beta-thymosins, small acidic peptides with multiple functions

The beta -thymosins are a family of highly conserved polar 5 kDa peptides o riginally thought to be thymic hormones. About 10 years ago, thymosin beta (4) as well as other members of this ubiquitous peptide family were identif ied as the main intracellular G-actin sequestering peptides, being present in high concentrations in almost every cell. beta -Thymosins bind monomeric actin in a 1:1 complex and act as actin buffers, preventing polymerization into actin filaments but supplying a pool of actin monomers when the cell needs filaments. Changes in the expression of beta -thymosins appear to be related to the differentiation of cells. Increased expression of beta -thym osins or even the synthesis of a beta -thymosin normally not expressed migh t promote metastasis possibly by increasing mobility of the cells. Thymosin beta (4) is detected outside of cells in blood plasma or in wound fluid. S everal biological effects are attributed to thymosin beta (4), oxidized thy mosin beta (4), or to the fragment, acSDKP, possibly generated from thymosi n beta (4). Among the effects are induction of metallo-proteinases, chemota xis, angiogenesis and inhibition of inflammation as well as the inhibition of bone marrow stem cell proliferation. However, nothing is known about the molecular mechanisms mediating the effects attributed to extracellular bet a -thymosins. (C) 2001 Elsevier Science Ltd. All rights reserved.