Abstract LB-48: Somatic mutation of the NMDAR subunit GRIN2A in malignant melanoma results in loss of tumor suppressor activity.
Authors: Prickett Todd D. , Hill Victoria , Gartner Jared , Zerlanko Brad , Jiang Jiji , Samaan May , Wunderlich John , Gutkind Silvio , Rosenberg Steven A. , Samuels Yardena 
Published: August 2014

Abstract
Glutamate receptors regulate many different cellular processes such as; homeostasis, growth, neurotransmission, proliferation, survival and cell death. These receptors are composed of two different major types; the ionotropic and the metabotropic family. The ionotropic glutamate receptors are composed of large complexes of multi-protein subunits creating ion channels in the cell plasma membranes that allow for influx or efflux of mono- or divalent cations (e.g., Ca2+)1. Upon binding of glutamate, these ligand gated-ion channels change their conformation giving rise to ion permeability and oscillations that in many neuronal cells (cerebellar granule cells, neurons, astrocytes, and glial cells) are important for synaptic transmissions, cellular migration and survival. We recently discovered the high prevalence of somatic mutations within one of the ionotropic glutamate receptors, GRIN2A, in malignant melanoma (1). Whole-exome sequencing of 14 tumor and matched normal samples from treatment naïve melanoma patients revealed that GRIN2A harbored 34 somatic mutations across 125 melanoma samples (25.2%). The mutations were distributed throughout the gene, with clustering of mutations within important functional domains. We also observed three recurrent alterations (S278F, E371K, and E1175K) as well as 5 nonsense mutations. Recently, additional groups have since observed high mutation frequencies of GRIN2A within separate melanoma cohorts, suggesting that genetic alteration of this gene is important (2-3). Functional characterization of a subset of GRIN2A mutants demonstrated loss of complex formation between GRIN1 and GRIN2A, decreased cell death, increased anchorage-independent growth in soft agar, increased migration and decreased Ca2+-channel influx promoting cell survival whilst expression of GRIN1:GRIN2A wild-type complexes resulted in decreased cell proliferation via Ca2+ -mediated programmed cell death. Depletion of endogenous GRIN2A in melanoma cells expressing wild-type GRIN2A resulted in increased proliferation compared to control. In contrast, shRNA depletion of GRIN2A in mutant cell lines had little to no effect. Our data shows that somatic mutation of GRIN2A results in decreased Ca2+-mediated apoptosis in melanoma cells causing increased survival and is the first to demonstrate the functional implications of GRIN2A mutations in melanoma. Importantly, our whole-exome study was the first to demonstrate that the glutamate signaling pathway is significantly altered in melanoma.
Citation Format: Todd D. Prickett, Victoria Hill, Jared Gartner, Brad Zerlanko, Jiji Jiang, May Samaan, John Wunderlich, Silvio Gutkind, Steven A. Rosenberg, Yardena Samuels. Somatic mutation of the NMDAR subunit GRIN2A in malignant melanoma results in loss of tumor suppressor activity. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-48. doi:10.1158/1538-7445.AM2013-LB-48