Prothymosin alpha mRNA levels vary with c-myc expression during tissue proliferation, viral infection and heat shock

Prothymosin α activates type I collagen to develop a fibrotic placenta in gestational diabetes

High-risk pregnancies, such as pregnancies with gestational diabetes mellitus (GDM), are becoming more common and as such, have become important public health issues worldwide. GDM increases the risks of macrosomia, premature infants, and preeclampsia. Although placental dysfunction, including fibrosis is associated with the development of GDM, factors that link these observations remain unknown. Prothymosin α (ProTα) is expressed in the placenta and is involved in cell proliferation and immunomodulation. It also plays an important role in insulin resistance and fibrosis. However, the role of ProTα in GDM is still unclear. In the present study, we found that fibrosis-related protein expressions, such as type I collagen (Col-1) were significantly increased in the placentae of ProTα transgenic mice. With elevated fibrosis-related protein expressions, placental weights significantly increased in GDM group. In addition, placental and circulating ProTα levels were significantly higher in patients with GDM (n=39), compared with the healthy group (n=102), and were positively correlated with Col-1 expression. Mice with streptozotocin (STZ)-induced GDM had increased ProTα, fasting blood glucose, Col-1, and placental weight, whereas plasma insulin levels were decreased. ProTα overexpression enhanced nuclear factor κB (NFκB) activation to increase fibrosis-related protein expressions in 3A-Sub-E trophoblasts, while treatment with an NFκB inhibitor reversed the effect of ProTα on fibrosis-related protein expressions. We further investigated whether ProTα is regulated by hyperglycemia-induced reactive oxygen species (ROS). In conclusion, ProTα increases the amount of placental connective tissue and thus contributes to the pathogenesis of placental fibrosis in GDM. Therefore, ProTα may be a novel therapeutic target for GDM.

Transcription factor-mediated proliferation and apoptosis in benign and malignant thyroid lesions

Transcription factors play an essential role in regulating both cell proliferation and programmed cell death. Proliferation and apoptosis-related transcription factor immunoexpression patterns were concomitantly investigated in tissue sections of normal thyroid, goiters, follicular adenomas and well-differentiated papillary and follicular carcinomas using antibodies against prothymosin alpha, E2F-1, p53, Bcl2, and Bax proteins. Proliferation and apoptotic indices were determined by Ki-67 immunoreactivity and the terminal deoxynucleotidyl transferase-mediated deoxy uridine triphosphate nick-end labeling technique, respectively. Prothymosin alpha and E2F-1 immunoexpression levels were found to be significantly elevated in well-differentiated carcinomas compared to adenomas, goiters and normal tissues (P < 0.05). Both proteins were directly correlated with the proliferation index (P < 0.05). E2F-1 was additionally correlated with the apoptotic index (P < 0.05). The majority of cases were negative for p53 staining. Positive Bcl2 immunostaining was detected in all thyroid histotypes. None of the normal tissues showed Bax immunoreactivity, while positive accumulation differed significantly between hyperplastic and neoplastic histotypes. Direct correlations were observed between prothymosin alpha and Bcl2 as well as between E2F-1 and Bax immunoexpression (P < 0.05). These data demonstrate that prothymosin alpha and E2F-1 are strongly involved in the proliferation processes of thyroid neoplasias. Furthermore, prothymosin alpha may promote cell survival through the Bcl2 anti-apoptotic pathway, while E2F-1-induced apoptosis via p53-independent pathways may be associated with transcriptional activation of bax pro-apoptotic gene.

Macromolecular translocation inhibitor II (Zn(2+)-binding protein, parathymosin) interacts with the glucocorticoid receptor and enhances transcription in vivo

