RESUMO
Increased levels of the proto-oncogene pituitary tumor-transforming gene 1 (PTTG) have been repeatedly reported in several human solid tumors, especially in endocrine-related tumors such as pituitary adenomas. Securin PTTG has a critical role in pituitary tumorigenesis. However, the cause of upregulation has not been found yet, despite analyses made at the gene, promoter and mRNA level that show that no mutations, epigenetic modifications or other mechanisms that deregulate its expression may explain its overexpression and action as an oncogene. We describe that high PTTG protein levels are induced by the RWD-containing sumoylation enhancer (RWDD3 or RSUME), a protein originally identified in the same pituitary tumor cell line in which PTTG was also cloned. We demonstrate that PTTG and RSUME have a positive expression correlation in human pituitary adenomas. RSUME increases PTTG protein in pituitary tumor cell lines, prolongs the half-life of PTTG protein and regulates the PTTG induction by estradiol. As a consequence, RSUME enhances PTTG transcription factor and securin activities. PTTG hyperactivity on the cell cycle resulted in recurrent and unequal divisions without cytokinesis, and the consequential appearance of aneuploidies and multinucleated cells in the tumor. RSUME knockdown diminishes securin PTTG and reduces its tumorigenic potential in a xenograft mouse model. Taken together, our findings show that PTTG high protein steady state levels account for PTTG tumor abundance and demonstrate a critical role of RSUME in this process in pituitary tumor cells.
Assuntos
Adenoma/metabolismo , Neoplasias Hipofisárias/metabolismo , Securina/metabolismo , Fatores de Transcrição/metabolismo , Animais , Células Cultivadas , Chlorocebus aethiops , Humanos , Masculino , Camundongos Nus , Estabilidade Proteica , Proto-Oncogene Mas , Ratos , Fatores de Transcrição/genéticaRESUMO
BACKGROUND: Hair follicle (HF) regeneration begins when signals from the mesenchyme-derived dermal papilla cells (DPC) reach multipotent epidermal stem cells in the bulge region. Wnt/ß-catenin signalling is known to affect mammalian hair growth positively. In androgenetic alopecia (AGA), androgens cause HF miniaturization through a mechanism that remains unclear. Circulating androgens act on DPC and alter paracrine factors that influence hair epithelial cells. OBJECTIVES: To elucidate the role of androgens in dermal papilla-induced differentiation of HF stem cells. METHODS: HF stem cell differentiation was evaluated in a coculture model with DPC or culturing with media conditioned by DPC after activation of androgen and Wnt/ß-catenin signalling pathways. To study the molecular cross-talk between the androgen and Wnt signalling pathway in DPC, we analysed the expression and activation of downstream Wnt signalling molecules in the presence of androgens. RESULTS: In a coculture model with human DPC from patients with AGA and HF stem cells, we observed that androgens abrogate hair differentiation evaluated by hair-specific keratin 6 expression. Wnt signalling activation restored the ability of androgen-treated DPC to induce differentiation. Androgen treatment revealed a significant decrease in the cytoplasmic/total ß-catenin protein ratio and upregulation of the activity of glycogen synthase kinase-3ß in DPC, indicative of canonical Wnt pathway inhibition. CONCLUSIONS: These results suggest that androgens deregulate DPC-secreted factors involved in normal HF stem cell differentiation via the inhibition of the canonical Wnt signalling pathway.