To determine how hyaluronidase increases certain cancer cell sensitivity to tumor necrosis factor (TNF) cytotoxicity, we report here the isolation and characterization of a hyaluronidase-induced murine WW domain-containing oxidoreductase (WOX1). WOX1 is composed of two N-terminal WW domains, a nuclear localization sequence, and a C-terminal alcohol dehydrogenase (ADH) domain. WOX1 is mainly located in the mitochondria, and the mitochondrial targeting sequence was mapped within the ADH domain. Induction of mitochondrial permeability transition by TNF, staurosporine, and atractyloside resulted in WOX1 release from mitochondria and subsequent nuclear translocation. TNF-mediated WOX1 nuclear translocation occurred shortly after that of nuclear factor-κB nuclear translocation, whereas both were independent events. WOX1 enhanced TNF cytotoxicity in L929 cells via its WW and ADH domains as determined using stable cell transfectants. In parallel with this observation, WOX1 also enhanced TRADD (TNF receptor-associated death domain protein) -mediated cell death in transient expression experiments. Antisense expression of WOX1 raised TNF resistance in L929 cells. Enhancement of TNF cytotoxicity by WOX1 is due, in part, to its significant down-regulation of the apoptosis inhibitors Bcl-2 and Bcl-xL (<85%), but up-regulation of pro-apoptotic p53 (∼200%) by the ADH domain. When overexpressed, the ADH domain mediated apoptosis, probably due to modulation of expression of these proteins. The WW domains failed to modulate the expression of these proteins, but sensitized COS-7 cells to TNF killing and mediated apoptosis in various cancer cells independently of caspases. Transient cotransfection of cells with both p53 and WOX1 induced apoptosis in a synergistic manner. WOX1 colocalizes with p53 in the cytosol and binds to the proline-rich region of p53 via its WW domains. Blocking of WOX1 expression by antisense mRNA abolished p53 apoptosis. Thus, WOX1 is a mitochondrial apoptogenic protein and an essential partner of p53 in cell death.
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