Glucose induces expression of rat pyruvate carboxylase through a carbohydrate response element in the distal gene promoter.

Pyruvate carboxylase is an enzyme of the so-called pyruvate cycling pathways, which have been proposed to contribute to glucose-stimulated insulin secretion in pancreatic beta-cells. In the rat insulinoma cell line 832/13, transcripts from both the distal and proximal gene promoter for pyruvate carboxylase are up-regulated by glucose, with pyruvate carboxylase being expressed mainly from the distal gene promoter. At position -408 to -392 relative to the transcription start site, the distal gene promoter was found to contain a ChoRE (carbohydrate response element). Its deletion abolishes glucose responsiveness of the promoter, and the sequence can mediate glucose responsiveness to a heterologous gene promoter. ChREBP (carbohydrate response element-binding protein) and its dimerization partner Mlx (Max-like protein X) bind to the ChoRE in vitro. ChREBP further binds to the distal promoter region at a high glucose concentration in situ. The E-box-binding transcription factors USF1/2 (upstream stimulatory factor 1/2) and E2A variant 2 [also known as E47 and TCF3 (transcription factor 3)] can also bind to the ChoRE. Overexpression of E2A diminishes the magnitude of the glucose response from the pyruvate carboxylase ChoRE. This illustrates that competition between ChREBP-Mlx and other factors binding to the ChoRE affects glucose responsiveness. We conclude that a ChoRE in the distal gene promoter contributes to the glucose-mediated expression of pyruvate carboxylase.

Serum glutamate levels correlate with Gleason score and glutamate blockade decreases proliferation, migration, and invasion and induces apoptosis in prostate cancer cells.

PURPOSE: During glutaminolysis, glutamine is catabolized to glutamate and incorporated into citric acid cycle and lipogenesis. Serum glutamate levels were measured in patients with primary prostate cancer or metastatic castrate-resistant prostate cancer (mCRPCa) to establish clinical relevance. The effect of glutamate deprivation or blockade by metabotropic glutamate receptor 1 (GRM1) antagonists was investigated on prostate cancer cells' growth, migration, and invasion to establish biologic relevance. EXPERIMENTAL DESIGN: Serum glutamate levels were measured in normal men (n = 60) and patients with primary prostate cancer (n = 197) or mCRPCa (n = 109). GRM1 expression in prostatic tissues was examined using immunohistochemistry (IHC). Cell growth, migration, and invasion were determined using cell cytotoxicity and modified Boyden chamber assays, respectively. Apoptosis was detected using immunoblotting against cleaved caspases, PARP, and γ-H2AX. RESULTS: Univariate and multivariate analyses showed significantly higher serum glutamate levels in Gleason score ≥ 8 than in the Gleason score ≤ 7 and in African Americans than in the Caucasian Americans. African Americans with mCRPCa had significantly higher serum glutamate levels than those with primary prostate cancer or benign prostate. However, in Caucasian Americans, serum glutamate levels were similar in normal research subjects and patients with mCRPC. IHC showed weak or no expression of GRM1 in luminal acinar epithelial cells of normal or hyperplastic glands but high expression in primary or metastatic prostate cancer tissues. Glutamate deprivation or blockade decreased prostate cancer cells' proliferation, migration, and invasion and led to apoptotic cell death. CONCLUSIONS: Glutamate expression is mechanistically associated with and may provide a biomarker of prostate cancer aggressiveness.