Vascular Endothelial Growth Factor, Its Receptor KDR/Flk-1, and Pituitary Tumor Transforming Gene in Pituitary Tumors

• DOI: 10.1210/jc.2002-020309
• Publication Date: 2002-09-05T17:22:39Z
• Authors: C. J. McCabe; K. Boelaert; L. A. Tannahill; A. P. Heaney; A. L. Stratford; J. S. Khaira; S. Hussain; M. C. Sheppard; J. A. Franklyn; N. J. L. Gittoes
• Keywords: Adenoma; 0301 basic medicine; Lymphokines; Base Sequence; Neovascularization, Pathologic; Receptor Protein-Tyrosine Kinases; Endothelial Growth Factors; Polymerase Chain Reaction; Recombinant Proteins; Neoplasm Proteins; 3. Good health; Gene Expression Regulation, Neoplastic; 03 medical and health sciences; Receptors, Vascular Endothelial Growth Factor; Amino Acid Substitution; Pituitary Gland; Mutagenesis, Site-Directed; Humans; Regression Analysis; Pituitary Neoplasms; Receptors, Growth Factor; RNA, Messenger; DNA Primers

Pituitary tumorigenesis is a poorly understood process involving dysregulation of the cell cycle, proliferation, and angiogenesis. The novel securin pituitary tumor transforming gene (PTTG) disrupts cell division and stimulates fibroblast growth factor (FGF)-2-mediated angiogenesis. We investigated expression of the angiogenic vascular endothelial growth factor (VEGF) and its receptor KDR/Flk-1 in 103 human pituitary tumors, and we assessed functional relationships between these genes in vitro. Nonfunctioning tumors (n = 81) demonstrated markedly raised VEGF mRNA (3.2-fold, P < 0.05) and protein concentrations, compared with normal pituitaries (n = 10). KDR was also highly induced in nonfunctioning tumors (14-fold, P < 0.001, n = 78) as well as in the whole cohort of pituitary tumors, compared with normal pituitary samples (14-fold, P < 0.0001, n = 100). In vitro, PTTG induced VEGF, but not KDR, expression in fetal neuronal NT2 cells (2.7-fold, P < 0.001, n = 8), MCF-7 breast carcinoma cells (1.9-fold, P = 0.03, n = 10), and choriocarcinoma JEG-3 cells (P = 0.0002, n = 8). A mutated PTTG construct that cannot be phosphorylated showed identical VEGF up-regulation (2.9-fold, P < 0.001, n = 8) in NT2 cells, compared with wild-type PTTG, but a further mutated construct with abrogation of the key protein:protein interaction domain of PTTG resulted in a significant reduction in VEGF stimulation, compared with wild-type (0.37-fold reduction, P < 0.001, n = 8). FGF-2 findings mirrored those of VEGF, although antibody depletion of secreted FGF-2 in the cell medium failed to influence VEGF up-regulation by PTTG. Overall, our findings implicate altered VEGF and KDR signaling in pituitary tumorigenesis, and we propose that PTTG stimulation of FGF-2 and VEGF expression in the presence of up-regulated growth factor receptors may account for angiogenic growth and progression of human pituitary tumors.