Poster V2 - MLL1-Menin interaction regulates cytokine-driven 3D cell migration

Introduction: Cell migration, particularly in three-dimensional (3D) environments, is a critical requirement for cancer metastasis – which causes the vast majority of cancer-related deaths. 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.

Materials and

Methods: MLL1 was depleted in triple-negative cancer (TNBC) cells, these cells were embedded in 3D collagen gels, and their migration was tracked by overnight live cell imaging. Protrusion generation was assessed by a machine learning algorithm. Pathways were validated at the RNA level (via qRT-PCR and RNA-seq) and protein level (via western blotting, immunofluorescence, and multiplex cytokine assays).

Results, Conclusions, and Discussions: 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. Cell migration impaired by MLL1 inhibition or depletion can be completely rescued by the supplementation of three cytokines: IL-6, IL-8, and TGF-β1. The MLL1-Menin interaction regulates protrusion generation via secretion of interleukins, IL-6 and IL-8, which activate actin filament assembly via pSTAT3/Arp2,Arp3 pathway. However, the underlying mechanism behind MLL1-Menin mediated 3D cell migration is non-linear. In the second mode of regulation of cell migration at a ‘deeper’ inhibition of the MLL1-Menin interaction, myosin II contractility is also controlled by the MLL1-Menin interaction, in addition to the protrusion generation described above. This modulation of myosin contractility by MLL1-Menin interaction is mediated entirely by the secretion of TGF-β1, which regulates the ROCK1,ROCK2/pMLC2 pathway via the transcription factor Gli2. These studies reveal that MLL1 plays a two-pronged role in 3D cell migration by controlling both actin filament assembly and myosin-based contractility. In vivo, MLL1 depletion decreases metastatic burden in mouse models of TNBC, thus improving survival. Administration of an MLL1-Menin inhibitor abrogated spontaneous metastasis and was also effective against pre-existent metastatic burden in syngeneic TNBC mouse models.
Overall, our studies show that MLL1 is an epigenetic regulator of 3D cancer cell migration, which exerts its effects by controlling both actin assembly and myosin contractility via production of the cytokines IL-6, IL-8, and TGF-β1.

Acknowledgements (Optional):