Abstract 4139: Role of Akt2 in cell survival and metastasis of colorectal cancer (CRC) cells
Authors: Agarwal Ekta 
Published: August 2015

Background: Colorectal Cancer (CRC) is the second highest cause of cancer related deaths in United States. Metastatic dissemination of CRC cells to distant organs (primarily to the liver and lungs) makes the disease more lethal and incurable. Inappropriate cell survival signaling mechanisms contribute to successful colonization of cells at metastatic sites. Akt is a major cell survival-signaling node, which undergoes aberrant activation in various types of cancer. The Akt family has three members: Akt1, Akt2 and Akt3 which share structural homology and have similar mechanism of activation; however, differences in the phenotype of Akt1, Akt2 and Akt3 knock out mice suggest that they have non-redundant functional characteristics. Recently Akt2 has been identified as a significant contributor to colon cancer malignancy in addition to Akt1. Earlier reports have shown that knockdown of Akt2 results in reduced liver metastasis of CRC cells, however there are no studies related to the mechanism responsible for the reduction in metastasis.

We observed a significant increase in the expression of Akt2 (microarray analysis) in liver metastatic samples formed by highly metastatic IGF1R-dependent CRC cells in comparison to the primary tumor. This was further confirmed by western blot and immunohistochemistry (IHC) analysis. Additionally, correlative studies using human primary colon carcinoma and corresponding liver metastatic samples showed a significant (p&lt;0.001) increase in the expression of Akt2. These preliminary data led us to hypothesize that Akt2 may be playing a role in regulating cell survival and metastasis of CRC cells.

Materials and Methods: IGF1R-dependent CRC cells (GEO and CBS) were used for the study. Two doxycycline inducible shRNAs for Akt2 were introduced by lentiviral transfection. Non-Targeting shRNA was used as control.

Results: shRNA-mediated knockdown of Akt2 led to reduction in the expression of XIAP and survivin. We and others have shown that these IAPs (XIAP and survivin) are implicated to play an important role in cancer cell survival and metastasis. Furthermore, loss of Akt2 resulted in loss of pBad (S136), which is an essential cell survival marker. Loss of pBad results in increased cell death by PARP activation. Akt2 knockdown also affects cell survival by increasing p21 and decreasing the expression of cyclin E. PCR array analysis for metastatic genes revealed that a metastatic suppressor gene MTSS1 was 9 fold increased on knockdown of Akt2. It has been shown that MTSS1 inhibits metastasis by affecting cell junction assembly and stability.

Conclusion: We have shown that loss of Akt2 promotes cell death and inhibits cell proliferation. This is the first study, which suggests the mechanism of Akt2 mediated cell death by XIAP and survivin downregulation. These results suggest that Akt2 inhibits metastasis by increasing the expression of MTSS1.

Citation Format: Ekta Agarwal. Role of Akt2 in cell survival and metastasis of colorectal cancer (CRC) cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4139. doi:10.1158/1538-7445.AM2015-4139