Pituitary tumor-transforming gene protein associates with ribosomal protein S10 and a novel human homologue of DnaJ in testicular cells

aarF domain containing kinase 5 gene promotes invasion and migration of lung cancer cells through ADCK5-SOX9-PTTG1 pathway

AarF domain containing kinase 5 (ADCK5) is a member of an atypical kinase family and overexpressed in many carcinomas including lung cancer, while the function of this protein has not been elucidated. Here we investigated the mechanism of ADCK5 involved in regulating invasion and migration of lung cancer cells, and showed that ADCK5 might regulate the expression of tumor oncogene human pituitary tumor transforming gene-1 (PTTG1) by phosphorylating transcription factor SOX9, therefore enhancing the migration and invasion capabilities of lung cancer cells. Mutagenesis of potential serine phosphorylation sites on SOX9 indicated that serine 181 might be required to maintain transcription activation of SOX9 as well as increase PTTG1 levels. The serine 181 site of SOX9 is in a motif that is targeted by ADCK5. The ADCK5-SOX9-PTTG1 pathway might be a potential therapeutic target for lung cancer.

Protein stabilization by RSUME accounts for PTTG pituitary tumor abundance and oncogenicity

Increased levels of the proto-oncogene pituitary tumor-transforming gene 1 (PTTG) have been repeatedly reported in several human solid tumors, especially in endocrine-related tumors such as pituitary adenomas. Securin PTTG has a critical role in pituitary tumorigenesis. However, the cause of upregulation has not been found yet, despite analyses made at the gene, promoter and mRNA level that show that no mutations, epigenetic modifications or other mechanisms that deregulate its expression may explain its overexpression and action as an oncogene. We describe that high PTTG protein levels are induced by the RWD-containing sumoylation enhancer (RWDD3 or RSUME), a protein originally identified in the same pituitary tumor cell line in which PTTG was also cloned. We demonstrate that PTTG and RSUME have a positive expression correlation in human pituitary adenomas. RSUME increases PTTG protein in pituitary tumor cell lines, prolongs the half-life of PTTG protein and regulates the PTTG induction by estradiol. As a consequence, RSUME enhances PTTG transcription factor and securin activities. PTTG hyperactivity on the cell cycle resulted in recurrent and unequal divisions without cytokinesis, and the consequential appearance of aneuploidies and multinucleated cells in the tumor. RSUME knockdown diminishes securin PTTG and reduces its tumorigenic potential in a xenograft mouse model. Taken together, our findings show that PTTG high protein steady state levels account for PTTG tumor abundance and demonstrate a critical role of RSUME in this process in pituitary tumor cells.

The PTTG1-targeting miRNAs miR-329, miR-300, miR-381, and miR-655 inhibit pituitary tumor cell tumorigenesis and are involved in a p53/PTTG1 regulation feedback loop

Deregulation of the pituitary tumor transforming gene (PTTG1), a newly discovered oncogene, is a hallmark of various malignancies, including pituitary tumors. However, the mechanisms regulating PTTG1 expression are still needed to be explored. MicroRNAs (miRNAs) are a novel class of small RNA molecules that act as posttranscriptional regulators of gene expression and can play a significant role in tumor development. Here, we identified a series of miRNAs, namely, miR-329, miR-300, miR-381 and miR-655, which could target PTTG1 messenger RNA and inhibit its expression. Interestingly, all four miRNAs significantly that are downregulated in pituitary tumors were mapped to the 14q32.31 locus, which acts as a tumor suppressor in several cancers. Functional studies show that the PTTG1-targeting miRNAs inhibit proliferation, migration and invasion but induce apoptosis in GH3 and MMQ cells. Furthermore, overexpression of a PTTG1 expression vector lacking the 3′UTR partially reverses the tumor suppressive effects of these miRNAs. Next, we identified the promoter region of PTTG1-targeting miRNAs with binding sites for p53. In our hands, p53 transcriptionally activated the expression of these miRNAs in pituitary tumor cells. Finally, we found that PTTG1 could inhibit p53 transcriptional activity to the four miRNAs. These data indicate the existence of a feedback loop between PTTG1 targeting miRNAs, PTTG1 and p53 that promotes pituitary tumorigenesis. Together, these findings suggest that these PTTG1-targeting miRNAs are important players in the regulation of pituitary tumorigenesis and that these miRNAs may serve as valuable therapeutic targets for cancer treatment.

