Pharmacological Inhibition of PTEN Rescues Dopaminergic Neurons by Attenuating Apoptotic and Neuroinflammatory Signaling Events.

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the selective degeneration of dopaminergic neurons in the substantia nigra pars compacta resulting in an irreversible and a debilitating motor dysfunction. Though both genetic and idiopathic factors are implicated in the disease etiology, idiopathic PD comprise the majority of clinical cases and is caused by exposure to environmental toxicants and oxidative stress. Fyn kinase activation has been identified as an early molecular signaling event that primes neuroinflammatory and neurodegenerative events associated with dopaminergic cell death. However, the upstream regulator of Fyn activation remains unidentified. We investigated whether the lipid and tyrosine phosphatase PTEN (Phosphatase and Tensin homolog deleted on chromosome 10) could be the upstream regulator of Fyn activation in PD models as PTEN has been previously reported to contribute to Parkinsonian pathology. Our findings, using bioluminescence resonance energy transfer (BRET) and immunoblotting, indicate for the first time that PTEN is a critical early stress sensor in response to oxidative stress and neurotoxicants in in vitro models of PD. Pharmacological attenuation of PTEN activity rescues dopaminergic neurons from neurotoxicant-induced cytotoxicity by modulating Fyn kinase activation. Our findings also identify PTEN's novel roles in contributing to mitochondrial dysfunction which contribute to neurodegenerative processes. Interestingly, we found that PTEN positively regulates interleukin-1ß (IL-1ß) and the transcription of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Taken together, we have identified PTEN as a disease course altering pharmacological target that may be further validated for the development of novel therapeutic strategies targeting PD.

PTEN controls glandular morphogenesis through a juxtamembrane ß-Arrestin1/ARHGAP21 scaffolding complex.

PTEN controls three-dimensional (3D) glandular morphogenesis by coupling juxtamembrane signaling to mitotic spindle machinery. While molecular mechanisms remain unclear, PTEN interacts through its C2 membrane-binding domain with the scaffold protein ß-Arrestin1. Because ß-Arrestin1 binds and suppresses the Cdc42 GTPase-activating protein ARHGAP21, we hypothesize that PTEN controls Cdc42 -dependent morphogenic processes through a ß-Arrestin1-ARHGAP21 complex. Here, we show that PTEN knockdown (KD) impairs ß-Arrestin1 membrane localization, ß-Arrestin1-ARHGAP21 interactions, Cdc42 activation, mitotic spindle orientation and 3D glandular morphogenesis. Effects of PTEN deficiency were phenocopied by ß-Arrestin1 KD or inhibition of ß-Arrestin1-ARHGAP21 interactions. Conversely, silencing of ARHGAP21 enhanced Cdc42 activation and rescued aberrant morphogenic processes of PTEN-deficient cultures. Expression of the PTEN C2 domain mimicked effects of full-length PTEN but a membrane-binding defective mutant of the C2 domain abrogated these properties. Our results show that PTEN controls multicellular assembly through a membrane-associated regulatory protein complex composed of ß-Arrestin1, ARHGAP21 and Cdc42.

The C-terminus region of ß-arrestin1 modulates VE-cadherin expression and endothelial cell permeability.

BACKGROUND: The endothelial specific cell-cell adhesion molecule, VE-cadherin, modulates barrier function and vascular homeostasis. In this context, we have previously characterized that VEGF (vascular endothelial growth factor) leads to VE-cadherin phosphorylation, ß-arrestin2 recruitment and VE-cadherin internalization in mouse endothelial cells. However, exactly how this VE-cadherin/ß-arrestin complex contributes to VEGF-mediated permeability in human endothelial cells remains unclear. In this study, we investigated in-depth the VE-cadherin/ß-arrestin interactions in human endothelial cells exposed to VEGF. FINDINGS: First, we demonstrated that VEGF induces VE-cadherin internalization in a clathrin-dependent manner in human umbilical vein endothelial cells (HUVEC). In addition to the classical components of endocytic vesicles, ß-arrestin1 was recruited and bound to phosphorylated VE-cadherin. Molecular mapping of this interaction uncovered that the C-terminus tail of ß-arrestin1, that comprises amino acids 375 to 418, was sufficient to directly interact with the phosphorylated form of VE-cadherin. Interestingly, the expression of the C-terminus tail of ß-arrestin1 induced loss of surface exposed-VE-cadherin, promoted monolayer disorganization and enhanced permeability. Finally, this effect relied on decreased VE-cadherin expression at the transcriptional level, through inhibition of its promoter activity. CONCLUSIONS: Altogether, our results demonstrate that ß-arrestin1 might play multiple functions collectively contributing to endothelial barrier properties. Indeed, in addition to a direct implication in VE-cadherin endocytosis, ß-arrestin1 could also control VE-cadherin transcription and expression. Ultimately, understanding the molecular mechanisms involved in VE-cadherin function might provide therapeutic tools for many human diseases where the vascular barrier is compromised.