Phosphorylation and nitration of tyrosine residues affect functional properties of Synaptophysin and Dynamin I, two proteins involved in exo-endocytosis of synaptic vesicles

Abstract

Phosphorylation and nitration of protein tyrosine residues are thought to play a role in signaling pathways at the nerve terminal and to affect functional properties of proteins involved in the synaptic vesicle (SV) exo-endocytotic cycle. We previously demonstrated that the tyrosine residues in the C-terminal domain of the SV protein Synaptophysin (SYP) are targets of peroxynitrite (PN). Here, we have characterized the association between SYP and c-src tyrosine kinase demonstrating that phosphorylation of Tyr(273) in the C-terminal domain of SYP is crucial in mediating SYP binding to and activation of c-src. SYP forms a complex with Dynamin I (DynI), a GTPase required for SV endocytosis, which may be regulated by tyrosine phosphorylation of SYP. We here report that, in rat brain synaptosomes treated with PN, the formation of SYP/DynI complex was impaired. Noteworthy, we found that DynI was also modified by PN. DynI tyrosine phosphorylation was down-regulated in a dose-dependent manner, while DynI tyrosine nitration increased. Using mass spectrometry analysis, we identified Tyr(354) as one nitration site in DynI. In addition, we tested DynI self-assembly and GTPase activity, which are enhanced by c-src-dependent tyrosine phosphorylation of DynI, and found that both were inhibited by PN. Our results suggest that the site-specific tyrosine residue modifications may modulate the association properties of SV proteins and serve as a regulator of DynI function via control of self-assembly, thus influencing the physiology of the exo-endocytotic cycle.

Tollip, an early regulator of the acute inflammatory response in the substantia nigra

“…The deleterious effect of the cerebral nitric oxide release has been extensively reviewed [69–71]. Notably, nitration affects protein functions [72, 73] and a role of NO overproduction in PD patients was already suggested 30 years ago [16, 17, 74]. Therefore, the greater propensity of Tollip KO mice to generate nitrosative stress indicates that Tollip may constitute a potential target for neuroprotective therapies aimed at reducing iNOS-mediated damage.…”

Forced swim test induces divergent global transcriptomic alterations in the hippocampus of high versus low novelty-seeker rats

“…Moreover, the upregulation of both Pfn (profilin) isoforms (i.e., 1 and 2; +2.709 and 2.396, respectively) that are prominent regulators of actin dynamics in the CNS is indicative of the cytoskeletal reorganization that possibly takes place upon FST exposure in the hippocampus of LR rats [45]. Moreover, FST appears to stimulate neurotransmitters' release in LR rats, as reflected by the upregulation of Dnm1 (dynamin 1; +2.388) which is involved in exo-endocytosis of synaptic vesicles [46] and Syt12 (synaptotagmin 12; +2.352) which is a synaptic vesicle phosphoprotein that modulates neurotransmitter release [47]. Hippocampal synaptotagmin mRNA levels were found to be enhanced upon immobilization stress in rats, in view of the effects of stress on synaptic plasticity [48].…”

Synaptic Vesicle-Recycling Machinery Components as Potential Therapeutic Targets

“…Its function may be regulated by phosphorylation at its C-terminal domain by calcium/calmodulindependent protein kinase II and tyrosine kinase (Alder et al, 1995;Daly and Ziff, 2002;Mallozzi et al, 2013). …”