title: A fluorescence-coupled assay for gamma aminobutyric acid (GABA) reveals metabolic stress-induced modulation of GABA content in neuroendocrine cancer.
abstract: Pathways involved in the synthesis of the neurotransmitter gamma-aminobutyric acid (GABA) have been implicated in the pathogenesis of high grade neuroendocrine (NE) neoplasms as well as neoplasms from a non-NE lineage. Using The Cancer Genome Atlas, overexpression of the GABA synthetic enzyme, glutamate decarboxylase 1 (GAD1), was found to be associated with decreased disease free-survival in prostate adenocarcinoma and decreased overall survival in clear cell renal cell carcinomas. Furthermore, GAD1 was found to be expressed in castrate-resistant prostate cancer cell lines, but not androgen-responsive cell lines. Using a novel fluorescence-coupled enzymatic microplate assay for GABA mediated through reduction of resazurin in a prostate neuroendocrine carcinoma (PNEC) cell line, acid microenvironment-induced stress increased GABA levels while alkaline microenvironment-induced stress decreased GABA through modulation of GAD1 and glutamine synthetase (GLUL) activities. Moreover, glutamine but not glucose deprivation decreased GABA through modulation of GLUL. Consistent with evidence in prokaryotic and eukaryotic organisms that GABA synthesis mediated through GAD1 may play a crucial role in surviving stress, GABA may be an important mediator of stress survival in neoplasms. These findings identify GABA synthesis and metabolism as a potentially important pathway for regulating cancer cell stress response as well as a potential target for therapeutic strategies.
authors.affiliation: Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri, United States of America ; Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America.
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Ippolito
authors.affiliation: Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri, United States of America ; BRIGHT Institute, Washington University School of Medicine, St. Louis, Missouri, United States of America ; Department of Cancer Systems Imaging, University of Texas M.D. Anderson Cancer Center, Houston, Texas, United States of America.
authors.forename: David
authors.initials: D
authors.lastname: Piwnica-Worms
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D001271:Atlases as Topic; D018278:Carcinoma, Neuroendocrine / Q000235:genetics / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D045744:Cell Line, Tumor; D057075:Enzyme Assays; D005453:Fluorescence; D015972:Gene Expression Regulation, Neoplastic; D005947:Glucose / Q000172:deficiency; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D005973:Glutamine / Q000172:deficiency; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D010078:Oxazines / Q000737:chemistry; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D015398:Signal Transduction; D013312:Stress, Physiological / Q000235:genetics; D016019:Survival Analysis; D014966:Xanthenes / Q000737:chemistry; D005680:gamma-Aminobutyric Acid / Q000032:analysis* / Q000378:metabolism
chemical_list: D010078:Oxazines; D014966:Xanthenes; D005973:Glutamine; C005843:resazurin; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1; D005974:Glutamate-Ammonia Ligase; D005947:Glucose