Fig. 3.

Inhibition of proliferation by ectopic expression of the active kinase domain is due to a secreted factor(s). (A) Conditioned medium was obtained by starting cultures of Ax4 cells transformed with pifkA-14 at 5 × 10⁵ cells per ml and growing them to 3 × 10⁶ cells per ml. Coumermycin was added for 24 h, and the culture medium was cleared of cells. Conditioned medium was added to half of the cells from a growing Ax4 culture to give the same titer as the other half of the culture, and the cell count was examined for another 72 h. The result shown is one of two trials, both of which resulted in inhibition of proliferation. (B) Reversibility of the inhibition of proliferation by coumermycin. Adm cells were grown in the absence of coumermycin (open squares). At 48 h, coumermycin was added to half of the culture (solid squares), resulting in inhibition of proliferation. After a further 24 h, the cells were transferred to fresh medium without coumermycin, resulting in enhanced proliferation.