Oncostatin M (OSM) inhibits the differentiation of pluripotent embryonic stem cells in vitro.

Oncostatin M (OSM) is a cytokine which shares a common gene structure and amino acid sequence similarity with leukemia inhibitory factor (LIF), granulocyte colony-stimulating factor (G-CSF) and interleukin 6 (IL-6), suggesting evolution from a common ancestral gene. These four cytokines share several biological activities including the ability to induce the differentiation of the murine M1 myeloid leukemic cell line. To further define the functional similarities within this family, we have investigated whether OSM can substitute for LIF in the maintenance in vitro of the undifferentiated state of pluripotent embryonic stem (ES) cells. In this study, we demonstrate that human recombinant OSM is similar to LIF in its ability to inhibit the differentiation of MBL-5 murine ES cells cultured in vitro. The level of differentiation was determined by morphological criteria and by the continued expression of the embryonic stem cell-specific surface antigen defined by the ECMA-7 monoclonal antibody. Competition binding studies demonstrate that OSM binds to the LIF receptor on MBL-5 ES cells. Our results implicate OSM as a developmental regulatory factor for embryonic stem cells in vivo.

Molecular cloning, sequence analysis, and functional expression of a novel growth regulator, oncostatin M.

Oncostatin M is a polypeptide of Mr approximately 28,000 that acts as a growth regulator for many cultured mammalian cells. We report the cDNA and genomic cloning, sequence analysis, and functional expression in heterologous cells of oncostatin M. cDNA clones were isolated from mRNA of U937 cells that had been induced to differentiate into macrophagelike cells by treatment with phorbol 12-myristate 13-acetate, and a genomic clone was also isolated from human brain DNA. Sequence analysis of these clones established the 1,814-base-pair cDNA sequence as well as exon boundaries. This sequence predicted that oncostatin M is synthesized as a 252-amino-acid polypeptide, with a 25-residue hydrophobic sequence resembling a signal peptide at the N terminus. The predicted oncostatin M amino acid sequence shared no homology with other known proteins, but the sequence of the 3' noncoding region of the cDNA contained an A + T-rich stretch with sequence motifs found in the 3' untranslated regions of many cytokine and lymphokine cDNAs. Oncostatin M mRNA of approximately 2 kilobase pairs was detected in phorbol 12-myristate 13-acetate-treated U937 cells and in activated human T cells. Transfection of cDNA encoding the oncostatin M precursor into COS cells resulted in the secretion of proteins with the structural and functional properties of oncostatin M. The unique amino acid sequence, expression by lymphoid cells, and growth-regulatory activities of oncostatin M suggest that it is a novel cytokine.