In vitro-translated diphtheria toxin A chain inhibits translation in wheat germ extracts: analysis of biologically active, caspase-3-resistant diphtheria toxin mutants

Hypoxia-regulated expression of attenuated diphtheria toxin A fused with hypoxia-inducible factor-1alpha oxygen-dependent degradation domain preferentially induces apoptosis of hypoxic cells in solid tumor

Tumor cells in hypoxic areas of solid tumors are resistant to conventional chemotherapy and radiotherapy and thus are obstacles of cancer therapy. We report here the feasibility of applying hypoxia-regulated expression of diphtheria toxin A (DT-A) for killing hypoxic tumor cells. The expression vector was constructed to express DT-A fused with hypoxia-inducible factor-1alpha (HIF-1alpha) oxygen-dependent degradation (ODD) domain under the control of vascular endothelial growth factor gene promoter and contain erythropoietin mRNA-binding protein (ERBP)-binding sequence downstream of the DT-A/ODD sequence. In vitro ubiquitination assay showed that DT-A/ODD, but not DT-A, was ubiquitinated as efficient as HIF-1alpha under normoxic conditions in a von Hippel-Lindau- and oxygen-dependent manner. DT-A/ODD exhibited a comparable translation inhibitory activity to DT-A. ERBP-binding sequence was effective in stabilizing mRNA under hypoxic conditions in various cell types. Transfection of the vector expressing DT-A/ODD into high-metastatic Lewis lung carcinoma (3LL) A11 cells resulted in induction of apoptosis independently of hypoxia, probably due to its extreme toxicity. However, transfection of the vector expressing attenuated DT-A(W153F)/ODD or DT-A(H21A)/ODD resulted in a hypoxia-dependent induction of apoptosis. Liposomal gene transfer of the vector encoding DT-A(W153F)/ODD induced apoptosis in hypoxic, but not in normoxic, areas of solid tumors established by A11 variant cells with higher resistance to hypoxia-induced apoptosis and inhibited the growth of hypoxic tumors established by 3LL-P29 cells. These results suggest that hypoxia-regulated expression of attenuated DT-A(W153F)/ODD fusion protein is potentially of use for killing hypoxic tumor cells with minimizing the damage to normoxic normal tissues.

Ganglion cells are required for normal progenitor- cell proliferation but not cell-fate determination or patterning in the developing mouse retina

The vertebrate retina develops from an amorphous sheet of dividing retinal progenitor cells (RPCs) through a sequential process that culminates in an exquisitely patterned neural tissue. A current model for retinal development posits that sequential cell-type differentiation is the result of changes in the intrinsic competence state of multipotent RPCs as they advance in time and that the intrinsic changes are influenced by continuous changes in the extracellular environment. Although several studies support the proposition that newly differentiated cells alter the extrinsic state of the developing retina, it is still far from clear what role they play in modifying the extracellular environment and in influencing the properties of RPCs. Here, we specifically ablate retinal ganglion cells (RGCs) as they differentiate, and we determine the impact of RGC absence on retinal development. We find that RGCs are not essential for changing the competence of RPCs, but they are necessary for maintaining sufficient numbers of RPCs by regulating cell proliferation via growth factors. Intrinsic rather than extrinsic factors are likely to play the critical roles in determining retinal cell fate.