Expression and purification of biologically active human OSF-1 in Escherichia coli.

OSF-1 (also known as pleiotrophin, HB-GAM, HBGF-8 or HBNF) is a heparin-binding, neurotrophic protein. Its tissue-specific expression in rats is developmentally regulated and the protein is highly conserved between species. The protein is believed to be involved in neuronal development. Previous experiments in our laboratory showed that OSF-1 is primarily expressed in brain and bone. The biological function of OSF-1 in bone is unknown. In order to overcome the limited availability of the native protein, we now report on the high-level expression of human OSF-1 in Escherichia coli. The protein is present in the form of inclusion bodies, which were isolated and solubilized. The partially purified protein was refolded and further purified employing heparin sepharose chromatography. N-terminal sequence determination revealed the same amino acid sequence as the natural mature protein. The isolated backfolded recombinant human OSF-1 did promote neurites outgrowth in primary cultures of cortical neurons.