Redemystifying MST1/hippo signaling

Post-translational regulation of FOXO

The Forkhead box O (FOXO) family transcription factors play critical roles in a series of cellular processes, including the cell cycle, cell death, metabolism, and oxidative stress resistance. FOXO proteins are subject to several post-translational modifications, which are closely related to their activity. In this paper, we review the post-translational modifications of FOXOs and their biological functions.

Regulation of neuronal cell death by c-Abl-Hippo/MST2 signaling pathway

Background

Mammalian Ste20-like kinases (MSTs) are the mammalian homologue of Drosophila hippo and play critical roles in regulation of cell death, organ size control, proliferation and tumorigenesis. MSTs exert pro-apoptotic function through cleavage, autophosphorylation and in turn phosphorylation of downstream targets, such as Histone H2B and FOXO (Forkhead box O). Previously we reported that protein kinase c-Abl mediates oxidative stress-induced neuronal cell death through phosphorylating MST1 at Y433, which is not conserved among mammalian MST2, Drosophila Hippo and C.elegans cst-1/2.

Methodology/Principal Findings

Using immunoblotting, in vitro kinase and cell death assay, we demonstrate that c-Abl kinase phosphorylates MST2 at an evolutionarily conserved site, Y81, within the kinase domain. We further show that the phosphorylation of MST2 by c-Abl leads to the disruption of the interaction with Raf-1 proteins and the enhancement of homodimerization of MST2 proteins. It thereby enhances the MST2 activation and induces neuronal cell death.

Conclusions/Significance

The identification of the c-Abl tyrosine kinase as a novel upstream activator of MST2 suggests that the conserved c-Abl-MST signaling cascade plays an important role in oxidative stress-induced neuronal cell death.