Overcoming Amino-Nogo-induced Inhibition of Cell Spreading and Neurite Outgrowth by 12-O-Tetradecanoylphorbol-13-acetate-type Tumor Promoters

Abstract

The N-terminal domain of NogoA, called amino-Nogo, inhibits axonal outgrowth and cell spreading via a largely unknown mechanism. In the present study, we show that amino-Nogo decreases Rac1 activity and inhibits fibroblast spreading. 12-OTetradecanoylphorbol-13-acetate-type tumor promoters, such as phorbol 12-myristate 13-acetate (PMA) and teleocidin, increase Rac1 activity and overcome the amino-Nogo-induced inhibition of cell spreading. The stimulating effect of tumor promoters on cell spreading requires activation of protein kinase D and the subsequent activation of Akt1. Furthermore, we identified Akt1 as a new signaling component of the amino-Nogo pathway. Akt1 phosphorylation is decreased by amino-Nogo. Activation of Akt1 with a cell-permeable peptide, TAT-TCL1, blocks the amino-Nogo inhibition. Finally, we provide evidence that these signaling pathways operate in neurons in addition to fibroblasts. Our results suggest that activation of protein kinase D and Akt1 are approaches to promote axonal regeneration after injury.Injured neurons in the adult mammalian central nervous system fail to regenerate, in part due to the existence of myelin-associated inhibitors (MAIs), 2 such as NogoA, myelinassociated glycoprotein, and oligodendrocyte-myelin glycoprotein (1). Two inhibitory regions of NogoA, a C-terminal 66-amino acid region (Nogo-66) and a lengthy N-terminal region (amino-Nogo), have been characterized based on their inhibitory function on cell spreading and neurite outgrowth (2). Nogo-66 and two other major MAIs, myelin-associated glycoprotein and oligodendrocyte-myelin glycoprotein, exert their inhibitory effects by interacting with a receptor complex that contains the Nogo receptor 1 (NgR1), Lingo-1, p75 NTR , and higher order gangliosides (1) or a newly identified receptor, PirB (paired immunoglobulin-like receptor-B) (3). However, amino-Nogo restricts non-neuronal cell spreading and axonal outgrowth (2, 4) through an unknown mechanism independent of the above NgR complex (5, 6). Despite evidence supporting the existence of a specific receptor on neurons and some nonneuronal cells (5), the identity of the amino-Nogo receptor(s) remains obscure. A recent study has provided evidence that amino-Nogo can bind to and selectively block signal transduction initiated by certain integrins (7).The intracellular signaling mechanisms responsible for amino-Nogo-induced inhibition of cell spreading and regeneration are not well understood. So far, Rho GTPases, mainly RhoA and Rac1, remain the most established mediators. Amino-Nogo activates RhoA and suppresses Rac1 in primary neurons (6,8). Activation of RhoA by MAIs has been extensively studied and is generally viewed as perhaps the key convergence point at which various MAIs exert similar functional outcomes (6, 8 -12). Blockade of RhoA signaling improves axonal regeneration in both in vitro and in vivo models (13). Rac1 activity, on the other hand, is required for neurite formation and neurite outgrowth on permissive substrates (14 -17). Although one of the con...

Association study of Nogo‐related genes with schizophrenia in a Japanese case–control sample

“…In addition, Deng et al [2010] reported that Nogo-A, one of the Nogo family proteins, elicits a decrease in the phosphorylation of the v-akt murine thymoma viral oncogene homolog 1 (Akt1), and inhibit cell spreading and neurite outgrowth, independent of the Nogo-Nogo receptor pathway. Phosphorylated AKT inactivates the glycogen synthase kinase 3 beta (GSK3b) that regulates cellular functions such as survival, growth, and cell migration [Cross et al, 1995;Aubry et al, 2009].…”

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“…NogoA is known to mediate neurite repulsion by negatively modulating actin assembly via small GTPases of the Rho family (28,32,45,46). The synaptic actin cytoskeleton is important for the regulation of neurotransmitter release in the presynaptic compartment as well as spine shape changes and anchorage of postsynaptic density (PSD)-associated molecules in the postsynaptic compartment (reviewed in ref.…”

Where no synapses go: gatekeepers of circuit remodeling and synaptic strength

“…Moreover, NogoΔ20 decreases CREB activation and leads to down-regulation of neuronal growth programs [77]. Conversely, pretreatment of primary neurons with crude myelin or Nogo66 attenuates BDNF-elicited activation of pAKT (Ser473) and p70S6K (Thr389) [38], and NogoΔ20 leads to a decrease in pAKT (Ser473) [84]. In a similar vein, CSPG binding to RPTPσ attenuates TrkB activity [85].…”