ABSTRACT
Polarized epithelia develop distinct cell surface domains, with the apical membrane acquiring characteristic morphological features such as microvilli. Cell polarization is driven by polarity determinants including the evolutionarily conserved partitioning-defective (PAR) proteins that are separated into distinct cortical domains. PAR protein segregation is thought to be a consequence of asymmetric actomyosin contractions. The mechanism of activation of apically polarized actomyosin contractility is unknown. Here we show that the Cdc42 effector MRCK activates myosin-II at the apical pole to segregate aPKC-Par6 from junctional Par3, defining the apical domain. Apically polarized MRCK-activated actomyosin contractility is reinforced by cooperation with aPKC-Par6 downregulating antagonistic RhoA-driven junctional actomyosin contractility, and drives polarization of cytosolic brush border determinants and apical morphogenesis. MRCK-activated polarized actomyosin contractility is required for apical differentiation and morphogenesis in vertebrate epithelia and Drosophila photoreceptors. Our results identify an apical origin of actomyosin-driven morphogenesis that couples cytoskeletal reorganization to PAR polarity signalling.
Subject(s)
Cell Membrane/enzymology , Cell Polarity , Epithelial Cells/enzymology , Myotonin-Protein Kinase/metabolism , Actomyosin/metabolism , Adaptor Proteins, Signal Transducing/metabolism , Animals , Animals, Genetically Modified , Caco-2 Cells , Cell Cycle Proteins/metabolism , Cell Differentiation , Dogs , Drosophila Proteins/genetics , Drosophila Proteins/metabolism , Drosophila melanogaster/cytology , Drosophila melanogaster/enzymology , Genotype , Guanine Nucleotide Exchange Factors/metabolism , Humans , Madin Darby Canine Kidney Cells , Membrane Proteins/metabolism , Morphogenesis , Myosin Type II/metabolism , Myotonin-Protein Kinase/genetics , Phenotype , Photoreceptor Cells, Invertebrate/enzymology , Protein Kinase C/metabolism , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolism , RNA Interference , Signal Transduction , Time Factors , Transfection , cdc42 GTP-Binding Protein/metabolismABSTRACT
The presence of a live cell cohabiting within another cell has fascinated scientists for many decades. Far from being a spurious event, many have attempted to uncover the molecular mechanism underlying this phenomenon. In this study, we observed anchorage-dependent MCF-7 cells internalizing neighboring epithelial cells (entosis) after siRNA-mediated silencing of the Metallothionein-2A (MT-2A) gene. MTs belong to a family of low-molecular weight proteins, which bind metal ions endogenously and its over-expression has been reported in a variety of cancers that include breast, prostate, and colon. We provide microscopic evidence at light and ultrastructural levels of the occurrence of entosis after altering MT expression in a subpopulation of MCF-7 breast cancer cells by silencing the MT-2A gene. Our results demonstrate that adheren junctions may play important roles in the formation of cell-in-cell cytostructure after MT-2A gene downregulation and the entotic process does not appear to involve genes associated with autophagy. Interiorized cells often underwent lysosomal degradation within the cytoplasmic body of the engulfing cell. It would appear that a subset of breast cancer cells could die via entosis after MT-2A gene silencing.
