FIGURE 6.

v-Src suppresses ATR-Chk1 signaling. A, HeLa S3-TR/v-Src cells were synchronized at the G₁/S boundary by exposure to thymidine. After release from thymidine block, doxycycline was added, and the cells were cultured for 6 h. Then the cells were exposed to 110 nm Adriamycin (ADR) and allowed to recover for the indicated times. SDS lysates were prepared and probed with the indicated antibodies. B, asynchronously growing HeLa S3 cells were exposed to 4 mm thymidine for 24 h. SDS lysates were prepared and probed with the indicated antibodies. C, HeLa S3-TR/v-Src cells were exposed to 4 mm thymidine for 24 h. Expression of v-Src was induced with doxycycline for 24 h. Cells were lysed in high salt buffer, and the lysates were probed with the indicated antibodies. D, the same experiment as in C. Cells were harvested at the indicate times after addition of thymidine and/or doxycycline. SDS lysates were prepared and probed with the indicated antibodies. Representative data from two independent experiments are shown. Async., asynchronously growing cells.