ZBP1 and neoplasm: It is worth mentioning that the sub-micromolar ZBP1 concentration that was recently measured in mouse embryonic fibroblasts is close to the previously estimated level of ZBP1 expression in a human cancer cell line (∼400,000 molecules per cell) (Liao et al., 2004), suggesting that our conclusions on the regulation of ZBP1-RNA interaction are not limited to developmental neurons but are relevant to the role of ZBP1 in promoting tumor metastasis.