Adrenocortical carcinoma (CCS) is a rare form of endocrine neoplasm, characterized by a high resistance to medical therapy and a significant tendency to relapse and metastasis.
One strategy to develop an effective therapy for ACC is the identification of some pathway useful as targets for innovative therapies. This strategy has never been used to fight ACC.
In this work, the expression and localization of HIF-1¿ will test in two cell lines deriving from adrenocortical carcinoma, H295R and SW-13. Subsequently, the biological effects induced by the silencing of the HIF1A gene will be investigated in the same models, in particular with reference to cell proliferation, glucose metabolism and invasiveness.
The transcription factors induced by hypoxia (HIFs, Hypoxia Inducible Factors), represent a family of proteins active in conditions of cellular stress, in particular hypoxia, able to stimulate the expression of target genes by binding to of the HRE (Hypoxia Responsive Elements) recognition sequences (Semenza, Nat Rev Canc '03). Among the various hypoxia-induced transcription factors identified so far, the most important and best characterized is HIF-1, whose activity is strictly dependent on the intracellular levels of HIF-1¿.
HIF-1¿ is encoded by the HIF1A gene, located on the long arm of chromosome 14, in the 14q23.2 locus and its synthesis is stimulated by the binding of various growth factors, cytokines and other signal molecules to their receptors, via the phosphatidyl pathway -inositol-3 kinase (PI3K) or MAP kinases (MAPK, kinase proteins activated by mitogens) (Semenza, '03). Under normal oxygenation conditions, HIF-1¿ has a very short half-life of about 5 minutes, therefore the levels of this protein are very low (Ke and Costa, Mol Pharmacol '06). HIF-1 regulates the transcription of numerous genes involved in different cellular processes. Among them, some of the most important are erythropoietin (EPO), implicated in the supply of O2 at a cellular level, VEGF, involved in angiogenesis, BCL2, which regulates cell death by apoptosis, MET, vimentin (VIM ) and MIC2 (CD99), involved in cell motility, in maintaining the structure of the cytoskeleton and in adhesion, metalloproteases (MMPs, matrix metal proteinases), which act at the level of the extracellular matrix, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and GLUT receptors, which are involved in glucose transport and energy maintenance, and IGF2, which regulates cell proliferation and survival (Ke and Costa, '06).
In solid tumors it happens rather frequently that there is a reduction in the partial pressure of O2 compared to normal levels, due to an alteration of the relationship between the consumption and supply of O2 to the cells. This alteration is due to the fact that the high proliferation rate is not supported by the rapid formation of new blood vessels, thus determining the formation of an abnormal vascular system and unable to meet the O2 needs of the entire formation neoplastic. This condition is definitive "tumor hypoxia" and can be caused by several factors, most of which are related to perfusion difficulties, diffusion and anemia (Harrison, Oncologist '04).
The neoplastic cells are able to adapt to the hypoxic microenvironment, characterized by a low O2 voltage, low glucose levels and acid pH, activating or inhibiting the expression of specific genes. The main mediator of the cellular response to O2 deficiency is HIF-1, whose activation is regulated by expression and stabilization and of the HIF-1¿ subunit. In many types of neoplasms, HIF-1¿ behaves like an oncogene, causing not only an increase in the fitness of tumor cells in situations of stress given by O2 deficiency, but often resulting in overexpressed and activated even in normal conditions oxygenation. This condition leads to an increase in genes that stimulate cell proliferation and survival, as well as other processes such as migration, invasiveness and neoangiogenesis (Semenza, Semin Cancer Biol '09).
In the field of endocrine tumors, the study of HIF-1¿ as oncogene is often associated with the characterization of the role of steroid hormones in its activation. In particular, in prostate cancer, androgens would seem to play an important role of activation against HIF-1¿, through an autocrine stimulation mechanism, mediated by tyrosine kinase receptors. The effect of estrogens on HIF-1¿ is less clear, but 2-methoxyestradiol (2-ME), a natural metabolite of estradiol, appears to be able to inhibit HIF-1¿ in vitro, and could be an important therapeutic option in those tumors characterized by excess estrogen (Kimbro and Simons, End Rel Canc '06).
Other endocrine neoplasms, such as pheochromocytoma, paraganglioma and pancreatic islet tumors, are characterized by a state defined as "pseudo-hypoxia", determined by the hyperactivation of HIF-1¿, which promotes both neoplastic progression and resistance to anticancer therapy (Jochmanová, J Natl Canc Inst '13).
The possibility of using HIF-1¿ as a therapeutic target in combination with hormone therapy represents a new and stimulating perspective regarding the treatment of endocrine tumors (Kimbro and Simons, '06; Jochmanová, '13).
The status of HIF-1¿ in the context of ACC has not yet been investigated, however the alterations in the molecular profile that characterize this neoplasm, in addition to other features, such as high resistance to radiotherapy and chemotherapy and a significant tendency to produce recurrences and metastases, suggest that HIF-1¿ may play a role in the onset and development of this tumor.