Involvement of tubulin and inhibitory G proteins in the interaction of Listeria monocytogenes with mouse hepatocytes.

Intracellular and cell-to-cell spread of Listeria monocytogenes has been considered exclusively actin dependent. By immunocytochemical techniques, we provide evidence for an involvement of inhibitory G proteins and tubulin in "comet tail" formation in L. monocytogenes-infected mouse hepatocytes

Protein tyrosine phosphatase κ and SHP-1 are involved in the regulation of cell-cell contacts at adherens junctions in the exocrine pancreas

Background: We have previously shown that cell contacts between pancreatic acinar cells dissociate early in pancreatitis and that this is a prerequisite for the development of pancreatic oedema. Here we studied the underlying mechanism. Methods: Employing experimental caerulein induced pancreatitis in vivo and isolated pancreatic acini ex vivo, in conjunction with protein chemistry, morphology, and electron microscopy, we determined whether cell contact regulation in the pancreas requires or involves: (1) changes in cadherin-catenin protein expression, (2) tyrosine phosphorylation of adhesion proteins, or (3) alterations in the actin cytoskeleton. Results: During initial cell-cell contact dissociation at adherens junctions, expression of adhesion proteins remained stable. At time points of dissociated adherens junctions, the cadherin-catenin complex was found to be tyrosine phosphorylated and internalised. The receptor type protein tyrosine phosphatase (PTP)κ was constitutively associated with the cadherin-catenin complex at intact cell contacts whereas following the dissociation of adherens junctions, the internalised components of the cadherin-catenin complex were tyrosine phosphorylated and associated with the cytosolic PTP SHP-1. In isolated acini, inhibition of endogenous protein tyrosine phosphatases alone was sufficient to induce dissociation of adherens junctions analogous to that found with supramaximal caerulein stimulation. Dissociation of actin microfilaments had no effect on adherens junction integrity. Conclusions: These data identify tyrosine phosphorylation as the key regulator for cell contacts at adherens junctions and suggest a definitive role for the protein tyrosine phosphatases PTPκ and SHP-1 in the regulation, maintenance, and restitution of cell adhesions in a complex epithelial organ such as the pancreas

Initial Characterization of Transgenic Mice Overexpressing Human Histamine H2 Receptors

In an integrative approach, we studied the role of histamine H(2 )receptors in the mouse heart. We noted that histamine, added cumulatively to the organ bath, failed to affect the force of contraction in left atrial preparations and did not change spontaneous heart rate in right atrial preparations from wild-type mice. By contrast, in the same preparations from mice that overexpressed the human H-2 receptor in a cardiac-specific way, histamine exerted concentration- and time-dependent positive inotropic and positive chronotropic effects. Messenger RNA of the human H-2 receptor was only detected in transgenic mice. Likewise, immunohistology and autoradiography only gave signals in transgenic but not in wild-type cardiac preparations. Similarly, a positive inotropic and positive chronotropic effect was observed with histamine in echocardiography of living transgenic mice and isolated perfused hearts (Langen-dorff preparation). Phosphorylation of phospholamban was increased in atrial and ventricular preparations from transgenic mice, but not in wild-type animals. The effects of histamine were mimicked by dimaprit and amthamine and antagonized by cimetidine. In summary, we generated a new model to study the physiologic and pathophysiologic cardiac role of the human H-2 receptor