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.

Identification, molecular cloning, and expression of a schistosome antigen displaying diagnostic potential

Recombinant DNA techniques were employed to address the problem of specificity in a serodiagnostic test for schistosomiasis. Immunoprecipitation of in vitro translation products of adult Schistosoma mansoni RNA with sera from Egyptian donors revealed that the human IgG response to schistosome proteins is highly heterogeneous, does not correlate with clinical status, and remains essentially unaltered 6 months after chemotherapeutic cure; peptides of 38 and 70 kDa are recognized by sera from patients infected with S. mansoni or S. haematobium but not by sera from individuals harboring other helminth infections. Using serum from C57BL/6J mice acutely infected with S. mansoni, which strongly reacts with these peptides and very weakly with other worm proteins, portions of the 70 kDa peptide were cloned from an expression cDNA library. The value and limitations of using recombinant schistosome antigens in serodiagnostic assays is discussed.

Molecular cloning of Schistosoma mansoni myosin

A cDNA library representative of adult Schistosoma mansoni mRNA populations was screened with serum from infected rats (refractory hosts), positive plaques being rescreened with serum from infected mice and humans. Based on general reactivity, one clone was selected for further study. As judged by immunofluorescence data, size of corresponding mRNA, and nucleotide sequence analysis, the recombinant expresses approximately 625 amino acids of a schistosome muscle myosin rod. Antibodies evoked by the protein do not cross-react with human cardiac or skeletal muscle, are not invariably stimulated in naturally infected human beings, and rise in titer after chemotherapeutic cure, findings which suggest that the antigen is not a causative agent of Katayama fever, and is probably presented by degenerating worms. The schistosome sarcomeric myosin gene, the most primitive examined to date, appears to be unique inasmuch as it may not be a member of a multigene family and encodes a single mRNA transcript; nonetheless, predicted higher order structure of its translation product is consistent with expected function.