Loss of G-Protein Pathway Suppressor 2 promotes tumor growth through activation of AKT signaling

G Protein Suppressor 2 (GPS2) is a multifunctional protein that exerts important roles in inflammation and metabolism in adipose, liver and immune cells. GPS2 has recently been identified as a significantly mutated gene in breast cancer and other malignancies and proposed to work as a putative tumor suppressor. However, molecular mechanisms by which GPS2 prevents cancer development and/or progression are largely unknown. Here, we have profiled the phenotypic changes induced by GPS2 depletion in MDA-MB-231 triple negative breast cancer cells and investigated the underlying molecular mechanisms. We found that GPS2-deleted MDA-MB-231 cells exhibited increased proliferative, migratory, and invasive properties in vitro, and conferred greater tumor burden in vivo in an orthotopic xenograft mouse model. Transcriptomic, proteomic and phospho-proteomic profiling of GPS2-deleted MBA-MB-231 revealed a network of altered signals that relate to cell growth and PI3K/AKT signaling. Overlay of GPS2-regulated gene expression with MDA-MB-231 cells modified to express constitutively active AKT showed significant overlap, suggesting that sustained AKT activation is associated with loss of GPS2. Accordingly, we demonstrate that the pro-oncogenic phenotypes associated with GPS2 deletion are rescued by pharmacological inhibition of AKT with MK2206. Collectively, these observations confirm a tumor suppressor role for GPS2 and reveal that loss of GPS2 promotes breast cancer cell proliferation and tumor growth through uncontrolled activation of AKT signaling. Moreover, our study points to GPS2 as a potential biomarker for a subclass of breast cancers that would be responsive to PI3K-class inhibitor drugs. Overall design: Transcriptomic profiling to examine effect of GPS2 depletion on the PI3K/AKT pathway using the MDA-MB231 cell line as a model. We carried out knockout and over-expression experiments using both wild type (WT) MB231 and the following modified MB231 cell lines: MB231-GPS2KO1, -KO2 (two independent pools with two different sets of sgRNAs targeting GPS2, made using CRISPR-Cas9 genome editing), MB231-myrAKT (MB231 cell line with myristoylated AKT, constitutively active AKT), MB231-GPS2KO1/2+MK (MB231-GPS2-KO cell lines treated with 10uM MK2206 (allosteric AKT inhibitor) for 4h prior to sample collection). We had 6 different conditions (WT, KO1 +/-MK, KO2 +/-MK, myr-akt) run in triplicate for a total of 18 samples run as 1 pool. This pool was run as two 75PE Next-Seq runs.