Non-Muscle Myosin II Regulates Neuronal Actin Dynamics by Interacting with Guanine Nucleotide Exchange Factors

Abstract

BackgroundNon-muscle myosin II (NM II) regulates a wide range of cellular functions, including neuronal differentiation, which requires precise spatio-temporal activation of Rho GTPases. The molecular mechanism underlying the NM II-mediated activation of Rho GTPases is poorly understood. The present study explored the possibility that NM II regulates neuronal differentiation, particularly morphological changes in growth cones and the distal axon, through guanine nucleotide exchange factors (GEFs) of the Dbl family.Principal FindingsNM II colocalized with GEFs, such as βPIX, kalirin and intersectin, in growth cones. Inactivation of NM II by blebbistatin (BBS) led to the increased formation of short and thick filopodial actin structures at the periphery of growth cones. In line with these observations, FRET analysis revealed enhanced Cdc42 activity in BBS-treated growth cones. BBS treatment also induced aberrant targeting of various GEFs to the distal axon where GEFs were seldom observed under physiological conditions. As a result, numerous protrusions and branches were generated on the shaft of the distal axon. The disruption of the NM II–GEF interactions by overexpression of the DH domains of βPIX or Tiam1, or by βPIX depletion with specific siRNAs inhibited growth cone formation and induced slender axons concomitant with multiple branches in cultured hippocampal neurons. Finally, stimulation with nerve growth factor induced transient dissociation of the NM II–GEF complex, which was closely correlated with the kinetics of Cdc42 and Rac1 activation.ConclusionOur results suggest that NM II maintains proper morphology of neuronal growth cones and the distal axon by regulating actin dynamics through the GEF–Rho GTPase signaling pathway.

ROCK1 and 2 differentially regulate actomyosin organization to drive cell and synaptic polarity

“…S2; Vicente-Manzanares and Horwitz, 2010 ). Furthermore, ROCK2 is the specific isoform that regulates the magnitude of Rac activation through RLC-S19 monophosphorylation, consistent with previous evidence that contractile forces decrease Rac activity ( Katsumi et al, 2002 ), although ROCK2 could also regulate Rac activity via NMII-mediated localization of Rac guanine exchange factors ( Shin et al, 2014 ). In addition to regulating myosin II–driven contractile force generation, ROCK2 also inactivates the actin-severing protein cofilin, via Ser3 phosphorylation, leading to increased adhesion and PSD size.…”

Cell type–dependent mechanisms for formin-mediated assembly of filopodia

“…This effect is likely due to the function of myosin II on retrograde flow and has been observed in other systems ( Medeiros et al. , 2006 ; Shin et al. , 2014 ).…”

Rac-mediated actin remodeling and myosin II are involved in KATP channel trafficking in pancreatic β-cells

“… 18 , 19 , 20 Furthermore, a functional link between MyoII and Rac1/Cdc42 GTPases in regulating actin dynamics was reported in migrating cells 21 and neuronal growth cones. 22 Together, these observations suggest the possibility that Rac GTPases or MyoII may mediate AMPK-dependent actin remodeling and K ATP channel trafficking in pancreatic β-cells. In the present study, we investigated this possibility using INS-1 cells.…”