title: The precursor of interleukin-1 alpha is phosphorylated at residue serine 90.
abstract: Mononuclear phagocytes release interleukin-1 (IL-1), a 17-kDa polypeptide with diverse biological activities. IL-1 is synthesized as a precursor (31 kDa) which lacks a signal sequence or hydrophobic domains that could facilitate transmembrane translocation. Possible postsynthetic modifications of IL-1 that might account for its cellular transport were examined. We found that lipopolysaccharide stimulated, but not unstimulated, murine macrophages incorporated 32PO4 into the IL-1 alpha precursor (31 kDa) predominantly at residue serine 90. Released IL-1 alpha (17 kDa) is not phosphorylated in agreement with peptide sequence data that the site of 32P incorporation is in the amino-terminal one-third of the precursor. Approximately 10% of the phosphorylated IL-1 alpha precursor is membrane bound and associated with a fraction enriched in lysosomal vesicles. Together these data suggest mechanisms by which the postsynthetic proteolysis of the IL-1 alpha precursor may be modified and cellular transport of IL-1 alpha is accomplished.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D007375:Interleukin-1 / Q000235:genetics* / Q000302:isolation & purification; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D051379:Mice; D008806:Mice, Inbred AKR; D008970:Molecular Weight; D010766:Phosphorylation; D011498:Protein Precursors / Q000235:genetics* / Q000302:isolation & purification; D011499:Protein Processing, Post-Translational; D012694:Serine
chemical_list: D007375:Interleukin-1; D011498:Protein Precursors; C043830:interleukin 1 precursor; D012694:Serine