Subcellular Localization of the Small GTPase Rab5a in Resting and Stimulated Human Neutrophils

The evidence that small GTPases of the Rab family are regulators of vesicle traffic which can influence various cell functions prompted us to investigate the potential role of one of these proteins, Rab5a, in human neutrophils. In this paper we show that a large amount of Rab5a is present in the cytosol of peripheral blood mature neutrophils. The remaining protein was found to be membrane and azurophilic granule associated. Upon neutrophil challenge with PMA for 10 min the amount of membrane-associated Rab5a was upregulated while the cytosolic content of the protein concomitantly decreased. These findings support the hypothesis that Rab5a could be involved in the mechanism of neutrophil activation by modulating the rate of endocytosis and/or vesicle fusion.