Expression,purification and characterization of the extracellular domain of human Flt3 ligand in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Fms-like tyrosine kinase 3 ligand (Flt3 ligand, FL) is a cytokine that affects the growth, survival and/or differentiation of hematopoietic cells through the activation of specific tyrosine kinase receptors, and is potentially useful for in vitro HSC amplification. To express the extracellular domain of human Flt3 ligand (hFL^ext) in Escherichia coli, we cloned hFL^ext and constructed the recombinant expression vector pET32a-hFL^ext. hFL^ext was successfully expressed in E. coli as a Trx fusion protein (Trx-hFL^ext) under IPTG (isopropyl-β-d-thiogalactopyranoside) induction for 12 h at 30°C. The Trx-hFL^ext protein, expressed in inclusion bodies even at a low induction temperature, was successfully refolded and purified using dialysis and affinity chromatography. The purified hFL^ext was biologically active and could effectively stimulate the proliferation of mouse bone marrow nucleated cells revealed by cell proliferation assay and colony forming assay. In addition, in synergize with G-CSF and TPO, recombinant purified hFL^ext could stimulate ex vivo expansion of murine Lin⁻Sca-1⁺c-Kit⁺ cells. Therefore, using the E. coli expression system and an affinity chromatography system, we successfully expressed, refolded, and purified a biologically active Trx-hFL^ext protein which might be potentially useful for in vitro HSC amplification.