Growth arrest of Chinese hamster ovary cells in serum-free medium: changes in cell morphology and the intracellular and prostaglandin-induced levels of cyclic AMP.

When Chinese hamster ovary (CHO) cells are shifted from medium which contains serum into serum-free medium, they complete one cell doubling and arrest in the G1 phase of the cell cycle. During the first 72 hr of arrest, there is little change in intracellular adenosine 3':5'-phosphate (cAMP) level, and the cells retain their usual epithelial-like morphology. After 96 hr, the cAMP level doubles, the magnitude of the prostaglandin E1-induced changes in cAMP increases threefold, and the cells convert from a rounded, epithelial-like shape to an elongated, fibroblast-like form. The fact that these biochemical and cellular transitions are subsequent to the growth arrest shows that the cAMP increase is not the cause of the growth arrest but is consistent with a role for cAMP in the control of cell morphology. In addition, these changes point to the importance of the G1 phase for initiating cAMP-related events.