The src-family protein-tyrosine kinase p59(hck) is located on the secretory granules in human neutrophils and translocates towards the phagosome during cell activation

Abstract

The src-family protein-tyrosine kinase p59(hck) is mainly expressed in neutrophils; however, its functional role in these cells is unknown. Several other src-family members are localized on secretory vesicles and have been proposed to regulate intracellular traffic. We have established here the subcellular localization of p59(hck) in human neutrophils. Immunoblotting of subcellular fractions showed that approx. 60% of the p59(hck) per cell is localized on the secretory granules; the other 40% is distributed equally between non-granular membranes and the cytosol. Immunofluorescence of neutrophils and HL60 cells suggests that the p59(hck)-positive granules are azurophil granules. Granular p59(hck) is highly susceptible to degradation by an azurophil-granule proteinase. Different forms of p59(hck) occur in the three subcellular compartments: a 61 kDa form is mainly found in the granules, a 59 kDa form is predominant in the non-granular membranes, whereas cytosolic p59(hck) migrates as a doublet at 63 kDa. During the process of phagocytosis-linked degranulation, induced by serum-opsonized zymosan in neutrophils or HL60 cells, granular p59(hck) translocates towards the phagosome. The subcellular localization of p59(hck) suggests that the enzyme could be involved in the regulation of the degranulation process.