A labile inhibitor blocks endo A gene transcription in murine undifferentiated embryonal carcinoma cells.

The endo A gene encoding for an intermediate filament protein, a cytokeratin is usually expressed in epithelial cells. The regulation of this gene, probed by using cycloheximide, an inhibitor of protein synthesis was studied in various cell lines. The lines explored were undifferentiated embryonal carcinoma PCC4 cells which normally do not express endo A gene, PCC4 cells cultivated permanently at 31 degrees C (PCC4-31), which are epithelial-like cells derived by differentiation from PCC4 cells, but which do express endo A gene, TDM1 cells, an epithelial teratocarcinoma cell line, and 3T6 mouse fibroblasts. Treatment of undifferentiated PCC4 cells by cycloheximide led to transcriptional induction of the endo A gene, and the same effect was observed after this treatment in PCC4-31 cells. By contrast, cycloheximide did not induce endo A gene expression in 3T6 cells, and reduced the transcriptional activity of this gene in TDM1 cells. We conclude that a labile inhibitor (or several) blocks endo A gene expression in undifferentiated PCC4 cells. We suggest that in these cells, the expression of the endo A gene is regulated both positively and negatively, possibly by a cellular E1A-like activity, as we previously demonstrated it for Py virus (C. Crémisi and C. Babinet, 1986 J. Virol. 59; 761-763). We further suggest that negative regulatory factors involved in this regulation are absent in TDM cells and reduced in PCC4-31 cells.