Anti-apoptotic effects of the alpha-helix domain of silkworm storage protein 1

Abstract

Apoptosis is a programmed cell death and a mechanism for the maintenance of multicellular organism homeostasis. In bioindustry, apoptosis during cell culture used to produce therapeutic proteins results in the reduction of productivity and quality. Thus, it is crucial to develop novel techniques and materials to inhibit apoptosis. Previous studies have found that storage protein 1 (SP1) has antiapoptotic effects on HeLa cells, but the part of SP1 responsible for the anti-apoptotic effects is unknown. Herein, the anti-apoptotic effects of the N-terminal, α-helix domain of SP1 (SPD1) were investigated by generating a cell line stably expressing SPD1. SPD1 expression conferred strong resistance to apoptosis induced by staurosporine (STS). SPD1 diminished the loss of the mitochondrial membrane potential and inhibited caspase-3 activation, suggesting that it acts as an upstream apoptosis inhibitor. SPD1 was also produced as a recombinant protein in E. coli and culture medium supplementation with recombinant SPD1 resulted in apoptosis inhibition in HeLa cells. The capability of SPD1 to penetrate cell membrane was also assessed, and the results show that it localized in the cytosol, as well as on the plasma membrane. This indicates that SPD1 is a cell-penetrating protein with high antiapoptotic activity. In conclusion, SPD1 is a novel protein responsible for the anti-apoptotic effect of SP1, and it can be considered as a new biomaterial that can minimize cell death and maximize productivity in biopharmaceutical industry. In addition, the miniaturization of SP1 in SPD1 can facilitate its practical usage as a culture medium supplement and cosmetic ingredient.