Induction of tumor-specific T lymphocyte responses in vivo by prothymosin alpha

Antitumor Reactive T-Cell Responses Are Enhanced In Vivo by DAMP Prothymosin Alpha and Its C-Terminal Decapeptide

Prothymosin α (proTα) and its C-terminal decapeptide proTα(100-109) were shown to pleiotropically enhance innate and adaptive immune responses. Their activities have been broadly studied in vitro, focusing primarily on the restoration of the deficient immunoreactivity of cancer patients' leukocytes. Previously, we showed that proTα and proTα(100-109) act as danger-associated molecular patterns (DAMPs), ligate Toll-like receptor-4, signal through TRIF- and MyD88-dependent pathways, promote the maturation of dendritic cells and elicit T-helper type 1 (Th1) immune responses in vitro, leading to the optimal priming of tumor antigen-reactive T-cell functions. Herein, we assessed their activity in a preclinical melanoma model. Immunocompetent mice bearing B16.F1 tumors were treated with two cycles of proTα or proTα(100-109) together with a B16.F1-derived peptide vaccine. Coadministration of proTα or proTα(100-109) and the peptide vaccine suppressed melanoma-cell proliferation, as evidenced by reduced tumor-growth rates. Higher melanoma infiltration by CD3+ T cells was observed, whereas ex vivo analysis of mouse total spleen cells verified the in vivo induction of melanoma-reactive cytotoxic responses. Additionally, increased levels of proinflammatory and Th1-type cytokines were detected in mouse serum. We propose that, in the presence of tumor antigens, DAMPs proTα and proTα(100-109) induce Th1-biased immune responses in vivo. Their adjuvant ability to orchestrate antitumor immunoreactivities can eventually be exploited therapeutically in humans.

Prothymosin-α enhances phosphatase and tensin homolog expression and binds with tripartite motif-containing protein 21 to regulate Kelch-like ECH-associated protein 1/nuclear factor erythroid 2-related factor 2 signaling in human bladder cancer

Prothymosin‐α (PTMA) is a small, acidic protein that is usually transported into the nucleus and involves many cellular and immunological functions. Previous studies demonstrated that aberrant location of PTMA expression exists in human bladder cancer, but the role of PTMA protein expression remains elusive. In this study, we created ectopic nuclear or cytoplasmic PTMA expression in human bladder cancer cells by infecting lentiviruses carrying wild type or deleted nuclear localization signal of the PTMA gene. The in vivo tumorigenesis assay showed PTMA protein with deleted nuclear localization signal promotes J82 xenograft tumor growth in mice and shortens their survival more so than the wild type. Chromatin immunoprecipitation showed that wild‐type PTMA protein binds to the PTEN promoter and enhances phosphatase and tensin homolog (PTEN) expression. Through immunoblot proteomics and in vivo ubiquitination studies, PTMA protein can bind with tripartite motif‐containing protein 21 (TRIM21) and block its ubiquitination. Also, TRIM21 can downregulate both forms of PTMA protein. In human bladder tumors, loss of nuclear PTMA expression was an unfavorable prognostic indicator for shorter disease‐free survival (hazard ratio, 1.54; P = 0.009). Our data support that nuclear PTMA protein serves as a tumor suppressor in bladder cancer through upregulating PTEN and orchestrating TRIM21 for the regulation of Nrf2 signaling.

Prothymosin Alpha and Immune Responses: Are We Close to Potential Clinical Applications?

The thymus gland produces soluble molecules, which mediate significant immune functions. The first biologically active thymic extract was thymosin fraction V, the fractionation of which led to the isolation of a series of immunoactive polypeptides, including prothymosin alpha (proTα). ProTα displays a dual role, intracellularly as a survival and proliferation mediator and extracellularly as a biological response modifier. Accordingly, inside the cell, proTα is implicated in crucial intracellular circuits and may serve as a surrogate tumor biomarker, but when found outside the cell, it could be used as a therapeutic agent for treating immune system deficiencies. In fact, proTα possesses pleiotropic adjuvant activity and a series of immunomodulatory effects (eg, anticancer, antiviral, neuroprotective, cardioprotective). Moreover, several reports suggest that the variable activity of proTα might be exerted through different parts of the molecule. We first reported that the main immunoactive region of proTα is the carboxy-terminal decapeptide proTα(100-109). In conjunction with data from others, we also revealed that proTα and proTα(100-109) signal through Toll-like receptor 4. Although their precise molecular mechanism of action is yet not fully elucidated, proTα and proTα(100-109) are viewed as candidate adjuvants for cancer immunotherapy. Here, we present a historical overview on the discovery and isolation of thymosins with emphasis on proTα and data on some immune-related new activities of the polypeptide and smaller immunostimulatory peptides thereof. Finally, we propose a compiled scenario on proTα's mode of action, which could eventually contribute to its clinical application.

