Do cancer cells die because of Nogo-B?

Nogo-A is a potent neurite outgrowth inhibitory protein in vitro and is suggested to play a role in the lack of regeneration in the central nervous system of adult higher vertebrates. A shorter splice isoform, ASY/Nogo-B, has recently been reported to act as a proapoptotic protein, the loss of which would be typical for cancer cells. Here, we show that the osteosarcoma cell line SaOS-2 and the cell line CHO do express high levels of endogenous Nogo-B and that stable transfectants overexpressing high levels of Nogo-B do not differ significantly from the respective parental wild-type or control cell lines both in respect to cell proliferation and to spontaneous apoptosis or cell death induced by staurosporine and tunicamycin. The deletion of the second transmembrane domain of Nogo-B, which has been claimed to abolish its proapoptotic activity, leads to a shift of the protein from the ER to a cytoplasmic localization, suggesting that ER stress of highly overexpressed Nogo-B may lead to aversive cellular reactions under particular conditions. Our data do not support a function of Nogo-B as a physiological proapoptotic protein in certain types of cancer.