The highly dynamic remodeling and cross talk of the microtubule and actin cytoskeleton support neuronal morphogenesis. Small RhoGTPases family members have emerged as crucial regulators of cytoskeletal dynamics. In this review we will comprehensively analyze findings that support the participation of RhoA, Rac, Cdc42, and TC10 in different neuronal morphogenetic events ranging from migration to synaptic plasticity. We will specifically address the contribution of these GTPases to support neuronal polarity and axonal elongation. V C 2012 Wiley Periodicals, Inc

Maintenance of endoplasmic reticulum (ER) proteostasis is controlled by a signalling network known as the unfolded protein response (UPR). Here, we identified filamin A as a major binding partner of the ER stress transducer IRE1α. Filamin A is an actin crosslinking factor involved in cytoskeleton remodelling. We show that IRE1α controls actin cytoskeleton dynamics and affects cell migration upstream of filamin A. The regulation of cytoskeleton dynamics by IRE1α is independent of its canonical role as a UPR mediator, serving instead as a scaffold that recruits and regulates filamin A. Targeting IRE1α expression in mice affected normal brain development, generating a phenotype resembling periventricular heterotopia, a disease linked to the loss of function of filamin A. IRE1α also modulated cell movement and cytoskeleton dynamics in fly and zebrafish models. This study unveils an unanticipated biological function of IRE1α in cell migration, whereby filamin A operates as an interphase between the UPR and the actin cytoskeleton.

Adaptation to endoplasmic reticulum (ER) stress depends on the activation of the unfolded protein response (UPR) stress sensor inositol-requiring enzyme 1a (IRE1a), which functions as an endoribonuclease that splices the mRNA of the transcription factor XBP-1 (X-box-binding protein-1). Through a global proteomic approach we identified the BCL-2 family member PUMA as a novel IRE1a interactor. Immunoprecipitation experiments confirmed this interaction and further detected the association of IRE1a with BIM, another BH3-only protein. BIM and PUMA doubleknockout cells failed to maintain sustained XBP-1 mRNA splicing after prolonged ER stress, resulting in early inactivation. Mutation in the BH3 domain of BIM abrogated the physical interaction with IRE1a, inhibiting its effects on XBP-1 mRNA splicing. Unexpectedly, this regulation required BCL-2 and was antagonized by BAD or the BH3 domain mimetic ABT-737. The modulation of IRE1a RNAse activity by BH3-only proteins was recapitulated in a cell-free system suggesting a direct regulation. Moreover, BH3-only proteins controlled XBP-1 mRNA splicing in vivo and affected the ER stress-regulated secretion of antibodies by primary B cells. We conclude that a subset of BCL-2 family members participates in a new UPR-regulatory network, thus assuming apoptosis-unrelated functions.

BackgroundRetroviral integration depends on the interaction between intasomes, host chromatin and cellular targeting cofactors as LEDGF/p75 or BET proteins. Previous studies indicated that the retroviral integrase, by itself, may play a role in the local integration site selection within nucleosomal target DNA. We focused our study on this local association by analyzing the intrinsic properties of various retroviral intasomes to functionally accommodate different chromatin structures in the lack of other cofactors.ResultsUsing in vitro conditions allowing the efficient catalysis of full site integration without these cofactors, we show that distinct retroviral integrases are not equally affected by chromatin compactness. Indeed, while PFV and MLV integration reactions are favored into dense and stable nucleosomes, HIV-1 and ASV concerted integration reactions are preferred into poorly dense chromatin regions of our nucleosomal acceptor templates. Predicted nucleosome occupancy around integration sites identified in infected cells suggests the presence of a nucleosome at the MLV and HIV-1 integration sites surrounded by differently dense chromatin. Further analyses of the relationships between the in vitro integration site selectivity and the structure of the inserted DNA indicate that structural constraints within intasomes could account for their ability to accommodate nucleosomal DNA and could dictate their capability to bind nucleosomes functionally in these specific chromatin contexts.ConclusionsThus, both intasome architecture and compactness of the chromatin surrounding the targeted nucleosome appear important determinants of the retroviral integration site selectivity. This supports a mechanism involving a global targeting of the intasomes toward suitable chromatin regions followed by a local integration site selection modulated by the intrinsic structural constraints of the intasomes governing the target DNA bending and dictating their sensitivity toward suitable specific nucleosomal structures and density.Electronic supplementary materialThe online version of this article (doi:10.1186/s12977-015-0145-9) contains supplementary material, which is available to authorized users.

