Wnt‐1 dependent activation of the survival factor NF‐κB 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-κB (NF-κB). We investigated the effect of Wnt-1 expression on cell survival and NF-κB activation using PC12 cells expressing Wnt-1 (PC12/Wnt1) and a reporter vector in which firefly luciferase expression is under the control of NF-κB consensus sequences. Serum deprivation caused apoptosis and decreased NF-κB activity in wild type PC12 cells. PC12/Wnt-1 cells showed less apoptosis in the absence of serum, and the levels of NF-κB activity were higher than in wild type PC12 cells. NF-κB 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 IκB-α that has been shown to prevent NF-κB activation. Agents known to inhibit NF-κB-induced apoptosis in PC12 as well as in PC12/Wnt-1 cells, indicating a role of NF-κB 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-κB activity in PC12 cells but caused only partial inhibition in PC12/Wnt-1 cells. The effect of Wnt-1 in activating NF-κB can be mimicked by inhibition of glycogen synthase kinase-3β (GSK-3β) with lithium or with a dominant negative GSK-3β. 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-κB. Wnt-1-induced activation of NF-κB is partially independent of PI-3 kinase and can be mimicked by inhibition of GSK-3β. J. Neurosci. Res. 61:21–32, 2000. © 2000 Wiley-Liss, Inc.