Akt Regulates Cell Survival and Apoptosis at a Postmitochondrial Level

Abstract

Phosphoinositide 3 kinase/Akt pathway plays an essential role in neuronal survival. However, the cellular mechanisms by which Akt suppresses cell death and protects neurons from apoptosis remain unclear. We previously showed that transient expression of constitutively active Akt inhibits ceramide-induced death of hybrid motor neuron 1 cells. Here we show that stable expression of either constitutively active Akt or Bcl-2 inhibits apoptosis, but only Bcl-2 prevents the release of cytochrome c from mitochondria, suggesting that Akt regulates apoptosis at a postmitochondrial level. Consistent with this, overexpressing active Akt rescues cells from apoptosis without altering expression levels of endogenous Bcl-2, Bcl-x, or Bax. Akt inhibits apoptosis induced by microinjection of cytochrome c and lysates from cells expressing active Akt inhibit cytochrome c induced caspase activation in a cell-free assay while lysates from Bcl-2–expressing cells have no effect. Addition of cytochrome c and dATP to lysates from cells expressing active Akt do not activate caspase-9 or -3 and immunoprecipitated Akt added to control lysates blocks cytochrome c–induced activation of the caspase cascade. Taken together, these data suggest that Akt inhibits activation of caspase-9 and -3 by posttranslational modification of a cytosolic factor downstream of cytochrome c and before activation of caspase-9.

IGF-I protects cortical neurons against ceramide-induced apoptosis via activation of the PI-3K/Akt and ERK pathways; is this protection independent of CREB and Bcl-2?

“…A protective role of Bcl-2 from ceramide-induced apoptosis has previously been observed in two neuronal cell lines [19,63] probably by blocking the release of cytochrome c from the mitochondria into the cytosol [27,62]. However, immunoblotting experiments of Bcl-2 showed that Bcl-2 expression was not modulated during IGF-I, ceramide or LY294002 treatments.…”

Anandamide-induced cell death in primary neuronal cultures: role of calpain and caspase pathways

“…Moreover, no protection was observed by suppression of caspase-8 or -9, the upstream regulatory caspases, which control caspase-3 activity and modulate the extrinsic or intrinsic pathways of neuronal apoptosis, respectively. [51][52][53][54] In addition, anandamide-induced cytotoxicity appeared prior to changes in caspase activity. These findings were further confirmed using neuroblastoma cell lines that expressed either caspase-9 or -8 dominant-negative mutants; again, anandamide-induced cell death was not modified in cells transfected with the dominantnegative constructs versus the empty vector.…”

MicroRNA-330 acts as tumor suppressor and induces apoptosis of prostate cancer cells through E2F1-mediated suppression of Akt phosphorylation

“…However, the major effect of E2F1 in conferring numerous survival advantages has been shown to be mediated through the activation of the Akt-signaling pathway (Chaussepied and Ginsberg, 2004;Liu et al, 2006). The activation of Akt was shown to be associated with the inhibition of various proapoptotic effectors and the suppression of Ask1/p38MAPK/JNK-mediated cell death (Kennedy et al, 1997;Zhou et al, 2000;Testa and Bellacosa, 2001;Tsuruta et al, 2002). In this study, we showed that miR-330 can significantly decrease the phosphorylation of targeted intracellular kinases (pAkt1, p-Akt2, p-Akt3 and p-GSK-3b) in PC-3 cells (Figure 4).…”