Abstract:
Using a yeast-two-hybrid approach, XIAP-associated factor 1 (Xaf1) was identified as an Akt-interacting protein.
Xaf1 is pro-apoptotic via different mechanisms. By contrast, Akt kinase is anti-apoptotic and is also involved in insulin signaling and various other cellular functions.
This work confirmed an interaction between Xaf1 and both Akt1 and Akt2 but not with Akt3 in human cells. When comparing with other Akt interacting proteins, Xaf1 is a strong binding partner. Furthermore, we determined the interacting domains of Xaf1, Akt1, and XIAP (X-linked inhibitor of apoptosis) and produced expression constructs lacking these domains. These constructs were then stably expressed in cell lines. In these cells, Xaf1 increased phosphorylation of Akt and additional proteins involved in the phosphoinositide 3 (PI-3)-kinase pathway. In addition, the interaction led to altered intracellular localization of the proteins. Moreover, Akt-Xaf1 interaction increased the rate of apoptosis.
This functional characterization provides evidence for a role of this protein interaction in PI-3-kinase / Akt signaling, in the intracellular localization of the proteins, and in apoptosis.