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

Abstract

Background/Aim: Glutamate receptor GRIK2, previously designated as GluR6, is best described in neuronal cells. However, its biological relevance in nonneuronal cells is not well understood. We have investigated the expression of this important protein in normal human fibroblasts as a function of cell proliferation. Materials and Methods: We introduced expression constructs of all five isoforms (A-E) of GRIK2 in normal human fibroblasts and investigated the cells for the presence and localization of GRIK2, as well as for cell proliferation and senescence over a period of 24 days. Results: The expression of GRIK2-A isoform led to immediate cessation of cell proliferation. However, the cell numbers increased by 1.5-to 9.0-fold in 24 days upon transfection with B, C, D and E isoforms, after which they entered a state of senescence. The decreased proliferation was reflected by incorporation of BrdU in only 2-8% of transfected cells even after culturing them for 16 days. Conclusion: Our results are indicative of an association between GRIK2 and aging of fibroblasts. Normal cells proliferate for a finite number of cell divisions before entering replicative senescence and eventually cell death. The interference with this normal cycle can either 707 This article is freely accessible online.

Alternative Promoters of GRIK2 (GluR6) Gene in Human Carcinoma Cell Lines Are Regulated by Differential Methylation of CpG Dinucleotides

“…In fact, the transfer of this region of the chromosome to a variety of carcinoma cells led to a senescence phenotype. The GluR6 gene maps to the minimal region responsible for inducing senescence in tumor cells [ 17 , 18 ]. Although GluR6 has primarily been investigated in the context of excitable cells, unique isoforms of this gene have now been described in non-neuronal cells as well.…”

“…The gene is transcribed into five isoforms (A, B, C, D, and E) in a tissue-specific manner by alternative usage of two distinct promoters in neuronal and non-neuronal cells, respectively [ 7 ]. We have previously shown that the introduction of expression constructs of GluR6 in normal fibroblasts and ovarian carcinoma cells induces senescence [ 17 , 18 ]. Our results indicate that GluR6 by itself is sufficient to induce senescence in tumor cells.…”