PTEN is recruited to specific microdomains of the plasma membrane during lactacystin-induced neuronal apoptosis

Silencing of circular RNA‑ZYG11B exerts a neuroprotective effect against retinal neurodegeneration

Ischemic retinal diseases are the major cause of vision impairment worldwide. Currently, there are no available treatments for ischemia‑induced retinal neurodegeneration. Circular RNAs (circRNAs) have emerged as important regulators of several biological processes and human diseases. The present study investigated the role of circRNA‑ZYG11B (circZYG11B; hsa_circ_0003739) in retinal neurodegeneration. Reverse transcription quantitative polymerase chain reaction (RT‑qPCR) demonstrated that circZYG11B expression was markedly increased during retinal neurodegeneration in vivo and in vitro. Cell Counting Kit‑8, TUNEL and caspase‑3 activity assays revealed that silencing of circZYG11B was able to protect against oxidative stress‑ or hypoxic stress‑induced retinal ganglion cell (RGC) injury. Furthermore, immunofluorescence staining and hematoxylin and eosin staining revealed that silencing of circZYG11B alleviated ischemia/reperfusion‑induced retinal neurodegeneration, as indicated by reduced RGC injury and decreased retinal reactive gliosis. In addition, luciferase reporter, biotin‑coupled miRNA capture and RNA immunoprecipitation assays revealed that circZYG11B could regulate RGC function through circZYG11B/microRNA‑620/PTEN signaling. Clinically, RT‑qPCR assays demonstrated that circZYG11B expression was markedly increased in the aqueous humor of patients with glaucoma. In conclusion, circZYG11B may be considered a promising target for the diagnosis and treatment of retinal ischemic diseases.

PDK1 regulates the survival of the developing cortical interneurons

Inhibitory interneurons are critical for maintaining the excitatory/inhibitory balance. During the development cortical interneurons originate from the ganglionic eminence and arrive at the dorsal cortex through two tangential migration routes. However, the mechanisms underlying the development of cortical interneurons remain unclear. 3-Phosphoinositide-dependent protein kinase-1 (PDK1) has been shown to be involved in a variety of biological processes, including cell proliferation and migration, and plays an important role in the neurogenesis of cortical excitatory neurons. However, the function of PDK1 in interneurons is still unclear. Here, we reported that the disruption of Pdk1 in the subpallium achieved by crossing the Dlx5/6-Cre-IRES-EGFP line with Pdk1^fl/fl mice led to the severely increased apoptosis of immature interneurons, subsequently resulting in a remarkable reduction in cortical interneurons. However, the tangential migration, progenitor pools and cell proliferation were not affected by the disruption of Pdk1. We further found the activity of AKT-GSK3β signaling pathway was decreased after Pdk1 deletion, suggesting it might be involved in the regulation of the survival of cortical interneurons. These results provide new insights into the function of PDK1 in the development of the telencephalon.

Cell Cycle Control by PTEN

Continuous and error-free chromosome inheritance through the cell cycle is essential for genomic stability and tumor suppression. However, accumulation of aberrant genetic materials often causes the cell cycle to go awry, leading to malignant transformation. In response to genotoxic stress, cells employ diverse adaptive mechanisms to halt or exit the cell cycle temporarily or permanently. The intrinsic machinery of cycling, resting, and exiting shapes the cellular response to extrinsic stimuli, whereas prevalent disruption of the cell cycle machinery in tumor cells often confers resistance to anticancer therapy. Phosphatase and tensin homolog (PTEN) is a tumor suppressor and a guardian of the genome that is frequently mutated or deleted in human cancer. Moreover, it is increasingly evident that PTEN deficiency disrupts the fundamental processes of genetic transmission. Cells lacking PTEN exhibit cell cycle deregulation and cell fate reprogramming. Here, we review the role of PTEN in regulating the key processes in and out of cell cycle to optimize genomic integrity.

Neuroprotective and anti-inflammatory roles of the phosphatase and tensin homolog deleted on chromosome Ten (PTEN) Inhibition in a Mouse Model of Temporal Lobe Epilepsy

Excitotoxic damage represents the major mechanism leading to cell death in many human neurodegenerative diseases such as ischemia, trauma and epilepsy. Caused by an excess of glutamate that acts on metabotropic and ionotropic excitatory receptors, excitotoxicity activates several death signaling pathways leading to an extensive neuronal loss and a consequent strong activation of astrogliosis. Currently, the search for a neuroprotective strategy is aimed to identify the level in the signaling pathways to block excitotoxicity avoiding the loss of important physiological functions and side effects. To this aim, PTEN can be considered an ideal candidate: downstream the excitatory receptors activated in excitotoxicity (whose inhibition was shown to be not clinically viable), it is involved in neuronal damage and in the first stage of the reactive astrogliosis in vivo. In this study, we demonstrated the involvement of PTEN in excitotoxicity through its pharmacological inhibition by dipotassium bisperoxo (picolinato) oxovanadate [bpv(pic)] in a model of temporal lobe epilepsy, obtained by intraperitoneal injection of kainate in 2-month-old C57BL/6J male mice. We have demonstrated that inhibition of PTEN by bpv(pic) rescues neuronal death and decreases the reactive astrogliosis in the CA3 area of the hippocampus caused by systemic administration of kainate. Moreover, the neurotoxin administration increases significantly the scanty presence of mitochondrial PTEN that is significantly decreased by the administration of the inhibitor 6 hr after the injection of kainate, suggesting a role of PTEN in mitochondrial apoptosis. Taken together, our results confirm the key role played by PTEN in the excitotoxic damage and the strong anti-inflammatory and neuroprotective potential of its inhibition.

