Neutrophil (PMN) inflammatory functions, including cell adhesion, diapedesis, and phagocyto-sis, are dependent on the mobilization and release of various intracellular granules/vesicles. In this study, I found that treating PMN with damnacanthal, a Ras family GTPase inhibitor, resulted in a specific release of secondary granules, but not primary or tertiary granules, and caused dy-sregulation of PMN chemotactic transmigration and cell surface protein interactions. Analysis of the activities of Ras members identified Ral GTPase as a key regulator during PMN activation and degranulation. In particular, Ral was active in freshly isolated PMN, while chemoattractant stimulation induced a quick deactivation of Ral that correlated with PMN degranulation. Over-expression of a constitutively active Ral (Ral23V) in PMN inhibited chemoattractant-induced secondary granule release. By subcellular fractionation, I found that Ral, which was associated
with the plasma membrane under the resting condition, was redistributed to secondary granules after chemoattractant stimulation. Blockage of cell endocytosis appeared to inhibit Ral transloca-tion intracellularly. In conclusion, these results demonstrate that Ral is a critical regulator in PMN that specifically controls secondary granule release during PMN response to chemoattrac-tant stimulation.