The transcription factor nuclear factor B (NF-B) regulates the expression of both antiapoptotic and proapoptotic genes. Death receptor 5 (DR5, TRAIL-R2) is a proapoptotic protein considered to be a potential target for cancer therapy, and its expression is mediated by NF-B. The mechanism of NF-B-induced DR5 expression is, however, unknown. Herein, we determined that etoposide-induced DR5 expression requires the first intronic region of the DR5 gene. Mutation of a putative NF-B binding site in this intron eliminates DR5 promoter activity, as do mutations in the p53 binding site in this region. Reduction in p53 expression also blocks p65 binding to the intronic region of the DR5 gene, indicating cooperation between p53 and p65 in DR5 expression. In contrast, the antiapoptotic stimulus, epidermal growth factor (EGF), fails to increase DR5 expression but effectively activates NF-B and induces p65 binding to the DR5 gene. EGF, however, induces the association of histone deacetylase 1 (HDAC1) with the DR5 gene, whereas etoposide treatment fails to induce this association. Indeed, HDAC inhibitors activate NF-B and p53 and upregulate DR5 expression. Blockage of DR5 activation decreased HDAC inhibitor-induced apoptosis, and a combination of HDAC inhibitors and TRAIL increased apoptosis. This provides a mechanism for regulating NF-B-mediated DR5 expression and could explain the differential roles NF-B plays in regulating apoptosis.Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF ligand family. It is capable of inducing apoptosis in transformed cancer cells but not in normal cells (14,53). TRAIL binds to two receptors, death receptor 4 (DR4, TRAIL-R1) and death receptor 5 (DR5, TRAIL-R2) (33,40,41,52,57). Upon binding, an adaptor protein called Fas-associated death domain (FADD) is recruited to the death receptors, forming a death-inducing signaling complex (46). Fas-associated death domain constitutively associates with procaspase 8 and, upon recruitment to death receptors, caspase 8 is activated. This leads to further caspase activation and release of mitochondrial proteins and, ultimately, to apoptosis (3, 38).Chemotherapeutic drugs, including etoposide and doxorubicin in combination with TRAIL, give a synergistic apoptotic response in cancer cells (11,21,43). This synergy is due partially to the ability of chemotherapeutic drugs and TRAIL to induce DR4 and DR5 expression. Up-regulation of DR5 in lung cancer cell lines is p53 dependent, and the p53-responsive element responsible for DR5 expression has been identified in the first intron region of the DR5 gene (47). Indeed, primary chronic lymphocytic leukemia cells lacking functional p53 fail to up-regulate DR5 following genotoxin treatment (20). Besides p53 involvement, blockage of the transcription factor NF-B effectively inhibits etoposide and TRAIL-induced DR5 expression and synergistic apoptotic response (11,42). The mechanism for NF-B up-regulation of DR5 is currently unknown, but a putative NF-B binding site has been i...

BackgroundImatinib mesylate (IM) induces clinical remission of chronic myeloid leukemia (CML). The Abelson helper integration site 1 (AHI-1) oncoprotein interacts with BCR-ABL and Janus kinase 2 (JAK2) to mediate IM response of primitive CML cells, but the effect of the interaction complex on the response to ABL and JAK2 inhibitors is unknown.MethodsThe AHI-1–BCR-ABL–JAK2 interaction complex was analyzed by mutational analysis and coimmunoprecipitation. Roles of the complex in regulation of response or resistance to ABL and JAK2 inhibitors were investigated in BCR-ABL + cells and primary CML stem/progenitor cells and in immunodeficient NSG mice. All statistical tests were two-sided.ResultsThe WD40-repeat domain of AHI-1 interacts with BCR-ABL, whereas the N-terminal region interacts with JAK2; loss of these interactions statistically significantly increased the IM sensitivity of CML cells. Disrupting this complex with a combination of IM and an orally bioavailable selective JAK2 inhibitor (TG101209 [TG]) statistically significantly induced death of AHI-1–overexpressing and IM-resistant cells in vitro and enhanced survival of leukemic mice, compared with single agents (combination vs TG alone: 63 vs 53 days, ratio = 0.84, 95% confidence interval [CI] = 0.6 to 1.1, P = .004; vs IM: 57 days, ratio = 0.9, 95% CI = 0.61 to 1.2, P = .003). Combination treatment also statistically significantly enhanced apoptosis of CD34+ leukemic stem/progenitor cells and eliminated their long-term leukemia-initiating activity in NSG mice. Importantly, this approach was effective against treatment-naive CML stem cells from patients who subsequently proved to be resistant to IM therapy.ConclusionsSimultaneously targeting BCR-ABL and JAK2 activities in CML stem/progenitor cells may improve outcomes in patients destined to develop IM resistance.