FIG. 4.

GADD34 induces apoptosis in SW480 cells. HRX fusion proteins abrogate GADD34-induced apoptosis and wild-type HRX induces apoptosis of SW480 cells after transfection and treatment with ionizing radiation. The mean percent apoptosis is shown for the transfected constructs below. Each column represents three separate experiments. (A) GADD34 induces apoptosis in SW480 cells, and the amino terminus is necessary for this effect. HRX fusion proteins, HRX-ENL and HRX-AF9, abrogate GADD34-induced apoptosis. The percent apoptosis of SW480 cells without transfection and without IR is approximately 8%, and after transfection of pSGADD34FL without IR it is approximately 17% (results of one trial only). GADD34FL encodes the full-length cDNA, and GADD34 encodes an amino-terminal deletion GADD34 protein (the clone retrieved from the yeast two-hybrid screen). (B) The HRX fusion protein HRX-ELL abrogates GADD34- induced apoptosis. (C) Wild-type HRX induces apoptosis in a dose-dependent fashion and does not inhibit GADD34-induced apoptosis. To the left is designated, in micrograms, the amount of wild-type HRX and GADD34 plasmid transfected. (D) GADD34 induces apoptosis in a dose-dependent fashion. HRX-ENL inhibits GADD34-induced apoptosis in a dose-dependent fashion. The inset shows an anti-myc Western blot from a SDS-PAGE gel (6% polyacrylamide) in a series of cotransfection experiments with increasing amounts of transfected pCSHRX plasmid (encoding myc-tagged wild-type HRX protein) with constant amounts of transfected pCSARQ2 plasmid (encoding myc-tagged HRX-ENL). The amounts of transfected plasmids are shown above in micrograms.