The Mechanism of Constitutive NF-kB Activity in Myeloma Cell Lines.

[Purpose] NF-kB has a key function in the transformation, proliferation and invasion of cancer cells as well as in resistance to radiotherapy and chemotherapy. Although constitutive NF-kB activation has been reported in many human tumors, the underlying factors and mechanisms responsible for constitutive NF-kB activation in myeloma cells has not been known. The purpose of this study was to determine the mechanism of constitutive NF-kB activity in myeloma cell lines and quantification of NF-kB activity in primary myeloma cells by expression of CD54 (a NF-kB target gene).

[Methods] We checked the constitutive expression of NF-kB family proteins by western blot analysis and possible dimer formation of different NF-kB family members by Immunoprecipitation-western blot reaction. Constitutive NF-kB DNA-binding activity and dimers that are responsible for NF-kB activity were analyzed by electrophoretic mobility shift assay (EMSA). Moreover, expression of different NF-kB target genes was done by RT-PCR.

[Results and discussion] Constitutive NF-kB activity was determined in myeloma cell lines and our results suggested that p50/RelB, p50/p50, p50/p52 dimers might be responsible for this. We also analyzed several NF-kB target gene expressions and found that the intensity of CD54 expression was positively correlated with total NF-kB DNA binding activity. Although there is no method to quantified NF-kB activity, it can be determine in terms of its target genes e.g. CD54. Therefore, this study provide the frame work for understanding the molecular mechanism of constitutive activation of NF-kB and would help to quantify NF-kB activation in primary myeloma cells.