Mutation in the Phosphorylation Sites of MAP Kinase Blocks Learning-Related Internalization of apCAM in Aplysia Sensory Neurons

Abstract

The synaptic growth that accompanies 5-HT-induced long-term facilitation of the sensory to motor neuron connection in Aplysia is associated with the internalization of apCAM at the surface membrane of the sensory neuron. We have now used epitope tags to examine the fate of each of the two apCAM isoforms (membrane bound and GPI-linked) and find that only the transmembrane form is internalized. This internalization can be blocked by overexpression of transmembrane constructs with a single point mutation in the two MAPK consensus sites, as well as by injection of a specific MAPK antagonist into sensory neurons. These data suggest MAPK phosphorylation at the membrane is important for the internalization of apCAMs and, thus, may represent an early regulatory step in the growth of new synaptic connections that accompanies long-term facilitation.

Chronic CXCL10 alters the level of activated ERK1/2 and transcriptional factors CREB and NF-κB in hippocampal neuronal cell culture

“…Recent studies show that in cultured mouse CNS neurons acutely applied CXCL10 (25 nM) can result in activation of the ERK1/2 pathway (Xia et al, 2000), a pathway that plays a central role in CNS synaptic functions and cell growth and survival (Bahr et al, 2002;Bailey et al, 1997;Fukunaga and Miyamoto, 1998;Hetman and Gozdz, 2004;Kornhauser and Greenberg, 1997;Vaudry et al, 2002;Waetzig and Herdegen, 2003). Little is known about the signal transduction pathways activated in CNS cells by chronic exposure to CXCL10.…”

“…Our previous immunohistochemical studies ( Nelson and Gruol, 2004) showed that the cultured hippocampal neurons are strongly immunoreactive for CXCR3, the receptor for CXCL10, whereas astrocytes are only weakly immunoreactive, consistent with higher level of CXCR3 in neurons than in glia and the effects of CXCL10 on signal transduction molecules occurring primarily in the neuronal population. ERK1/2 activation plays a key role in promoting neuronal growth, differentiation, survival, as well as in long-term memory (Bailey et al, 1997;Fukunaga and Miyamoto, 1998;Hetman and Gozdz, 2004;Kornhauser and Greenberg, 1997). However, sustained ERK1/2 activation has been associated with neuronal death (Alessandrini et al, 1999;Murray et al, 1998;Runden et al, 1998).…”

“…Our current studies showing that chronic exposure to CXCL10 alters the levels of cell specific proteins in the hippocampal cultures also provides evidence for a CXCL10 signaling pathway in the hippocampal cells. Although limited information is available on the signaling pathway activated by CXCL10 in CNS neurons and glia, it has been reported that acute exposure to CXCL10 can activate the ERK1/2 pathway in neurons (Bonacchi et al, 2001;Xia et al, 2000), a pathway that mediates a number of neuronal functions including synaptic plasticity, neuronal growth, differentiation, and survival (Bahr et al, 2002;Bailey et al, 1997;Fukunaga and Miyamoto, 1998;Hetman and Gozdz, 2004;Kornhauser and Greenberg, 1997;Vaudry et al, 2002;Waetzig and Herdegen, 2003). In the hippocampal cultures, acute exposure to CXCL10 increased the level of activated (i.e., phosphorylated) ERK1/2 (no effect on total ERK1/2), consistent with an involvement of the ERK1/2 pathway in the actions of acute CXCL10 on the hippocampal cells (Nelson and Bajova, 2007) However, It is unknown if the ERK1/2 pathway is involved in actions of CXCL10 in the hippocampal cultures under conditions of chronic CXCL10 exposure.…”

“…Binding of CXCL10 to CXCR3 can activate a variety of intracellular signal transduction pathways (Bonacchi et al, 2001;Moser and Loetscher, 2001;Xia et al, 2000), including the Ras/ERK signaling pathway, a pathway that is known to play an important role in functions such as growth, differentiation, survival, and long-term memory (Bahr et al, 2002;Bailey et al, 1997;Fukunaga and Miyamoto, 1998;Hetman and Gozdz, 2004;Kornhauser and Greenberg, 1997;Vaudry et al, 2002;Waetzig and Herdegen, 2003). However, prolonged activation of ERK has been reported to participate in neuronal death induced by various stimuli (Alessandrini et al, 1999;Murray et al, 1998;Runden et al, 1998).…”

Plasticity and Second Messengers During Synapse Development

“…In Aplysia, ApMAPKinase, the homolog of P44/42-extracellular-signal-regulated-kinase (ERK), plays a major role in long-term facilitation (LTF; Bailey et al, 1997). LTF elicits translocation of activated ApMAPKinase into the neuronal nucleus, and the internalization of ApCAM, a homolog of Neuronal-Cell-Adhesion-Molecule (NCAM) in mouse, and FasII in flies (Mayford et al, 1992).…”