Abstract 3608: MLL1 regulates cytokine-driven cell migration and metastasis
Authors: Nair Praful R. , Danilova Ludmila , Gómez-de-Mariscal Estibaliz , Kim Dongjoo , Fan Rong , Muñoz-Barrutia Arrate , Fertig Elana , Wirtz Denis 
Published: April 2023

Abstract
Cell migration, particularly in three-dimensional (3D) environments, is a critical requirement for metastasis - the spread of cancer cells from a primary tumor to distant sites. Despite causing the vast majority of cancer-related deaths, targeting metastasis remains challenging clinically. Cancer cell migration can be triggered and maintained by elevated levels of cytokines, which are presumed to be predominantly secreted by immune cells in the tumor microenvironment. However, recent work has highlighted the importance and impact of cytokine production by cancer cells themselves. While the signaling cascades that regulate cell migration have been studied extensively, the epigenetic regulation of cell migration is still poorly understood. MLL1 is a histone methyltransferase, which along with its scaffold protein Menin, is integral to methylation at the histone 3 lysine 4 (H3K4) site. Here, we show that the MLL1-Menin interaction is essential for the migration of cancer cells and that the disruption of this interaction impairs cell migration and metastasis. MLL1 depletion reduces 3D cell migration in vitro and led to lesser metastatic burden and prolonged survival in vivo. Reduced lung metastatic burden was observed even after accounting for the difference in the growth rate of primary tumors. Mechanistically, MLL1-Menin interaction controls actin filament assembly via the IL-6/pSTAT3/Arp3 axis and acto-myosin contractility via the TGF-β1/Gli2/ROCK1/2/pMLC2 axis, which together regulate dynamic protrusion generation and 3D cell migration. MLL1-Menin inhibition also decreases cell proliferation by inhibiting mitosis and cell cycle-related pathways. MLL1 depletion decreases primary tumor growth, metastatic spread, and metastatic outgrowth in mouse models of triple-negative breast cancer (TNBC), thus improving survival. When comparing metastatic burden at a threshold tumor size, rather than at a timepoint, MLL1 depletion still lowered metastatic burden. Combining an MLL1-Menin inhibitor with Paclitaxel, a standard TNBC chemotherapeutic, abrogated tumor growth and metastasis in a syngeneic TNBC mouse model. Overall, our studies show that MLL1 is an epigenetic regulator of 3D cancer cell migration, which exerts its effects by controlling the production of the key cytokines IL-6 and TGF-β1. Our in vivo studies demonstrate the potential of targeting the MLL1-Menin interaction in metastasis prevention and its potential to be combined with currently administered chemotherapeutics.
Citation Format: Praful R. Nair, Ludmila Danilova, Estibaliz Gómez-de-Mariscal, Dongjoo Kim, Rong Fan, Arrate Muñoz-Barrutia, Elana Fertig, Denis Wirtz. MLL1 regulates cytokine-driven cell migration and metastasis. [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 3608.