Characterization of two thymosins as immune-related genes in common carp (Cyprinus carpio L.)

Prothymosin alpha (ProTα) and thymosin beta (Tβ) belong to thymosin family, which consists of a series of highly conserved peptides involved in stimulating immune responses. ProTα b and Tβ are still poorly studied in teleost. Here, the full-length cDNAs of ProTα b and Tβ-like (Tβ-l) were cloned and identified in common carp (Cyprinus carpio L.). The expressions of carp ProTα b and Tβ-l exhibited rise-fall pattern and then trended to be stable during early development. After spring viraemia of carp virus (SVCV) infection, the carp ProTα b and Tβ-l transcripts were significantly up-regulated in some immune-related organs. When transiently over-expressed carp ProTα b and Tβ-l in zebrafish, these two proteins up-regulated the expressions of T lymphocytes-related genes (Rag 1, TCR-γ, CD4 and CD8α). These results suggest that carp ProTα b and Tβ may ultimately enhance the immune response during viral infection and modulate the development of T lymphocytes in teleost.

Toll-like receptor agonists: current status and future perspective on their utility as adjuvants in improving anticancer vaccination strategies

Toll-like receptor (TLR) agonists possess remarkable properties, particularly with regard to dendritic cell activation, promoting Th1-type cytokine production and optimizing cytotoxic T-cell responses. Preclinical and clinical studies conducted to date show that TLR agonists can improve currently applied anticancer vaccination protocols. Although these have resulted in the US FDA approval of three TLR agonists for use in humans, their abundant application encounters limitations, principally due to dose-limiting toxicity evoking from systemic cytokine production. Here, using selected examples of clinical studies, we provide a concise review regarding the knowledge acquired thus far on the adjuvant use of TLR agonists as cancer vaccine components. We also provide evidence on the exploitation of a novel TLR agonist, prothymosin-α, which enhances the efficacy of tumor-reactive effectors without causing severe adverse effects.

Prothymosin α and a prothymosin α-derived peptide enhance T(H)1-type immune responses against defined HER-2/neu epitopes

Background

Active cancer immunotherapies are beginning to yield clinical benefit, especially those using peptide-pulsed dendritic cells (DCs). Different adjuvants, including Toll-like receptor (TLR) agonists, commonly co-administered to cancer patients as part of a DC-based vaccine, are being widely tested in the clinical setting. However, endogenous DCs in tumor-bearing individuals are often dysfunctional, suggesting that ex vivo educated DCs might be superior inducers of anti-tumor immune responses. We have previously shown that prothymosin alpha (proTα) and its immunoreactive decapeptide proTα(100–109) induce the maturation of human DCs in vitro. The aim of this study was to investigate whether proTα- or proTα(100–109)-matured DCs are functionally competent and to provide preliminary evidence for the mode of action of these agents.

Results

Monocyte-derived DCs matured in vitro with proTα or proTα(100–109) express co-stimulatory molecules and secrete pro-inflammatory cytokines. ProTα- and proTα(100–109)-matured DCs pulsed with HER-2/neu peptides induce T_H1-type immune responses, prime autologous naïve CD8-positive (+) T cells to lyse targets expressing the HER-2/neu epitopes and to express a polyfunctional profile, and stimulate CD4+ T cell proliferation in an HER-2/neu peptide-dependent manner. DC maturation induced by proTα and proTα(100–109) is likely mediated via TLR-4, as shown by assessing TLR-4 surface expression and the levels of the intracellular adaptor molecules TIRAP, MyD88 and TRIF.

