Recombinant derivatives of the human high-mobility group protein HMGB2 mediate efficient nonviral gene delivery

Certain natural peptides and proteins of mammalian origin are able to bind and condense plasmid DNA, a prerequisite for the formation of transfection-competent complexes that facilitate nonviral gene delivery. Here we have generated recombinant derivatives of the human high-mobility group (HMG) protein HMGB2 and investigated their potential as novel protein-based transfection reagents. A truncated form of HMGB2 encompassing amino acids 1-186 of the molecule was expressed in Escherichia coli at high yield. This HMGB2(186) protein purified from bacterial lysates was able to condense plasmid DNA in a concentration-dependent manner, and mediated gene delivery into different established tumor cell lines more efficiently than poly(L-lysine). By attaching, via gene fusion, additional functional domains such as the HIV-1 TAT protein transduction domain (TAT(PTD)-HMGB2(186)), the nuclear localization sequence of the simian virus 40 (SV40) large T-antigen (SV40(NLS)-HMGB2(186)), or the importin-beta-binding domain (IBB) of human importin-alpha (IBB-HMGB2(186)), chimeric fusion proteins were produced which displayed markedly improved transfection efficiency. Addition of chloroquine strongly enhanced gene transfer by all four HMGB2(186) derivatives studied, indicating cellular uptake of protein-DNA complexes via endocytosis. The IBB-HMGB2(186) molecule in the presence of the endosomolytic reagent was the most effective. Our results show that recombinant derivatives of human HMGB2 facilitate efficient nonviral gene delivery and may become useful reagents for applications in gene therapy.