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

Abstract

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)k 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 PTPk and SHP-1 in the regulation, maintenance, and restitution of cell adhesions in a complex epithelial organ such as the pancreas.

Determination of the integral refractive index of cells in suspension by digital holographic phase contrast microscopy

“…The refractive index of the micro carriers is found to be independent from the radius with an average refractive index bead 1.3383 0.0003 n = ± (N bead = 27). In a third experiment, three different types of living pancreas tumor cells [13,14] (PaTu 8988 T, PaTu 8988 S, and PaTu 8988 T pLXIN E-Cadherin) in suspension were investigated. For the experiments the cells were trypsinized and holograms of the cells in culture medium (DMEM containing 5 % FCS and 5 % horse serum, n medium =1.337 ± 0.001) were recorded by application of a 40× microscope lens (Zeiss LD Achroplan 40×/0.6 Korr).…”

Analysis of actin dependent processes in pancreatic tumor cells

“…For scanning electron microscopy (SEM) we fixated the cells with 1 % glutaraldehyde [3]. Dehydrated and dried cells were coated with platinum and carbon and analyzed using a standard SEM.…”

Pentoxifylline Prevents Loss of PP2A Phosphatase Activity and Recruitment of Histone Acetyltransferases to Proinflammatory Genes in Acute Pancreatitis

“…Calcineurin-or Ser/ Thr phosphatase PP2B-mediates pancreatic zymogen activation in acinar cells (Husain et al, 2007). Inhibition of protein tyrosine phosphatases causes dissociation of cell contacts in pancreatic acini as a prerequisite for the development of pancreatic edema (Schnekenburger et al, 2005). Furthermore, expression of the transmembrane protein tyrosine phosphatase CD45 decreases in the course of acute pancreatitis in parallel with the up-regulation of TNF-␣ (de Dios et al, 2006).…”