Conclusions

Our results suggest that proTα and proTα(100–109) induce both the maturation and the T cell stimulatory capacity of DCs. Although further studies are needed, evidence for a possible proTα and proTα(100–109) interaction with TLR-4 is provided. The initial hypothesis that proTα and the proTα-derived immunoactive decapeptide act as “alarmins”, provides a rationale for their eventual use as adjuvants in DC-based anti-cancer immunotherapy.

Prothymosin alpha: a ubiquitous polypeptide with potential use in cancer diagnosis and therapy

The thymus is a central lymphoid organ with crucial role in generating T cells and maintaining homeostasis of the immune system. More than 30 peptides, initially referred to as "thymic hormones," are produced by this gland. Although the majority of them have not been proven to be thymus-specific, thymic peptides comprise an effective group of regulators, mediating important immune functions. Thymosin fraction five (TFV) was the first thymic extract shown to stimulate lymphocyte proliferation and differentiation. Subsequent fractionation of TFV led to the isolation and characterization of a series of immunoactive peptides/polypeptides, members of the thymosin family. Extensive research on prothymosin α (proTα) and thymosin α1 (Tα1) showed that they are of clinical significance and potential medical use. They may serve as molecular markers for cancer prognosis and/or as therapeutic agents for treating immunodeficiencies, autoimmune diseases and malignancies. Although the molecular mechanisms underlying their effect are yet not fully elucidated, proTα and Tα1 could be considered as candidates for cancer immunotherapy. In this review, we will focus in principle on the eventual clinical utility of proTα, both as a tumor biomarker and in triggering anticancer immune responses. Considering the experience acquired via the use of Tα1 to treat cancer patients, we will also discuss potential approaches for the future introduction of proTα into the clinical setting.

Proteomic exploitation on prothymosin α-induced mononuclear cell activation

Prothymosin alpha (ProTalpha) is an acidic polypeptide associated both with cell proliferation and immune regulation. Although ProTalpha's immunomodulating activity is well established at cellular level, limited information is available regarding the signaling pathways triggered by ProTalpha. Using 2-DE proteomic technology, we investigated changes in protein expression of ProTalpha-stimulated peripheral blood mononuclear cells (PBMC) in the course of a 3-day incubation. Using healthy donor- and cancer patient-derived PBMC, 12 gels were studied, identifying 53 differing protein spots via PMF comparison analysis. Among others, we identified interleukin-1 receptor-associated kinase 4, heat-shock protein 90, lipocalin 2, ribophorin 1, eukaryotic elongation factor 2, 14-3-3 protein, L-plastin, and MX2 protein, all of which were found to be overexpressed upon ProTalpha activation. Based on the physiological role of upregulated proteins, we propose the following model for ProTalpha's immunological mode of action: on day 1, ProTalpha triggers monocyte activation, possibly via toll-like receptor signaling, and enhances antigen presentation, consequently promoting and stabilizing monocyte-T-cell immune synapse; on day 2, activated monocytes produce interleukin (IL)-1, while T-cell receptor triggering promotes T-cell proliferation and IL-2 production; finally, on day 3, ProTalpha-activated PBMC express proteins related to adhesion and cytotoxic effector functions, both contributing to the increase of their lytic activity.

Prothymosin α Lacking the Nuclear Localization Signal as an Effective Gene Therapeutic Strategy in Collagen-Induced Arthritis

