Abstract 4295: PHLPP suppresses epithelial-mesenchymal transition and cancer cell invasion by negatively regulating RAF1 activity.

Abstract

Abstract PHLPP belongs to a family of protein phosphatases that have previously been shown to inhibit Akt-mediated cell proliferation and survival signaling in cancers. Here, we demonstrate that PHLPP exerts its tumor suppressor function by negatively regulating the RAF/MEK/ERK pathway to inhibit cell migration and invasion. Specifically, we identify the oncogenic protein kinase RAF1 as an interacting protein and a novel substrate of PHLPP. PHLPP dephosphorylates the S338 site of RAF1 and inactivates the kinase both in vitro and in cells. Loss of PHLPP expression largely increases the amplitude and duration of RAF/MEK/ERK signaling in cells, whereas overexpression of PHLPP inhibits the pathway. Functionally, knockdown of PHLPP induces epithelial-mesenchymal transition (EMT)-like phenotype, which coincides with a significant increase in migration and invasion in colon cancer cells. Furthermore, we show that upregulation of transcription factors ZEB1 and ZEB2 is responsible for increased invasiveness observed in PHLPP knockdown cells. Taken together, we have identified a novel role of PHLPP in suppressing EMT and cell motility in colon cancer cells by directly antagonizing RAF1 function. Citation Format: Xin Li, Payton D. Stevens, Tianyan Gao. PHLPP suppresses epithelial-mesenchymal transition and cancer cell invasion by negatively regulating RAF1 activity. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4295. doi:10.1158/1538-7445.AM2013-4295