CONICET | Buscador de Institutos y Recursos Humanos

The goal of our laboratory is to exploit the emerging information on deregulated signaling circuitries and individual genomic and molecular alterations to develop new precision therapies to prevent and treat cancer. Specifically, we have focused on the study of cAMP and its coupled signal transduction pathway, and recently on the use of different approaches to study Pancreatic Ductal Adenocarcinoma (PDAC) initiation and progression. PDAC is one of the most lethal types of tumors and one of the biggest therapeutic challenges for modern oncology. Despite the recent improvement in survival, the 5-year survival rate remains below 5-8%. Therefore, there is a great clinical need to identify key molecular and cellular regulators of tumor progression and invasion in order to develop new therapeutic strategies. The carcinogenic process of pancreatic cancer accounts for an accumulation of mutations and genetic lesions in signaling pathways linked to cell proliferation, motility and survival. In the last few decades, several mutations leading to the activation of oncogenes (such as KRAS, GNAS, and BRAF) and the inhibition of tumor suppressor genes (such as p16/CDNKN2A, TP53, SMAD4/DPC4, and BRCA2) have been identified. These mutations are present in the earliest-stages and lowest-grade premalignant lesions of the disease, suggesting that they could be essential for its development/progression and therefore, conceivably therapeutic targets. Interestingly, frequent activating mutations in GNAS, gene encoding for the stimulatory Gα subunit (Gαs), are not the only alterations on the canonical cAMP signaling pathway described in PDAC. Recent studies identified that 59% of the tested human PDAC samples exhibit an elevated Gαs expression compared to normal tissues, and 72% show an increment in the expression of phosphorylated substrates of cAMP-dependent kinase (PKA), a downstream effector of the Gαs-protein-coupled receptor-cAMP signaling pathway. Altogether, these observations indicate that cAMP cascade is commonly activated in PDAC, and suggest an oncogenic potential for this signaling pathway. Nonetheless, this assumption points to an intriguing paradox based on the fact that the activation of cAMP pathway has been classically associated with inhibition of cell proliferation and migration in PDAC. Due to the critical role of cAMP in cellular biology, the time-course levels of this second messenger are strictly regulated by several mechanisms, including its degradation by phosphodiesterases, its compartmentalization, the desensitization of GPCR, and its extrusion to the extracellular compartment mainly mediated by the Multidrug Resistance-Associated Protein 4 (MRP4/ABCC4). In recent years, numerous publications describe the anti-proliferative effects of MRP4 inhibition, its potential as a marker of poor prognosis and its up-regulation in several tumors. However, little is known about the mechanisms involved in the anti-proliferative effects of MRP4 inhibition and there are limited studies of its potential as a therapeutic target. We have recently described that enhanced intracellular cAMP levels upregulate MRP4 expression through the activation of cAMP/Epac/Rap1 signaling pathway. Considering the frequent cAMP-signaling deregulation observed in PDAC, we hypothesize that pancreatic cancer cells could be ?addicted? to high levels of MRP4, relying on active cAMP extrusion to provide a survival advantage, and therefore highlighting a therapeutically exploitable difference between cancerous and normal cells. In this study we showed that MRP4 expression is upregulated in human pancreatic cancer and may influence patient outcome. MRP4 inhibition abrogated cell migration and proliferation in vitro by both, activating the cAMP/Epac/Rap1 signaling pathway and reducing extracellular cAMP levels. Interestingly, the extruded cAMP acted as an autocrine/paracrine mitogenic signal and silencing MRP4 strongly impaired tumor growth and tumorigenicity in a mouse xenograft model. Our results strongly indicate that MRP4 could represent an excellent therapeutic target for pancreatic ductal adenocarcinoma.