Ca2+ and calmodulin are involved in the processes conferring stability to DNA in proliferating neoplastic cells

We have examined, in proliferating neoplastic cells, the effect on DNA of EGTA (a chelator of Ca2+) and W7 (an inhibitor of calmodulin). The treatment results in release of single-stranded DNA fragments (2-10 kb) from pre-labelled HMW DNA. When DNA from synchronized neoplastic cells in S phase is examined, almost all pre-labelled DNA appears as short fragments. However, fragmentation does not occur in growth-arrested cells or in normal cells. Furthermore, fragmentation can be prevented by incubating cells in excessive amounts of Ca2+. Hence Ca2+ and the Ca2+-binding protein calmodulin are involved in the processes conferring stability to DNA in proliferating neoplastic cells.