Stimulation of exocytotic degranulation by microinjection of the ras oncogene protein into rat mast cells.

To investigate the possible role of ras proteins in the secretory process, we have microinjected the proto oncogenic and oncogenic forms of the human H-ras protein into rat peritoneal mast cells. Mast cells are secretory cells which, upon appropriate stimulus, liberate histamine and other mediators of the acute inflammatory reaction by exocytotic degranulation. We report here that microinjection of the ras oncogene protein into mast cells induces exocytotic degranulation. In contrast, microinjection of similar amounts of the proto-oncogenic protein has little apparent effect on mast cells. Degranulation induced by injection of the ras oncogene protein occurs in the absence of an external stimulus and requires the presence of external calcium. The ultrastructural features of exocytotic degranulation in mast cells injected with the ras oncogene protein are similar to those seen when mast cells are activated by soluble ligands. Our results suggest that ras proteins may be involved, possibly as regulatory elements, in cellular functions that control exocytosis.