Prothymosin alpha (ProT) is regulated by c-Myc, an oncoprotein overexpressed in synovium of rheumatoid arthritis, and is associated with cell proliferation. However, ProT also exerts immunomodulatory activities. The growth-promoting activity of ProT can be abolished by deleting its nuclear localization signal (NLS). In this study, we showed that AdProTDeltaNLS, an adenoviral vector encoding ProT lacking the NLS, did not enhance the proliferation of synovial fibroblasts. AdProTDeltaNLS treatment abolished the up-regulation of the MIP-1alpha promoter activity induced by TNF-alpha in synovial fibroblasts. AdProTDeltaNLS suppressed macrophage chemotaxis and reduced macrophage infiltration into the ankle joints in rats with collagen-induced arthritis (CIA). Neutralization test confirmed the involvement of MIP-1alpha in macrophage chemotaxis. Administration of AdProTDeltaNLS reduced the severity of CIA in the clinical, radiographic, and histological aspects. The levels of TNF-alpha (mean +/- SEM, 1261.9 +/- 107.9 vs 2880.1 +/- 561.4 pg/mg total protein; p < 0.05), IL-1beta (56.8 +/- 8.0 vs 109.2 +/- 4.9 pg/mg total protein; p < 0.01), and MIP-1alpha (41.7 +/- 3.6 vs 55.2 +/- 1.1 pg/mg total protein; p < 0.05) in the ankle joints were lower in the AdProTDeltaNLS-treated rats with CIA than those in their control counterparts. In the AdProTDeltaNLS-treated ankle joints, matrix metalloproteinase-9 expression was decreased by 40% and infiltrating macrophages reduced by 50%. Our results demonstrate that intra-articular delivery of AdProTDeltaNLS significantly ameliorated the clinical course of CIA in rats. This study is the first to suggest that ProT lacking the NLS may have therapeutic potential for the management of rheumatoid arthritis.

The immunologically active site of prothymosin alpha is located at the carboxy-terminus of the polypeptide. Evaluation of its in vitro effects in cancer patients

Prothymosin alpha (proTalpha) is a 109 amino acid long polypeptide presenting distinct immunoenhancing activity in vitro and in vivo. Recent reports suggest that in apoptotic cells, proTalpha is cleaved by caspases at its carboxy(C)-terminus generating potentially bioactive fragments. In this study, we identified the peptide segment of proTalpha presenting maximum immunomodulatory activity. Calf thymus proTalpha was trypsinised, and the five fragments produced (spanning residues 1-14, 21-30, 31-87, 89-102 and 103-109) were tested for their ability to stimulate healthy donor- and cancer patient-derived peripheral blood mononuclear cell (PBMC) proliferation in autologous mixed lymphocyte reaction (AMLR), natural killer and lymphokine-activated killer cell activity, intracellular production of perforin, upregulation of adhesion molecules and CD25 expression. ProTalpha(89-102) and proTalpha(103-109) significantly fortified healthy donor-lymphocytes' immune responses to levels comparable to those induced by intact proTalpha. These effects were more pronounced in cancer patients, where peptides proTalpha(89-102) and proTalpha(103-109) partly, however significantly, restored the depressed AMLR and cytolytic ability of PBMC, by simulating the biological activity exerted by intact proTalpha. ProTalpha(1-14), proTalpha(21-30) and proTalpha(31-87) marginally upregulated lymphocyte activation. This is the first report showing that proTalpha's immunomodulating activity can be substituted by its C-terminal peptide(s). Whether generation and externalization of such immunoactive proTalpha fragments occurs in vivo, needs further investigation. However, if these peptides can trigger immune responses, they may eventually be used therapeutically to improve some PBMC functions of cancer patients.

Identification of N-terminal acetylation of recombinant human prothymosin α in Escherichia coli

Functional modification of protein through N-terminal acetylation is common in eukaryotes but rare in prokaryotes. Prothymosin alpha is an essential protein in immune stimulation and apoptosis regulation. The protein is N-terminal acetylated in eukaryotes, but similar modification has never been found in recombinant protein produced in prokaryotes. In this study, two mass components of recombinant human prothymosin alpha expressed in Escherichia coli were identified and separated by RP-HPLC. Mass spectrometry of the two components showed that one of them had a 42 Da mass increment as compared with the theoretical mass of human prothymosin alpha, which suggested a modification of acetylation. The mass of another one was equal to that of the theoretical one. Peptides mass spectrometry of the modified component showed that the 42-Da mass increment occurred in the N-terminal peptide domain, and MS/MS peptide sequencing of the N-terminal peptide found that the acetylated modification occurred at the N-terminal serine residue. So, part of the recombinant human prothymosin alpha produced by E. coli was N-terminal acetylated. This finding adds a new clue for the mechanism of acetylated modification in prokaryotes, and also suggested a new method for production of N-terminal modificated prothymosin alpha and thymosin alpha1.

