Lack of palmitoylation redirects p59(Hck) from the plasma membrane to p61(Hck)-positive lysosomes

Hck, a protein-tyrosine kinase of phagocytes, is the unique member of the S rc family expressed under two alternatively translated isoforms differing i n their N-terminal site of acylation: p61(Hck) has an additional 21-amino a cid sequence comprising a single myristoylation motif, whereas p59(Hck) N t erminus has myristoylation and palmitoylation sites. To identify the molecu lar determinants involved in the targeting of each isoform, they were fused to GFP and expressed in HeLa and CHO cells. p61(Hck) was associated with l ysosomal vesicles, whereas p59(Hck) was found at the plasma membrane and to a low extent associated with lysosomes. Their unique N-terminal domains we re sufficient to target GFP to the corresponding intracellular compartments . Mutation of the palmitoylation site of p59(Hck) redirected this isoform t o lysosomes, indicating that the palmitoylation state governs the associati on of p59(Hck) with the plasma membrane or with lysosomes. In addition, bot h isoforms and the nonpalmitoylated p59(Hck) mutant were found on the Golgi apparatus, suggesting a role of this organelle in the subcellular sorting of Hck isoforms. Regarding their subcellular localizations, we propose that bi-acylated p59(Hck) might transduce plasma membrane receptor signals, whe reas p61(Hck) and the nonpalmitoylated p59(Hck) might control the biogenesi s of phagolysosomes, two functions yet proposed for Hck in phagocytes.