THE IMMUNOGLOBULIN LIGHT CHAIN RELATED PROTEIN GAMMA-5 IS EXPRESSED ON THE SURFACE OF MOUSE PRE-B-CELL LINES AND CAN FUNCTION AS A SIGNAL TRANSDUCING MOLECULE

Abelson Leukemia Virus-transformed mouse cell lines with an early pre-B phenotype carry partially rearranged or unrearranged Ig-H genes and consequently do not express intact IgM-H protein (mu-protein). Such early-mu- pre-B cells express an intracellular protein complex of the pre-B cell specific 22 kDa protein lambda-5 and a 16 kDa protein designated p16. Late pre-B cell lines which carry a rearranged IgM-H chain gene in which a continuous translational reading frame has been established in the fused V - D - J element express intact mu-protein, which forms an intracellular complex with lambda-5 and p16. We show here that both the lambda-5/p16 or the mu/lambda-5/p16 complexes can be immunoprecipitated from lysates of cells surface labeled with I-125. Thus early pre-B cells express the lambda-5/p16 complex on the cell surface in the absence of mu-protein, while mu+ late pre-B cells express a surface mu/lambda-5/p16 complex. To investigate a possible signal transduction function of the lambda-5/p16 and mu/lambda-5/p16 complexes on the surface of pre-B cell lines we measured the changes in intracellular free Ca2+ after treatment of cells with anti-lambda-5 or anti-mu antibodies. Two mu- early pre-B cell lines showed a rapid and transient increase in intracellular free Ca2+ when incubated with anti-lambda-5 antibodies but not when incubated with anti-mu, while the mu+ late pre-B cell line CB32 showed a rapid and transient increase in intracellular Ca2+ after incubation with anti-lambda-5 or anti-mu. These results show that both the lambda-5/p16 and the mu/lambda-5/p16 cell surface protein complexes can transduce an external signal to the inside of the cell, which implicates these complexes in the regulation of pre-B cell physiology.