Abstract 1447: Elucidating the mechanism of Dock7-mediated cellular transformation

Abstract

Abstract Akt is a serine/threonine protein kinase that receives signals from a plethora of external and internal stimuli in order to promote survival and regulate cellular growth and metabolism. Akt is part of the highly conserved PI3K/Akt signaling axis and is classically regulated by its interaction with the phosphoinositide, PIP3, and its subsequent phosphorylation at S473 and S308 by the mTOR complex 2 (mTORC2) and 3-Phosphoinositide-dependent protein kinase 1 (PDK1), respectively. Altered Akt activity has been linked to numerous diseases, such as cancer, diabetes and neurodegenerative diseases. Specifically, PI3K/Akt deregulation occurs in approximately one third of human cancers and ~40% of breast cancers. My research focuses on Dock7, a Guanine Nucleotide Exchange Factor (GEF) for the small GTPases Cdc42 and Rac1, and a novel player in the regulation of Akt activity and stability. Dock7 belongs to the Dock family of atypical GEFs and contains two evolutionarily conserved domains, DHR1 (a putative lipid binding domain) and DHR2 (the catalytic GEF domain). The expression level of Dock7 correlates with an unfavorable prognosis in liver cancer patients, and it is highly expressed in triple-negative breast cancers. Studies in our laboratory showed Dock7 is essential for the transformed properties of several cancer cell lines, and that it interacts with Akt in co-immunoprecipitation assays. In order to decipher the mechanism by which Dock7 mediates transformation, I created a Crispr-Cas9 Dock7 Knock-out HeLa cell line. I proceeded to confirm that these cells are not able to grow in an anchorage independent manner nor in serum free conditions, two hallmarks of transformation. Furthermore, in comparison to the phosphorylation status of Akt in parental HeLa cells, I found that in Dock7 KO HeLa cells, Akt is not phosphorylated at the S473 site in the absence of growth factors, indicative of lower basal activity. Accordingly, phosphorylation of downstream effectors of Akt is also downregulated. Besides promoting the phosphorylation state of Akt, Dock7 plays a role in the stability of the Akt protein during certain cellular stresses, highlighting a versatile and important role for Dock7 in Akt regulation and a potential target for therapeutic intervention in tumors where Akt is deregulated. Citation Format: Oriana Y. Teran Pumar, Kristin F. Wilson, Richard A. Cerione. Elucidating the mechanism of Dock7-mediated cellular transformation [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1447.