antibody Technique; D006412:Hematopoietic Stem Cells / Q000502:physiology*; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000737:chemistry*; D007148:Immunoglobulin mu-Chains / Q000737:chemistry*; D008562:Membrane Glycoproteins / Q000032:analysis; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000032:analysis; D017346:Protein Serine-Threonine Kinases / Q000032:analysis; D011505:Protein-Tyrosine Kinases / Q000032:analysis; D011947:Receptors, Antigen, B-Cell / Q000032:analysis; D015398:Signal Transduction
D015703:Antigens, CD; D051925:CD79 Antigens; C497881:CD79A protein, human; C497883:CD79B protein, human; D007147:Immunoglobulin Light Chains; D007148:Immunoglobulin mu-Chains; D008562:Membrane Glycoproteins; D010750:Phosphoproteins; D011947:Receptors, Antigen, B-Cell; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases