FIGURE 1.

EGF induces TGase activation in HeLa cells. A, serum-starved HeLa cells were treated with EGF for the indicated times and then lysed. The cell extracts were immunoblotted with the indicated antibodies. B, HeLa cells were cultured in medium containing 0.2% FBS (low serum medium) without (Untreated) or with either RA or EGF. One day later the cells were lysed, and the extracts were immunoblotted with TGase and actin antibodies (top and bottom panels, respectively). The GTP-binding activities of TGase in the cell lysates were determined using a photoaffinity labeling assay with [α-³²P]GTP (middle panel). C, the levels of TGase transamidation activity in the cell extracts were also determined by assaying the incorporation of BPA into lysate proteins. The assays were performed three times, and the results of each assay were quantified by densitometry, averaged together, and graphed as -fold increases in transamidation activity relative to the control. The error bars indicate ±S.D.