Abstract 5817: LKB1 overcomes RAS pathway-mediated loss of epithelial integrity

Abstract

Abstract Oncogenic RAS pathway disassembles cell-cell and cell-basement membrane junctions, thus promoting epithelial cell motility and invasion. To find tumor proteomic changes responsible for the disrupting effects of RAS on epithelial integrity, we explored cBioportal cell line proteomics data across all cancer types for correlations between oncogenic KRAS or HRAS mutations and possible regulators of epithelial integrity. We found inverse correlation between these RAS mutations and tumor suppressor LKB1 protein levels in a cohort where LKB1 was not inactivated by a mutation. Furthermore, LKB1 protein levels were also positively correlated with NF2 protein (a negative regulator of RAS) in human breast tumors and inversely correlated with c-RAF (RAS effector) activating phosphorylation at serine 338 in breast cancer cell lines. We sought to functionally clarify the relationship between RAS pathway and LKB1, finding that an ectopic constitutive or inducible expression of HRASV12 downregulates LKB1 protein in mammary epithelial MCF10A cells and HMEC-hTERT cells. Furthermore, RAS-mutant MCF10A cells regained LKB1 protein levels upon treatment with MEK/ERK inhibitors. We establish that the RAS-mediated downregulation of LKB1 protein occurs through proteasomal activity. LKB1 reconstituted MCF10A-HRASV12 (RAS-LKB1) cells displayed restored desmoplakin, γ-catenin and E-cadherin pericellular immunostaining pattern in monolayer cultures, suggesting restoration of desmosomes and adherence junctions. We also cultured RAS-LKB1 cells in 3D egg-white and observe restoration of E-cadherin, γ-catenin, α6-integrin, and laminin-332, indicating a rescue of epithelial integrity in 3D context. Our findings suggest that LKB1 rescues mutant RAS-mediated disruption of cell-cell and cell-basement membrane junctions and general epithelial integrity. Our current aim is to define how LKB1 suppresses RAS mediated disruption of breast epithelial integrity, that is expected to shed new light into early stages of tumor invasion and uncover novel therapeutic opportunities via restoration of LKB1. Citation Format: Topi A. Tervonen, Shishir M. Pant, Johanna Englund, Juha Klefström. LKB1 overcomes RAS pathway-mediated loss of epithelial integrity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5817.