Neuroblastoma-derived sulfhydryl oxidase, a new member of the sulfhydryl oxidase/Quiescin6 family, regulates sensitization to interferon gamma-induced cell death in human neuroblastoma cells.

In neuroblastoma cells, apoptotic programs can be activated by cytokines and cytostatic drugs. Apoptotic dysfunction confers resistance against therapeutic drugs and is a major complication for achieving optimal therapy response. Deregulated expression of the MYCN gene is a critical determinant in neuroblastoma progression, and one of the pleiotropic functions of the MYCN protein is cellular sensitization to cytokine-induced and drug-induced apoptosis. By using the functional approach of technical knockout (TKO), we have identified five genes that regulate sensitization for IFN-gamma-induced cell death. Most efficient among them is the newly identified SOXN (neuroblastoma-derived sulfhydryl oxidase), which comprises 12 exons and maps to 9q34.3. SOXN encodes a putative protein of 698 amino acids that contains a signal sequence, a protein-disulfide-isomerase-type thioredoxin and a yeast ERV1 domain and is highly homologous to members of the sulfhydryl oxidase/Quiescin6 family. The SOXN protein is predominantly located in the plasma and in the nuclear membrane. Antisense SOXN confers resistance to IFN-gamma-induced apoptosis. In contrast, ectopic overexpression of sense-SOXN sensitizes the cells to induced cell death. These results identify SOXN as a major player in regulating the sensitization of neuroblastoma cells for IFN-gamma-induced apoptosis.

Ataxin-2 promotes apoptosis of human neuroblastoma cells.

Neuroblastoma is a highly heterogeneous tumor of young children. Although many advances have been made towards understanding the molecular mechanisms dictating the phenotypic heterogeneity, the prognosis of children with neuroblastoma, particularly of progressively growing variants, has remained dire. About 10% of neuroblastomas regress spontaneously, probably by apoptosis, while another 20% have amplified the MYCN gene resulting in a poor prognosis. In pursuit of identifying cell death-associated genes in neuroblastoma, we encountered the SCA2 gene, coding for ataxin-2, as an important player. Here, we report that enforced expression of wild-type ataxin-2, but not of mutant ataxin-2, sensitizes neuroblastoma cells for apoptosis. In line with this, higher levels of ataxin-2 were detected in apoptotic cells compared to nonapoptotic cells. Neuroblastoma tumors with amplified MYCN contain significantly less ataxin-2 protein than tumors without amplified MYCN. Collectively, our data suggest that ataxin-2 has an important role in regulating the susceptibility of neuroblastoma cells to apoptotic stimuli in vitro and in vivo.