Kovács, Kálmán

Vascular endothelial growth factor (VEGF) acts primarily as an endothelial cell mitogen via the specific receptors Flk-1 and Flt-1. To help further define the possible role of VEGF in the control of pituitary cell function, we examined Flk-1 expression in normal rat pituitaries and in GH3 cells. Flk-1 expression was studied by immunohistochemistry, in situ hybridization, and double-labeling immunofluorescence combined with confocal laser microscopy. In normal rat pituitaries, Flk-1-immunoreactive cells appeared widely distributed only in the anterior lobe and were not detected in the intermediate or posterior lobe. Apart from the adenohypophysial cells, Flk-1 immunopositivity was also evident in endothelial cells of many capillaries distributed throughout the gland. Immunohistochemistry also showed that majority of GH3 cells expressed Flk-1 protein. In situ hybridization showed conclusive staining with the antisense probe and confirmed the immunohistochemical results. The double immunofluorescence method revealed Flk-1 expression in all types of hormone-producing adenohypophysial cells but not in folliculostellate cells. The percentage of immunopositive cells varied among the various cell types. The present study demonstrates that pituitary cells are not only sources of VEGF but also targets of this multifunctional substance, supporting the concept that VEGF functions as an autocrine/paracrine factor in the pituitary.

Leptin is a key mediator in the maintenance of neuroendocrine homeostasis. Recently, leptin and leptin receptor expression were demonstrated in non-tumorous and adenomatous human pituitaries. This study was performed to determine the subcellular localization of leptin in human adenohypophyses ( n = 3) and in various types of pituitary adenoma ( n = 16). Immunoelectron microscopy showed leptin immunolabeling in most hormone-producing cells of the human non-tumorous adenohypophysis, but not in stellate cells. Labeling was noted over secretory granules. Immunocytochemistry using double labeling revealed leptin expression in GH-, ACTH-, TSH-, and FSH/LH-containing cells but not in PRL cells. The percentage of immunopositive cells and the intensity of immunostaining varied considerably among the various cell types. Immunoelectron microscopy with double gold labeling showed co-localization of leptin and adenohypophysial hormones in the same secretory granules. Among pituitary tumors, leptin immunolabeling was evident only in corticotroph adenomas. Compared to non-tumorous corticotrophs, leptin immunoexpression was less abundant in corticotroph adenomas. The presence of leptin and adenohypophysial hormones in the same secretory granules suggests that leptin is secreted concomitantly with various adenohypophysial hormones and that its release is under the control of hypothalamic stimulating and inhibiting hormones. (J Histochem Cytochem 48:1147–1152, 2000)

Objective. We investigated the correlation between immunohistochemical expression of the pituitary tumor transforming gene (PTTG) and pituitary adenoma subtype. Methods. Pituitary adenomas (n = 89) were stained for PTTG using the streptavidin—biotin—peroxidase complex method and a monoclonal PTTG antibody. Results. PTTG staining was found to be cytoplasmic with a pronounced paranuclear expression pattern. Reactivity was highest in growth hormone (GH) adenomas as compared with other tumors, including prolactin (PRL), follicle-stimulating hormone/luteinizing hormone/α subunit, as well as adrenocorticotrophic hormone—secreting adenomas. PRL adenomas exhibited the lowest expression levels. Among GH adenomas, untreated tumors demonstrated significantly higher PTTG levels than octreotide-treated examples. Although dopamine agonist—treated PRL adenomas tended to show lower expression levels, statistical significance was not reached. Conclusions. Our finding that PTTG was differentially expressed in pituitary adenoma subtypes suggests a cell-specific function for PTTG. Moreover, treatment of GH adenomas with somatostatin analogues lowered PTTG expression. Further investigation into mechanisms mediating cell-specific expression of PTTG is warranted.

