FIG. 5.

The ras oncogene-transformed PA-1 cell lines constitutively expressing PC4 have a nontumorigenic phenotype and are sensitive to RA-induced differentiation. PC4 cDNA was cloned into an SV40-driven pZeoSV vector that carries a gene encoding resistance to zeomycin for selection in human cells. 9113, ras-transformed PA-1 cells; 9113 Zeo #1 and #2, control transfections of 9113 cells with pZeoSV vector; 9113 PC4 #1 and #2, PC4-transfected 9113 cells. (A) PC4-transfected ras-transformed PA-1 cells have high levels of PC4. Nuclear extracts were prepared from the cells, subjected to Western blotting, and probed with a PC4-specific antiserum. The mobilities of molecular markers are shown on the left. (B) PC4-transfected ras-transformed PA-1 cells have a high endogenous level of AP-2 activity. Four micrograms of 3× AP-2–CAT was transfected into the cells, and the CAT activity was determined. The low-level endogenous AP-2 activity of 9113 cells was set to 1 to calculate the fold inductions, which are shown at the bottom. (C) The ras-transformed PA-1 cells constitutively expressing PC4 grow slowly, with a flattened morphology, and are sensitive to RA.