Korean J Physiol Pharmacol.  2020 Jan;24(1):121-126. 10.4196/kjpp.2020.24.1.121.

Ezrin-radixin-moesin proteins are regulated by Akt-GSK3β signaling in the rat nucleus accumbens core

• Kim WY
• Cai WT
• Jang JK
• Kim JH

• KMID: 2466576
• DOI: http://doi.org/10.4196/kjpp.2020.24.1.121

Abstract

The ezrin-radixin-moesin (ERM) proteins are a family of membrane-associated proteins known to play roles in cell-shape determination as well as in signaling pathways. We have previously shown that amphetamine decreases phosphorylation levels of these proteins in the nucleus accumbens (NAcc), an important neuronal substrate mediating rewarding effects of drugs of abuse. In the present study, we further examined what molecular pathways may be involved in this process. By direct microinjection of LY294002, a PI3 kinase inhibitor, or of S9 peptide, a proposed GSK3β activator, into the NAcc core, we found that phosphorylation levels of ERM as well as of GSK3β in this site are simultaneously decreased. These results indicate that ERM proteins are under the regulation of Akt-GSK3β signaling pathway in the NAcc core. The present findings have a significant implication to a novel signal pathway possibly leading to structural plasticity in relation with drug addiction.

Keyword

Drug addiction; Glycogen synthase kinase; Nucleus accumbens; Protein kinase B; Signal transduction

MeSH Terms

Amphetamine
Animals
Glycogen Synthase Kinases
Humans
Membrane Proteins
Microinjections
Negotiating
Neurons
Nucleus Accumbens*
Phosphorylation
Phosphotransferases
Plastics
Proto-Oncogene Proteins c-akt
Rats*
Reward
Signal Transduction
Street Drugs
Substance-Related Disorders
Amphetamine
Glycogen Synthase Kinases
Membrane Proteins
Phosphotransferases
Plastics
Proto-Oncogene Proteins c-akt
Street Drugs

Figure

• 

  Fig. 1 Microinjection of LY294002 into the nucleus accumbens (NAcc) core decreases phosphorylation levels of activates protein kinase B (Akt), glycogen synthase kinase 3β (GSK3β), and ezrin-radixin-moesin (ERM) in this site. (A) The NAcc core region where tissues were taken out is shown (cross-hatched circles). Punches (1.2 mm diameter) were prepared bilaterally and pooled for each individual animal's protein isolation. Line drawing is from Paxinos and Watson (2004) [32] and depicts the caudal surface of a coronal section (1.0 mm thick) extending 1.70–2.70 mm from bregma. (B–D) Representative Western blots are shown. Values for the band intensities were first normalized to β-actin and then the average values for the ratio of phosphorylated to total proteins in each group were expressed as mean + standard error of the mean relative to saline control group. Symbols indicate significant differences as revealed by post-hoc Bonferroni comparisons following one-way ANOVA. **p < 0.01, ***p < 0.001, significantly different compared to saline control rats. Numbers for each group are 6.

• 

  Fig. 2 Microinjection into the nucleus accumbens (NAcc) core of S9 peptide, a proposed activator of glycogen synthase kinase 3β (GSK3β), lowers phosphorylation levels of GSK3β, and ezrin-radixin-moesin (ERM) in this site. (A) A diagram showing the S9 peptide with short amino acid sequences competitive against a phosphorylation site at serine 9 of endogenous GSK3β. (B, C) Representative Western blots are shown. Values for the band intensities were first normalized to β-actin and then the average values for the ratio of phosphorylated to total proteins in each group were expressed as mean + standard error of the mean relative to saline control group. Symbols indicate significant differences as revealed by posthoc Bonferroni comparisons following one-way ANOVA. *p < 0.05, significantly different compared to saline control rats. Numbers for each group are 5 to 6.

• 

  Fig. 3 A hypothetical diagram depicts a signal pathway where activates protein kinase B (Akt) and glycogen synthase kinase 3β (GSK3β) position as possible upstream effectors to ezrin-radixin-moesin (ERM). (Left) GSK3β is normally inactive when phosphorylated, for example, by its upstream effector, Akt, while ERM is active contributing to the maintenance of cell structures. (Middle) When LY294002 is present, as Akt becomes inactive, so does GSK3β active by less chance of phosphorylation. Interestingly, ERM also becomes inactive correspondingly. (Right) With S9 peptide entered, Akt is now competing with S9 against its phosphorylation site of GSK3β, so there is more chance that active (un-phosphorylated) form of GSK3β exists. Again with S9, ERM becomes inactive correspondingly, suggesting that it is under the regulation of Akt and GSK3β.

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