| Abstract |
The therapy of patients suffering from chronic diseases demands the repetitive use of drugs in order to alleviate the pain. However, that gradually leads to increasing drug tolerance necessitating larger drug doses to achieve the same effect. The later further increases the risk of side effects and addiction. Opioid analgetic drugs, such as morphine, fentanyl etc, exert their function by binding to μ opioid receptors (MOR) that belong to the GPCR receptor family. Such drugs act on mesoaccumbens dopamine system that projects from the Vental Tagmented Area (VTA) to the Nucleus Accumbens (NAc). RGS proteins regulate the activity and the effectiveness of μ opioid receptor after its activation, regulating the downstream signaling cascade in cells. Three RGS family members, RGS9-2, RGS4, and RGSz were previously shown to act as essential modulatory regulators of the opiate drug actions. Spinophilin, a dendritic protein is highly expressed in dendric spines and functions as a scaffolding protein for many other proteins as well. Spinophilin has a pivotal role in mediating signaling transduction and the orchestration of plasticity of dendric spines. However, the role of spinophilin in the adaptive process underlying opiate addiction is not fully understood. By using immunoprecipitation approach, the present study examined the interaction of spinophilin with specific RGS proteins, RGS9-2, RGS4, RGSz in NAc and how such interactions are altered following the administration of different drugs, i.e. fentanyl and morphine. Here, we show that all three RGS proteins interact with spinophilin under basal conditions. Moreover, confocal microscopic analysis in transiently transfected HEK293 cells revealed that spinophilin co-localize with MOR receptor. However, after treatment with morphine MOR receptor was internalized in cellular compartments distinct from those found of spinophilin. The cellular position of spinophilin was observed with live imagine experiments in MEF cells transfected with spinophilin::GFP vector. Finally, in order to examine if spinophilin plays a role in correct placement of RGS in plasma membrane, we performed immunochemistry experiments on WT and KO MEF cell lines for spinophilin protein. In the absence of spinophilin, RGS9-2 protein was not correctly placed at the plasma membrane. Together, these data suggest that spinophilin plays an essential role in MOR functional response as well as in the adaptive changes associated with opiate addiction.
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Ο ρόλος της πρωτεΐνης spinophilin στη μεταγωγή σήματος στο σχηματισμό σηματοδοτικών συμπλοκών στα βασικά γάγγλια του εγκεφάλου