The proto-oncogene PBF binds p53 and is associated with prognostic features in colorectal cancer

The PTTG1-binding factor (PBF) is a transforming gene capable of eliciting tumor formation in xenograft models. However, the precise role of PBF in tumorigenesis and its prognostic value as a cancer biomarker remain largely uncharacterised, particularly in malignancies outside the thyroid. Here, we provide the first evidence that PBF represents a promising prognostic marker in colorectal cancer. Examination of a total of 39 patients demonstrated higher PBF expression at both the mRNA (P = 0.009) and protein (P < 0.0001) level in colorectal tumors compared to matched normal tissue. Critically, PBF was most abundant in colorectal tumors associated with Extramural Vascular Invasion (EMVI), increased genetic instability (GI) and somatic TP53 mutations, all features linked with recurrence and poorer patient survival. We further demonstrate by glutathione-S-transferase (GST) pull-down and coimmunoprecipitation that PBF binds to the tumor suppressor protein p53, as well as to p53 mutants (Δ126-132, M133K, V197E, G245D, I255F and R273C) identified in the colorectal tumors. Importantly, overexpression of PBF in colorectal HCT116 cells interfered with the transcriptional activity of p53-responsive genes such as mdm2, p21 and sfn. Diminished p53 stability (> 90%; P < 0.01) was also evident with a concurrent increase in ubiquitinated p53. Human colorectal tumors with wild-type TP53 and high PBF expression also had low p53 protein levels (P < 0.05), further emphasizing a putative interaction between these genes in vivo. Overall, these results demonstrate an emerging role for PBF in colorectal tumorigenesis through regulating p53 activity, with implications for PBF as a prognostic indicator for invasive tumors.

Pituitary-tumour-transforming-gene 1 expression in testicular cancer

Genomic instability is a feature of germ cell tumours. The pituitary-tumour-transforming-gene 1 (PTTG1) is the major effector of chromosome segregation during mitosis, protecting the cell from aneuploidy. The protein expression of this gene has been evaluated in testicular tumours by immunohistochemistry. Formalin-fixed and paraffin-embedded specimens of testicular tissues from 83 patients undergoing therapeutic orchidectomy for seminomas (n = 53), embryonal carcinoma (n = 10), yolk sac tumour (n = 10) and teratoma (n = 10) were examined. Seminoma was associated with in situ carcinoma (CIS) in 23 samples. PTTG1 immunostaining was performed using rabbit anti-PTTG1 as a primary antibody. In CIS, only isolated cells showed nuclear staining for PTTG1. In the peripheral area of seminoma, PTTG1 was mostly detected as localised in the nucleus; in the central area of seminoma, PTTG1 staining was more intense in cytoplasm. PTTG1-positive cells were also present in the areas of seminoma infiltration. On the other hand, in embryonal carcinoma, cells had a diffuse positive immunostaining, mainly cytoplasmatic, while we did not observe an expression of PTTG1 in yolk sac tumour and mature teratoma. We firstly identified the PTTG1 expression pattern in normal testis, CIS and testicular cancer. Further investigation is needed to clarify the functional activity of PTTG1 in testicular oncogenesis.

The pituitary tumor transforming gene in thyroid cancer

The pituitary tumor transforming gene (PTTG) is a multifunctional proto-oncogene that is over-expressed in various tumors including thyroid carcinomas, where it is a prognostic indicator of tumor recurrence. PTTG has potent transforming capabilities in vitro and in vivo, and many studies have investigated the potential mechanisms by which PTTG contributes to tumorigenesis. As the human securin, PTTG is involved in critical mechanisms of cell cycle regulation, whereby aberrant expression induces aneuploidy. PTTG may further contribute to tumorigenesis through its role in DNA damage response pathways and via complex interactions with hormones and growth factors. Furthermore, PTTG over-expression negatively impacts upon the efficacy of radioiodine therapy in thyroid cancer, through repression of expression and function of the sodium iodide symporter. Given its various roles at all disease stages, PTTG appears to be an important oncogene in thyroid cancer. This review discusses the current knowledge of PTTG with particular focus on its role in thyroid cancer.

Pituitary tumor-transforming gene and its binding factor in endocrine cancer

The pituitary tumor-transforming gene (PTTG1) encodes a multifunctional protein (PTTG) that is overexpressed in numerous tumours, including pituitary, thyroid, breast and ovarian carcinomas. PTTG induces cellular transformation in vitro and tumourigenesis in vivo, and several mechanisms by which PTTG contributes to tumourigenesis have been investigated. Also known as the human securin, PTTG is involved in cell cycle regulation, controlling the segregation of sister chromatids during mitosis. This review outlines current information regarding PTTG structure, expression, regulation and function in the pathogenesis of neoplasia. Recent progress concerning the use of PTTG as a prognostic marker or therapeutic target will be considered. In addition, the PTTG binding factor (PBF), identified through its interaction with PTTG, has also been established as a proto-oncogene that is upregulated in several cancers. Current knowledge regarding PBF is outlined and its role both independently and alongside PTTG in endocrine and related cancers is discussed.

PTTG: an important target gene for ovarian cancer therapy

Pituitary tumor transforming gene (PTTG), also known as securin is an important gene involved in many biological functions including inhibition of sister chromatid separation, DNA repair, organ development, and expression and secretion of angiogenic and metastatic factors. Proliferating cancer cells and most tumors express high levels of PTTG. Overexpression of PTTG in vitro induces cellular transformation and development of tumors in nude mice. The PTTG expression levels have been correlated with tumor progression, invasion, and metastasis. Recent studies show that down regulation of PTTG in tumor cell lines and tumors in vivo results in suppression of tumor growth, suggesting its important role in tumorigenesis. In this review, we focus on PTTG structure, sub-cellular distribution, cellular functions, and role in tumor progression with suggestions on possible exploration of this gene for cancer therapy.

