The Expression of CD56 Is Frequently Accompanied with the Expression of Neuronal Cell Markers and Its Down-Regulation Is Induced by IL-6 in Human Myeloma Cells.

Human myeloma cells have the marked phenotypic heterogeneity of surface marker expressions, possibly because of loss of PAX-5 expression. Especially, ectopic expression of CD56, one of non-B cell lineage markers, is frequently detected on primary myeloma cells from more than 80% patients with overt myeloma. However, only 2 (NOP2 and AMO1) out of 10 myeloma cell lines were CD56(+). In primary myeloma cells as well as CD56(−) myeloma cell lines, the treatment with forskolin could induce the expression of CD56 in the in vitro culture. In most CD56(+) primary myeloma cells as well as myeloma cell lines, the expressions of neuronal cell markers such as neuron specific enolase (NSE), nestin, β-tubulin III or chromogranin A were found coincidentally. By gene expression profiling, CD56(+) myeloma cell lines showed the marked expressions of transcription factors involved in neuronal cell lineage. On the other hand, addition of IL-6 down-regulated the expression of CD56 in CD56(+) myeloma cell lines in the in vitro culture. In 13 out of 60 patients with overt myeloma, these myeloma cells showed CD56(−) and their values of plasma CRP were significantly increased and MPC-1(−)CD45(+) immature myeloma cells were also increased compared to those in CD56(+) myeloma cases. Therefore, these results indicate that the expression of CD56 is possibly due to phenotypic changes into neuronal cell lineage, and IL-6 can block these phenotypic changes, keeping PAX-5(−) myeloma cells being uncommitted cells to any lineage.