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Vol. 18, Issue 9, 3429-3439, September 2007
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*Epithelial Pathobiology Research Unit, Department of Pathology and Laboratory Medicine, Emory University, Atlanta, GA 30322; and Institut National de la Santé et de la Recherche Médicale, U627, Université de Nice-Sophia Antipolis, Faculté de Médecine, 06107 Nice, France
Submitted April 6, 2007;
Revised June 6, 2007;
Accepted June 20, 2007
Monitoring Editor: Ben Margolis
Apical junctional complex (AJC) plays a vital role in regulation of epithelial barrier function. Disassembly of the AJC is observed in diverse physiological and pathological states; however, mechanisms governing this process are not well understood. We previously reported that the AJC disassembly is driven by the formation of apical contractile acto-myosin rings. In the present study, we analyzed the signaling pathways regulating acto-myosin–dependent disruption of AJC by using a model of extracellular calcium depletion. Pharmacological inhibition analysis revealed a critical role of Rho-associated kinase (ROCK) in AJC disassembly in calcium-depleted epithelial cells. Furthermore, small interfering RNA (siRNA)-mediated knockdown of ROCK-II, but not ROCK-I, attenuated the disruption of the AJC. Interestingly, AJC disassembly was not dependent on myosin light chain kinase and myosin phosphatase. Calcium depletion resulted in activation of Rho GTPase and transient colocalization of Rho with internalized AJC proteins. Pharmacological inhibition of Rho prevented AJC disassembly. Additionally, Rho guanine nucleotide exchange factor (GEF)-H1 translocated to contractile F-actin rings after calcium depletion, and siRNA-mediated depletion of GEF-H1 inhibited AJC disassembly. Thus, our findings demonstrate a central role of the GEF-H1/Rho/ROCK-II signaling pathway in the disassembly of AJC in epithelial cells.
Address correspondence to: Asma Nusrat (anusrat{at}emory.edu) or Stanislav N. Samarin (ssamari{at}emory.edu).
Abbreviations used: AJ, adherens junction; AJC, apical junctional complex; GEF, guanine nucleotide exchange factor; JAM, junctional adhesion molecule; MLCK, myosin light chain kinase; MNMM, mammalian non-muscle myosin; MYPT, myosin phosphatase target subunit; RMLC, regulatory myosin light chain; ROCK, Rho-associated kinase; TEER, transepithelial electrical resistance; TJ, tight junction.
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