A subset of signal transduction pathways is required for hippocampal growth cone collapse induced by ephrin‐A5

Abstract

The Eph family tyrosine kinase receptors and their ligands, ephrins, play key roles in a wide variety of physiological and pathological processes including tissue patterning, angiogenesis, bone development, carcinogenesis, axon guidance, and neural plasticity. However, the signaling mechanisms underlying these diverse functions of Eph receptors have not been well understood. In this study, effects of Eph receptor activation on several important signal transduction pathways are examined. In addition, the roles of these pathways in ephrin-A5-induced growth cone collapse were assessed with a combination of biochemical analyses, pharmacological inhibition, and overexpression of dominant-negative and constitutively active mutants. These analyses showed that ephrin-A5 inhibits Erk activity while activates c-Jun N-terminal kinase. However, regulation of these two pathways is not required for ephrin-A5-induced growth cone collapse in hippocampal neurons. Artificial Erk activation by expression of constitutively active Mek1 and B-Raf failed to block ephrin-A5 effects on growth cones, and inhibitors of the Erk pathway also failed to inhibit collapse by ephrin-A5. Inhibition of JNK had no effects on ephrin-A5-induced growth cone collapse either. In addition, inhibitors to PKA and PI3-K showed no effects on ephrin-A5-induced growth cone collapse. However, pharmacological blockade of phosphotyrosine phosphatase activity, the Src family kinases, cGMP-dependent protein kinase, and myosin light chain kinase significantly inhibited ephrin-A5-induced growth cone collapse. These observations indicate that only a subset of signal transduction pathways is required for ephrin-A5-induced growth cone collapse.

NO Orchestrates the Loss of Synaptic Boutons from Adult “Sick” Motoneurons: Modeling a Molecular Mechanism

“…Therefore, NO/cGMP/PKG-induced synapse remodeling is dependent on RhoA/ROCK signaling, involving phosphorylation of the ROCK substrate MLC before synapse withdrawal in vitro. This is supported by previous studies showing that cGMP/PKG together with ROCK and/or MLCK mediates growth cone collapse responses to ephrin-B1, ephrin-A5, and semaphorin 3A in cells from different origins [189,190,217]. The function of MLCK is likely to be mediated through MLC phosphorylation, leading to myosin activation and actomyosin contraction [200].…”

Redox-guided axonal regrowth requires cyclic GMP dependent protein kinase 1: Implication for neuropathic pain

“…antagonism of this repulsion signal was also reported [42] and one study suggested that the outcome may depend on the polarization of the neuronal membrane [59]. PKG1 was also found to act downstream of Ephrin- and Slit- mediated repulsion signals [60], [61] but PKG1 also acted downstream of p53-mediated growth cone extension [42]. It has to be considered that neurite and axon elongation are contributed by shaft stretching [62], which was not specifically addressed and may contribute to the controversy.…”

Nitric Oxide Induces Pathological Synapse Loss by a Protein Kinase G-, Rho Kinase-Dependent Mechanism Preceded by Myosin Light Chain Phosphorylation

“…Increased RhoA/ROCK activity resulting from long-term action of the NO/cGMP/PKG cascade has been previously suggested in arterial smooth muscle cells (Sauzeau et al, 2003), in the penis (Bivalacqua et al, 2007), and in hearts from diabetic rats (Soliman et al, 2008). In this sense, cGMP/PKG together with ROCK and/or MLC-kinase mediates growth cone collapse responses to ephrin-B1, -A5, and Semaphorin 3A in cells from different origins (Dontchev and Letourneau, 2002;Mann et al, 2003;Yue et al, 2008). The function of MLC-kinase is likely to be mediated through MLC phosphorylation, leading to myosin activation and actomyosin contraction (Luo, 2002).…”