Author(s): Vaz, Cátia Alexandra Vicente
Date: 2015
Persistent ID: http://hdl.handle.net/10400.6/3988
Origin: uBibliorum
Project/scholarship: info:eu-repo/grantAgreement/FCT/FARH/SFRH%2FBD%2F70316%2F2010/PT;
Subject(s): Cancro da próstata - Terapêutica; Metabolismo glicolítico; Regucalcina; Apoptose; Domínio/Área Científica::Ciências Médicas::Biomedicina
Prostate Cancer (PCa) is one of the most common cancers in men and continues to be a source of considerable morbidity and mortality worldwide. The progression of PCa from an early stage, confined to prostate, to a more aggressive phenotype is characterized by the loss of androgen-responsiveness, which means that tumor cells gain the ability to growth independently of the circulating androgens. Furthermore, the neoplastic transformation of prostate cells and tumor progression to more aggressive stages require several genetic and metabolic alterations. Warburg firstly demonstrated that tumor cells predominantly use glycolysis for obtaining energy in detriment of oxidative phosphorylation, with the production of high amounts of lactate. This metabolic adaptation is common to the majority of cancers and is now established as a hallmark of cancer. However, the alterations in the glycolytic metabolism that occur in the progression to the androgen-independent stage of PCa as well as the role of androgens in regulating the glycolytic flux are poorly studied. Regucalcin (RGN) is a calcium (Ca2+)-binding protein that plays a determinant role in the maintenance of intracellular Ca2+ homeostasis. RGN also has been suggested as a tumor suppressor protein, since it is involved in the regulation of proliferation, apoptosis, and diverse metabolic pathways, and its antioxidant properties also have been reported. In addition, androgens, Ca2+ and age, all well-known factors implicated in PCa development, regulate RGN expression in different tissues but their action in prostate remains to be elucidated. It was also demonstrated that RGN is under expressed in human PCa cases comparatively to normal tissues, which suggest that the loss of RGN may be an event favoring tumor development. Moreover, considering the biological processes under the influence of RGN it is also predictable that it may exert a crucial role in the maintenance of cell tissue homeostasis. Notwithstanding, little is known about the factors that regulate RGN expression in the prostate, and no studies exist regarding the role of RGN in the regulation of cell proliferation, apoptosis, Ca2+ homeostasis, and metabolism in this tissue. The present thesis firstly established the glycolytic profile of androgen-responsive (LNCaP) and non-responsive (PC3) PCa cells. We demonstrated that LNCaP and PC3 cells display a distinct glycolytic profile, with PC3 presenting higher production and export of lactate as a result of increased expression of target regulators of this metabolic pathway. The role of androgens in the regulation of the glycolytic flux in PCa cells was also studied. Treatment of LNCaP cells with 5α-dihydrotestosterone (DHT, 10nM) significantly increased glucose uptake, glycolysis rate and the export of lactate by upregulating the expression of important regulators of glycolysis, in a mechanism that seems to involve the androgen receptor (AR). These results highlighted the importance of controlling glucose and lactate metabolism as possible therapeutic approaches in PCa. The effect of androgens, Ca2+ and age on the expression of RGN in prostate cells in vitro and in vivo was investigated. The expression of RGN in rat prostate was downregulated by androgens and aging. Administration of extracellular Ca2+ to human prostate cells differentially regulated the expression of RGN in LNCaP and PNT1A cells in a time- and dose-dependent manner, with effects more pronounced in the up-regulation of RGN expression in PNT1A cells. The fact that androgens and Ca2+ regulate RGN levels in prostate cells, and the evidence of RGN down-regulation with aging, strongly points this protein as an important target in the regulation of prostatic physiology. Indeed, the work of this thesis also proved the role of RGN in controlling the crucial mechanisms involved in prostate cells homeostasis. RGN exerted a negative effect on the expression of Ca2+ sensing receptor, which was essential in the promotion of Ca2+-dependent proliferation, as demonstrated by in vitro and in vivo assays. In addition, overexpression of RGN suppressed cell proliferation, apoptosis and the glycolytic metabolism in rat prostate, as a result of the regulation of the expression and activity of several proteins involved in these pathways. RGN also decreased lipid peroxidation in rat prostate, which supports their cytoprotective function. Finally, we verified that augmented levels of RGN improved the antioxidant defenses, prevented the age-induced resistance to apoptosis, and the excessive proliferation usually found in the prostate of aged animals. The obtained results suggest that the manipulation of RGN levels may prevent the development of aged-associated diseases in rat prostate. In conclusion, the main findings of this dissertation pointed androgens as the “good friends” of PCa cells, since they increase the glycolytic flux in PCa cells, which is stimulated with the progression of disease. In contrast, loss of RGN expression with aging led to deregulation of different mechanisms crucial for the maintenance of prostate physiology, and thus it may contribute to the emergence of aged-associated pathophysiologic alterations, and to the neoplastic transformation. The results presented here also suggest future approaches for the management of PCa, which could passing by: i) the development of new therapeutic strategies based on the use of combined therapies, targeting AR and glycolytic metabolic regulators; and ii) the manipulation of RGN expression as a therapeutic option.
