Cleavage of a hydrophilic C-terminal domain increases growth-inhibitory activity of oncostatin M.
Oncostatin M is a polypeptide cytokine, produced by normal and malignant hematopoietic cells, that has several in vitro activities, including the ability to inhibit growth of cultured carcinoma cells. Here we present a structural and functional comparison of two oncostatin M-related proteins (Mr 36,000 and 32,000) secreted by COS cells transfected with oncostatin M cDNA. The smaller of these forms lacked a hydrophilic C-terminal domain comprising predominantly basic amino acids. This domain was also absent from native oncostatin M produced by U937 cells. The 32,000-Mr form of oncostatin M was not produced by cells transfected with plasmids (G195 and G196) in which a potential trypsinlike cleavage site within the hydrophilic C-terminal domain was altered by site-directed mutagenesis. A 32,000-Mr fragment was produced by trypsin treatment of the 36,000-Mr form of oncostatin M. These observations suggest that the 32,000-Mr form of oncostatin M was derived from the 227-amino-acid propeptide by proteolytic cleavage at or near the paired basic residues at positions 195 and 196. Pro-oncostatin M was equally active in radioreceptor assays as the processed form but was 5- to 60-fold less active in growth inhibition assays. Likewise, nonprocessed mutant protein encoded by plasmid G196 was equally active in the radioreceptor assays as the processed form but was five- to ninefold less active in growth inhibition assays. Thus, the highly charged C-terminal domain of pro-oncostatin M is not required for receptor binding or growth-inhibitory activity but may alter the functional properties of the molecule. Propeptide processing of oncostatin M may be important for regulating in vivo activities of this cytokine.
Linsley
P S
PS
Oncogen, Seattle, Washington 98121.
Kallestad
J
J
Ochs
V
V
Neubauer
M
M
D000595:Amino Acid Sequence; D002478:Cells, Cultured; D004252:DNA Mutational Analysis; D006031:Glycosylation; D006131:Growth Inhibitors / Q000235:genetics; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation; D053683:Oncostatin M; D010455:Peptides / Q000235:genetics / Q000494:pharmacology*; D011499:Protein Processing, Post-Translational; D013329:Structure-Activity Relationship
D006131:Growth Inhibitors; D010455:Peptides; D053683:Oncostatin M