Papel de las isoformas de AKT en la progresión del cáncer de próstataregulación por la fosfotirosina fosfatasa SHP-1

Abstract

BACKGROUND: Prostate cancer is one of the most frequent malignancies between men both in Europe and Spain, altough the death of patients is caused for metastatic neoplasm in other organs different from primary tumoral site. So, understanding the metastatic cascade of intracellular signaling is highly neccessary for developing new therapeutic targets. PI3K/AKT is a well established signaling pathway, wich leads to phosphoinositol generation. This second messenger is involved in controlling several cell features like cell cycle, cellular adhesion and migration. On the other hand, SHP-1 is a phosphotyrosine phosphatase, mainly expressed in non-heamatopoietic tissues and moderately expressed in epithelial tissues, whose roles in cancer progression are currently being unraveled. In this sense, our group described that SHP-1 regulates cell proliferation by an interrelationship with PI3K/AKT pathway in PC-3 cells. However, we did not describe the roles of the main PI3K downstream effector, the AKT kinase. Three AKT isoforms has been described, and recents studies were focused in its non-redundant functions indicating that exists an isoform-dependent control, for instance, of glucose homeostasis or cellular migration. AIMS: To establish the role of different AKT isoforms in regulating cellular process implied in tumour progression, as well as to analyse whether SHP-1 acts as a PI3K/AKT regulator, studying the context and consequences of that relationship. METHODS: We use RNA interference to downregulate the expression of AKT isoforms and evaluate their impact on PC-3 cells proliferation, adhesion and migration and the AKT-related efectors involved in regulating the aforementioned processes. We also used siRNA sequences to knockdown SHP-1 and analyse its contribution to the PI3K/AKT pathway regulation. CONCLUSIONS: AKT isoforms exert non-redundant roles with regard to cell cycle regulation. In this sense, AKT2 promotes CDK6/cyclin D1 complexes formation, through regulating cyclin expression. This isoform also controls pRb expression and cyclin E levels. AKT2 promotes p27 expression and its nuclear localization, too. Taken together, these results points to an AKT2-dependent cell cycle regulation in PC-3 cells, with no contribution of AKT1 or 3 in this role. On the other hand, AKT1 showed to be involved in the fine control of cellular adhesion and migration, by its interactions with efectors of paramount importance for those characteristics like FAK, small GTPasas of Rho family and Src. Although two AKT isoforms presented differential roles, we did not observe any specific role for AKT3 in controling PC-3 cells proliferation, adhesion or migration. With regard to SHP-1, we confirmed that this phosphatase regulates PI3K kinase activity, interacting specifically with AKT1, and affecting its activation. We also observed that its presence is neccessary for the maintenance of complex platforms of signaling nucleated around Src, FAK, p85 and AKT1. In summary, our work demonstrated that SHP-1 is a new and key regulator of PI3K/AKT enzimatic function, and that AKT isoforms could be considered as an innovative therapeutic target for metastatic disease.