Thymosin beta-NB Is the Human Isoform of Rat Thymosin beta15

N-acetyl-seryl-aspartyl-lysyl-proline is a valuable endogenous antifibrotic peptide for kidney fibrosis in diabetes: An update and translational aspects

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is an endogenous peptide that has been confirmed to show excellent organ-protective effects. Even though originally discovered as a modulator of hemotopoietic stem cells, during the recent two decades, AcSDKP has been recognized as valuable antifibrotic peptide. The antifibrotic mechanism of AcSDKP is not yet clear; we have established that AcSDKP could target endothelial-mesenchymal transition program through the induction of the endothelial fibroblast growth factor receptor signaling pathway. Also, recent reports suggested the clinical significance of AcSDKP. The aim of this review was to update recent advances of the mechanistic action of AcSDKP and discuss translational research aspects.

Thymosins in multiple sclerosis and its experimental models: moving from basic to clinical application

BACKGROUND

Multiple sclerosis (MS) afflicts more than 2.5 million individuals worldwide and this number is increasing over time. Within the past years, a great number of disease-modifying treatments have emerged; however, efficacious treatments and a cure for MS await discovery. Thymosins, soluble hormone-like peptides produced by the thymus gland, can mediate immune and non-immune physiological processes and have gained interest in recent years as therapeutics in inflammatory and autoimmune diseases.

METHODS

Pubmed was searched with no time constraints for articles using a combination of the keywords "thymosin/s" or "thymus factor/s" AND "multiple sclerosis", mesh terms with no language restriction.

RESULTS

Here, we review the state-of-the-art on the effects of thymosins on MS and its experimental models. In particular, we describe what is known in this field on the roles of thymosin-α1 (Tα1) and -β4 (Tβ4) as potential anti-inflammatory as well as neuroprotective and remyelinating molecules and their mechanisms of action.

CONCLUSION

Based on the data that Tα1 and Tβ4 act as anti-inflammatory molecules and as inducers of myelin repair and neuronal protection, respectively, a possible therapeutic application in MS for Tα1 and Tβ4 alone or combined with other approved drugs may be envisaged. This approach is reasonable in light of the current clinical usage of Tα1 and data demonstrating the safety, tolerability and efficacy of Tβ4 in clinical practice.

Thymosin beta4 and its posttranslational modifications

Thymosin beta(4) as well as the other members of the beta-thymosin family are important G-actin sequestering peptides. The chemical properties, the biosynthesis, and posttranslational modifications (PTMs) of these peptides are discussed. During biosynthesis of thymosin beta(4) the initiator methionine is removed and the N-terminus is acetylated. Research on proteomics revealed several acetylated lysine residues and two phosphorylated threonine residues. The enormous number of phosphorylable and acetylable sites in the human proteome raises the question about the biological significance of these PTMs in the context of beta-thymosins. Presently, this question cannot be answered because neither the concentration of these modified beta-thymosins in cells is known nor the consequences of the modifications on the biological function(s) of beta-thymosins have been studied yet. Thymosin beta(4) is also posttranslationally modified by transglutaminase forming covalent bonds with other molecules. Prolyl oligopeptidase generates ac-SDKP from thymosin beta(4). The concentration of C-terminal peptide fragments of thymosin beta(4) is elevated in the blood of patients with rheumatoid arthritis.

Vertebrate beta-thymosins: conserved synteny reveals the relationship between those of bony fish and of land vertebrates

Using conservation of synteny I show how the four thymosins expressed by teleost fish are related to the three of tetrapods, which is not evident from their protein sequences. This clarification was aided by identification of a novel thymosin of reptilians that replaces the beta10 thymosin of mammals. Recent reconstruction of the ancestral vertebrate genome suggests that divergence of beta-thymosins began with duplication preceding the two rounds of whole genome duplication.

Differential regulation of human thymosin beta 15 isoforms by transforming growth factor beta 1

We recently identified an additional isoform of human thymosin beta 15 (also known as NB-thymosin beta, gene name TMSB15A) transcribed from an independent gene, and designated TMSB15B. The purpose of this study was to investigate whether these isoforms were differentially expressed and functional. Our data show that the TMSB15A and TMSB15B isoforms have distinct expression patterns in different tumor cell lines and tissues. TMSB15A was expressed at higher levels in HCT116, DU145, LNCaP, and LNCaP-LN3 cancer cells. In MCF-7, SKOV-3, HT1080, and PC-3MLN4 cells, TMSB15A and TMSB15B showed approximately equivalent levels of expression, while TMSB15B was the predominant isoform expressed in PC-3, MDA-MB-231, NCI-H322, and Caco-2 cancer cells. In normal human prostate and prostate cancer tissues, TMSB15A was the predominant isoform expressed. In contrast, normal colon and colon cancer tissue expressed predominantly TMSB15B. The two gene isoforms are also subject to different transcriptional regulation. Treatment of MCF-7 breast cancer cells with transforming growth factor beta 1 repressed TMSB15A expression but had no effect on TMSB15B. siRNA specific to the TMSB15B isoform suppressed cell migration of prostate cancer cells to epidermal growth factor, suggesting a functional role for this second isoform. In summary, our data reveal different expression patterns and regulation of a new thymosin beta 15 gene paralog. This may have important consequences in both tumor and neuronal cell motility.

The mouse thymosin beta15 gene family displays unique complexity and encodes a functional thymosin repeat

We showed earlier that human beta-thymosin 15 (Tb15) is up-regulated in prostate cancer, confirming studies from others that propagated Tb15 as a prostate cancer biomarker. In this first report on mouse Tb15, we show that, unlike in humans, four Tb15-like isoforms are present in mouse. We used phylogenetic analysis of deuterostome beta-thymosins to show that these four new isoforms cluster within the vertebrate Tb15-clade. Intriguingly, one of these mouse beta-thymosins, Tb15r, consists of two beta-thymosin domains. The existence of such a repeat beta-thymosin is so far unique in vertebrates, though common in lower eukaryotes. Biochemical data indicate that Tb15r potently sequesters actin. In a cellular context, Tb15r behaves as a bona fide beta-thymosin, lowering central stress fibre content. We reveal that a complex genomic organization underlies Tb15r expression: Tb15r results from read-through transcription and alternative splicing of two tandem duplicated mouse Tb15 genes. Transcript profiling of all mouse beta-thymosin isoforms (Tb15s, Tb4 and Tb10) reveals that two isoform switches occur between embryonic and adult tissues, and indicates Tb15r as the major mouse Tb15 isoform in adult cells. Tb15r is present also in mouse prostate cancer cell lines. This insight into the mouse Tb15 family is fundamental for future studies on Tb15 in mouse (prostate) cancer models.

Functional and profiling studies prove that prostate cancer upregulated neuroblastoma thymosin β is the true human homologue of rat thymosin β15

A peptide with a sequence identical to rat thymosin beta(Tb)15 was reported to be upregulated in human prostate cancer. However, in this report we provide evidence that TbNB, initially identified in human neuroblastoma, is the only Tb isoform upregulated in human prostate cancer and that the Tb15 sequence is not present herein. In addition, we demonstrate that human TbNB has a higher affinity for actin in comparison to Tb4 and promotes cell migration. In combination, this experimentally validates TbNB as functional homologue of rat Tb15 in the human organism and clarifies the current composition of the human Tb family.