Abstract A70: Akt2 gain or Akt1 loss drives invasion and aggressiveness in breast cancer
Authors: Perrone Cecilia , Riggio Marina , May Maria , Polo Maria Laura , Rodriguez Jimena , Kaen Diego Lucas , Lanari Claudia , Novaro Virginia 
Published: May 2016

Despite the improvement in the early diagnosis and the use of modern therapies, breast cancer is the second cause of death, after lung cancer, in women around the world, and this is mainly due to metastasis development distant organs.

PI3K/Akt pathway is deregulated in almost 50% of breast carcinomas, and is associated to therapy resistance. Currently, there are increasing clinical trials that combine endocrine treatments with PI3K/Akt inhibitors to delay tumor resistance and to avoid tumor progression. However, these inhibitors do not distinguish between the isoform specific function of Akt1, Akt2 and Akt3. Several evidences in different models of cancer show that Akt1 and Akt2 are expressed in different stages of cancer progression, with Akt1 involved in tumor proliferation during the first steps of the carcinogenic process, and Akt2 involved in the invasive phenotype. The aim of this work was to study Akt1 and Akt2 isoforms, focusing on their particular role in cell migration and invasion in human breast tumor samples and in two human breast cancer cell lines.

Tissue microarray analysis in a small cohort of human advanced breast cancer samples showed a positive association between invasive grade, Akt2 expression and E-cadherin loss. Interestingly, E-cadherin presents a heterogeneous staining in each sample, being weaker in the more invasive areas and stronger in the non-invasive areas.

To understand the specific role of each isoform of Akt on tumor phenotype, T47D and IBH-6 human breast cancer cell lines were stably transfected to specifically inhibit Akt1 (shAkt1) or Akt2 (shAkt2) and the resulting phenotype in cell culture and in xenografts were analyzed. We found that Akt1 silencing inhibited cell growth through S6 and cyclin-D1 regulation, but induced cell migration and invasion in IBH-6 2D and 3D cell cultures. Contrarily, Akt2 silencing had no effect on cell proliferation but significantly inhibited cell adhesion and invasion. These phenotypes were accompanied by an opposite regulation of β1-Integrin, FAK, MMP9, F-actin and vimentin expression. Simultaneous silencing of Akt1 and Akt2 isoforms showed that Akt1 has an anti-migratory effect per se and not by upregulating Akt2 levels.

Interestingly, in IBH-6 and T47D xenograft studies we observed that shAkt1 cells grew significantly more slowly than control tumors, but displayed a ducto-lobulillar invasive phenotype, similar to the phenotype gained with Akt2 overactivation by myristoylated Akt2. Contrarily, shAkt2 tumors showed no differences in growth rate, with no infiltrating morphology when compared to control tumors. Immunohistochemical analysis showed low E-cadherin and high vimentin expression in invasive T47D shAkt1 tumors, and the opposite pattern in T47D shAkt2 tumors. We are currently assessing Akt1 status, vimentin, β1-integrin, FAK and MMP9 levels in human samples to relate them with in vitro and xenografts results.

Altogether, these results indicate that Akt2 overexpression as well as Akt1 inhibition play important roles in the acquisition of an invasive and aggressive phenotype. The status of each isoform-driven pathway is relevant in the design of targeted therapies that could be more effective and selective in each tumor stage.

Citation Format: Cecilia Perrone, Marina Riggio, Maria May, Maria Laura Polo, Jimena Rodriguez, Diego Lucas Kaen, Claudia Lanari, Virginia Novaro. Akt2 gain or Akt1 loss drives invasion and aggressiveness in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr A70.