Thymosinalpha1 stimulates cell proliferation by activating ERK1/2, JNK, and increasing cytokine secretion in human pancreatic cancer cells

In this study, we investigated the expression and function of thymosinalpha1 (Thyalpha1) in human pancreatic cancer. We found that human pancreatic cancer cell lines Panc-1, Panc03.27, ASPC-1, and PL45 cells significantly over-expressed the mRNA of Thyalpha1 as compared to the normal human pancreatic ductal epithelium (HPDE) cells.. Thyalpha1 mRNA and protein levels were also over-expressed in clinical pancreatic adenocarcinoma specimens. In addition, synthetic Thyalpha1 significantly promoted Panc-1 cell proliferation and increased phosphorylation of ERK1/2 and JNK. Furthermore, Thyalpha1 increased the secretion of multiple cytokines including IL-10, IL-13, and IL-17 in Panc-1 cells. Thus, Thyalpha1 may have a new role in pancreatic cancer pathogenesis.

Boosting immune response to hepatitis B DNA vaccine by coadministration of Prothymosin alpha-expressing plasmid

DNA vaccines induce protective humoral and cell-mediated immune responses in several animal models. However, compared to conventional vaccines, DNA vaccines usually induce poor antibody responses. In this study, we report that coadministration of a hepatitis B virus (HBV) DNA vaccine with prothymosin alpha as an adjuvant improves antibody responses to HBV S antigen. We also observed higher seroconversion rates and higher antibody titers. Prothymosin alpha appears to increase the number and affinity of hepatitis B surface antigen-specific, gamma interferon-secreting T cells and to enhance cellular immune response to the PreS2S DNA vaccine. Interestingly, administering the DNA separately from the prothymosin alpha plasmid abrogated the enhancement of DNA vaccine potency. The results suggest that prothymosin alpha may be a promising adjuvant for DNA vaccines.

Development and immunochemical evaluation of antibodies Y for the poorly immunogenic polypeptide prothymosin alpha

Since conserved mammalian polypeptides are believed to exhibit enhanced immunogenicity in avian species, hens were immunized against the poorly immunogenic, highly conserved mammalian polypeptide prothymosin alpha (ProTalpha), i.e. against either non-conjugated ProTalpha (isolated from bovine thymus) or ProTalpha conjugated to keyhole limpet hemocyanin (ProTalpha/KLH). The antibodies Y were isolated from the egg yolk and evaluated through suitable dot-blot and ELISA systems in parallel with antibodies G isolated from the antiserum of rabbits immunized against the same immunogens. As revealed, antibodies Y and G of low titer and/or affinity were obtained against non-conjugated ProTalpha, while antibodies Y against ProTalpha/KLH had a better apparent titer, could better discriminate between ProTalpha and the closely related bioactive peptide thymosin alpha 1, and were obtained at much larger quantities than the corresponding antibodies G.

Prothymosin alpha-receptor associates with lipid rafts in PHA-stimulated lymphocytes

Lipid rafts are specialized plasma membrane microdomains in which glycosphingolipids and cholesterol are major structural components. Their relative insolubility to nonionic detergents is the most widely used method to purify these structures. Several signalling proteins are associated with these microdomains in T lymphocytes, including receptors for growth factors and cytokines. ProTalpha is a highly conserved and widely distributed protein whose physiological functions remain elusive. In previous works we identified, by means of affinity cross-linking, affinity chromatography and fluorescence microscopy, a set of binding proteins for ProTalpha in human lymphoblasts. Now, this work goes deeply in that ProTalpha receptor description revealing, by different experimental approaches, its presence in lipid rafts. Moreover, our results fit a model in which a tyrosine phosphorylation signalling cascade confined to rafts is initiated upon ProTalpha receptor recognition, which represents an important and promising finding in the research for elucidating the molecular mechanisms underlying the immunomodulatory functions of ProTalpha.

