Myristoylation and differential palmitoylation of the HCK protein-tyrosine kinases govern their attachment to membranes and association with caveolae.
The human proto-oncogene HCK encodes two versions of a protein-tyrosine kinase, with molecular weights of 59,000 (p59hck) and 61,000 (p61hck). The two proteins arise from a single mRNA by alternative initiations of translation. In this study, we explored the functions of these proteins by determining their locations within cells and by characterizing lipid modifications required for the proteins to reach those locations. We found that p59hck is entirely associated with cellular membranes, including the organelles known as caveolae; in contrast, only a portion of p61hck is situated on membranes, and none is detectable in preparations of caveolae. These distinctions can be attributed to differential modification of the two HCK proteins with fatty acids. Both proteins are at least in part myristoylated, p59hck more so than p61hck. In addition, however, p59hck is palmitoylated on cysteine 3 in the protein. Palmitoylation of the protein requires prior myristoylation and, in turn, is required for targeting to caveolae. These findings are in accord with recent reports for other members of the SRC family of protein-tyrosine kinases. Taken together, the results suggest that HCK and several of its relatives may participate in the functions of caveolae, which apparently include the transduction of signals across the plasma membrane to the interior of the cell.
Robbins
S M
SM
Department of Microbiology, University of California, San Francisco 94143-0552, USA.
Quintrell
N A
NA
Bishop
J M
JM
D000215:Acylation; D000595:Amino Acid Sequence; D002451:Cell Compartmentation; D002458:Cell Fractionation; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008074:Lipoproteins / Q000378:metabolism; D008969:Molecular Sequence Data; D019814:Myristic Acid; D009227:Myristic Acids / Q000378:metabolism*; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism*; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051572:Proto-Oncogene Proteins c-hck; D015398:Signal Transduction
D008074:Lipoproteins; C000715470:MAS1 protein, human; D009227:Myristic Acids; D010169:Palmitic Acids; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D019814:Myristic Acid; D019308:Palmitic Acid; D011505:Protein-Tyrosine Kinases; C496631:HCK protein, human; D051572:Proto-Oncogene Proteins c-hck