Novel spliced variants of ionotropic glutamate receptor GluR6 in normal human fibroblast and brain cells are transcribed by tissue specific promoters

Abstract

The members of the ionotropic glutamate receptor family, namely, a-amino-3-hydroxy-S-methyl-4-isoxazole propionate (AMPA), kainate, and N-methyl-D-aspartate (NMDA) receptors, are important mediators of the rapid synaptic transmission in the central nervous system. We have investigated the splicing pattern and expression of the kainate receptor subunit GluR6 in human fibroblast cell lines and brain tissue. We demonstrate the expression of GluR6A variant specifically in brain, and four variants, namely, GluR6B, GluR6C, GluR6D and GluR6E in fibroblast cell lines. The variants GluR6D and GluR6E have not been described before, and appear to be specific for non-neuronal cells. Genomic analysis and cloning of the sequence preceding the transcribed region led to the identification of two tissue specific promoters designated as neuronal promoter PN and non-neuronal promoter PNN. We have used RNA ligase mediated RACE and in silico analyses to locate two sets of transcription start sites, and confirmed specific transcripts initiated by PN and PNN in brain cells and fibroblasts, respectively. The domain structure of variants GluR6D and GluR6E revealed the absence of three transmembrane domains. The lack of these domains suggests that the mature receptors arising from these variant subunits may not function as active channels. Based on these structural features in GluR6D and GluR6E, and the observations that GluR6B, GluR6C, GluR6D and GluR6E are exclusively expressed in non-neuronal cells, it is likely that these receptor subunits function as non-channel signaling proteins.

Senescence of Normal Human Fibroblasts Relates to the Expression of Ionotropic Glutamate Receptor GluR6/Grik2

“…The cells transduced with the EGFP construct by itself showed a protein band of ~27 kD, which corresponds to the predicted size of EGFP. These results clearly demonstrate the expression of expected sizes of transduced GRIK2 isoforms in the transfected fibroblasts (8).…”

“…These isoforms arise from the action of two promoters and the alternative splicing of the pre-mRNA molecule (7). While the Grik2-A isoform is transcribed from the neuronal promoter, the non-neuronal promoter is activated in epithelial cells to produce other isoforms (8).…”

Splicing and editing of ionotropic glutamate receptors: a comprehensive analysis based on human RNA-Seq data

“…S14A). The corresponding splice event has been detected before [110], but the 5′-exon appears to be shorter than reported. Apart from splicing, a polymorphic TAA region is present in the 3′-UTR [111].…”

Autism and intellectual disability in a patient with two microdeletions in 6q16: a contiguous gene deletion syndrome?

“…Zhawar et al found GluR6 receptor subunits to be differentially expressed with expression of the GluR6A variant specifically in brain [24]. Studies on mice lacking the GluK2 subunit of kainate receptors, for which GRIK2 encodes, observed reduced social interaction and altered executive functions.…”