Phosphoinositide 3 kinase enhancer (PIKE) is a recently identified nuclear GTPase that activates nuclear phosphoinositide 3-kinase (PI3 kinase). We have identified, cloned and characterized a new form of PIKE, designated PIKE-L, which, unlike the nuclear PIKE-S, localizes to both the cytoplasm and the nucleus. We demonstrate physiologic binding of PIKE-L to Homer, an adaptor protein known to link metabotropic glutamate receptors to multiple intracellular targets including the inositol 1,4,5-trisphosphate receptor (IP3R). We show that activation of group I metabotropic glutamate receptors (mGluRIs) enhances formation of an mGluRI-Homer-PIKE-L complex, leading to activation of PI3 kinase activity and prevention of neuronal apoptosis. Our findings indicate that this complex mediates the well-known ability of agonists of mGluRI to prevent neuronal apoptosis.

Akt/PKB is a crucial regulator of diverse cellular processes and contributes to cancer progression. Activation of Akt is essentially dependent on phosphatidylinositol (PI) 3-kinase signaling. Here, we describe a novel mediator of Akt that is independent of PI 3-kinase. This mediator, PIKE-A, is a PIKE isoform and contains GTPase, pleckstrin homology, ArfGAP, and ankyrin repeats domains. PIKE-A directly binds to activated Akt but not PI 3-kinase in a guanine nucleotide-dependent way and stimulates the kinase activity of Akt. Overexpression of PIKE-A enhances Akt activity and promotes cancer cell invasion, whereas dominant-negative PIKE-A and PIKE-A knockdown markedly inhibit these processes. Our results demonstrate that PIKE-A is a physiologic regulator of Akt and an oncogenic effector of cell invasion.

We previously reported the role of vascular endothelial growth factor (VEGF) secreted by mesenchymal stem cells (MSCs) in protecting against neonatal hyperoxic lung injuries. Recently, the paracrine protective effect of MSCs was reported to be primarily mediated by extracellular vesicle (EV) secretion. However, the therapeutic efficacy of MSC-derived EVs and the role of the VEGF contained within EVs in neonatal hyperoxic lung injury have not been elucidated. The aim of the study was to determine whether MSC-derived EVs attenuate neonatal hyperoxic lung injury and, if so, whether this protection is mediated via the transfer of VEGF. We compared the therapeutic efficacy of MSCs, MSC-derived EVs with or without VEGF knockdown, and fibroblast-derived EVs in vitro with a rat lung epithelial cell line challenged with H2O2 and in vivo with newborn Sprague-Dawley rats exposed to hyperoxia (90%) for 14 days. MSCs (1 × 105 cells) or EVs (20 µg) were administered intratracheally on postnatal day 5. The MSCs and MSC-derived EVs, but not the EVs derived from VEGF-knockdown MSCs or fibroblasts, attenuated the in vitro H2O2-induced L2 cell death and the in vivo hyperoxic lung injuries, such as impaired alveolarization and angiogenesis, increased cell death, and activated macrophages and proinflammatory cytokines. PKH67-stained EVs were internalized into vascular pericytes (22.7%), macrophages (21.3%), type 2 epithelial cells (19.5%), and fibroblasts (4.4%) but not into vascular endothelial cells. MSC-derived EVs are as effective as parental MSCs for attenuating neonatal hyperoxic lung injuries, and this protection was mediated primarily by the transfer of VEGF.

RPS3, a conserved, eukaryotic ribosomal protein of the 40 S subunit, is required for ribosome biogenesis. Because ribosomal proteins are abundant and ubiquitous, they may have additional extraribosomal functions. Here, we show that human RPS3 is a physiological target of Akt kinase and a novel mediator of neuronal apoptosis. NGF stimulation resulted in phosphorylation of threonine 70 of RPS3 by Akt, and this phosphorylation was required for Akt binding to RPS3. RPS3 induced neuronal apoptosis, up-regulating proapoptotic proteins Dp5/Hrk and Bim by binding to E2F1 and acting synergistically with it. Akt-dependent phosphorylation of RPS3 inhibited its proapoptotic function and perturbed its interaction with E2F1. These events coincided with nuclear translocation and accumulation of RPS3, where it functions as an endonuclease. Nuclear accumulation of RPS3 results in an increase in DNA repair activity to some extent, thereby sustaining neuronal survival. Abolishment of Akt-mediated RPS3 phosphorylation through mutagenesis accelerated apoptotic cell death and severely compromised nuclear translocation of RPS3. Thus, our findings define an extraribosomal role of RPS3 as a molecular switch that accommodates apoptotic induction to DNA repair through Akt-mediated phosphorylation.Nerve growth factor (NGF) deprivation and DNA damage can activate the intrinsic apoptotic pathway, causing cytochrome c release and caspase-dependent cell death in many cell types, including sympathetic neurons (1-5). NGF regulates neuronal apoptosis through a variety of cellular signaling mechanisms, especially the phosphoinositide 3-kinase (PI3K)/Akt pathway (6). Akt signaling promotes cell survival by phosphorylating and controlling downstream effectors in both the cytoplasm and the nucleus. For instance, Akt phosphorylates the proapoptotic Bcl-2 family member BAD (7) that belongs to the cytoplasmic apoptotic apparatus. In addition, Akt inhibits chromatin condensation during apoptosis by phosphorylating ACINUS, a nuclear factor required for apoptotic chromatin condensation (8). PI3K and Akt are predominantly located in the cytoplasm, but they are also found in the nucleus or translocate there upon stimulation by growth factors (9 -11) or DNA damage (9 -12).Ribosomal protein S3 (RPS3) is a component of the 40 S ribosomal subunit and is involved in its maturation (13). A growing body of evidence suggests that ribosomal proteins are capable of extraribosomal functions. For example, RPS3, also known as UV endonuclease III, appears to possess a general base damage endonuclease that participates in the cleavage of DNA lesions caused by UV irradiation. In addition, both RPS3 and ribosomal protein P0 have an apurinic/apyrimidinic (AP) 2 endonuclease activity functioning in DNA repair at the 3Ј side of AP sites after DNA damage (14 -16). In addition, ribosomal proteins may have apoptotic functions as follows: RPS3-a is involved in the apoptotic process in NIH3T3 cells (17), and knockdown of rpS3 leads to significant cell survival after hydrogen peroxid...