BackgroundStable insertion of the retroviral DNA genome into host chromatin requires the functional association between the intasome (integrase·viral DNA complex) and the nucleosome. The data from the literature suggest that direct protein–protein contacts between integrase and histones may be involved in anchoring the intasome to the nucleosome. Since histone tails are candidates for interactions with the incoming intasomes we have investigated whether they could participate in modulating the nucleosomal integration process.ResultsWe show here that histone tails are required for an optimal association between HIV-1 integrase (IN) and the nucleosome for efficient integration. We also demonstrate direct interactions between IN and the amino-terminal tail of human histone H4 in vitro. Structure/function studies enabled us to identify amino acids in the carboxy-terminal domain of IN that are important for this interaction. Analysis of the nucleosome-binding properties of catalytically active mutated INs confirmed that their ability to engage the nucleosome for integration in vitro was affected. Pseudovirus particles bearing mutations that affect the IN/H4 association also showed impaired replication capacity due to altered integration and re-targeting of their insertion sites toward dynamic regions of the chromatin with lower nucleosome occupancy.ConclusionsCollectively, our data support a functional association between HIV-1 IN and histone tails that promotes anchoring of the intasome to nucleosomes and optimal integration into chromatin.Electronic supplementary materialThe online version of this article (10.1186/s12977-017-0378-x) contains supplementary material, which is available to authorized users.

Insulin-like growth factor 2 (IGF2) protects against Huntington´s disease through the extracellular disposal of protein aggregates.

The neuronal cytoskeleton regulates numerous processes that occur in normal homeostasis. Under pathological conditions such as those of Alzheimer's disease (AD), major alterations in cytoskeleton organization have been observed and changes in both microtubules and actin filaments have been reported. Many neurodegenerative consequences of AD are linked to the production and accumulation of amyloid peptides (Aβ) and their oligomers, produced from the internal cleavage of the amyloid-β protein precursor. We previously reported that fibrillar Aβ1-42 (fAβ) treatment of hippocampal neurons induced an increase in Rac1 and Cdc42 activities linking fAβ effects with changes in actin dynamics. Here we show fAβ-induces increased activity of PAK1 and cyclin-dependent kinase 5, and that p21-activated kinase (PAK1) activation targets the LIMK1-cofilin signaling pathway. Increased cofilin dephosphorylation under conditions of enhanced LIM-Kinase 1 (LIMK1) activity suggests that fAβ co-stimulates bifurcating pathways impacting cofilin phosphorylation. Overexpression of slingshot (SSH) prevents the augment of F-actin induced by fAβ after 24 h, suggesting that fAβ-induced changes in actin assembly involve both LIMK1 and SSH. These results suggest that fAb may alter the PAK1/LIMK1/cofilin axis and therefore actin organization in AD.

Physiological levels of ROS support neurite outgrowth and axonal specification, but the mechanisms by which ROS are able to shape neurons remain unknown. Ca 2ϩ , a broad intracellular second messenger, promotes both Rac1 activation and neurite extension. Ca 2ϩ release from the endoplasmic reticulum, mediated by both the IP3R1 and ryanodine receptor (RyR) channels, requires physiological ROS levels that are mainly sustained by the NADPH oxidase (NOX) complex. In this work, we explore the contribution of the link between NOX and RyR-mediated Ca 2ϩ release toward axonal specification of rat hippocampal neurons. Using genetic approaches, we find that NOX activation promotes both axonal development and Rac1 activation through a RyR-mediated mechanism, which in turn activates NOX through Rac1, one of the NOX subunits. Collectively, these data suggest a feedforward mechanism that integrates both NOX activity and RyR-mediated Ca 2ϩ release to support cellular mechanisms involved in axon development.