Ras-Mediated Evasion Of Detachment-Induced Cell Death Involves Differential Signaling Pathways For Metabolism And Anoikis

In order for successful metastasis to occur, cells must overcome anoikis, a caspase-dependent cell death process triggered by detachment from the extracellular matrix (ECM). In addition, recent studies have revealed that ECM-detached cells must also rectify detachment-induced metabolic defects that compromise cell survival. However, the precise signals involved in the inhibition of anoikis and the restoration of proper cell metabolism during ECM-detachment are poorly understood. Of particular interest to our studies is the oncogene Ras, which is constitutively active in approximately 30% of all cancers and is well known to be regulate cell death pathways and metabolism. We have discovered that Ras facilitates the survival of ECM-detached cancer cells by utilizing distinct signaling pathways to block anoikis and regulate metabolism. Using MCF-10A cells engineered to overexpress oncogenic Ras and HCT116 cells (which contain an activating Ras mutation), we investigated the signaling pathways downstream of Ras that facilitate the survival of ECM-detached cells. Interestingly, we discovered that while Ras-mediated PI(3)K signaling is critical for rectifying metabolic defects during ECM-detachment, the downstream effector is not Akt, but rather SGK-1. SGK-1 stimulates glucose uptake, enhances ATP generation, promotes luminal filling in 3-dimensional cell culture, and drives anchorage-independent growth in soft agar. Interestingly, our data also indicate that oncogenic Ras utilizes an entirely distinct signaling pathway to block anoikis. We discovered that Ras diminishes the expression of the phosphatase PHLPP1. This inhibits the dephosphorylation-induced activation of a signaling cascade that culminates in the activation of pro-apoptotic p38 MAPK. In aggregate, these data unveil a novel survival strategy utilized by ECM-detached cancer cells and implicate both SGK-1 and PHLPP1 function downstream of Ras during ECM-detachment. The molecular mechanisms unveiled here could be utilized for the design of novel therapies that eliminate ECM-detached, metastatic cancer cells with Ras mutations through simultaneous modulation of SGK-1 and PHLPP1. Citation Format: Joshua A. Mason, Calli Versagli, Amy Leliaert, Sienna Durbin, Cassandra Buchheit, Zachary Schafer. Ras-mediated evasion of detachment-induced cell death involves differential signaling pathways for metabolism and anoikis. [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 2148. doi:10.1158/1538-7445.AM2015-2148