Subcellular targeting and dynamic regulation of PTEN: implications for neuronal cells and neurological disorders

PTEN is a lipid and protein phosphatase that regulates a diverse range of cellular mechanisms. PTEN is mainly present in the cytosol and transiently associates with the plasma membrane to dephosphorylate PI(3,4,5)P3, thereby antagonizing the PI3-Kinase signaling pathway. Recently, PTEN has been shown to associate also with organelles such as the endoplasmic reticulum (ER), the mitochondria, or the nucleus, and to be secreted outside of the cell. In addition, PTEN dynamically localizes to specialized sub-cellular compartments such as the neuronal growth cone or dendritic spines. The diverse localizations of PTEN imply a tight temporal and spatial regulation, orchestrated by mechanisms such as posttranslational modifications, formation of distinct protein–protein interactions, or the activation/recruitment of PTEN downstream of external cues. The regulation of PTEN function is thus not only important at the enzymatic activity level, but is also associated to its spatial distribution. In this review we will summarize (i) recent findings that highlight mechanisms controlling PTEN movement and sub-cellular localization, and (ii) current understanding of how PTEN localization is achieved by mechanisms controlling posttranslational modification, by association with binding partners and by PTEN structural or activity requirements. Finally, we will discuss the possible roles of compartmentalized PTEN in developing and mature neurons in health and disease.

Interference with the PTEN-MAST2 interaction by a viral protein leads to cellular relocalization of PTEN

PTEN (phosphatase and tensin homolog deleted on chromosome 10) and MAST2 (microtubule-associated serine and threonine kinase 2) interact with each other through the PDZ domain of MAST2 (MAST2-PDZ) and the carboxyl-terminal (C-terminal) PDZ domain-binding site (PDZ-BS) of PTEN. These two proteins function as negative regulators of cell survival pathways, and silencing of either one promotes neuronal survival. In human neuroblastoma cells infected with rabies virus (RABV), the C-terminal PDZ domain of the viral glycoprotein (G protein) can target MAST2-PDZ, and RABV infection triggers neuronal survival in a PDZ-BS-dependent fashion. These findings suggest that the PTEN-MAST2 complex inhibits neuronal survival and that viral G protein disrupts this complex through competition with PTEN for binding to MAST2-PDZ. We showed that the C-terminal sequences of PTEN and the viral G protein bound to MAST2-PDZ with similar affinities. Nuclear magnetic resonance structures of these complexes exhibited similar large interaction surfaces, providing a structural basis for their binding specificities. Additionally, the viral G protein promoted the nuclear exclusion of PTEN in infected neuroblastoma cells in a PDZ-BS-dependent manner without altering total PTEN abundance. These findings suggest that formation of the PTEN-MAST2 complex is specifically affected by the viral G protein and emphasize how disruption of a critical protein-protein interaction regulates intracellular PTEN trafficking. In turn, the data show how the viral protein might be used to decipher the underlying molecular mechanisms and to clarify how the subcellular localization of PTEN regulates neuronal survival.

PTEN: A molecular target for neurodegenerative disorders

PTEN (phosphatase and tensin homologue deleted in chromosome 10) was first identified as a candidate tumour suppressor gene located on chromosome 10q23. It is considered as one of the most frequently mutated genes in human malignancies. Emerging evidence shows that the biological function of PTEN extends beyond its tumour suppressor activity. In the central nervous system PTEN is a crucial regulator of neuronal development, neuronal survival, axonal regeneration and synaptic plasticity. Furthermore, PTEN has been linked to the pathogenesis of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis. Recently increased attention has been focused on PTEN as a potential target for the treatment of brain injury and neurodegeneration. In this review we discuss the essential functions of PTEN in the central nervous system and its involvement in neurodegeneration.

Topography of signaling molecules as detected by electron microscopy on plasma membrane sheets isolated from non-adherent mast cells

Immunolabeling of isolated plasma membrane (PM) sheets combined with high-resolution electron microscopy is a powerful technique for understanding the topography of PM-bound signaling molecules. However, this technique has been mostly confined to analysis of membrane sheets from adherent cells. Here we present a rapid, simple and versatile method for isolation of PM sheets from non-adherent cells, and show its use for examination of the topography of Fcepsilon receptor I (FcepsilonRI) and transmembrane adaptors, LAT (linker for activation of T cells) and NTAL (non-T cell activation linker), in murine bone marrow-derived mast cells (BMMC). The data were compared with those obtained from widely used but tumor-derived rat basophilic leukemia (RBL) cells. In non-activated cells, FcepsilonRI was distributed either individually or in small clusters of comparable size in both cell types. In multivalent antigen-activated BMMC as well as RBL cells, FcepsilonRI was internalized to a similar extent, but, strikingly, internalization in BMMC was not preceded by formation of large (~200 nm) aggregates of FcepsilonRI, described previously in activated RBL cells. On the other hand, downstream adaptor proteins, LAT and NTAL, were localized in independent domains in both BMMC and RBL cells before and after FcepsilonRI triggering. The combined data demonstrate unexpected properties of FcepsilonRI signaling assemblies in BMMC and emphasize the importance of studies of PM sheets isolated from non-tumor cells.

Phosphatase PTEN in neuronal injury and brain disorders

The phosphatase and tensin homologue PTEN was originally identified as a tumor suppressor. In the CNS, mutation or inactivation of PTEN is best known for playing a tumorigenic role in the molecular pathogenesis of glioblastoma. However, recent studies show that PTEN is associated with several brain diseases other than cancer, suggesting a broader role of PTEN in CNS pathophysiology. Here, we review the evidence for the crucial involvement of PTEN in neuronal injury as well as in neurological and psychiatric disorders, and discuss the potential of PTEN as a molecular target for the development of a novel CNS therapeutic strategy.