A crosslinking analysis of GAP-43 interactions with other proteins in differentiated N1E-115 cells

The influence of GAP-43 on orientation of cell division through G proteins

Recent studies have shown that GAP-43 is highly expressed in horizontally dividing neural progenitor cells, and G protein complex are required for proper mitotic-spindle orientation of those progenitors in the mammalian developing cortex. In order to verify the hypothesis that GAP-43 may influence the orientation of cell division through interacting with G proteins during neurogenesis, the GAP-43 RNA from adult C57 mouse was cloned into the pEGFP-N1 vector, which was then transfected into Madin-Darby Canine Kidney (MDCK) cells cultured in a three-dimensional (3D) cell culture system. The interaction of GAP-43 with Gαi was detected by co-immunoprecipitation (co-IP), while cystogenesis of 3D morphogenesis of MDCK cells and expression of GAP-43 and Gαi were determined by immunofluorescence and Western blotting. The results showed are as follows: After being transfected by pEGFP-N1-GAP-43, GAP-43 was localized on the cell membrane and co-localized with Gαi, and this dramatically induced a defective cystogenesis in 3D morphogenesis of MDCK cells. The functional interaction between GAP-43 and Gαi proteins was proven by the co-IP assay. It can be considered from the results that the GAP-43 is involved in the orientation of cell division by interacting with Gαi and this should be an important mechanism for neurogenesis in the mammalian brain.

Capture of D2 dopamine receptor signaling complexes in striatal cells for mass spectrometry proteomic analysis

In recent years advancements in proteomic techniques have contributed to the understanding of protein interaction networks (Interactomes) in various cell types. Today, high throughput proteomics promises to define virtually all of the components of a signaling and a regulatory network within cells for various molecules including membrane-spanning receptors. The D2 dopamine receptor (D2R) is a primary mediator of dopamine transmission in the brain. Signaling through D2Rs has been linked to dopamine-mediated effects on motivation, reward, locomotion and addiction to drugs of abuse. In the striatum, the D2R is a key mediatory of dopamine transmission. Actions on this receptor are an important pharmacological property of various drugs including typical antipsychotics and drugs of abuse. Here we provide an approach for the identification protein interaction networks of the D2R within striatal cells. We discuss key assays and techniques, such as cellular membrane protein fractionation, western blot analysis, magnetic bead coimmunoprecipitation, and liquid chromatography electrospray ionization (LC-ESI) mass spectrometry, that can be used for the isolation and characterization of D2R protein interaction networks. This approach presents a reliable method for the identification and characterization of D2R signaling within cells.

Expression of GAP-43 in fibroblast cell lines influences the orientation of cell division

The orientation (vertical or horizontal) of cell division is known to be critical for neural cell fate determination during neurogenesis. At the onset of neurogenesis, neurogenic progenitor cells are dividing with the cleavage plane parallel to the ventricular surface (horizontal division), which would lead to critical apical components being unequally distributed to both their two daughter cells. The daughter cells lack of inheritance is going to differentiate into the neuron. Recent studies have shown that GAP-43 is highly expressed in horizontally dividing neural progenitor cells in the forebrain of mammals. Based on findings from in vivo studies, GAP-43 is locally associated with the centrosome and is required for centrosome positioning, suggesting that GAP-43 may be involved in neurogenesis through regulating the orientation of cell division. With a fibroblast cell model, our results show that both GFP expressing and control cells had the same potential (p>0.05) with regard to dividing orientation (either vertical or horizontal to the cells long axis). On the other hand, we found that GAP-43 was localized on the membrane instead of the centrosome during all phases of mitosis within GAP-43 transgenic cells, but expressing of GAP-43 could make the cells dividing more likely along their long axis (p<0.05). Our observations suggest that GAP-43 might link the cell membrane and spindle pole and consequently participate in controlling cleavage orientation during cell division.

GAP43 shows partial co-localisation but no strong physical interaction with prolyl oligopeptidase

It has recently been proposed that prolyl oligopeptidase (POP), the cytosolic serine peptidase with neurological implications, binds GAP43 (Growth-Associated Protein 43) and is implicated in neuronal growth cone formation, axon guidance and synaptic plasticity. We investigated the interaction between GAP43 and POP with various biophysical and biochemical methods in vitro and studied the co-localisation of the two proteins in differentiated HeLa cells. GAP43 and POP showed partial co-localisation in the cell body as well as in the potential growth cone structures. We could not detect significant binding between the recombinantly expressed POP and GAP43 using gel filtration, CD, ITC and BIACORE studies, pull-down experiments, glutaraldehyde cross-linking and limited proteolysis. However, glutaraldehyde cross-linking suggested a weak and transient interaction between the proteins. Both POP and GAP43 interacted with artificial lipids in our in vitro model system, but the presence of lipids did not evoke binding between them. In native polyacrylamide gel electrophoresis, GAP43 interacted with one of the three forms of a polyhistidine-tagged prolyl oligopeptidase. The interaction of the two proteins was also evident in ELISA and we have observed co-precipitation of the two proteins during co-incubation at higher concentrations. Our results indicate that there is no strong and direct interaction between POP and GAP43 at physiological conditions.