Direct transactivation of the anti-apoptotic gene apolipoprotein J (Clusterin) by B-MYB

B-MYB is a ubiquitously expressed transcription factor involved in the regu lation of cell survival, proliferation, and differentiation. In an attempt to isolate B-MYB-regulated genes that may explain the role of B-MYB in cell ular processes, representational difference analysis was performed in neuro blastoma cell lines with different levels of B-MYB expression. One of the g enes, the mRNA levels of which were enhanced in B-MYB expressing cells, was ApoJ/Clusterin(SGP-2/TRMP-2) (ApoJ/Clusterin), previously implicated in re gulation of apoptosis and tumor progression. Here we show that the human Ap oJ/Clusterin gene contains a Myb binding site in its 5' flanking region, wh ich interacts with bacterially synthesized B-MYB protein and mediates B-MYB -dependent transactivation of the ApoJ/Clusterin promoter in transient tran sfection assays. Endogenous ApoJ/Clusterin expression is induced in mammali an cell lines following transient transfection of a B-MYB cDNA, Blockage of secreted clusterin by a monoclonal antibody results in increased apoptosis of neuroblastoma cells exposed to the chemotherapeutic drug doxorubicin. T hus, activation of ApoJ/Clusterin by B-MYB may be an important step in the regulation of apoptosis in normal and diseased cells.