Wnt-1 dependent activation of the survival factor NF-kappaB in PC12 cells

Abstract

Expression of the Wnt-1 oncogene in PC12 cells induces morphological and biochemical changes, including up-regulation of cell adhesion and lack of differentiation in response to growth factors. The survival of PC12 cells is known to be mediated in part by phosphatidylinositol-3 kinase (PI-3 kinase)-dependent activation of the transcription factor nuclear factor-kappaB (NF-kappaB). We investigated the effect of Wnt-1 expression on cell survival and NF-kappaB activation using PC12 cells expressing Wnt-1 (PC12/Wnt1) and a reporter vector in which firefly luciferase expression is under the control of NF-kappaB consensus sequences. Serum deprivation caused apoptosis and decreased NF-kappaB activity in wild type PC12 cells. PC12/Wnt-1 cells showed less apoptosis in the absence of serum, and the levels of NF-kappaB activity were higher than in wild type PC12 cells. NF-kappaB activity was also increased by the transient expression of Wnt-1 in PC12 cells and it was completely inhibited in both PC12 and PC12/Wnt-1 cells by a dominant negative mutant IkappaB-alpha that has been shown to prevent NF-kappaB activation. Agents known to inhibit NF-kappaB-induced apoptosis in PC12 as well as in PC12/Wnt-1 cells, indicating a role of NF-kappaB activation in the anti-apoptotic effect of Wnt-1. Inhibition of PI-3 kinase with wortmannin, or with a dominant negative p85 regulatory subunit of the PI-3 kinase, blocked NF-kappaB activity in PC12 cells but caused only partial inhibition in PC12/Wnt-1 cells. The effect of Wnt-1 in activating NF-kappaB can be mimicked by inhibition of glycogen synthase kinase-3beta (GSK-3beta) with lithium or with a dominant negative GSK-3beta. Our results show that expression of Wnt-1 increases survival of PC12 cells in the absence of serum by activating the anti-apoptotic factor NF-kappaB. Wnt-1-induced activation of NF-kappaB is partially independent of PI-3 kinase and can be mimicked by inhibition of GSK-3beta.