Expression of bovine activin-A and inhibin-A in recombinant baculovirus-infected Spodoptera frugiperdaSf21 insect cells

Abstract

Currently, bioactive activin and inhibin for investigative purposes are obtained either by purification from bovine or porcine follicular fluid or have been kindly supplied in limited amounts by Genentech. The latter are recombinant formulations produced in cultured monkey kidney CV-1 cells. The aims of this study were to assess the potential of the baculovirus expression system as an alternative means to produce recombinant activin and inhibin. Towards these goals, two recombinant baculoviruses, AcBovACT A and AcBovINH A, were constructed. AcBovACT A contains a contiguous copy of the bovine β A-inhibin/activin structural gene encoding the β A-preproprotein whereas AcBovINH A contains contiguous copies of the bovine α-inhibin and β A-inhibin/activin structural genes encoding the α- and β A-preproproteins, respectively. Western blot analyses, using monoclonal antibodies specific for the mature portions of the α-inhibin and β A-inhibin/activin subunits, demonstrated that Spodoptera frugiperda Sf21 cells infected with either recombinant virus secreted mature homodimeric activin-A into the medium. In addition, Sf21 cells infected with the recombinant AcBovINH A virus were found also to produce substantial amounts of the α-inhibin precursor protein. However, the mature portion of the latter is not secreted into the medium but is retained within infected cells in an incompletely processed form(s). The recombinant activin-A secreted by Sf21 cells infected with the AcBovACT A virus was shown to possess activin bioactivity when analysed by in vitro bioassay and, therefore, provides an alternative route to mammalian cell expression for the production of recombinant activin-A.