Mouse proximal tubular cells (BUMPT), when cultured in the absence of growth factors, activate a default apoptotic pathway. Although Wnt signaling antagonizes the effect of pro-apoptotic triggers, its role in regulating the default pathway of apoptosis is less well defined. The present study examines the hypothesis that lithium (Li⁺) and (2'Z,3'E)-6- bromoindirubin-3'-oxime (BIO), two glycogen synthase kinase 3 (GSK3) inhibitors, promote survival of growth factor-deprived renal epithelial cells by activating the Wnt pathway. These studies demonstrate that Li⁺ and BIO activate Wnt signaling as indicated by the following changes: phosphorylation (inhibition) of GSK3; decreased phosphorylation of -catenin, (a GSK3 substrate); nuclear translocation of -catenin; specific transcriptional activation of Tcf/catenin-responsive pTopflash constructs and an increase in the expression of cyclin D1 (indicative of a pro-mitogenic cell response). In addition, Li⁺ or BIO significantly increase the phosphorylation (activation) of Akt, an anti-apoptotic protein, and inhibit apoptosis (decrease both annexin V staining and caspase 3 activation), during serum deprivation. Inhibition of phosphatidylinositol 3-kinase (responsible for Akt activation) either by wortmanin or Ly294002 prevented Li⁺ or BIO-induced Akt phosphorylation and reduces cell survival without altering the phosphorylation state of GSK3. Li⁺ or BIO also increases the expression of insulin-like growth factor-II (IGF-II), a potent proliferative signaling protein. Li+ or BIO-free conditioned medium harvested from Li⁺ or BIO-exposed cells also induced Akt phosphorylation, mimicking the protective effect of the two GSK3 inhibitors on serumstarved cells. Furthermore, the effect of conditioned medium on Akt phosphorylation could be inhibited by either Ly294002 or IGF-binding protein. BIO, a specific GSK3 inhibitor, replicated the protective effect of Li⁺ on cell viability, suggesting that GSK3 activation is important for initiating the apoptotic pathway. Taken together, these data suggest that Li⁺ or BIO promote renal epithelial cell survival by inhibiting apoptosis through GSK3-dependent activation of the Wnt pathway and subsequent release of IGFII. Extracellular IGF-II serves as an autocrine survival factor that is responsible, in part, for activating the anti-apoptotic PI3 kinase-Akt pathway during serum deprivation.