Ultrastructural and Molecular Evidence of Macroautophagy in Functioning PitNETs and Experimental Pituitary Tumors.

INTRODUCTION: Macroautophagy is a lysosome-mediated degradation process that controls the quality of cytoplasmic components and organelles, with its regulation depending on autophagy-related proteins (Atg) and with Beclin1/Atg6 and microtubule-associated protein light chain 3 (LC3/Atg8) being key players in the mammalian autophagy. As reports on this mechanism in the field of pituitary neuropathology and neuroendocrinology are scarce, our study analyzed the ultrastructural signs of macroautophagy and the expression of Beclin1 and LC3 proteins in human functioning PitNETs and in experimental pituitary tumors. METHODS: A group of humans functioning PitNETs and an experimental lactotroph model in rats of the F344 strain stimulated with estradiol benzoate (BE) were used. Ultrastructural and molecular evidence of the macroautophagic process was evaluated using different techniques. RESULTS: In functioning PitNETs cohort, 60% exhibited evidence of macroautophagy, with a significant difference found for Beclin1 and LC3 between macro- and micro-PitNETs (p < 0.05). In the experimental model, the expression of both Beclin1 and LC3 proteins was immunopositive in normal and tumoral glands when analyzed by immunofluorescence, Western blot, and immunohistochemistry. In the experimental model, protein expression was associated with increased glandular size and weight. CONCLUSIONS: Our study revealed evidence of macroautophagy at the pituitary level and the important role of Beclin1 and LC3 in the progression of functioning PitNETs, implying that this mechanism participate in regulating pituitary cell growth.

[Update on mechanisms of pituitary tumorigenesis.] / Actualización sobre mecanismos de tumorogénesis hipofisaria.

Pituitary adenomas are intracranial neoplasms that originate from the adeno-pituitary cells, are mostly benign and slow growing. However, a small percentage can be aggressive and spread locally and / or remotely as malignancies. In recent years, progress has been made in understanding the biology of pituitary tumors, identifying mutations in the germline, somatic lines, and epigenetic mechanisms. Objective: review the updated bibliography on the mechanisms of pituitary tumorigenesis. Data source: bibliographic search was performed using the MEDLINE (PubMed), LILACS and Google Scholar databases since 2010 to April 2020. Conclusion: Knowledge and information on pituitary tumorogenesis mechanisms increased in recent decades, and new neoplastic pathways are recognized. However, there are currently few therapeutic approaches to act specifically on the underlying tumor genesis pathway identified in each case.

Los adenomas hipofisarios son neoplasias intracraneales que surgen de las células del lóbulo anterior de la glándula, benignos y de crecimiento lento en su gran mayoría. Sin embargo, un pequeño porcentaje puede mostrar un comportamiento clínicamente agresivo y diseminarse localmente y/o a distancia como verdaderas neoplasias malignas. Durante los últimos años, se observó un importante avance en el conocimiento de la biología de los tumores hipofisarios, identificándose mutaciones de las líneas germinal, somática y mecanismos epigenéticos. Objetivo: revisar la bibliografía actualizada sobre los mecanismos que contribuyen a la tumorogénesis hipofisaria. Fuente de datos: se realizó una búsqueda bibliográfica utilizando las bases de datos de MEDLINE (PubMed), LILACS y Google Scholar desde 2010 hasta abril de 2020. Conclusión: El conocimiento e información sobre los mecanismos asociados a la formación de tumores hipofisarios incrementó a lo largo de las últimas décadas, y se reconocen nuevas vías de desarrollo neoplásico. Sin embargo, en la actualidad existen pocos enfoques terapéuticos para actuar específicamente sobre la vía de génesis tumoral subyacente identificada en cada caso.

Association of PTP4A3 expression and tumour size in functioning pituitary adenoma: a descriptive study.

BACKGROUND: PTP4A3 is a subclass of a protein tyrosine phosphatase super family and is expressed in a range of epithelial neoplasms. We evaluated PTP4A3 expression and its association with clinicopathological parameters in different types of functioning pituitary adenomas. METHODS: A total of 34 functioning pituitary adenomas samples were evaluated in this observational study. PTP4A3 expression was examined by immunohistochemical staining, and, possible correlations between PTP4A3 and some clinicopathological variables were investigated. RESULTS: PTP4A3 was expressed in 19 out of 34 tumours (55%), at the cytoplasmic level of tumorous cells. Moreover, there was significant association (p=0.042) between PTP4A3 expression and tumorous size. CONCLUSIONS: PTP4A3 was expressed in more than half of the tumours analysed, with there being a significant association with the tumorous size of functioning adenomas. This allows to speculate that PTP4A3 may regulate tumour growth, although further investigations are necessary to determine if this phosphatase can serve as a biomarker or used as a therapeutic target in pituitary macroadenomas.

Trastuzumab inhibits pituitary tumor cell growth modulating the TGFB/SMAD2/3 pathway.

In pituitary adenomas, early recurrences and resistance to conventional pharmacotherapies are common, but the mechanisms involved are still not understood. The high expression of epidermal growth factor receptor 2 (HER2)/extracellular signal-regulated kinase (ERK1/2) signal observed in human pituitary adenomas, together with the low levels of the antimitogenic transforming growth factor beta receptor 2 (TBR2), encouraged us to evaluate the effect of the specific HER2 inhibition with trastuzumab on experimental pituitary tumor cell growth and its effect on the antiproliferative response to TGFB1. Trastuzumab decreased the pituitary tumor growth as well as the expression of ERK1/2 and the cell cycle regulators CCND1 and CDK4. The HER2/ERK1/2 pathway is an attractive therapeutic target, but its intricate relations with other signaling modulators still need to be unraveled. Thus, we investigated possible cross-talk with TGFB signaling, which has not yet been studied in pituitary tumors. In tumoral GH3 cells, co-incubation with trastuzumab and TGFB1 significantly decreased cell proliferation, an effect accompanied by a reduction in ERK1/2 phosphorylation, an increase of SMAD2/3 activation. In addition, through immunoprecipitation assays, a diminution of SMAD2/3-ERK1/2 and an increase SMAD2/3-TGFBR1 interactions were observed when cells were co-incubated with trastuzumab and TGFB1. These findings indicate that blocking HER2 by trastuzumab inhibited pituitary tumor growth and modulated HER2/ERK1/2 signaling and consequently the anti-mitogenic TGFB1/TBRs/SMADs cascade. The imbalance between HER2 and TGFBRs expression observed in human adenomas and the response to trastuzumab on experimental tumor growth may make the HER2/ERK1/2 pathway an attractive target for future pituitary adenoma therapy.