The Akt Proto-oncogene Links Ras to Pak and Cell Survival Signals

Abstract

The Ras oncogene regulates cellular proliferation, differentiation, transformation, and survival through multiple downstream signals. Ras signals through its effector phosphoinositide 3 (PI3) kinase to the Pak protein kinase (p65 pak ), but the steps from Ras to Pak remain to be elucidated. PI3 kinase can stimulate the small G protein, Rac, a direct activator of Pak, as well as the Akt proto-oncogene, a serine-threonine protein kinase. We found that activated Akt stimulated Pak, whereas a dominant negative Akt inhibited Ras activation of Pak in transfection assays. Akt stimulation of Pak was not inhibited by dominant negative mutants of either Rac or Cdc42 suggesting that Akt activated Pak through a GTPase-independent mechanism. We also developed a novel cell-free system to study Ras activation of Pak. In this system Ras activated Pak only in the presence of a crude cell extract but failed to activate Pak when Akt was immunodepleted from the extract. Akt protects cells from apoptosis through phosphorylation of downstream targets such as the Bcl-2 family member, Bad. We found that activated Pak decreased apoptosis and increased phosphorylation of Bad, whereas dominant negative Pak increased apoptosis and decreased phosphorylation of Bad. These studies define a new oncogene-mediated cell survival signal.

[6]-Shogaol inhibits melanogenesis in B16 mouse melanoma cells through activation of the ERK pathway

“…It has been reported that activation of MEK/ERK leads to phosphorylation of MITF at serine 73, resulting in its degradation [28,38] . The PI3K⁄Akt pathway plays an important role in cell growth regulation and apoptosis inhibition [39,40] . In addition, activation of the PI3K⁄Akt pathway reduces tyrosinase transcription and melanogenesis in B16F10 cells [17,29] .…”

P-21-activated protein kinase-1 functions as a linker between insulin and Wnt signaling pathways in the intestine

“…Plasmids, DNA transfection, cell culture and MTT assay The dominant negative PAK-1 plasmid, the K299R mutant, and the vector control, were gifts from Dr Jefferey Field (Sells et al, 1997;Tang et al, 2000). DNA transfection was performed using Lipofectamine (Invitrogen Life Technology) according to the manufacturer's instructions.…”

Pseudorabies virus US3-mediated inhibition of apoptosis does not affect infectious virus production

“…The effects of US3 on the actin cytoskeleton have recently been attributed to an interaction of US3 with p21-activated kinases (PAKs) 1 and 2, and extracellular PRV virus titres were reduced in PAK2 2/2 cells (Van den Broeke et al, 2009b). Interestingly, PAKs are not only involved in rearrangements of the actin cytoskeleton, but also in anti-apoptotic effects (Cotteret et al, 2003;Gnesutta et al, 2001;Jakobi et al, 2001;Rudel & Bokoch, 1997;Schurmann et al, 2000;Tang et al, 2000). Based on our current study, we hypothesize that the reduced PRV titres on PAK2 2/2 cells are probably due to the effect of PAK2 on the actin cytoskeleton, rather than the effect of PAK2 on apoptosis.…”