Wnt signaling plays a critical role in development and oncogenesis. Although significant progress has been made in understanding the downstream signaling cascade of Wnt signaling, little is known regarding Wnt signaling modification of the cell death machinery. Given that numerous oncogenes transform cells by providing cell survival function, we hypothesized that Wnt signaling may inhibit apoptosis. Here, we report that cells expressing Wnt-1 were resistant to cancer therapy–mediated apoptosis. Wnt-1 signaling inhibited the cytochrome c release and the subsequent caspase-9 activation induced by chemotherapeutic drugs, including both vincristine and vinblastine. Furthermore, we found that Wnt-1–mediated cell survival was dependent on the activation of β-catenin/T cell factor (Tcf) transcription. Inhibition of β-catenin/Tcf transcription by expression of the dominant-negative mutant of Tcf-4 blocked Wnt-1–mediated cell survival and rendered cells sensitive to apoptotic stimuli. These results provide the first demonstration that Wnt-1 inhibits cancer therapy–mediated apoptosis and suggests that Wnt-1 may exhibit its oncogenic potential through a mechanism of anti-apoptosis
