Conflicting reports implicate the scaffolding protein RACK1 in the progression of breast cancer. PP2A has a well-established role as a tumour suppressor within signalling pathways but is also known to play a pro-carcinogenic role in certain circumstances [1]. RACK1 has been identified as a direct binding partner of PP2A to regulate cell migration and stabilize PP2A activity [2]. Our objective was to further characterise the interaction between PP2A and RACK1 in breast cancer cells. The PP2A holoenzyme is assembled in MCF-7 cells and we found that both the C subunit and A subunit of PP2A are assembled on the RACK1 scaffold. We used immobilized peptide arrays representing the entire PP2A-Catalytic protein to identify amino acids on the C subunit of PP2A that are required for the binding of RACK1. Once identified, these sites were mutated and expressed in the context of the full length PP2A C subunit protein and stable cell lines were generated. When the RACK1/PP2A interaction was disrupted, cells exhibited reduced PP2A phosphatase activity, confirming the role for RACK1 in stabilizing PP2A activity. We used the stable cell lines to determine that disruption of the RACK1/PP2A complex also reduces the adhesion, proliferation, migration and invasion of this breast cancer cell model. The work has significantly advanced our understanding of the RACK1/PP2A complex and indicates a pro-carcinogenic role for the RACK1/PP2A complex. This work has highlighted a novel mechanism to target PP2A activity and may provide a potential therapeutic target in the treatment of breast cancer.

1. Kiely, M. and P.A. Kiely, PP2A: The Wolf in Sheep's Clothing? Cancers, 2015. 7(2): p. 648-669.

2. Kiely, P.A., et al., Tyrosine 302 in RACK1 is essential for insulin-like growth factor-I-mediated competitive binding of PP2A and β1 integrin and for tumor cell proliferation and migration. Journal of Biological Chemistry, 2008. 283(34): p. 22952-22961.

Citation Format: Maeve Kiely, Rosemary O’Connor, David Adams, George S. Baillie, Patrick A. Kiely. Disruption of the RACK1/PP2A complex results in a decrease in the adhesion, proliferation, migration and invasion capabilities of breast cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 204.