Cloning and characterization of human oncostatin M promoter

Oncostatin M (OSM), an IL-6 subfamily cytokine, inhibits proliferation and causes morphological changes in many tumor cell lines, GM-CSF, phorbol-12-m yristate-13-acetate (PMA), and lipopolysaccharide (LPS) induce OSM expressi on. To investigate the mechanisms governing OSM promoter activity, we have cloned and partially sequenced an 8.5 kb fragment of human genomic DNA imme diately 5' of the OSM coding region and mapped the transcription start site . Transient transfection assays with a series of 5' deletion plasmids demon strated maximal reporter activity in U937 cells with a minimum 304 bp const ruct, The 5'-proximal region of the human OSM gene contains a C/EBP consens us element around -45 bp and several GC-rich regions around -60, each of wh ich is responsible for basal promoter activity. Electrophoretic mobility sh ift assay coupled with supershift analysis confirmed the presence of a cis- acting binding site for activated STAT5 complexes following GM-CSF treatmen t. Furthermore, transient transfection studies demonstrated a loss of GM-CS F responsiveness in reporter constructs containing mutations within this ST AT element, Our results establish that C/EBP and an as yet unidentified GC- rich binding transcription factor are responsible for basal OSM promoter ac tivity, while GM-CSF-stimulated OSM expression is driven by activated STAT5 complexes binding to a cis-acting STAT element on the OSM promoter.