PUTRESCINE-STIMULATED INTRACELLULAR CA2-CELLS( RELEASE FOR INVASIVENESS OF RAT ASCITES HEPATOMA)

Our previous study showed that treatment of highly invasive rat ascite s hepatoma (LC-AH) cells with alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, decreased both their intracellu lar level of putrescine and their in vitro invasion of a monolayer of calf pulmonary arterial endothelial (CPAE) cells, and that both these decreases were completely reversed by exogenous putrescine, but not sp ermidine or spermine, Here we show that all adhering control (DFMO-unt reated) cells migrated beneath CPAE monolayer with morphological chang e from round to cauliflower-shaped cells (migratory cells), DFMO treat ment increased the number of cells that remained round without migrati on (nonmigratory cells), Exogenous putrescine, but not spermidine or s permine, induced transformation of all nonmigratory cells to migratory cells with a concomitant increase in their intracellular Ca2+ level, [Ca2+](i). The putrescine-induced increase in their [Ca2+](i) preceded their transformation and these effects of putrescine were not affecte d by antagonists of the voltage-gated Ca2+ channel, but were completel y suppressed by ryanodine, which also suppressed the invasiveness of t he control cells, The DFMO-induced decreases in both [Ca2+](i) and the invasiveness of the cells were restored by thapsigargin, which elevat ed [Ca2+](i) by inhibiting endoplasmic Ca2+-ATPase, indicating that th apsigargin mimics the effects of putrescine, These results support the idea that putrescine is a cofactor for Ca2+ release through the Ca2channel in the endoplasmic reticulum that is inhibited by ryanodine, t his release being initiated by cell adhesion and being a prerequisite for tumor cell invasion.