Calcium: calmodulin and cancer.

When several fast-growing Morris hepatoma tissue lines are compared with normal adult liver tissue, the following observations are made: calmodulin activity is increased in the cytoplasm and decreased in the membrane of the tumor cells. Total calcium is increased three- to fivefold in the tumors. Cyclic AMP phosphodiesterase activity is increased, whereas cyclic GMP phosphodiesterase activity is decreased. In addition, several of the fast-growing Morris hepatoma tissue lines have a new calcium-binding protein that is not observed in adult liver tissue. It is probable that the Ca2+-calmodulin complex is very active in these rapidly growing tumors.