Roles of thymosins in cancers and other organ systems

Thymosins are small peptides, originally identified from the thymus, but now known to be more widely distributed in many tissues and cells. Thymosins are divided into three main groups, alpha-, beta-, : and gamma-thymosins, based on their isoelectric points. alpha-thymosins (ProTalpha, Talphal) have nuclear localization and are involved in transcription and/or DNA replications; whereas beta-thymosins (Tbeta4, Tbeta10, Tbetal5) have cytoplasmic localization and show high affinity to G-actin for cell mobility. Furthermore, it is well known that both alpha- and beta-thymosins play important roles in modulating immune response, vascular biology, and cancer pathogenesis. More importantly, thymosins may have significant clinical applications. They may serve as molecular markers for the diagnosis and prognosis of certain diseases. In addition, they could be molecular targets of certain diseases or be used as therapeutic agents to treat certain diseases. However, the molecular mechanisms of action of thymosins are largely unknown. This review not only presents recent advances of basic science research of thymosins and their clinical applications but provides thoughtful views for future directions of investigation on thymosins.

Identification of receptors for prothymosin alpha on human lymphocytes

Prothymosin alpha (ProTalpha) is a highly conserved and widely distributed protein whose physiological functions remain elusive. In previous work we identified high and low affinity-binding sites for ProTalpha in lymphoid cells. Here we demonstrate, by affinity cross-linking and affinity chromatography, the existence of three binding partners (31, 29, and 19 kDa) for ProTalpha in the membrane of PHA-activated lymphoblasts. These surface molecules possess the expected affinity and specificity for a ProTalpha receptor. Examination of the expression of this complex of molecules by flow cytometry reveals that they bind ProTalpha in a specific and saturable way. In addition, the distribution of the receptor on the cell surface was studied by fluorescence microscopy; a cap-like structure at one of the poles of the cells was identified. These results represent a new and promising approach in the research on ProTalpha, opening the way toward the understanding of the molecular mechanism of action of this protein.

Fifteen years of prothymosin alpha: contradictory past and new horizons

Prothymosin alpha (ProTalpha) is a highly acidic and small protein of only 111 amino acids with an unusual primary structure. One would expected it to play an essential role in the organism, as it has a wide distribution and is high conserved among mammals, yet its exact function remains elusive. Despite the number of effects described for ProTalpha, intracellular and extracellular, none are accepted as its physiological role. Furthermore, many other aspects of its biology still remain obscure. In this review, we discuss the structural properties, location, gene family, functions and immunomodulatory activities of and cellular receptors for ProTalpha. These topics are addressed in an attempt to reconcile opposing outlooks while emphasizing those points where scant investigations do exist. We have also re-evaluated some previous results in light of the structural properties of ProTalpha and have found that molecular mimetism could be the underlying basis. This molecular mimicry hypothesis provides a clue that must not be overlooked for a realistic appraisal of future results.

Prothymosin alpha 1 effects, in vitro, on the antitumor activity and cytokine production of blood monocytes from colorectal tumor patients

Recent animal studies demonstrate that prothymosin alpha 1 (ProT alpha) enhances the antitumor response by stimulation of mononuclear phagocyte functions. The present study was aimed at characterizing the in vitro effects by ProT alpha on blood monocytes from human colon cancer patients. Purified peripheral blood monocytes were studied in terms of tumor cytostatic ability and cytokine production after incubation with ProT alpha or interferon (rIFN-gamma) and transforming growth factor-beta (TGF beta), used as reference substances. SW620 colon carcinoma cells were used as tumor target cells in growth inhibition experiments. The level of baseline growth inhibitory activity of unstimulated patient's monocytes was significantly lower than that of normal monocytes. The defective antitumor activity of patient monocytes was associated with a higher production of the inhibitory monokines prostaglandin E2 (PGE2) and TGF beta. The stimulation of monocytes by ProT alpha and/or rIFN-gamma elevated the average antitumor activity in all donor groups. The ProT alpha-induced increase was associated with a significantly higher monocytic secretion of IL-1 beta and TNF-alpha. Moreover, the concentrations of TGF beta and PGE2 in the culture supernatants decreased significantly, when patient's monocytes were treated with ProT alpha and/or rIFN-gamma. Additionally, ProT alpha enhanced the diminished antitumor activity of TGF beta-treated normal monocytes. These results suggest that ProT alpha selectively regulates distinct functions of blood monocytes, the effect of this cytokine varying with the parameter and donor population examined. These data provide a rational and biological endpoint for further studies with ProT alpha as an activator of mononuclear function in colon cancer.