Thymosin beta 4 synergizes with human granulocyte-macrophage colony-stimulating factor in maintaining bone marrow proliferation

Thymosin beta4 upregulates the expression of hepatocyte growth factor and downregulates the expression of PDGF-beta receptor in human hepatic stellate cells

Hepatic stellate cells (HSCs) are the main producers of type I collagen in the liver, and therefore are responsible, in part, for the fibrous scar observed in cirrhotic livers. Although there is no approved treatment for this deadly disease, drugs inducing HSC apoptosis in animals (gliotoxin) and hepatocyte regeneration in man (hepatocyte growth factor [HGF]), have been used successfully in ameliorating liver fibrosis. In this communication we investigated whether thymosin beta(4) (Tbeta(4)), an actin-sequestering peptide that prevents scarring of the heart after a myocardial infarction and that prevents kidney fibrosis in animals, has the potential to be used to treat liver fibrosis. To this end we studied whether the administration of Tbeta(4) to HSCs could alter the expression of genes encoding for extracellular matrix components, as well as those required for differentiation of HSCs. Our preliminary findings show that Tbeta(4) had no effect on the expression of alpha2 (I) collagen, tissue inhibitor of metalloproteinases-1, and matrix metalloproteinase-2 mRNAs. However, it upregulated the expression of HGF and downregulated the expression of platelet-derived growth factor-beta receptor mRNAs in these cells. Overall, these findings suggest that Tbeta(4) has antifibrogenic potential.

Identification of the positive and negative cis-elements involved in modulating the constitutive expression of mouse thymosin beta4 gene

We previously showed that the -278 to +410 region of mouse thymosin beta4 (mT,beta4) gene supports high levels of reporter gene expression in NIH3T3 cells. This region contains part of the 5'-flanking sequences (-278 to -1), the intact first exon (+1 to +133), and portion of the first intron (+134 to +410). However, the size of this exon is much longer than those of its rat and human counterparts. To resolve the question regarding this size discrepancy, transcription start site for the mTbeta4 gene was re-examined by primer extension and bioinformatics analyses. We found that the first exon of mTbeta4 gene spans 56 bp with its cap site situated in a putative initiator highly similar to the consensus mammalian sequence. In addition, a TATA box-like motif and two consecutive downstream promoter elements were also found. To delineate the cis-elements involved in modulating the constitutive expression of mTbeta4 gene, transient transfection assay was performed. Interestingly, expression level of the reporter gene driven by the -117 to +56 region of mTbeta4 gene was approximately 8-fold higher than that directed by the SV40 promoter and significant promoter activity was found to be associated with the smaller (-56 to +56) fragment. A nuclear protein-bound silencer was located in the region between the -167 and -118 and an enhancer whose effect did not seem to be dependent on protein binding was identified in the downstream (-117 to -88) region. However, neither of these cis-elements affected reporter expression driven by a SV40 promoter. Intriguingly, mTbeta4 promoter functioned well in human colorectal (SW480) and cervical (HeLa) carcinoma cells. Taken together, our findings not only provide crucial information for further elucidation of the transcriptional regulation of mTbeta4 gene but also raise the possibility of utilizing its promoter to produce large quantity of recombinant proteins in mammalian cells.

N-acetyl-seryl-aspartyl-lysyl-proline stimulates angiogenesis in vitro and in vivo

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), a natural inhibitor of pluripotent hematopoietic stem cell proliferation, has been suggested as capable of promoting an angiogenic response. We studied whether Ac-SDKP stimulates endothelial cell proliferation, migration, and tube formation; enhances angiogenic response in the rat cornea after implantation of a tumor spheroid; and increases capillary density in rat hearts with myocardial infarction (MI). In vitro, an immortal BALB/c mouse aortic endothelial 22106 cell line was used to determine the effects of Ac-SDKP on endothelial cell proliferation and migration and tube formation. In vivo, a 9L-gliosarcoma cell spheroid (250-300 microm in diameter) was implanted in the rat cornea and vehicle or Ac-SDKP (800 microg.kg(-1).day(-1) ip) infused via osmotic minipump. Myocardial capillary density was studied in rats with MI given either vehicle or Ac-SDKP. We found that Ac-SDKP 1) stimulated endothelial cell proliferation and migration and tube formation in a dose-dependent manner, 2) enhanced corneal neovascularization, and 3) increased myocardial capillary density. Endothelial cell proliferation and angiogenesis stimulated by Ac-SDKP could be beneficial in cardiovascular diseases such as hypertension and MI. Furthermore, because Ac-SDKP is mainly cleaved by ACE, it may partially mediate the cardioprotective effect of ACE inhibitors.