Macromolecular translocation inhibitor II (MTI-II), which was first identified as an in vitro inhibitor of binding between the highly purified glucocorticoid receptor (GR) and isolated nuclei, is an 11.5-kDa Zn(2+)-binding protein that is also known as ZnBP or parathymosin. MTI-II is a small nuclear acidic protein that is highly conserved in rats, cows, and humans and widely distributed in mammalian tissues, yet its physiological function is unknown. To elucidate its in vivo function in relation to GR, we transiently transfected mammalian cells with an expression plasmid encoding MTI-II. Unexpectedly, we found that the expression of MTI-II enhances the transcriptional activity of GR. The magnitude of the transcriptional enhancement induced by MTI-II is comparable with that induced by the steroid receptor coactivator SRC-1. In contrast, MTI-II had little effect on the transcriptional activity of estrogen receptor. Immunoprecipitation analysis showed that in the presence of glucocorticoid hormone, GR coprecipitates with MTI-II, and, vice versa, MTI-II coprecipitates with GR. The expression of various deletion mutants of MTI-II revealed that the central acidic domain is essential for the enhancement of GR-dependent transcription. Microscopic analysis of MTI-II fused to green fluorescent protein and GR fused to red fluorescent protein in living HeLa cells showed that MTI-II colocalizes with GR in discrete subnuclear domains in a hormone-dependent manner. Coexpression of MTI-II with the coactivator SRC-1 or p300 further enhances GR-dependent transcription. Immunoprecipitation analysis showed that in the presence of glucocorticoid hormone, p300 and CREB-binding protein are coprecipitated with MTI-II. Furthermore, the knockdown of endogenous MTI-II by RNAi reduces the transcriptional activity of GR in cells. Moreover, expression of MTI-II enhances the glucocorticoid-dependent transcription of the endogenous glucocorticoid-inducible enzyme in cells. Taken together, these results indicate that MTI-II enhances GR-dependent transcription via a direct interaction with GR in vivo. Thus, MTI-II is a new member of the GR-coactivator complex.

The thymosins. Prothymosin alpha, parathymosin, and beta-thymosins: structure and function

The studies on thymosins were initiated in 1965, when the group of A. White searched for thymic factors responsible for the physiological functions of thymus. To restore thymic functions in thymic-deprived or immunodeprived animals, as well as in humans with primary immuno-deficiency diseases and in immunosuppressed patients, a standardized extract from bovine thymus gland called thymosin fraction 5 was prepared. Thymosin fraction 5 indeed improved immune response. It turned out that thymosin fraction 5 consists of a mixture of small polypeptides. Later on, several of these peptides (polypeptide beta 1, thymosin alpha 1, prothymosin alpha, parathymosin, and thymosin beta 4) were isolated and tested for their biological activity. The research of many groups has indicated that none of the isolated peptides is really a thymic hormone; nevertheless, they are biologically important peptides with diverse intracellular and extracellular functions. Studies on these functions are still in progress. The current status of knowledge of structure and functions of the thymosins is discussed in this review.

Prothymosin alpha functions as a cellular oncoprotein by inducing transformation of rodent fibroblasts in vitro

Prothymosin alpha (ProTalpha), a cellular molecule known to be associated with cell proliferation, is transcriptionally up-regulated on expression of c-myc and interacts with histones in vitro and associates with histone H1 in cells. Previous studies have also shown that ProTalpha is involved in chromatin remodeling. Recent studies have shown that ProTalpha interacts with the acetyl transferase p300 and an essential Epstein-Barr virus protein, EBNA3C, involved in regulation of viral and cellular transcription. These studies suggest a potential involvement in regulation of histone acetylation through the association with these cellular and viral factors. In the current studies, we show that heterologous expression of ProTalpha in the Rat-1 rodent fibroblast cell line results in increased proliferation, loss of contact inhibition, anchorage-independent growth, and decreased serum dependence. These phenotypic changes seen in transfected Rat-1 cells are similar to those observed with a known oncoprotein, Ras, expressed under the control of a heterologous promoter and are characteristic oncogenic growth properties. These results demonstrate that the ProTalpha gene may function as an oncogene when stably expressed in Rat-1 cells and may be an important downstream cellular target for inducers of cellular transformation, which may include Epstein-Barr virus and c-myc.

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.

Modulation of histone acetyltransferase activity through interaction of epstein-barr nuclear antigen 3C with prothymosin alpha

The Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA3C) is essential for EBV-dependent immortalization of human primary B lymphocytes. Genetic analysis indicated that amino acids 365 to 992 are important for EBV-mediated immortalization of B lymphocytes. We demonstrate that this region of EBNA3C critical for immortalization interacts with prothymosin alpha (ProTalpha), a cellular protein previously identified to be important for cell division and proliferation. This interaction maps to a region downstream of amino acid 365 known to be involved in transcription regulation and critical for EBV-mediated transformation of primary B lymphocytes. Additionally, we show that EBNA3C also interacts with p300, a cellular acetyltransferase. This interaction suggests a possible role in regulation of histone acetylation and chromatin remodeling. An increase in histone acetylation was observed in EBV-transformed lymphoblastoid cell lines, which is consistent with increased cellular gene expression. These cells express the entire repertoire of latent nuclear antigens, including EBNA3C. Expression of EBNA3C in cells with increased acetyltransferase activity mediated by the EBV transactivator EBNA2 results in down-modulation of this activity in a dose-responsive manner. The interactions of EBNA3C with ProTalpha and p300 provide new evidence implicating this essential EBV protein EBNA3C in modulating the acetylation of cellular factors, including histones. Hence, EBNA3C plays a critical role in balancing cellular transcriptional events by linking the biological property of mediating inhibition of EBNA2 transcription activation and the observed histone acetyltransferase activity, thereby orchestrating immortalization of EBV-infected cells.

