Myosin II isoforms identify distinct functional modules that support integrity of the epithelial zonula adherens


Classic cadherin receptors cooperate with regulators of the actin cytoskeleton to control tissue organization in health and disease. At the apical junctions of epithelial cells, the cadherin ring of the zonula adherens (ZA) couples with a contiguous ring of actin filaments1,2,3 to support morphogenetic processes such as tissue integration and cellular morphology4,5. However, the molecular mechanisms that coordinate adhesion and cytoskeleton at these junctions are poorly understood. Previously we identified non-muscle myosin II as a target of Rho signalling that supports cadherin junctions in mammalian epithelial cells6. Myosin II has various cellular functions, which are increasingly attributable to the specific biophysical properties and regulation of its different isoforms7. Here we report that myosin II isoforms have distinct and necessary roles at cadherin junctions. Although two of the three mammalian myosin II isoforms are found at the ZA, their localization is regulated by different upstream signalling pathways. Junctional localization of myosin IIA required E-cadherin adhesion, Rho/ROCK and myosin light-chain kinase, whereas junctional myosin IIB depended on Rap1. Further, these myosin II isoforms support E-cadherin junction integrity by different mechanisms. Myosin IIA RNA-mediated interference (RNAi) selectively perturbed the accumulation of E-cadherin in the apical ZA, decreased cadherin homophilic adhesion and disrupted cadherin clustering. In contrast, myosin IIB RNAi decreased filament content, altered dynamics, and increased the lateral movement of the perijunctional actin ring. Myosin IIA and IIB therefore identify two distinct functional modules, with different upstream signals that control junctional localization, and distinct functional effects. We propose that these two isoform-based modules cooperate to coordinate adhesion receptor and F-actin organization to form apical cadherin junctions.

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Figure 1: Myosin (Myo) IIA and myosin IIB localize to apical epithelial junctions.
Figure 2: Differential regulation of myosin IIA and myosin IIB localization at apical junctions.
Figure 3: Myosin IIA and myosin IIB are necessary for ZA integrity.
Figure 4: Homophilic adhesion and lateral clustering of E-cadherin requires myosin IIA but not myosin IIB.
Figure 5: Myosin IIB regulates the apical F-actin ring.


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We thank our colleagues who provided reagents, especially Jim Bear for the pLL5.0 lentiviral construct, Rachel Murphy and Nigel McMillan for training us in lentiviral work, Regine Hartmann for her assistance with cloning, Suzie Verma and Carmen Buttery for assistance with tissue culture, and our colleagues in the laboratory for their untiring support and encouragement. The work in Australia was funded by the National Health and Medical Research Council (NHMRC) of Australia; that in the USA was supported by the National Institutes of Health (NIH). Confocal microscopy was performed at the Australian Cancer Research Foundation (ACRF) Cancer Biology Imaging Centre at the Institute for Molecular Bioscience, established with the generous support of the ACRF. We gratefully acknowledge the help and advice of Guanghui Wang and the NIH National Heart, Lung and Blood Institute Proteomics Core Facility. M.S. was an Erwin Schroedinger postdoctoral fellow of the Austrian Science Fund (FWF), and R.G.P. and A.S.Y. are Research Fellows of the NHMRC.

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M.S. and A.S.Y. conceived and designed the experiments. M.S., H.L.C., E.M.K., M.A.C. and C.F. performed experiments and data analysis. J.M.L. and N.A.H. contributed to data analysis. R.G.P., E.M.K. and R.S.A. contributed to discussions and intellectual input. M.S. and A.S.Y. wrote the paper.

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Correspondence to Alpha S. Yap.

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Smutny, M., Cox, H., Leerberg, J. et al. Myosin II isoforms identify distinct functional modules that support integrity of the epithelial zonula adherens. Nat Cell Biol 12, 696–702 (2010).

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