Abstract 1549: Ectopic expression of a glutamate receptor gene, glur6, induces growth arrest and senescence in breast and ovarian tumor cells

Applying a functional strategy we determined that Glur6 gene plays a role in the cell senescence. Using chromosome transfer method, we previously identified a YAC clone that carries a cell senescence gene, SEN6A, mapping at 6q21. Human data base search identified GluR6, a kainate type ionotropic glutamate receptor gene, to represent SEN6A. Glutamate receptors are primarily located on the membrane of neuronal cells and are important mediators of rapid synaptic transmission in central nervous system. We cloned GluR6 gene by RT-PCR and defined the structure, splicing pattern and its role in the cell growth and cancer. Five GluR6 splice variants (A-E), transcribed from two different promotes, are differentially expressed in brain and other tissues and cultured cells. GluR6A, specifically expressed in brain, is transcribed from promoter 2, while GluR6 (B-E), transcribed from promoter 1, are expressed in other tissues. GluR6 is either turned off or expressed at reduced level in breast and ovarian tumor cells, whereas its expression is elevated in aged (senescent) cells. Full length cDNAs (open reading frames) for each of the five transcript isoforms of GluR6 were cloned, in frame with EGFP, in a retroviral vector, PQCXIP, and introduced into breast and ovarian tumor cell lines T47D, MCF.7 and SKOV3. Analysis of gene transfer clones revealed that GluR6 expression inhibit the proliferation of breast and ovarian tumor cells leading to senescence. Cells expressing transferred GluR6 gene displayed the doubling time of 60-96 hours that gradually extended to 3-4 days, ending in complete growth arrest and senescence. The gene transfer senescent cells lacked DNA synthesis and were positive for SA-βgal staining. In controls, the transfer of empty vector or vector carrying a truncated GluR6 gene did not affect the growth of tumor cells. In addition control cultures were negative for SA-βgal staining and positive for DNA replication. Our preliminary data shows that GluR6 may function through AKT and ROS pathways. In conclusion, in this study we show that GluR6, which normally functions in neurotransmission and is implicated in a number of neurological disorders, may also be involved in the development and progression of cancer. Thus, pathways related to GluR6 expression may prove to be new novel targets for cancer therapy. Modulation of GluR6 function through small molecule and/or glutamate antagonists has the potential to modify the behavior of tumors in terms of their migration, invasion and metastasis. Drugs already developed for the treatment of neurological disorders can be tested for treatment of cancer. Citation Format: Raghbir S. Athwal, Vikramjit K. Zhawar, Gurpreet Kaur. Ectopic expression of a glutamate receptor gene, glur6, induces growth arrest and senescence in breast and ovarian tumor cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1549. doi:10.1158/1538-7445.AM2014-1549