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The activation of protein kinases C (PKCs) is an essential step in integrin-dependent cell adhesion and spreading. In this report we examined the effect of the phorbol ester PMA, a PKC activator, on adhesion, spreading and migration of a colon carcinoma cell line, HT29-D4. Treatment with PMA increased the rate of cell spreading and induced the migration of these cells towards purified matrix proteins in haptotaxis assays on Boyden chambers. PMA-induced effects were the result of PKCs activation, as shown by using the inactive isomer 4alpha-PMA and PKCs inhibitors. The involvement of integrins in the phorbol ester-induced cell migration was demonstrated both by the absence of migration of cells plated on membranes coated with poly-L-lysine and by the use of function blocking antibodies. Thus, interactions between alpha 2beta1, alpha3beta1, alpha6beta4, alpha vbeta5, alphavbeta6 integrins and their specific ligands are necessary for the PKC-mediated migration. However, adhesion, immunoprecipitation and immunocytofluorometry experiments clearly showed that HT29-D4 cell haptotaxis induced by PKC activation is not a consequence of quantitative or qualitative changes in the cell surface integrins. We also demonstrated that PKCs were able to activate the MAP kinase pathway and that the impediment of MAP kinase activation resulted in the loss of cell migration. Moreover, stimulation of the insulin-like growth factor I signalling pathway led to MAP kinase activation and to the induction of cell migration. In addition, the growth factor-induced motility of HT29-D4 cells was affected both by PKC and MAP kinase cascade inhibitors. It thus appears that both integrin ligation and MAP kinase activation by PKCs are required to promote the migration of HT29-D4 cells.

Porcine thyroid cells in culture are able to reorganize into well-polarized follicle-like structures in the presence of cAMP analogs. These follicles exhibit on their basolateral membrane domain the Na+/I−symporter which allows iodide to accumulate in the thyrocytes. The initial rate of iodide influx through the Na+/I−symporter is inhibited up to 98% by the chloride channel blockers. 5 nitro-2(3-phenylpropylamino)benzoic acid and 3′,5-Dichlorodiphenylamine-2-carboxylic acid are the most effective inhibitors, with a K0.5value of 60 μM. This inhibition is not secondary to inhibition of chloride transport. Other chloride transporter blockers have been studied but showed lesser activities.