Neuritic complexity of hippocampal neurons depends on WIP‐mediated mTORC1 and Abl family kinases activities

Abstract

IntroductionNeuronal morphogenesis is governed mainly by two interconnected processes, cytoskeletal reorganization, and signal transduction. The actin‐binding molecule WIP (Wiskott‐Aldrich syndrome protein [WASP]‐interacting protein) was identified as a negative regulator of neuritogenesis. Although WIP controls activity of the actin‐nucleation‐promoting factor neural WASP (N‐WASP) during neuritic differentiation, its implication in signal transduction remains unknown.MethodsUsing primary neurons from WIP‐deficient and wild‐type mice we did an immunofluorescence, morphometric, and biochemical analysis of the signaling modified by WIP deficiency.ResultsHere, we describe the WIP contribution to the regulation of neuritic elaboration and ramification through modification in phosphorylation levels of several kinases that participate in the mammalian target of rapamycin complex 1 (mTORC1)‐p70S6K (phosphoprotein 70 ribosomal protein S6 kinase, S6K) intracellular signaling pathway. WIP deficiency induces an increase in the number of neuritic bifurcations and filopodial protrusions in primary embryonic neurons. This phenotype is not due to modifications in the activity of the phosphoinositide 3 kinase (PI3K)‐Akt pathway, but to reduced phosphorylation of the S6K residues Ser411 and Thr389. The resulting decrease in kinase activity leads to reduced S6 phosphorylation in the absence of WIP. Incubation of control neurons with pharmacological inhibitors of mTORC1 or Abl, two S6K regulators, conferred a morphology resembling that of WIP‐deficient neurons. Moreover, the preferential co‐distribution of phospho‐S6K with polymerized actin is altered in WIP‐deficient neurons.ConclusionThese experiments identify WIP as a member of a signaling cascade comprised of Abl family kinases, mTORC1 and S6K, which regulates neuron development and specifically, neuritic branching and complexity. Thus, we postulated a new role for WIP protein.

Restoration of HDAC1 Enzymatic Activity after Stroke Protects Neurons from Ischemia/Reperfusion Damage and Attenuates Behavioral Deficits in Rats

“…Neuronal function and status are highly associated with neurite complexity, regulated through complex intracellular signaling events [ 35 , 36 ]. Therefore, we evaluated the neurite outgrowth pattern in terms of total neurite length, process number, and branch number in cultured cortical neurons.…”

WIP, YAP/TAZ and Actin Connections Orchestrate Development and Transformation in the Central Nervous System

“…Furthermore, stimulated by several growth factors the Akt-mTORC1-S6K pathway is involved in actin cytoskeleton reorganization (Jaworski and Sheng, 2006) and S6K promotes actin filament crosslinking and stabilization by directly binding F-actin, depending on the level of S6K phosphorylation (Moresco et al, 2005). WIP not only plays a cytoskeletal role, but also governs signaling through mTORC1-and Abl-dependent modulation of the S6K pathway, which controls neuritic extension and branching (Franco-Villanueva et al, 2015).…”

Crosstalk between WIP and Rho family GTPases

“…We observed dysfunction of some Akt downstream elements in WIP-deficient neurons, although further work is needed to link mTORC1 dysfunction, F-actin polymerization and RhoA in these cells. [39][40][41] Many data support an essential role for WIP and GTPases, not only in tumor cell migration but also in cancer stem cell proliferation. These data allow the proposal of a molecular mechanism involved in cell proliferation, differentiation and actin cytoskeleton dynamics, all instrumental features in cell transformation and invasiveness.…”

“…The lack of WIP in hippocampal neurons co-cultured with astrocytes leads to increased dendritic spine size and Factin levels. 39,40 Identification of the molecular mechanism underlying this phenotype showed direct involvement of increasing amounts of the RhoA GTPase but not of Cdc42 or Rac1, whose levels appear to be normal. Absence of WIP produces a three-fold increase in RhoA levels as well as consistently higher RhoA activity and membrane-associated distribution.…”