Subcellular Distribution of Thymosin β₄

Abstract

The localization of Oregon Green cadaverine-labeled thymosin beta(4), its fragments, and variants was investigated in cytoplasm-depleted A431 cells and in microinjected cells without and with fixation. The studied thymosin beta(4) variants included substitutions of the lysine residues within the basic cluster (14-KSKLKK-19) and the actin-binding motif (17-LKKTETQ-23). In contrast to Oregon Green cadaverine, none of the variants or fragments of thymosin beta(4) could pass the intact nuclear pore of cytoplasm-depleted cells and were hence excluded from the nucleus. However, an equal distribution of all thymosin beta(4) variants was observed in living cells. The nuclear localization is neither dependent on the actin-binding ability of thymosin beta(4) nor on its basic lysine cluster. The equal distribution of the beta-thymosins, the ability of the fragments thymosin beta(4)(1-26) and beta(4)(27-43) to enter the nucleus in intact cells immediately after injection, and their exclusion from cytoplasm-depleted nuclei make it unlikely that they are transported by a single transport protein. A passive but regulated diffusion could explain the described ability of thymosin beta(4) to shuttle into the nucleus.

Cellular Trafficking of Thymosin Beta-4 in HEPG2 Cells Following Serum Starvation

“…According to this study, the Tβ4 cytoplasmic-nuclear diffusion might be due to changes in the barrier function of the nuclear pores [17].…”

“…On the other hand, a passive but regulated diffusion has been proposed as the mechanism that could explain the ability of Tβ4 to shuttle into the nucleus [17]. According to this study, the Tβ4 cytoplasmic-nuclear diffusion might be due to changes in the barrier function of the nuclear pores [17].…”

“…On the contrary, another study using different Tβ4 variants, underlined a possible passive but regulated diffusion that might shuttle this peptide into the nucleus, suggesting that Tβ4 translocation could be regulated by the change of the pore permeability [17].…”

Molecular Characterization, Tissue Distribution, Subcellular Localization and Actin-Sequestering Function of a Thymosin Protein from Silkworm

“…Tβ protein family has a relatively conserved motif ‘LKKTET’ involving Tβ binding to actin [29], [30]. Interestingly, through bioinformatics analysis, it is found that BmTHY also has a relatively conserved motif ‘LKHTET’ with only one amino acid difference from ‘LKKTET’.…”

“…BmTHY was found mostly in the nucleus but was also observed in the cytoplasm. Some actin-binding proteins have been previously reported to localize intracellularly to or shuttle into the nucleus [30], [40], [41], [42]. For example, Huff [40] reported that Tβ4 served as a G-actin sequestering peptide in the nucleus and was specifically translocated into the cell nucleus by an active transport mechanism, requiring an unidentified soluble cytoplasmic factor.…”