Requirements of src family kinase activity associated with CD45 for myeloma cell proliferation by interleukin-6

Specific intracellular signals mediated by interleukin-6 (IL-6) receptor complexes, such as signal transducer and activator of transcription 3 (STAT 3) and extracellular signal-regulated kinase (ERK) 1/2, are considered to be responsible for inducing a variety of cellular responses. In multiple myeloma, IL-6 only enhanced the proliferation of CD45(+) tumor cells that harbored the IL-6-independent activation of src family kinases even though STAT3 and ERK1/2 could be activated in response to IL-6 in both CD45(+) and CD45(-) cells. Furthermore, the IL-6-induced proliferation of CD45(+) U266 myeloma cells was significantly suppressed by Lyn-specific antisense oligodeoxynucleotides or a selective src kinase inhibitor. These results indicate that the activation of both STAT3 and ERK1/2 is not enough for IL-6-induced proliferation of myeloma cell lines that require src family kinase activation independent of IL-6 stimulation. Thus, the activation of the src family kinases associated with CD45 expression is a prerequisite for the proliferation of myeloma cell lines by IL-6. We propose a mechanism for IL-6-induced cell proliferation that is strictly dependent upon the cellular context in myelomas.