RESUMO
Symmetry-breaking polarization enables functional plasticity of cells and tissues and is yet not well understood. Here we show that epithelial cells, hard-wired to maintain a static morphology and to preserve tissue organization, can spontaneously switch to a migratory polarized phenotype after relaxation of the actomyosin cytoskeleton. We find that myosin II engages actin in the formation of cortical actomyosin bundles and thus makes it unavailable for deployment in the process of dendritic growth normally driving cell motility. Under low-contractility regimes, epithelial cells polarize in a front-back manner owing to the emergence of actin retrograde flows powered by dendritic polymerization of actin. Coupled to cell movement, the flows transport myosin II from the front to the back of the cell, where the motor locally 'locks' actin in contractile bundles. This polarization mechanism could be employed by embryonic and cancer epithelial cells in microenvironments where high-contractility-driven cell motion is inefficient.
Assuntos
Actinas/metabolismo , Actomiosina/metabolismo , Movimento Celular/fisiologia , Polaridade Celular/fisiologia , Células Epiteliais/fisiologia , Algoritmos , Animais , Ligação Competitiva , Adesão Celular/fisiologia , Linhagem Celular , Cães , Células Epiteliais/metabolismo , Células Madin Darby de Rim Canino , Microscopia Confocal , Microscopia de Fluorescência , Modelos Biológicos , Miosina Tipo II/genética , Miosina Tipo II/metabolismo , Polimerização , Interferência de RNA , Gravação em VídeoRESUMO
Deregulated Myc triggers a variety of intrinsic tumor suppressor programs that serve to restrain Myc's oncogenic potential. Since Myc activity is also required for normal cell proliferation, activation of intrinsic tumor suppression must be triggered only when Myc signaling is oncogenic. However, how cells discriminate between normal and oncogenic Myc is unknown. Here we show that distinct threshold levels of Myc govern its output in vivo: low levels of deregulated Myc are competent to drive ectopic proliferation of somatic cells and oncogenesis, but activation of the apoptotic and ARF/p53 intrinsic tumor surveillance pathways requires Myc overexpression. The requirement to keep activated oncogenes at a low level to avoid engaging tumor suppression is likely an important selective pressure governing the early stages of tumor microevolution.
