LOSS OF CYTOKERATIN EXPRESSION AND FORMATION OF ACTIN STRESS FIBERS IN DEDIFFERENTIATED MDCK-C7 CELL-LINES

MDCK-C7 cells dedifferentiated either by transient alkaline stress (C7 F cells) or by transfection with a constitutively active mutant of the mitogen-activated protein kinase kinase MEK1 (C7caMEK1 cells) were an alyzed by western blot and immunofluorescence microscopy to compare th e expression of different cytokeratins, vimentin, and alpha-smooth mus cle actin. Expression of all cytokeratins tested, the type II-neutral and basic cytokeratins CK5;, CK7, CK8 as well as the type I-acidic ker atins CK17 and CK19, was substantially reduced in dedifferentiated cel l lines C7F and C7caMEK1 when compared with epithelial wild type MDCK- C7: cells or mock-transfected MDCK-C7 cells. While vimentin expression was detected in all of the four MDCK-C7 cell lines examined, only the dedifferentiated cell lines C7F and C7caMEK1, which have been reporte d to express highly active ERK2, exhibited formation of alpha-smooth m uscle actin-containing stress fibers. Taken together our results show that, associated with an increase in ERK2 activity, an epithelial to m esenchymal dedifferentiation occured in both MDCK-C7F cells and caMEK1 -transfected MDCK-C7 cells. (C) 1997 Academic Press.