Neuroblastoma is the most frequent, extracranial solid tumor in children with still poor prognosis in stage IV disease. In this study, we analyzed FOXO3-phosphorylation and cellular localization in tumor biopsies and determined the function of this homeostasis regulator in vitro and in vivo. FOXO3-phosphorylation at threonine-32 (T32) and nuclear localization in biopsies significantly correlated with stage IV disease. DNA-damaging drugs induced nuclear accumulation of FOXO3, which was associated with elevated T32-phosphorylation in stage IV-derived neuroblastoma cells, thereby reflecting the in situ results. In contrast, hypoxic conditions repressed PKB-activity and caused dephosphorylation of FOXO3 in both, stroma-like SH-EP and high-stage-derived STA-NB15 cells. The activation of an ectopically-expressed FOXO3 in these cells reduced viability at normoxia, but promoted growth at hypoxic conditions and elevated VEGF-C-expression. In chorioallantoic membrane (CAM) assays STA-NB15 tumors with ectopic FOXO3 showed increased micro-vessel formation and, when xenografted into nude mice, a gene-dosage-dependent effect of FOXO3 in high-stage STA-NB15 cells became evident: low-level activation increased tumor-vascularization, whereas hyper-activation repressed tumor growth.The combined data suggest that, depending on the mode and intensity of activation, cellular FOXO3 acts as a homeostasis regulator promoting tumor growth at hypoxic conditions and tumor angiogenesis in high-stage neuroblastoma.

Forkhead box O class transcription factors are homeostasis regulators that control cell death, longevity and therapy-resistance. In neuroblastoma (NB), nuclear FOXO3 correlates with stage M disease and poor prognosis. To analyze whether FOXO3 contributes to drug-resistance in this childhood cancer, we investigated how different high-stage-derived NB cells respond to the activation of an ectopic FOXO3 allele. We found endogenous FOXO3 mostly localized to the nucleus—upon activation of an ectopic, 4OHT-activated FOXO3(A3)ER fusion protein two of the cell lines underwent apoptosis, whereas in the others FOXO3-activation even increased survival during drug-treatment. In the latter cell type, FOXO3 did not induce the BH3-only protein BCL2L11/BIM due to impaired binding of FOXO3 to the BIM-promoter, but still activated other FOXO3 targets. It was shown before that FOXO3 and TP53 physically interact with each other at two different regions—the TP53-N-terminus binds to the FOXO3-DNA binding domain (DBD) and the FOXO3-C-terminus interacts with the TP53-DBD. Interestingly, cell lines that undergo FOXO3-induced cell death carry homozygous point mutations in the TP53-DBD near the structural hotspot-mutation-site R175H, which abrogated FOXO3–TP53 interaction. In contrast, in FOXO3-death-resistant cells no point mutations in the TP53-DBD were found—in these cells FOXO3–TP53 complexes are formed and FOXO3-binding to the BIM-promoter, but not the induction of the detoxifying protein SESN3, were prevented, which in turn increased chemo-protection in this type of high-stage-derived NB cells. Our combined data suggest that FOXO3 steps in as a death inducer in case of TP53-mutation, whereas functional TP53 alters FOXO3-target-promoter-recognition, which prevents death induction by FOXO3 and instead increases chemo-protection and survival of NB cells. This novel mechanism may explain the low incidence of TP53 mutation in high-stage NB at diagnosis and suggests FOXO3 as a therapeutic target for this childhood malignancy.

Loss of CDKN2A/p16INK4A in hematopoietic stem cells is associated with enhanced self-renewal capacity and might facilitate progression of damaged stem cells into pre-cancerous cells that give rise to leukemia. This is also reflected by the frequent loss of the INK4A locus in acute lymphoblastic T-cell leukemia. T-cell acute lymphoblastic leukemia cells designed to conditionally express p16INK4A arrest in the G 0 /G 1 phase of the cell cycle and show increased sensitivity to glucocorticoid-and tumor necrosis factor receptor superfamily 6-induced apoptosis. To investigate the underlying molecular mechanism for increased death sensitivity, we interfered with specific steps of apoptosis signaling by expression of anti-apoptotic proteins. We found that alterations in cell death susceptibility resulted from changes in the composition of pro-and anti-apoptotic BCL2 proteins, i.e. repression of MCL1, BCL2, and PMAIP1/ Noxa and the induction of pro-apoptotic BBC3/Puma. Interference with Puma induction by short hairpin RNA technology or retroviral expression of MCL1 or BCL2 significantly reduced both glucocorticoid-and FAS-induced cell death in p16INK4A -reconstituted leukemia cells. These results suggest that Puma, in concert with MCL1 and BCL2 repression, critically mediates p16 INK4A -induced death sensitization and that in human T-cell leukemia the deletion of p16 INK4A confers apoptosis resistance by shifting the balance of pro-and anti-apoptotic BCL2 proteins toward apoptosis protection.

It is shown for the first time that FOXO3/FKHRL1 induces caspase-8 expression via the ATM-CREB pathway independent of caspase-8 gene methylation status. Induction of caspase-8 by the DNA-methylation inhibitor 5-azadC also depends on FOXO3, suggesting that 5-azadC triggers gene expression via the FOXO3-ATM-CREB pathway.

Several studies indicate a pathogenetic role of T-lymphocytes with specificity for heat shock proteins (HSP) in rheumatoid arthritis (RA). Surprisingly, there are no experimental data for B-lymphocytes with specificity for HSE To investigate whether B-lymphocytes from rheumatoid synovial tissue show a specificity for HSP 60 we immortalized synovial tissue B-lymphocytes by the electrofusion technique and tested the specificity of the B-cell clones for HSP 60 by ELISA. Tissue samples from four patients with classic, active RA were used in this study. The isolated cells were electrofused in strongly hypo-osmolar medium with cells either of the mouse strain X63-AgS-653 (Ag8) or the heteromyeloma strain HAB-1. Clones positive for IgG, the IgG fraction of the supernatant of the isolated synovial cells and the IgG of the serum of the patients were tested in an ELISA for reactivity to the recombinant HSP 60 of Yersinia enterocolitica, which shows great homology with mycobacterial HSP 65 and human HSP 60. The expression of this HSP 60 was studied in normal and rheumatoid synovial tissue using a polyclonal rabbit serum against HSP 60 from Y. enterocolitica (Ye HSP 60). In this way we investigate differences in the expression of HSP 60 and compared the pattern of this HSP60 with the pattern of mycobacterial HSP65 and human HSP 60 described by others. In three of four patients 10 IgG secreting B-cell clones showing a specificity for HSP 60 were detected. IgG specific for HSP 60 was also detected in the supernatant of the isolated synovial cells before fusion and in the serum of these patients. HSP 60 was demonstrated immunohistochemically within the rheumatoid synovial tissue and showed stronger expression with a different distribution when compared with the expression in norreal synovial tissue. B-cell clones from rheumatoid synovial tissue thus exhibit a specificity for bacterial HSP 60, and a monospecific rabbit serum against this HSP shows strong reactivity within the rheumatoid synovial tissue. It may be postulated that a humoral HSP 60 response, initially directed against an infectious agent, could react with cross-reactive epitopes of rheumatoid synovial tissue or with self-HSP perpetuating the local inflammatory process.