Thymosins: chemistry and biological properties in health and disease

This paper will review the historical background that has generated our present interest in the actions of the thymosins in biological therapy. It will also discuss the multiple actions of the thymosins in the immune, endocrine and central nervous systems. The isolation from the thymus gland of the thymosins, a family of biologically active molecules with hormone-like properties, was first described in 1966 by AL Goldstein and A White. Since that time, significant progress has been made in understanding the role of the thymosins in immunity and the nature of the growth factors, cytokines and chemokines they modulate. The thymosins include a family of biochemically and functionally distinct polypeptides with clinically important physiological properties. In the early 1970s, preclinical studies establishing the immunorestorative effects of a partially purified thymosin preparation termed thymosin fraction 5 (TF5) provided the scientific foundation for the first clinical trials with TF5 in 1974. TF5 was effective in turning on the immune systems of a number of children with DiGeorge syndrome and other thymic dysplasias. These trials led to further interest in the active components in TF5 and to the chemical characterisation of the biologically active thymosins. Several of these molecules are showing significant promise in the clinic in the areas of cancer, infectious diseases and wound healing.

Thymosin beta(4) reduces lethality and down-regulates inflammatory mediators in endotoxin-induced septic shock

Thymosin beta(4) (Tbeta(4)), a highly conserved peptide with immunomodulatory properties, is the major actin-sequestering peptide in mammalian cells. Recent studies have established that Tbeta(4) can accelerate wound healing in full thickness skin wounds and following burn injuries to the cornea. In the eye studies, the accelerated healing due to Tbeta(4) was accompanied by a significant reduction in polymorphonuclear leukocyte (PMN) infiltration and a several-fold decrease in interleukin-1beta (p< or =0.015) and 6-keto-prostaglandin F(1alpha) (6-keto-PGF1alpha, p< or =0.05). Given the recognized role of proinflammatory cytokines in septic shock and of extracellular F- and G-actin in the pathophysiology of multiple organ dysfunction, we have investigated the role of Tbeta(4) in sepsis. We report that an LD(50) dose of LPS (24 mg/kg) in rats resulted in a significant reduction of Tbeta(4) levels in the blood. Furthermore, administration of 100 microg of Tbeta(4) immediately following and at 2 and 4 h after an LD(50) dose of LPS (60 mg/kg) in mice significantly reduced mortality rates (p< or =0.024) and lowered blood levels of a number of inflammatory cytokines, eicosanoids, and other molecules that are highly elevated following endotoxin administration. In studies in human subjects given low doses of endotoxin (4 ng/kg LPS) and in patients with septic shock, we have also observed significant decreases in blood levels of Tbeta(4). The rapid disappearance of Tbeta(4) in the blood following LPS administration or during septic shock suggests that Tbeta(4) may be involved in early events leading to activation of the inflammatory cascade and ultimately the clinical sequelae of sepsis. The results of this study indicate that Tbeta(4) may have utility in the clinic in the treatment of septic shock and in syndromes associated with actin toxicities.

The tetrapeptide AcSDKP, an inhibitor of primitive hematopoietic cell proliferation, induces angiogenesis in vitro and in vivo

The tetrapeptide acetyl-Ser-Asp-Lys-Pro (AcSDKP), purified from bone marrow and constitutively synthesized in vivo, belongs to the family of negative regulators of hematopoiesis. It protects the stem cell compartment from the toxicity of anticancer drugs and irradiation and consequently contributes to a reduction in marrow failure. This current work provides experimental evidence for another novel biologic function of AcSDKP. We report that AcSDKP is a mediator of angiogenesis, as measured by its ability to modulate endothelial cell function in vitro and angiogenesis in vivo. AcSDKP at nanomolar concentrations stimulates in vitro endothelial cell migration and differentiation into capillary-like structures on Matrigel as well as enhances the secretion of an active form of matrix metalloproteinase-1 (MMP-1). In vivo, AcSDKP promotes a significant angiogenic response in the chicken embryo chorioallantoic membrane (CAM) and in the abdominal muscle of the rat. Moreover, it induces the formation of blood vessels in Matrigel plugs implanted subcutaneously in the rat. This is the first report demonstrating the ability of AcSDKP to interact directly with endothelial cells and to elicit an angiogenic response in vitro and in vivo.

