Analysis of expression of nuclear factor kappa B (NF-kappa B) in multiple myeloma: downregulation of NF-kappa B induces apoptosis

Nuclear factor-kappaB (NF-kappaB) is an important transcription factor that regulates survival in many cells. Activated NF-kappaB has been shown to pr otect some haematopoietic neoplastic cells from apoptosis. In the present s tudy, we analysed NF-kappaB status in 13 primary samples from patients with multiple myeloma (MM) and in four myeloma cell lines including U266, RPMI 8226, HS-Sultan and K620. Constitutive activation of NF-kappaB was evaluate d by either immunohistochemistry or immunofluorescence using a monoclonal m ouse anti-human p65 (Rel A) antibody, which recognizes the unbound, active form of p65 (Rel A). Constitutively active NF-kappaB was present in all MM patient samples as well as in all four myeloma cell lines. Inhibition of co nstitutively active NF-kappaB. by either proteasome inhibitors (MG132, glio toxin) or inhibitors of I kappaB phosphorylation (Bay117082, and Bay117085) , induced apoptosis as demonstrated by both flow cytometric analysis and li ght microscopic morphological evaluation. This chemically induced apoptosis was associated with decreased DNA binding of nuclear NF-kappaB as determin ed by the electrophoretic mobility shift assay. In addition, adenovirus vec tor with dominant negative I kappaB alpha (Ad51 kappaB) was used for inhibi tion of NF-kappaB in the U266 cell line. Compared with wild-type, super-rep ressor-treated cells showed an increased level of apoptosis. These results suggest that constitutive expression of NF-kappaB plays an important role i n plasma cell survival in MM.