Effects of acute vs. chronic phorbol ester exposure on transepithelial permeability and epithelial morphology

Abstract

In previous experiments we have shown that acute (30 minutes) exposure to phorbol esters or other protein kinase C activators causes increased transepithelial permeability, specifically by the increased paracellular permeability through tight junctions. However, the role of protein kinase C activators in carcinogenesis is predicted upon a chronic exposure of an effective dose at frequent intervals for a prolonged period of time. We therefore sought to determine the effect of chronic phorbol ester exposure on transepithelial permeability by exposing cells of the polar renal epithelial cell line, LLC-PK1, to phorbol esters for time periods as long as 16 weeks. The following changes ensued: (1) after the initial drop in transepithelial resistance due to phorbol ester exposure, i.e., an increase in transepithelial permeability (in the acute phase of exposure), an adaptive response occurs as transepithelial resistances in chronically exposed cultures recover to approximately 50% of control values, (2) the cell sheets in chronically exposed cultures lose their acute responsiveness of transepithelial permeability to phorbol ester exposure, (3) cell sheet architecture changes as cells occasionally multilayer and actual polyp-like cell masses appear at high frequency, and (4) cytosolic protein kinase C activity decreases to 50% of control level with acute exposure and then is further decreased to less than 1% of control level in chronically treated cells; membrane-associated PKC activity is not as sharply decreased. The possible role of transepithelial permeability in carcinogenesis and the value of chronically treated epithelial cell cultures as a model for two-stage carcinogenesis are discussed.

Src Family Kinases Phosphorylate Protein Kinase C δ on Tyrosine Residues and Modify the Neoplastic Phenotype of Skin Keratinocytes

“…4A, inset). By inverted phase contrast microscopy, domes were identical to those reported to be PKC-dependent fluid-filled hemicysts in LLC-PK1 pig kidney cortical cells (33) (Fig. 4B).…”

“…Furthermore, domes were induced in the absence of PD 173958 by transfecting PKC ␦ tyrosine phosphorylation-defective mutants Y64F and Y565F. The domes forming in our study appear to be identical to those studied extensively by Mullin and collaborators in LLC-PK1 pig kidney epithelial cells (33). In that model, dome formation represents a differentiated phenotype in which functionally intact tight junctions form at confluence in the presence of high calcium medium.…”

Physiological effect of protein kinase C on ENaC-mediated lung liquid regulation in the adult rat lung

“…The effect of PMA in our experiments does not appear to be due to a change in epithelial permeability, although this has been previously described (21,35). Samples of perfusate taken during and at the end of the experiments were analyzed for the presence of Blue Dextran and vitamin B12, and neither tracer was found to be present.…”

Claudin-1, -3 and -4 proteins and mRNA expression in benign and malignant breast lesions: a research study

“…Alterations in the number, appearance and permeability of TJs have been described in various tumour types [21,29]. Abnormalities in TJ permeability and number greatly influence the transepithelial flux of growth factors [30] and hence the development of epithelial tumours [31]. In two cases, both normal breast tissue and tumour sample were investigated by transmission electron microscopy.…”