Surface μ heavy chain expressed on pre-B lymphomas transduces Ca2+ signals but fails to cause growth arrest of pre-B lymphomas

Abstract Little is known about the role of signals transduced by cell surface IgM (sIgM) expressed during early B cell development. A subclone (1.6) of the late pre-B cell lymphoma 70 Z 3. 12 was used to study signal transduction by surface μ heavy (H) chain before and after transition to the early immature B cell stage, and the functional consequences thereof. Although κ L chain expression can be induced on 1.6 cells by LPS or cytokines, immunoprecipitations indicated that the non-induced 1.6 cells expressed μ H chain with an alternative protein(s) which may be a surrogate light chain(s). Consistent with this, anti-μ but not anti-κ or anti-λ antibodies caused transient Ca 2+ mobilization in noninduced 1.6 cells. The Ca 2+ signal was derived from both intracellular stores and Ca 2+ influx in either noninduced cells or in cells that had been preinduced to express κ L chain. Thus, the ability of μ H chain to mobilize Ca 2+ as a second messenger does not depend upon the expression of mature L chains. The immature B lymphomas, WEHI-231 and CH1, express mature forms of IgM and undergo growth arrest when stimulated by anti-μ antibody. In contrast, signals generated by μ H chain on either noninduced or preinduced 1.6 cells or in the sIgM + pre-B cell transfectant 300-19 μλ 36 8 did not cause growth arrest. These results suggest that μ H chain expressed on pre-B cells is capable of mobilizing Ca 2+ , but that this signal alone is insufficient to induce growth arrest in the pre-B cell.