Parasporin-1Ab, a novel Bacillus thuringiensis cytotoxin preferentially active on human cancer cells in vitro.

The non-insecticidal Bacillus thuringiensis strain B0195 produces parasporin (PS) whose cytocidal activity is preferential for human cancer cells. This study identified two ps genes, ps1Aa3 and ps1Ab1, from the strain B0195. The former gene was 2,169-bp long, encoding an 81 kDa protein (PSLAa3) whose aminoacid sequence was 100% identical to that of the reference protein PS1Aa1. The latter gene was 2,178-bp long, encoding a novel protein of 82 kDa, PS1Ab1, whose sequence was 86.4% identical to that of PS1Aa1. The recombinant protein of PS1Ab1, synthesized in transformed B. thuringiensis cells, induced marked cytopathy in HeLa cells (human uterus cervix cancer cells) upon proteolytic activation. The cytopathy was characterized by cell-ballooning, followed by gradual cell-shrinking. Unlike HeLa cells, non-cancer UtSMC cells (human uterine smooth muscle-cells) were not susceptible to PS1Ab1.