Thymosin beta_4 and Its N-Terminal Tetrapeptide,AcSDKP,Inhibit Proliferation,and Induce Dysplastic,Non-Apoptotic Nuclei and Degranulation of Mast Cells

摘要

Thymosin beta_4 (Tbeta_4),a 5 kDa polypeptide,is a member of the beta-thymosin family.It acts as the principal intracellular G-actin sequestering peptide and exhibits extracellular functions in angiogenesis and wound healing.The N-terminus of Tbeta_4 contains a bioactive tetrapeptide,acSDKP,a negative regulator of hematopoietic stem-cell proliferation.Here,we show that both peptides inhibit mast-cell proliferation over the concentration range of 10~(-6) to 10~(-17) M with the maximum effect of both at 10~(-14) M.Both Tbeta_4 and acSDKP caused dysplastic mast-cell nuclei that were confirmed by DAPI fluorescent staining.Flow-cytometric analysis of ploidy revealed that the dysplastic nuclei were not multinucleated,but fragmented nuclei in G2 growth arrest.We could further demonstrate that 10~(-8) or 10~(-14) M Tbeta_4 or acSDKP induce mast-cell degranulation.A concentration of 10~(-8) M Tbeta_4 or acSDKP caused 57 or 89% degranulation,respectively.A number of tryptic fragments of Tbeta_4 were assayed beside intact Tbeta_4 and the tetrapeptide,and found to be inactive.