Mol Cell | Han Junhai's group reveals the molecular mechanism of polyglutamine binding protein 1 regulating translation elongation and affecting synaptic plasticity

Protein biosynthesis in cells is strictly and finely regulated, which allows organisms to cope with various survival needs.

Translation extension is the most energy-consuming step in protein synthesis, which determines the efficiency and accuracy of protein synthesis.

This step is mainly regulated by the eEF2K/eEF2 pathway.
Various signaling pathways such as Ca2+ /calmodulin, p38 MAPK, S6K, mTOR and PKA affect the phosphorylation level of eEF2 by regulating the activity of eEF2K, thereby inhibiting or activating translation extension .

In nerve cells, the eEF2K/eEF2 pathway is essential for activity-dependent synaptic plasticity and memory consolidation.
One important unanswered question is whether other factors can antagonize the effect of eEF2K and directly participate in the regulation of eEF2 phosphorylation.
So that the cells maintain sufficient sensitivity and reactivity.

Recently, Molecular Cell published online the research results PQBP1 promotes translational elongation and regulates hippocampal mGluR-LTD by suppressing eEF2 phosphorylation of the Han Junhai research group of the School of Life Science and Technology of Southeast University.

The study found that the mental retardation-related protein PQBP1 can directly bind to eEF2 to regulate its phosphorylation level, and it is an important component of the dynamic regulatory network of the eEF2K/eEF2 pathway.

Interfering with the interaction of PQBP1 and eEF2 in hippocampal neurons can lead to impaired synaptic plasticity and abnormal cognitive function.

This discovery provides a new mechanism explanation for PQBP1-related intellectual developmental disorders.
At the same time, because PQBP1 is widely expressed in tissues, it is involved in development, differentiation, viral infection, and tumorigenesis.
The newly discovered PQBP1-eEF2-eEF2K regulation The mechanism also provides new ideas for the treatment of neurological diseases, viral infections and tumors.

The team of Professor Junhai Han from the School of Life Science and Technology of Southeast University has long been committed to the study of the pathogenesis of childhood autism and neurodevelopment-related diseases.

Renpenning syndrome is an X chromosome-linked mental retardation caused by mutations in the polyglutamine binding protein 1 (PQBP1) gene [1].

PQBP1 is mainly located in the nucleus and participates in the process of gene transcription and mRNA shearing [2-5], but whether PQBP1 is distributed in the cytoplasm has a separate function has not been very clear.

Kunde et al.
found that PQBP1 interacts with many RNA-binding proteins such as FMRP, KSRP, etc.
, and is located on RNA particles in the cytoplasm, and may be involved in the transport of mRNA [6].

Junhai Han’s team was the first to find that PQBP1 in the cytoplasm is mainly distributed in the components containing mRNPs, 40S, 60S ribosomal subunits and 80S monomeric ribosomes in Drosophila and cell models, and is responsible for the target mRNA from the mRNP complex.
Transport to the translation ribosome, PQBP1 affects the development of photoreceptor cells by mediating the expression of the membrane protein Chaooptin, revealing the new molecular function of PQBP1 involved in mRNA translation in the cytoplasm [7].

In this study, their team continued to conduct in-depth research on the mechanism of PQBP1 in the regulation of protein synthesis in higher mammals.

Dr.
Yuqian Shen from the research group of Professor Junhai Han used the method of immunoprecipitation to identify the interaction molecules of cytoplasmic PQBP1 by mass spectrometry, and found that cytoplasmic PQBP1 interacts with many protein molecules related to the translation process such as ribosomal proteins and elongation factors.
The extension factor eEF2 has the highest abundance.After careful biochemical analysis, the researchers determined that PQBP1 can directly bind to the T56 phosphorylation site of translation elongation factor eEF2 through its WW domain, thereby protecting eEF2 from phosphorylation by its exclusive kinase eEF2K and promoting protein synthesis.

