Decreased Expression Levels of CD54 Associated with Decreased Activity of CXCL12 in Primary Myeloma Cells

In order to evaluate NF-kB activity in the primary myeloma cells, we examined the expressionlevels of CD54 by a flow cytometer. First, we confirmed that the expression levels of CD54 showed good correlation with the levels of DNA binding activity for NF-kB in human myeloma cell lines. Primary myeloma cells unexpectedly revealed lower expression levels of CD54 compared to normal BM plasma cells, while plasma cells from MGUS had high expression levels of CD54 as same as normal BM plasma cells. Furthermore, the expression levels of CD54 on these plasma cells showed the significantly positive correlation with the plasma levels of CXCL12 (SDF-1α) in their BM aspirates, and the expression levels of CXCR4, the receptor for CXCL12, decreased on primary myeloma cells compared to normal BM plasma cells. It was also confirmed that addition of CXCL12 in the in vitro culture significantly induced up-regulation of CD54 expressions in primary myeloma cells. Furthermore, myeloma cells with lower expressions of CD54 were unstable in the in vitro culture, resulting in the marked reduction of viable cell number; this was also the case where cell lines with lower or no expression of CD54 were sensitive to H₂O₂ treatment. Therefore, these data suggest that primary myeloma cells have lower expression levels of CD54, possibly lower NF-kB activities and different stability of in vitro survival from normal BM plasma cells, depending on expression levels of CD54.