Expression of pituitary tumour transforming gene (PTTG) and fibroblast growth factor-2 (FGF-2) in human pituitary adenomas: relationships to clinical tumour behaviour.

OBJECTIVE: Pituitary tumour transforming gene (PTTG) encodes a multifunctional protein that is implicated in initiating and perpetuating pituitary adenoma growth. PTTG appears to have key regulatory functions in determining control of many fundamental cellular events including mitosis, cell transformation, DNA repair and gene regulation. Several of these events are mediated through interactions with PTTG binding factor (PBF) and fibroblast growth factor-2 (FGF-2). Given this background, we have determined the expression of PTTG, PBF, FGF-2 and its receptor FGF-R-1 in a large cohort of pituitary adenomas and have sought associations between levels of gene expression and clinical markers of tumour behaviour. PATIENTS AND METHODS: We used real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analyses to measure PTTG, PBF, FGF-2 and FGF-R-1 expression in ex vivo pituitary tumours (N = 121). Clinical data, including accurate radiological assessment of tumour characteristics, were used to determine any associations between gene expression and tumour behaviour. RESULTS: PTTG was increased significantly (fivefold, P = 0.005) in adenomas compared with normal pituitaries. We also demonstrated that PBF was similarly raised in adenomas (sixfold, P = 0.0001), and was significantly correlated with PTTG expression. FGF-2 and its receptor FGF-R-1 were also raised in adenomas compared with normal pituitary tissue. Moreover, significantly enhanced expression of FGF-R-1 was observed in invasive adenomas compared with other pituitary tumours. CONCLUSIONS: Our data support a fundamental role for PTTG-mediated upregulation of FGF-2 signalling in pituitary tumorigenesis and growth, and suggest that receptor-mediated mechanisms of growth factor action may be critically important. Further prospective studies are required to determine whether measurement of FGF-R-1 mRNA will be of clinical use as a prognostic marker in patients with pituitary adenomas.

Vascular endothelial growth factor, its receptor KDR/Flk-1, and pituitary tumor transforming gene in pituitary tumors.

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.