Abstract:Cell migration through extracellular matrices requires nuclear deformation, which depends on nuclear stiffness. In turn, chromatin structure contributes to nuclear stiffness, but the mechanosensing pathways regulating chromatin during cell migration remain unclear. Here, we demonstrate that WD repeat domain 5 (WDR5), an essential component of H3K4 methyltransferase complexes, regulates cell polarity, nuclear deformability and migration of lymphocytes in vitro and in vivo, independent of transcriptional activity, suggesting non-genomic functions for WDR5. Similarly, depletion of RbBP5 (another H3K4 methyltransferase subunit) promotes similar defects. We reveal that a 3D environment increases the H3K4 methylation dependent on WDR5, and results in a globally less compacted chromatin conformation. Further, using atomic force microscopy, nuclear particle tracking and nuclear swelling experiments, we detect changes in nuclear mechanics that accompany the epigenetic changes induced in 3D conditions. Indeed, nuclei from cells in 3D environments were softer, and thereby more deformable, compared to cells in suspension or cultured in 2D conditions, again dependent on WDR5. Dissecting the underlying mechanism, we determined that actomyosin contractility, through the phosphorylation of myosin by MLCK (myosin light chain kinase), controls the interaction of WDR5 with other components of the methyltransferase complex, which in turn upregulates H3K4 methylation activation in 3D conditions. Taken together, our findings reveal a novel non-genomic function for WDR5 in regulating H3K4 methylation induced by 3D environments, physical properties of the nucleus, cell polarity and cell migratory capacity. 3 Significance:Cells require nuclear deformation to squeeze through tissue matrices. We have discovered that WDR5 (an epigenetic modulator of H3K4 methylation) is fundamental for cell polarity and migration in vitro and in vivo, independently of transcription. We have uncovered that the interactions between cells and the surrounding 3D confined conditions induce the upregulation of H3K4me3. Moreover, 3D environments control the deformability and the mechanical properties of the nucleus. We have identified that loss of WDR5 abrogates the H3K4 methylation and the nuclear changes induced by 3D conditions. Mechanistically, we found that MLCK and myosin function was required for WDR5-mediated H3K4 methylation in 3D matrices. Our findings uncover new functions of the epigenetic machinery when cells move through constricted conditions.

SummaryAberrant WNT signaling drives colorectal cancer (CRC). Here, we identify TIAM1 as a critical antagonist of CRC progression through inhibiting TAZ and YAP, effectors of WNT signaling. We demonstrate that TIAM1 shuttles between the cytoplasm and nucleus antagonizing TAZ/YAP by distinct mechanisms in the two compartments. In the cytoplasm, TIAM1 localizes to the destruction complex and promotes TAZ degradation by enhancing its interaction with βTrCP. Nuclear TIAM1 suppresses TAZ/YAP interaction with TEADs, inhibiting expression of TAZ/YAP target genes implicated in epithelial-mesenchymal transition, cell migration, and invasion, and consequently suppresses CRC cell migration and invasion. Importantly, high nuclear TIAM1 in clinical specimens associates with increased CRC patient survival. Together, our findings suggest that in CRC TIAM1 suppresses tumor progression by regulating YAP/TAZ activity.

Summary Melanocytes, replenished throughout life by melanocyte stem cells (MSCs), play a critical role in pigmentation and melanoma. Here, we reveal a function for the metastasis-associated phosphatase of regenerating liver 3 (PRL3) in MSC regeneration. We show that PRL3 binds to the RNA helicase DDX21, thereby restricting productive transcription by RNAPII at master transcription factor (MITF)-regulated endolysosomal vesicle genes. In zebrafish, this mechanism controls premature melanoblast expansion and differentiation from MSCs. In melanoma patients, restricted transcription of this endolysosomal vesicle pathway is a hallmark of PRL3-high melanomas. Our work presents the conceptual advance that PRL3-mediated control of transcriptional elongation is a differentiation checkpoint mechanism for activated MSCs and has clinical relevance for the activity of PRL3 in regenerating tissue and cancer.