Multisite mutation of monomer survivin with enhanced effect on apoptosis regulation of breast cancer cells

Survivin is an important protein in regulating both cell apoptosis and proliferation. It has attracted growing attentions in recent years as a promising target for cancer therapy. Previous studies have revealed that monomeric survivin regulated apoptosis in a more significant way than the wild-type survivin that generally contains a large portion of its dimers. In order to investigate the roles of monomeric mutant survivin apoptosis and cell cycle regulation of human cancer cells, we developed and tested three dominant-negative mutants with multisite mutations (MSM) including TAT-survivin^34/101/102, TAT-survivin^{34/117/101/102} and TAT-survivin^117/101/102. Results revealed that MSM mutants remained as monomers under ambient conditions, and induced cells (breast cancer Bcap-37 cells) apoptosis even more efficiently, primarily through the caspase-dependent and Bcl-2-related pathways, than non-monomeric mutants. We further identified that the TAT-survivin^34/101/102 and TAT-survivin^117/101/102 MSM significantly inhibited the proliferation of Bcap-37 cells and arrested cells in S and G₂/M phases, while TAT-survivin^{34/117/101/102} arrested cells in G₂/M phase. It appeared to us that TAT-survivin^34/101/102 and TAT-survivin^117/101/102 also inhibited cell proliferation more significantly. These findings suggest that such MSM afford monomeric survivin with promising potentials for cancer therapy.