Gene cloning and expression of soluble thrombopoietin functional domain by harnessing Rosetta-gami expression system

Background: Thrombopoietin (TPO) is an important cytokine that has a critical role in regulating hematopoietic stem cells (HSCs) proliferation and megakaryocyte differentiation. Because of scares amount of this protein in human plasma, in many biotechnological centers around the world, recombinant production of this protein has been carried out. This study was aiming to gene cloning and expression of recombinant thrombopoietin. Methods: This research is an experimental laboratory study carried out in Blood Transfusion Research Center, Tehran, Iran, from July 2016 to August 2017. At the beginning HepG2 cell line was cultured and RNA extraction was performed. Extracted RNA was used as template for cDNA synthesis and subsequently the synthesized cDNA was adopted to isolate TPO gene through polymerase chain reaction (PCR) reaction using designed primers. After isolating the TPO sequence from HepG2 cell line, the designated sequence was inserted into pET32 vectors. Recombinant plasmid was amplified by meriting from DH5α replicating system. The amplified plasmids were sequenced via chain termination method. Next step was transforming the recombinant plasmid into Rosetta-gami bacteria to express the recombinant protein. In order to induce protein expression, an appropriate amount of isopropyl β-D-1-thiogalactopyranoside (IPTG) was added to growth media, then bacterial lysate of expression host was prepared and assayed via polyacrylamide gel electrophoresis and western blotting test. Results: After sequencing of recombinant plasmid, it was confirmed that TPO sequence has been successfully colonized in adopted vector. Subsequent to induction of recombinant protein, total cell protein analysis affirmed that recombinant protein has been expressed in its soluble form at cytoplasmic condition. Location of expected recombinant protein band on polyacrylamide gel and reaction of recombinant protein with His-tag monoclonal antibody at western blotting was asserting that expressed protein is the one of interest. Conclusion: Rosetta-gami bacteria has capability of expressing recombinant thrombopoietin in its soluble form. By harnessing this method of recombinant protein expression, it would be possible to take advantage of high throughout bacterial expression system which would not produce inclusion body and its product doesn’t need further processing and refolding.