Harringtonine Run-Off [10] experiments show that knocking down PQBP1 reduces the rate of translation extension.

The researchers further used the aminoacyl-tRNA analog Puromycin to label the nascent protein [8] and found that the synthesis of the nascent protein was significantly reduced after PQBP1 was knocked down in the cell line.

At the same time, using the methionine analogue HPG to label the neonatal protein [9], they found that the neonatal protein in the primary liver cells of the PQBP1 conditional knockout mice was significantly reduced, verifying that PQBP1 is a key factor necessary for protein synthesis.

eEF2K/eEF2 is very important for activity-dependent synaptic plasticity.

In the metabotropic glutamate receptor-dependent long-term inhibition (mGluR-LTD), DHPG activates mGluR, and the activated mGluR activates eEF2K through the influx of calcium ions to promote the phosphorylation of eEF2, inhibit the translation elongation process, and make the total Protein synthesis decreases, but it will increase the rapid translation of the synaptic activity-related molecule Arc/Arg3.
1.
Arc/Arg3.
1 forms a complex with Endo and Dyn, and induces endocytosis of AMPA receptors to mediate synaptic plasticity LTD The production [10].

PQBP1 is highly expressed in the hippocampal neurons of adult mice.
Previous studies have focused on the role of PQBP1 in the development process, but people know little about its function in mature neurons.

Junhai Han’s team then investigated whether the PQBP1/eEF2 interaction would affect synaptic function.
They also found that knocking out PQBP1 in hippocampal neurons resulted in abnormally increased phosphorylation levels of eEF2 and damaged mGluR-LTD.
The mice showed obvious recognition.
Known dysfunction, and the use of AAV vector exogenous expression of PQBP1 protein fragment that can bind to eEF2 in knockout mice can successfully rescue the phenotype. Injection of peptides that interfere with the binding of PQBP1/eEF2 into the hippocampus of normal mice also caused mGluR-LTD-related cognitive dysfunction.

They further found that the abnormal increase in phosphorylation level of eEF2 caused by knocking out PQBP1 kept the background expression of Arc/Arg3.
1 protein at a high level.
When mGluR was activated by DHPG, no further increase caused by rapid translation occurred.
.

Their study clearly showed that the rapid and dynamic changes in the expression level of Arc/Arg3.
1 rather than the absolute amount during the activation of the mGluR receptor induce long-term inhibition.

Therefore, this study clearly analyzes the function of PQBP1 in mature neurons for the first time, deepens our understanding of the regulation mechanism of synaptic plasticity, and provides a new explanation for the pathogenic mechanism of mental retardation caused by PQBP1 mutation.
.

PQBP1 is widely expressed in tissues and is involved in development, proliferation, viral infection, and tumorigenesis.
This newly discovered regulatory mechanism of PQBP1-EF2-eEF2K is closely related to neuropsychiatric diseases, viral infections, and cancers.
May become a potential therapeutic target for these diseases.

Figure 1: Schematic diagram of the mechanism that PQBP1 regulates hippocampal mGluR-LTD by inhibiting eEF2 phosphorylation and promoting translation elongation Associate researcher Zhang Zichao and postdoctoral fellow Cheng Shanshan are the co-first authors of the research paper.

The Han Junhai research group of the School of Life Science and Technology of Southeast University is openly recruiting associate researchers and post-doctoral fellows in electrophysiology and bioinformatics.

The research group has published a series of papers in authoritative journals such as Molecular Cell, Neuron, Dev Cell, Current Biology, PLos Biology, EMBO J, JNs, etc.
For more information, please refer to the website: https://ils.
seu.
edu.
cn/2015 /0331/c22871a282856/page.
htm Resume delivery (If you are interested, please send your resume (including scientific research experience, published papers, recommendation letters, etc.
) to): https://jinshuju.
net/f/ZqXwZt or scan the QR code for delivery Link to the original resume: https://doi.
org/10.
1016/j.
molcel.
2021.
01.
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