Pathogenesis of Pituitary Tumors

ArticleinProgress in brain research 182(10):207-27 · December 2010with6 Reads
DOI: 10.1016/S0079-6123(10)82009-6 · Source: PubMed
Abstract
Pituitary tumors are common and mostly benign neoplasia which cause excess or deficiency of pituitary hormones and compressive damage to adjacent organs. Oncogene activation [e.g. PTTG (pituitary tumor-transforming gene) and HMGA2], tumor suppressor gene inactivation (e.g. MEN1 and PRKAR1A), epigenetic changes (e.g. methylation) and humoral factors (e.g. ectopic production of stimulating hormones) are all possible pituitary tumor initiators; the micro-environment of pituitary tumors including steroid milieu, angiogenesis and abnormal cell adhesion further promote tumor growth. Senescence, a cellular defence mechanism against malignant transformation, may explain the benign nature of at least some pituitary tumors. We suggest that future research on pituitary tumor pathogenesis should incorporate systems approaches, and address regulatory mechanisms for pituitary cell proliferation, development of new animal models of pituitary tumor and isolation of functional human pituitary tumor cell lines.
    • "Despite the suggested monoclonal origin of pituitary adenomas, several studies showed that more than one cell type can be found in pituitary adenoma [9, 10]. This can be explained by the fact that pituitary tumors may contain several tumor clones arising independently from expansion of individual cells [11]. On the other hand, there is a hypothesis that pituitary adenomas contain a subpopulation of tumor stem cells or other multipotent cells that drive their composition, growth, invasion, and resistance to therapy. "
    [Show abstract] [Hide abstract] ABSTRACT: Pituitary adenomas are one of the most common endocrine and intracranial neoplasms. Although they are theoretically monoclonal in origin, several studies have shown that they contain different multipotent cell types that are thought to play an important role in tumor initiation, maintenance, and recurrence after therapy. In the present study, we isolated and characterized cell populations from seven pituitary somatotroph, nonhormonal, and lactotroph adenomas. The obtained cells showed characteristics of multipotent mesenchymal stromal cells as observed by cell morphology, cell surface marker CD90, CD105, CD44, and vimentin expression, as well as differentiation to osteogenic and adipogenic lineages. They are capable of growth and passaging under standard laboratory cell culture conditions and do not manifest any hormonal cell characteristics. Multipotent mesenchymal stromal cells are present in pituitary adenomas regardless of their clinical manifestation and show no considerable expression of somatostatin 1–5 and dopamine 2 receptors. Most likely obtained cells are a part of tissue-supportive cells in pituitary adenoma microenvironment.
    Full-text · Article · Jan 2016
    • "Our experiment does not allow us to distinguish whether increased expression of Hedgehog related genes is pathogenetically associated with the development of these benign pituitary tumours or reflects an endogenous compensating mechanism of somatotrophs to tumor growth initiated by other factors, such as oncogene activation, tumor suppressor gene inactivation , epigenetic changes (e.g. methylation) or ectopic secretion of stimulating hormones [29]. In our study Notch-3 and Jagged-1 expression was found significantly increased in non-functioning pituitary adenomas, compared to normal human pituitary tissue, in line with previous reports [14], while Hes1 expression that suppresses transcription of Notch target genes was significantly decreased. "
    [Show abstract] [Hide abstract] ABSTRACT: Several studies have demonstrated the role of Wnt and Notch signaling in the pathogenesis of pituitary adenomas, but data are scarce regarding the role of Hedgehog signaling. In this study we investigated the differential expression of gene targets of the Hedgehog signaling pathway. Formalin-fixed, paraffin-embedded specimens from adult patients who underwent transphenoidal resection and normal human pituitary tissues that were obtained from autopsies were used. Clinical information and data from pre-operative MRI scan (extracellular tumor extension, tumor size, displacement of the optic chiasm) were retrieved from the Hospital's database. We used a customized RT(2) Profiler PCR Array, to investigate the expression of genes related to Notch and Hedgehog signaling pathways (PTCH1, PTCH2, GLI1, GLI3, NOTCH3, JAG1, HES1, and HIP). A total of 52 pituitary adenomas (32 non-functioning adenomas, 15 somatotropinomas and 5 prolactinomas) were used in the final analysis. In non-functioning pituitary adenomas there was a significant decrease (approximately 75%) in expression of all hedgehog related genes that were tested, while Notch3 and Jagged-1 expression was found significantly increased, compared with normal pituitary tissue controls. In contrast, somatotropinomas demonstrated a significant increase in expression of all Hedgehog related genes and a decrease in the expression of Notch3 and Jagged-1. There was no significant difference in the expression of Hedgehog and Notch related genes between prolactinomas and healthy pituitary tissues. Hedgehog signalling appears to be activated in somatotropinomas but not in non-functioning pituitary adenomas in contrast to the expression pattern of Notch signalling pathway.
    Full-text · Article · Nov 2015
    • "In the last decade, the pathogenesis of pituitary adenomas has been extensively studied in humans, and to a lesser degree in the dogs. Genes or transcription factors identified in this way as being relevant to pituitary oncogenesis can be tested in experimental knock-out or transgenic mouse models [10, 11] or cell lines [12] . The Rb knockout mouse model has been widely used in pituitary adenoma research, since heterozygous mice develop pituitary adenomas [13]. "
    [Show abstract] [Hide abstract] ABSTRACT: Pituitary surgery generates pituitary tissue for histology, immunohistochemistry, and molecular biological research. In the last decade, the pathogenesis of pituitary adenomas has been extensively studied in humans, and to a lesser degree in dogs, and tumor oncogenesis has been studied in knock-out mice, often by means of quantitative reversed-transcriptase PCR (RT-qPCR). A precondition of such analyses is that so-called reference genes are stably expressed regardless of changes in disease status or treatment. In this study, the expression of six frequently used reference genes, namely, tata box binding protein (tbp), tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, zeta polypeptide (ywhaz), hydroxymethylbilane synthase (hmbs), beta-2-microglobulin (b2m), succinate dehydrogenase complex subunit A (sdha), and glyceraldehyde 3 phosphate dehydrogenase 1 (gapdh), was studied in pituitary tissue (normal and adenoma) from three species (humans, mice, and dogs). The stability of expression of these reference genes differed between species and between healthy and diseased tissue within one species. Quantitative analysis based on a single reference gene that is assumed to be stably expressed might lead to wrong conclusions. This cross-species analysis clearly emphasizes the need to evaluate the expression stability of reference genes as a standard and integral aspect of study design and data analysis, in order to improve the validity of the conclusions drawn on the basis of quantitative molecular analyses.
    Full-text · Article · Oct 2013
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