Molecular targets of bortezomib on adult T-cell leukemia cells

BACKGROUND: The molecular mechanism of proteasome inhibitor-mediated anti-cancer activity has been logically hypothesized that the major pathway is inhibition of nuclear factor kappa-B (NF-kB) cascades, however, the precise mechanism is still unclear. Adult T-cell leukemia (ATL) is a fatal neoplasia derived from HTLV-1 infected T lymphocytes exhibiting constitutive activation of NF-kB. AIM: To elucidate the complex molecular mechanism of anti-tumor effect of the proteasome inhibitor, bortezomib in ATL cells, we attempted to perform network-based gene expression profiling. METHODS and RESULTS: Assessment of gene regulation by microarray analysis revealed that down-regulation of genes involved in anti-apoptosis (i.e., BCL2, and IAP5), up-regulation of genes related with apoptosis (i.e., FAF1), heat shock proteins (i.e., HSPA, HSPCA), and oxygen stress (i.e., heme oxygenase-1: HMOX-1). Gene network analysis employing the Bayesian statistical framework also suggests that HMOX-1 which is known as an inducer of reactive oxygen species (ROS), as well as SPARC play an important role in bortezomib-treated ATL cells. The HMOX-1 inhibitor, ZnPP, in addition to bortezomib partially inhibited the apoptotic effect of bortezomib on TaY cells. CONCLUSION: Our results suggest that in addition to the inhibition of NF-kB, bortezomib activated ROS pathway through HMOX-1, and SPARC may participate bortezomib-induced apoptosis, providing novel insight into the bortezomib mediated anti-tumor activity in ATL cells. Keywords: dose response and time course For dual color analysis, cDNA obtained from uninfected TaY cells was labeled with Cy3 as a reference, and cDNA obtained from the HHV-6B infected cells was labeled with Cy5.