ABSTRACT
N-methyl-D-aspartate receptors (NMDARs), a subtype of glutamate-gated ion channels, play a central role in epileptogenesis. Recent studies have identified an increasing number of GRIN2A (a gene encoding the NMDAR GluN2A subunit) mutations in patients with epilepsy. Phenotypes of GRIN2A mutations include epilepsy-aphasia disorders and other epileptic encephalopathies, which pose challenges in clinical treatment. Here we identified a heterozygous GRIN2A mutation (c.1341T>A, p.N447K) from a boy with Rolandic epilepsy by whole-exome sequencing. The patient became seizure-free with a combination of valproate and lamotrigine. Functional investigation was carried out using recombinant NMDARs containing a GluN2A-N447K mutant that is located in the ligand-binding domain of the GluN2A subunit. Whole-cell current recordings in HEK 293T cells revealed that the N447K mutation increased the NMDAR current density by ~1.2-fold, enhanced the glutamate potency by 2-fold, and reduced the sensitivity to Mg inhibition. These results indicated that N447K is a gain-of-function mutation. Interestingly, alternative substitutions by alanine and glutamic acid at the same residue (N447A and N447E) did not change NMDAR function, suggesting a residual dependence of this mutation in altering NMDAR function. Taken together, this study identified human GluN2A N447K as a novel mutation associated with epilepsy and validated its functional consequences in vitro. Identification of this mutation is also helpful for advancing our understanding of the role of NMDARs in epilepsy and provides new insights for precision therapeutics in epilepsy.
Subject(s)
Adolescent , Humans , Male , Epilepsy, Rolandic , Genetics , Mutation , Receptors, N-Methyl-D-Aspartate , GeneticsABSTRACT
<p><b>BACKGROUND</b>In our previous study, we found that DAZAP2 was the most significantly down regulated gene when differential screening of complementary DNA (cDNA) chips were used to analyze mRNA isolated from bone marrow mononuclear cells from newly diagnosed multiple myeloma (MM) patients without anticancer treatment. In this study, we observed DAZAP2 mRNA and protein expression in the mononuclear cells from MM bone marrow and investigated its role in the pathogenesis of MM.</p><p><b>METHODS</b>The full-length cDNA of DAZAP2 was cloned and sequenced from mononuclear cells from human bone marrow. The nucleotide and amino acid sequences of DAZAP2 were analyzed using the ClustalW program. A dendrogram was constructed by multiple sequence alignment using ClustalW and amino acid sequence identity/similarity was derived based on comparisons attained using the MegAlign software. The recombinant pEGFP expression vector was constructed and the confocal microscopy was used for the localization of the DAZAP2 protein in transfected COS7 cells. The expression of DAZAP2 mRNA was detected by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) and the expression level of DAZAP2 protein was detected by Western blotting analysis in MM samples.</p><p><b>RESULTS</b>DAZAP2 proteins of vertebrates is highly conserved in evolution. It contains a proline-rich region, several potential SH2 and SH3 domain-binding motifs and a possible protein kinase C (PKC) phosphorylation site. We showed by confocal microscopy that the DAZAP2 protein predominantly resides in the cytoplasm with a discrete pattern of punctuated distribution. The expression of DAZAP2 was not detected in 24 of 36 MM samples by semi-quantitative RT-PCR. In contrast, DAZAP2 expression was detected in all 30 normal controls. The expression level of DAZAP2 protein was assayed by Western blotting analysis, showing a robust down-regulation in MM patients (P < 0.001) that matched with the results of the RT-PCR.</p><p><b>CONCLUSIONS</b>DAZAP2 is downregulated in MM samples and it may be a signal molecule in MM cells. DAZAP2 is involved in the pathogenesis of MM and could be used as a genetic marker for MM.</p>