INTESTINAL HT-29 CELLS WITH DYSFUNCTION OF E-CADHERIN SHOW INCREASED PP60SRC ACTIVITY AND TYROSINE PHOSPHORYLATION OF P120-CATENIN

1. HT-29 M6 cells are a subpopulation of HT-29 cells that, contrarily to the parental cells, establish tight cell contacts and differentiate . Cell-to-cell contacts in HT-29 M6 cells are also regulated by protei n kinase C; addition of the phorbol ester phorbol 12-myristate 13-acet ate (PMA) decreases the homotypic contacts of these cells. We show her e that HT-29 cells or HT-29 M6 cells treated with PMA contain lower le vels of functional E-cadherin, determined by analysing the association of this protein with the cytoskeleton. No significant differences in the localization of alpha-, beta-, or p120-catenins were detected unde r the three different conditions. 2. Dysfunction of E-cadherin can be reversed by incubation of HT-29 cells with the tyrosine kinase inhibit or herbimycin A. On the other hand an augmentation of c-src activity i n HT-29 cells or HT-29 M6 cells treated with PMA was observed with res pect to control HT-29 M6 cells. The phosphorylation status of catenins was also investigated; in HT 29 or in HT-29 M6 cells treated with PMA , dysfunction of E-cadherin was accompanied by an increased phosphoryl ation of p120-catenin and by an elevated association of this protein t o E-cadherin. These results suggest a role for pp60src and the pp60src substrate p120-catenin in the control of E-cadherin function in HT-29 cells.