| Research Abstract |
Survivin, an inhibitor of apoptosis protein, is highly expressed in adult T-cell leukemia/lymphoma (ATL), and associated with chemotherapy resistance. Specifically overexpression of survivin has been reported in almost all human malignancies, but not detectable in normal tissues, making survivin targeted therapy an attractive ATL therapy strategy. Survivin is functioning as a homodimer, and interacts with XIAP through N-terminal single globular baculovirus IAP repeat (BIR) domain, protecting XIAP from ubiquitination and increasing its stability that promotes caspase-9 inhibition. In this study, peptides containing the survivin sequence for homodimer formation between Val89 and Lys103 (PTD-(89-103aa)), and the sequence for interacting with XIAP between Lys15 and Met38 (PTD-(15-38aa)), adding the protein transduction domains (PTD) of TAT protein to their amino-terminals for cell permeable, were synthesized. The growth of various leukemia cell lines (ATL cell lines S1T and MT2, leukemia c
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ell lines HL60, NB4, K562, Jurkat) was strongly inhibited after 2 hr incubation with PTD-(15-38aa). However, no growth suppression was observed in the normal cell lines, lung fibroblast cells HEL and Normal Human Umbilical Vein Endothelial Cells HUVEC. Significant cell death of S1T cells was observed after 2hr treatment with PTD-(15-38aa) by Giemsa staining. The proportion of apoptosis fraction estimated by FACS with Annexin V and PI staining in S1T cells was increased in the dose dependent manner. However, Degradation of caspase-9, caspase-3 and PARP was not detected by immunoblotting. Unexpectedly, we found that PTD-(15-38aa) treatment caused a dose dependent increase in the expression of LC3-II and decrease in the expression of p62. These results indicated that autophagy involved in the PTD-(15-38aa)-induced apoptosis in S1T cells. The effect of PTD-(15-38aa) on the interacting of survivin with XIAP was investigated in COS cells co-transfected with Flag-XIAP and Myc-survivin by immunopreciptation. Contrary to expectation, PTD-(15-38aa) dose dependently enhanced the binding of survivin with XIAP. These results suggested that PTD-(15-38aa) strongly inhibited the proliferation of leukemia cells, specifically ATL cells, and caspase activation is not involved in the induction of autophagy- mediated apoptosis by PTD-(15-38aa). Less
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