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This review extensively reports data from the literature concerning the complex relationships between the stress-induced c-Jun N-terminal kinases (JNKs) and the four main cytoskeleton elements, which are actin filaments, microtubules, intermediate filaments, and septins. To a lesser extent, we also focused on the two membrane-associated cytoskeletons spectrin and ESCRT-III. We gather the mechanisms controlling cytoskeleton-associated JNK activation and the known cytoskeleton-related substrates directly phosphorylated by JNK. We also point out specific locations of the JNK upstream regulators at cytoskeletal components. We finally compile available techniques and tools that could allow a better characterization of the interplay between the different types of cytoskeleton filaments upon JNK-mediated stress and during development. This overview may bring new important information for applied medical research.

Fenestrae are transcellular plasma membrane pores that mediate blood-tissue exchange in specialised vascular endothelia. The composition and biogenesis of the fenestra remain enigmatic. We isolated and characterised the protein composition of large patches of fenestrated plasma membrane, termed sieve plates. Loss-of-function experiments demonstrated that two components of the sieve plate, moesin and annexin II, were positive and negative regulators of fenestra formation, respectively. Biochemical analyses showed that moesin is involved in the formation of an actin-fodrin submembrane cytoskeleton that was essential for fenestra formation. The link between the fodrin cytoskeleton and the plasma membrane involved the fenestral pore protein PV-1 and Na,K-ATPase, which is a key regulator of signalling during fenestra formation both in vitro and in vivo. These findings provide a conceptual framework for fenestra biogenesis, linking the dynamic changes in plasma membrane remodelling to the formation of a submembrane cytoskeletal signalling complex.

Numerous reports have linked cytoskeleton-associated proteins with the regulation of epithelial Na+ channel (ENaC) activity. The purpose of the present study was to determine the effect of actin cytoskeleton disruption by cytochalasin E on ENaC activity in Xenopus 2F3 cells. Here, we show that cytochalasin E treatment for 60 min can disrupt the integrity of the actin cytoskeleton in cultured Xenopus 2F3 cells. We show using single channel patch-clamp experiments and measurements of shortcircuit current that ENaC activity, but not its density, is altered by cytochalasin E-induced disruption of the cytoskeleton. In nontreated cells, 8 of 33 patches (24%) had no measurable ENaC activity, whereas in cytochalasin E-treated cells, 17 of 32 patches (53%) had no activity. Analysis of those patches that did contain ENaC activity showed channel open probability significantly decreased from 0.081 ± 0.01 in nontreated cells to 0.043 ± 0.01 in cells treated with cytochalasin E. Transepithelial current from mpkCCD cells treated with cytochalasin E, cytochalasin D, or latrunculin B for 60 min was decreased compared with vehicle-treated cells. The subcellular expression of fodrin changed significantly, and several protein elements of the cytoskeleton decreased at least twofold after 60 min of cytochalasin E treatment. Cytochalasin E treatment disrupted the association between ENaC and myristoylated alanine-rich C-kinase substrate. The results presented here suggest disruption of the actin cytoskeleton by different compounds can attenuate ENaC activity through a mechanism involving changes in the subcellular expression of fodrin, several elements of the cytoskeleton, and destabilization of the ENaC-myristoylated alanine-rich C-kinase substrate complex. [ABSTRACT FROM AUTHOR]

Abstract: Decreases in the expression of connexin 43 and the integrity of gap junctions in cardiac muscle, induced by the constitutive activation of the c-Jun N-terminal kinase (JNK) signaling pathway, have been linked to conduction defects and sudden cardiac failure in mice [Petrich BG, Gong X , Lerner DL , Wang X , Brown JH , Saffitz JE , Wang Y. c-Jun N-terminal kinase activation mediates downregulation of connexin 43 in cardiomyocytes. Circ Res. 91 (2002) 640–647; B.G. Petrich, B.C. Eloff, D.L. Lerner, A. Kovacs, J.E. Saffitz, D.S. Rosenbaum, Y. Wang, Targeted activation of c-Jun N-terminal kinase in vivo induces restrictive cardiomyopathy and conduction defects. J. Biol. Chem. 2004;279: 15330–15338]. We examined the membrane cytoskeletal protein, αII-spectrin, which associates with connexin 43, to learn if changes in its association with connexin 43 are linked to the instability of gap junctions. Several forms of αII-spectrin are expressed in the heart, including one, termed αII-SH3i, which contains a 20-amino-acid sequence next to the SH3 domain of repeat 10. In adult mouse heart, antibodies to all forms of αII-spectrin labeled the sarcolemma, transverse (“t-”) tubules and intercalated disks of cardiomyocytes. In contrast, antibodies specific for αII-SH3i labeled only gap junctions and transverse tubules. In transgenic hearts, in which the JNK pathway was constitutively activated, αII-SH3i was lost specifically from gap junctions but not from t-tubules while other isoforms of αII-spectrin were retained at intercalated disks. Immunoprecipitations confirmed the decreased association of αII-SH3i with connexin 43 in transgenic hearts compared to controls. Furthermore, activation of JNK in neonatal myocytes blocked the formation of gap junctions by exogenously expressed Cx43-GFP fusion protein. Similarly, overexpression of the SH3i fragment in the context of repeats 9–11 of αII-spectrin specifically caused the accumulation of Cx43-GFP in the perinuclear region and inhibited its accumulation at gap junctions. These results support a critical role for the αII-SH3i isoform of spectrin in intracellular targeting of Cx43 to gap junctions and implicates αII-SH3i as a potential target for stress signaling pathways that modulate intercellular communication. [Copyright &y& Elsevier]

Cell swelling is known to result in unfolding of membrane invaginations and restructuring of F-actin. The effect of cell swelling on the intracellular distributions of other cytoskeletal proteins that constitute the submembrane cortical cytoskeleton is virtually unknown. This study focuses on the effects of cell swelling on non-erythroidal spectrin (fodrin, also known as spectrin II), a predominant component of the membrane cytoskeleton. The intracellular distribution of spectrin in vascular endothelial cells was studied by optical sectioning using a 3-D deconvolution microscopy system. Our results show that once bovine aortic endothelial cells (BAECs) reach confluency, the non-erythroidal spectrin is localized in the submembrane regions of the cells. Analysis of the intensity profiles of the non-erythroidal spectrin under isotonic and hypotonic conditions show that: (a) the width of the submembrane spectrin staining increases gradually with time within the first 5 minutes after the osmotic shock; (b) significant recovery is observed after 10 minutes even if the cells are maintained in hypotonic medium, and (c) spectrin distribution is altered by disrupting F-actin with latrunculin A but not by stabilizing F-actin with jasplakinolide. We suggest that cell swelling results in partial translocation of the submembrane spectrin to the cytosol and that it may play a major role in initiation of swelling-induced cellular events. [ABSTRACT FROM AUTHOR]