Ca(2+) elevations are fundamental to cardiac physiology-stimulating contraction and regulating the gene transcription that underlies hypertrophy. How Ca(2+) specifically controls gene transcription on the background of the rhythmic Ca(2+) increases required for contraction is not fully understood. Here we identify a hypertrophy-signaling module in cardiac myocytes that explains how Ca(2+) discretely regulates myocyte hypertrophy and contraction. We show that endothelin-1 (ET-1) stimulates InsP(3)-induced Ca(2+) release (IICR) from perinuclear InsP(3)Rs, causing an elevation in nuclear Ca(2+). Significantly, we show that IICR, but not global Ca(2+) elevations associated with myocyte contraction, couple to the calcineurin (CnA)/NFAT pathway to induce hypertrophy. Moreover, we found that activation of the CnA/NFAT pathway and hypertrophy by isoproterenol and BayK8644, which enhance global Ca(2+) fluxes, was also dependent on IICR and nuclear Ca(2+) elevations. The activation of IICR by these activity-enhancing mediators was explained by their ability to stimulate secretion of autocrine/paracrine ET-1.

The mechanism by which classical cadherins mediate cell adhesion and, in particular, the roles played by calcium and Trp2, the second amino acid in the N-terminal domain, have long been controversial. We have used antibodies to investigate the respective contributions of Trp2 and calcium to the stability of the N-terminal domain of N-cadherin. Using a peptide antibody to the βB strand in domain 1, which detects a disordered structure, we show that both Trp2 and calcium play crucial parts in regulating stability of the domain. The epitope for another antibody, mAb GC4, has been mapped to the base of domain 1. Binding of GC4 to this epitope was shown to depend on intramolecular `docking' of Trp2 into the domain 1 structure. Using this property, we provide evidence that calcium regulates a dynamic equilibrium between docked and undocked Trp2. Finally, a novel technique has been developed to test whether Trp2 cross-intercalation between cadherin molecules from adjacent cells (strand exchange) is central to cadherin-mediated cell adhesion. Guided by crystal structures showing strand exchange, we have introduced single cysteine point mutations into N-cadherin domain 1 in such a way that a disulphide bond will form between opposing N-cadherin molecules during cell adhesion if strand exchange occurs. The bond requires complementary cysteines to be precisely juxtaposed according to the strand exchange model. Our results demonstrate that the disulphide bond forms as predicted. This provides compelling evidence that strand exchange is indeed a primary event in cell adhesion by classical cadherins.

ErratumHarrison, O. J., Corps, E. M. and Kilshaw, P. J. (2005). Cadherin adhesion depends on a salt bridge at the N-terminus. J. Cell Sci. 118, 4123-4130.The e-press version of this article that was published on 23rd August 2005 contains two errors on p. 4128. In the legend to Fig. 6, the penultimate sentence should read: Aggregation was assessed by microscopy. In the right-hand column, paragraph 2, the last sentence should read: It is not known whether similar changes to the ␤A strand in cadherins would modulate intramolecular docking of Trp2 and alter the free energy balance in favour of strand exchange.Both the published print and online versions of this article are correct. We apologise to the authors and readers for these mistakes.

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SummaryThe integrin aE(CD103)b7 (aEb7) is expressed by intraepithelial lymphocytes, dendritic cells and regulatory T cells. It plays an important role in the mucosal immune system by retaining lymphocytes within the epithelium and is involved in graft rejection, immunity against tumours and the generation of gut-homing effector cells. In gut and breast, the ligand for aEb7 is E-cadherin but in human oral mucosa and skin, there is evidence that lymphocytes use an alternative, unknown, ligand. In the present study, the I domain of the human aE subunit, which contains the E-cadherin-binding site, was locked in a highly active, 'open' and an inactive, 'closed' conformation by the introduction of disulphide bonds and these domains were expressed as IgG Fc fusion proteins. aE fusion proteins recognize E-cadherin, the only known ligand for aEb7. This interaction was inhibited by an antibody that blocks the aE-binding site on E-cadherin and by the omission of Mn 2+ , which is essential for integrin function in vitro. The locked 'open' conformation of aE adhered to human oral and skin keratinocytes, including the E-cadherin-negative H376 cell line, and this was not inhibited by blocking antibody against the aEb7-binding site on E-cadherin, providing further evidence for the existence of an alternative ligand for aEb7 in skin and oral mucosa. The interaction with E-cadherin and the alternative ligand was Mn 2+ dependent and mediated by the metal ion-dependent coordination site (MIDAS) of the locked 'open' aE I domain, independently of the b7 subunit.