Nuclear distribution of prothymosin alpha and parathymosin: evidence that prothymosin alpha is associated with RNA synthesis processing and parathymosin with early DNA replication

Prothymosin alpha and parathymosin are two ubiquitous small acidic nuclear proteins that are thought to be involved in cell cycle progression, proliferation, and cell differentiation. In an effort to investigate the molecular function of the two proteins, we studied their spatial distribution by indirect immunofluorescence labeling and confocal scanning laser microscopy in relation to nuclear components involved in transcription, translation, and splicing. Results indicate that both proteins exhibit a punctuated nuclear distribution and are excluded by nucleoli. The distribution of prothymosin alpha in the nucleus is related to that of transcription sites, whereas the distribution of parathymosin correlates with early replication sites. This implies that prothymosin alpha and parathymosin are involved in transcription and replication, respectively. In addition to the punctate distribution, prothymosin alpha also is found concentrated in 1-6 nuclear domains per cell. These domains are found in more than 80% of randomly growing T24 human bladder carcinoma cells. They have a diameter of 0.2-2.5 microm, their size being inversely related to the number of domains per cell. The domains disappear during mitosis and the protein is excluded from the metaphase chromosomes. Double-labeling experiments associate these prothymosin alpha domains with PML and CstF64 containing nuclear bodies, but not with hnRNP-I containing domains or coiled bodies.

Prothymosin alpha modulates the interaction of histone H1 with chromatin

Prothymosin alpha (ProTalpha) is an abundant acidic nuclear protein that may be involved in cell proliferation. In our search for its cellular partners, we have recently found that ProTalpha binds to linker histone H1. We now provide further evidence for the physiological relevance of this interaction by immunoisolation of a histone H1-ProTalpha complex from NIH 3T3 cell extracts. A detailed analysis of the interaction between the two proteins suggests contacts between the acidic region of ProTalpha and histone H1. In the context of a physiological chromatin reconstitution reaction, the presence of ProTalpha does not affect incorporation of an amount of histone H1 sufficient to increase the nucleosome repeat length by 20 bp, but prevents association of all further H1. Consistent with this finding, a fraction of histone H1 is released when H1-containing chromatin is challenged with ProTalpha. These results imply at least two different interaction modes of H1 with chromatin, which can be distinguished by their sensitivity to ProTalpha. The properties of ProTalpha suggest a role in fine tuning the stoichiometry and/or mode of interaction of H1 with chromatin.

Prothymosin alpha promotes cell proliferation in NIH3T3 cells

Thymic hormones have immunomodulatory effects on T cells and hence have been used clinically to restore the immunity of immunodeficient patients as well as to enhance the cellular immunity of cancer patients. Prothymosin alpha, which is a member of the thymic hormone family, has recently been suggested to act as a nuclear protein participating in the stimulation of cell proliferation. To characterize the biological activities ofprothymosin alpha in vitro, we established NIH3T3 cell transformants that constitutively express higher prothymosin alpha protein and its mRNA compared with the wild-type counterpart. Cells that overexpressed prothymosin alpha increased the proliferative activity assayed by the [3H]-thymidine incorporation or by the cell cycle analysis with the fluorescent-activated cell sorter. The results provide direct evidence that prothymosin alpha plays a role in cell proliferation by shortening the duration of the G1 phase.

Regulation of prothymosin alpha during the cell cycle

A number of studies have indicated that the small nuclear acidic protein prothymosin alpha is associated with cellular-proliferation events. For example, c-myc causes immediate transcriptional activation of prothymosin alpha, and prothymosin alpha antisense oligonucleotides inhibit myeloma cell division. To investigate the regulation of prothymosin alpha, we examined its mRNA and protein levels during the cell cycle of mononuclear cells and fibroblastic cells. We isolated immunoreactive material from cellular extracts and immunolocalized the protein to the nucleus during the cell cycle. We reported here that the material present in the cells is prothymosin alpha rather than the amino-terminal peptide thymosin alpha 1. [3H]Thymidine-incorporation studies associate maximum accumulation of mRNA and protein with the S/G2 phase of the cell cycle. This induction of prothymosin alpha mRNA seems to resemble cyclin B expression and is more pronounced in fibroblasts. Moreover, transient-transfection experiments indicate that transcription factor E2F is a strong positive regulator of the prothymosin alpha gene. Our results are consistent with the hypothesis that prothymosin alpha is involved in proliferation checkpoints of the cell cycle.