Object The aim of this work was to investigate the immunohistochemical expression of nestin, a member of the intermediate filament family, in adenohypophysial vasculature during development and progression of pituitary infarction. Methods Forty-five nontumorous adenohypophyses and 34 pituitary adenomas of various types, all exhibiting acute or healing infarcts, were examined immunohistochemically using the streptavidin-biotin-peroxidase complex method. Results In both adenohypophyses and pituitary adenomas without infarction, nestin was expressed in only a few capillaries and endothelial cells. In acute infarcts without a vascular response, no nestin was demonstrable within necrotic capillaries (50 cases). In organizing infarcts, newly formed vessels spreading into necrotic zones showed nestin expression in all capillaries and practically every endothelial cell (25 cases). In the hypocellular, fibrotic scar phase, only a few vessels (4) were apparent, and immunoreactivity was focal and mild. Conclusions Nestin is strongly expressed in newly formed capillaries and is downregulated when infarcts transform to fibrous tissue. Nestin expression may provide valuable insight into the process of pituitary angiogenesis.

Abstract Galectin-3 (Gal-3), a β-galactoside-binding protein is expressed in a specific cell–type manner in pituitary tumors. Here we questioned the mechanism of Gal-3 expression in pituitary tumors, by using methylation-specific PCR and DNA sequence analyses to analyze the methylation status of the promoter region of the LGALS3 gene. DNA analysis of a human pituitary tumor, breast carcinoma cell lines, and thyroid carcinoma cell lines showed that in cells expressing Gal-3 protein, the LGALS3 gene was unmethylated, whereas in Gal-3 null cells, the promoter of the LGALS3 gene was methylated. Treatment of cells with 30 μmol/L 5-aza-2′-deoxycytidine induced Gal-3 mRNA and protein expression. Among pituitary tumors, 30% (7/23), mainly in follicle-stimulating hormone/luteinizing hormone–producing (38%) and null cell (57%) adenomas, the promoter of the LGALS3 was found to be methylated and silenced, although prolactin- and adrenocorticotropic hormone–producing tumors, which were unmethylated, expressed the Gal-3 protein. These results show for the first time that Gal-3 expression is regulated in part by promoter methylation in pituitary as well as in other tumors. Because it is functionally involved in cancer progression and metastasis, Gal-3 may serve as a possible therapeutic target in the treatment of pituitary tumors.

ABSTRACT OBJECTIVE To determine the clinical presentation, imaging characteristics, microscopic and ultrastructural characteristics, and treatment outcomes of patients with clinically silent pituitary corticotroph adenomas. METHODS All silent corticotroph adenomas diagnosed at the Mayo Clinic during the years 1975 through 1997 were selected from the files of the Mayo Tissue Registry. RESULTS We studied 23 cases, occurring in 16 male and 7 female patients (age range, 11–79 yr; mean age, 48 yr), who presented with headaches (50%), visual field defects (61%), extraocular muscle paresis (13%), hypopituitarism (26%), and galactorrhea/amenorrhea (43%/29% of the female patients). No patients exhibited clinical hypercortisolism. All tumors were macroadenomas (2.4 ± 0.8 cm; range, 1.5–4.0 cm) and exhibited suprasellar extension in 87% of the cases and hemorrhage, necrosis, and/or cystic changes in 61%. All tumors stained were variably periodic acid-Schiff-, adrenocorticotropic hormone-, and β-endorphin-positive, particularly Subtype I lesions. Ultrastructural classification was performed in 19 cases. In a comparison of Subtype I and II tumors, differences were observed with respect to sex (male/female, 1.4:1 versus 6:1), preoperative hyperprolactinemia (5 of 16 versus 0 of 6 cases), preoperative hypopituitarism (9 of 16 versus 5 of 7 cases), radiographic or gross invasion (7 of 16 versus 5 of 7 cases), and partial or total postoperative pituitary failure (6 of 16 versus 6 of 6 cases). The overall median postoperative follow-up period was 4.9 years (range, 0.3–16.6 yr); 54% of the patients had persistent or recurrent tumors. CONCLUSION Clinically silent corticotroph adenomas behave in an aggressive manner and are characterized by the following: lack of clinical signs or symptoms of Cushing's syndrome and normal cortisol levels; no or only minor elevations of serum adrenocorticotropic hormone levels; macroadenomas with hemorrhagic infarction; and presentation dominated by mass effect symptoms. The high persistence/recurrence rate underscores the need for long-term follow-up.