Neutrophil secretory vesicles are the intracellular reservoir for GPI-80, a protein with adhesion-regulating potential

The subcellular localization of GPI-80, a novel, adhesion-regulating protei n, was investigated in human neutrophils. Surface expression of GPI-80 was determined by FACS analysis as well as by the ability for phospholipase C t o cleave the protein from the cell surface, Increasing amounts of GPI-80 we re exposed on the cell surface after weak stimulation with the chemoattract ant fMLF, suggesting that the protein call be translocated to the plasma me mbrane from intracellular stores. By subcellular fractionation of the neutr ophils, GPI-80 was defined as a component of a light membrane fraction, con taining secretory vesicles and plasma membranes, and it was absent from the neutrophil granule fractions. Separation of the plasma membranes front the secretory vesicles by flotation gradient fractionation confirmed that the GPI-80 was localized in the mobilizable secretory vesicles by approximately 50%, and the rest was plasma membrane-bound, Thus,,ve identify secretory v esicles as the reservoir of GPI-80 from which it may translocate to the pla sma membrane after weak stimulation of the cells.