RESUMO
The serum response factor (SRF) coactivator myocardin-related transcription factor A (MAL/MKL1/MRTF-A), the nuclear transport and activity of which is regulated by monomeric actin, has been implicated in tension-based regulation of SRF-mediated transcriptional activity. However, the mechanisms involved remain unclear. We used fibroblasts grown within collagen matrices to explore whether MRTF-A transport is regulated by tissue tension. We show that MRTF-A nuclear accumulation following stimulation with serum, actin drugs or acute mechanical stress is prevented within mechanically loaded, anchored matrices at tensional homeostasis. This is accompanied by a higher G/F actin ratio, defective nuclear import and increased cofilin expression. We propose that tension regulates MRTF-A/SRF activity through cofilin-mediated modulation of actin dynamics.
Assuntos
Homeostase , Fator de Resposta Sérica/metabolismo , Transativadores/genética , Transativadores/metabolismo , Actinas/genética , Actinas/metabolismo , Transporte Ativo do Núcleo Celular , Animais , Linhagem Celular , Cofilina 1/biossíntese , Cofilina 1/metabolismo , Proteínas de Ligação a DNA/metabolismo , Regulação para Baixo , Camundongos , Células NIH 3T3 , Fator de Resposta Sérica/genética , Transdução de Sinais , Estresse Fisiológico , Fatores de Transcrição/metabolismoRESUMO
To preserve epithelial barrier function, dying cells are squeezed out of an epithelium by "apoptotic cell extrusion." Specifically, a cell destined for apoptosis signals its live neighboring epithelial cells to form and contract a ring of actin and myosin II that squeezes the dying cell out of the epithelial sheet. Although most apoptotic cells extrude apically, we find that some exit basally. Localization of actin and myosin IIA contraction dictates the extrusion direction: basal extrusion requires circumferential contraction of neighboring cells at their apices, whereas apical extrusion also requires downward contraction along the basolateral surfaces. To activate actin/myosin basolaterally, microtubules in neighboring cells reorient and target p115 RhoGEF to this site. Preventing microtubule reorientation restricts contraction to the apex, driving extrusion basally. Extrusion polarity has important implications for tumors where apoptosis is blocked but extrusion is not, as basal extrusion could enable these cells to initiate metastasis.
Assuntos
Apoptose/fisiologia , Células Epiteliais/metabolismo , Epitélio/metabolismo , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Microtúbulos/metabolismo , Actinas/metabolismo , Animais , Biomarcadores/metabolismo , Linhagem Celular , Polaridade Celular , Cães , Células Epiteliais/citologia , Células Epiteliais/efeitos dos fármacos , Fatores de Troca do Nucleotídeo Guanina/genética , Humanos , Miosina Tipo II/metabolismo , Nocodazol/farmacologia , Paclitaxel/farmacologia , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Fatores de Troca de Nucleotídeo Guanina Rho , Moduladores de Tubulina/farmacologia , Peixe-Zebra/anatomia & histologia , Peixe-Zebra/crescimento & desenvolvimento , Peixe-Zebra/metabolismoRESUMO
The role of myosin II in mitosis is generally thought to be restricted to cytokinesis. We present surprising new evidence that cortical myosin II is also required for spindle assembly in cells. Drug- or RNAi-mediated disruption of myosin II in cells interferes with normal spindle assembly and positioning. Time-lapse movies reveal that these treatments block the separation and positioning of duplicated centrosomes after nuclear envelope breakdown (NEBD), thereby preventing the migration of the microtubule asters to opposite sides of chromosomes. Immobilization of cortical movement with tetravalent lectins produces similar spindle defects to myosin II disruption and suggests that myosin II activity is required within the cortex. Latex beads bound to the cell surface move in a myosin II-dependent manner in the direction of the separating asters. We propose that after NEBD, completion of centrosome separation and positioning around chromosomes depends on astral microtubule connections to a moving cell cortex.