Bone marrow stem cell protection from chemotherapy by low--molecular-weight compounds

The stem cells of the bone marrow have the capacity for both self-renewal and derivation of all the blood cell lineages. Consequently, toxicity to these cells can result in neutropenia, agranulocytosis, thrombocytopenia, pancytopenia, or aplastic anemia. Many anticancer drugs adversely affect the bone marrow, and neutropenia is a common limiting factor in dose escalation. In this review, we discuss agents that appear to have potential as bone marrow sparing agents. Computerized catalogs of the National Library of Medicine and Medline were searched for reports on low-molecular-weight compounds that detailed effects on the hematopoietic progenitor cells. The most promising agents are the endogenous peptides p-glutamic acid-glutamic acid-aspartic acid-cysteine-lysine and acetyl-serine-aspartic acid-lysine-proline, and the exogenous compounds amifostine and ammonium trichloro[dioxoethylene-O,O']tellurate, but several others are also discussed. These compounds preserve stem cell function in the presence of antineoplastic drugs of diverse pharmacological classes, and they do so by various mechanisms of action. Their present status in clinical practice is also detailed. More needs to be learned about their mechanisms of action and therapeutic potential, but the results are encouraging for some of these compounds and more clinical trials should be expected.

Comparison of the effects of AcSDKP, thymosin beta4, macrophage inflammatory protein 1alpha and transforming growth factor beta on human leukemic cells

We have compared the effects of AcSDKP, Thymosin beta4 (Tbeta4), MIP1alpha and TGFbeta on acute myeloid leukemia (AML) and B-lineage acute lymphoid leukemia (B-ALL) cells using liquid cultures in the presence of GM-CSF, IL-3 and SCF for AML cells and IL-3 and IL-7 for ALL cells. Each molecule was added daily and cell proliferation was evaluated on day 3 by thymidine incorporation. Whereas TGFbeta was found inhibitory in all the AML and B-ALL cases studied, MIP1alpha was inhibitory in 6/12 AML cases and had no effect on B-ALL cells. AcSDKP and Tbeta4 showed an inhibitory effect in a few cases but only at high doses which were inactive on normal cells. Thus, our study not only confirms the effect of TGFbeta, MIP1alpha and AcSDKP on AML cells but also provides new data concerning their effect on B-ALL and the possible inhibitory effect of AcSDKP at high doses. Furthermore, we show for the first time the effect of Tbeta4 on leukemic cells. Altogether, our data indicate differences of sensitivity of leukemic cells to negative regulators, some leukemias being inhibited by one or several of these molecules whereas others were unresponsive to all used. The clinical relevance of these observations still remains to be determined.

The antiproliferative activity of the tetrapeptide Acetyl-N-SerAspLysPro, an inhibitor of haematopoietic stem cell proliferation, is not mediated by a thymosin beta 4-like effect on actin assembly

Acetyl-N-SerAspLysPro (AcSDKP), known as a negative regulator of haematopoiesis, has been principally reported as an inhibitor of haematopoietic pluripotent stem cell proliferation. The tetrapeptide sequence is identical to the N-terminus of thymosin beta 4 (T beta 4), from which it has been suggested that it may be derived. Recently, evidence was shown that T beta 4 plays a role as a negative regulator of actin polymerization leading to the sequestration of its monomeric form. The structural similarity between the N-terminus of T beta 4 and AcSDKP has raised the possibility that AcSDKP may also participate in intracellular events leading to actin sequestration. The effect of T beta 4 on the proliferation of haematopoietic cells was compared to that of AcSDKP. The results revealed that T beta 4, like AcSDKP, exerts an inhibitory effect on the entry of murine primitive bone marrow cells into cell cycle in vitro. Qualitative electrophoretic analysis and quantitative polymerization assays were used to investigate the role of AcSDKP in actin polymerization. AcSDKP does not affect actin assembly at concentrations up to 50 microM, and does not compete with T beta 4 for binding to G-actin. These results suggest that AcSDKP is not involved in cell cycle regulation via an effect on the process of actin polymerization.