Regulated expression of alternate transcripts from the mouse oncostatin M gene: implications for interleukin-6 family cytokines.

Oncostatin M (OSM) is a member of the IL-6 family of polyfunctional cytokines. The characterized murine OSM transcript consists of three exons and encodes a secreted protein. Investigations of mOSM expression using the ribonuclease protection assay demonstrated novel sites of expression in undifferentiated but not differentiated pluripotent cells, and revealed the existence of alternatively spliced mOSM transcripts. cDNAs representing a novel mOSM transcript (mOSM 13) containing exon 1 spliced directly to exon 3 were isolated from bone marrow using Rapid Amplification of cDNA Ends (RACE) PCR and RT-PCR approaches. Expression of the mOSM 13 transcript was regulated in a tissue-specific manner and independently of mOSM transcript production, suggesting that its production is biologically significant. Splicing of exon 1 directly to exon 3 disrupts the OSM open reading frame of mOSM 13. Initiation of translation at sites within exon 3 of mOSM 13 would yield N-terminally truncated OSM proteins that are localized within the cell. The omission of exon 2 by alternate splicing and the production of intracellular proteins with alternate biological activities are conserved among several IL-6 family cytokines and are one manifestation of a more general phenomenon; the production of alternate cytokine transcripts encoding intracellular and extracellular proteins.