Pituitary tumor transforming gene 1 regulates Aurora kinase A activity

Pituitary tumor transforming gene 1 (PTTG1), a transforming gene highly expressed in several cancers, is a mammalian securin protein regulating both G1/S and G2/M phases. Using protein array screening, we showed PTTG1 interacting with Aurora kinase A (Aurora-A), and confirmed the interaction using co-immunoprecipitation, His-tagged pull-down assays and intracellular immunofluorescence colocalization. PTTG1 transfection into HCT116 cells prevented Aurora-A T288 autophosphorylation, inhibited phosphorylation of the histone H3 Aurora-A substrate and resulted in abnormally condensed chromatin. PTTG1-null cell proliferation was more sensitive to Aurora-A knock down and to Aurora kinase Inhibitor III treatment. The results indicate that PTTG1 and Aurora-A interact to regulate cellular responses to anti-neoplastic drugs. PTTG1 knockdown is therefore a potential approach to improve the efficacy of tumor Aurora kinase inhibitors.

Pituitary tumor-transforming gene: physiology and implications for tumorigenesis

Pituitary tumor-transforming gene-1 (PTTG1) is overexpressed in a variety of endocrine-related tumors, especially pituitary, thyroid, breast, ovarian, and uterine tumors, as well as nonendocrine-related cancers involving the central nervous, pulmonary, and gastrointestinal systems. Forced PTTG1 expression induces cell transformation in vitro and tumor formation in nude mice. In some tumors, high PTTG1 levels correlate with invasiveness, and PTTG1 has been identified as a key signature gene associated with tumor metastasis. Increasing evidence supports a multifunctional role of PTTG1 in cell physiology and tumorigenesis. Physiological PTTG1 properties include securin activity, DNA damage/repair regulation and involvement in organ development and metabolism. Tumorigenic mechanisms for PTTG1 action involve cell transformation and aneuploidy, apoptosis, and tumorigenic microenvironment feedback. This paper reviews recent advances in our understanding of PTTG1 structure and regulation and addresses known mechanisms of PTTG1 action. Recent knowledge gained from PTTG1-null mouse models and transgenic animals and their potential application to subcellular therapeutic targeting PTTG1 are discussed.

Identification of a heat-shock protein Hsp40, DjB1, as an acrosome- and a tail-associated component in rodent spermatozoa

Iba1 is a 17-kDa EF-hand protein highly expressed in the cytoplasm of elongating spermatids in testis. Using Iba1 as a bait, we performed yeast Two-hybrid screening and isolated a heat-shock protein Hsp40, DjB1, from cDNA library of mouse testis. To characterize DjB1 that is encoded by Dnajb1 gene, we carried out immunoblot analyses, in situ hybridization, and immunohistochemistry. Immunoblot analyses showed that DjB1was constitutively expressed in mouse testis and that its expression level was not changed by heat shock. Dnajb1 mRNA was exclusively expressed in spermatocytes and round spermatids in mouse testis, and Dnajb1 protein DjB1 was predominantly expressed in the cytoplasm of spermatocytes, round spermatids, and elongating spermatids. In mature mouse spermatozoa, DjB1 was localized in the middle and the end pieces of flagella as well as in association with the head (acrosomal region). Association of DjB1 with the acrosomal region in sperm head was also observed in rat spermatozoa. These data suggested that DjB1, which was constitutively expressed in postmeiotic spermatogenic cells in testis, was integrated into spermatozoa as at least two components, that is, sperm head and tail of rodent spermatozoa.

Differential prioritization between relevance and redundancy in correlation-based feature selection techniques for multiclass gene expression data

Background

Due to the large number of genes in a typical microarray dataset, feature selection looks set to play an important role in reducing noise and computational cost in gene expression-based tissue classification while improving accuracy at the same time. Surprisingly, this does not appear to be the case for all multiclass microarray datasets. The reason is that many feature selection techniques applied on microarray datasets are either rank-based and hence do not take into account correlations between genes, or are wrapper-based, which require high computational cost, and often yield difficult-to-reproduce results. In studies where correlations between genes are considered, attempts to establish the merit of the proposed techniques are hampered by evaluation procedures which are less than meticulous, resulting in overly optimistic estimates of accuracy.

Results

We present two realistically evaluated correlation-based feature selection techniques which incorporate, in addition to the two existing criteria involved in forming a predictor set (relevance and redundancy), a third criterion called the degree of differential prioritization (DDP). DDP functions as a parameter to strike the balance between relevance and redundancy, providing our techniques with the novel ability to differentially prioritize the optimization of relevance against redundancy (and vice versa). This ability proves useful in producing optimal classification accuracy while using reasonably small predictor set sizes for nine well-known multiclass microarray datasets.

Conclusion

For multiclass microarray datasets, especially the GCM and NCI60 datasets, DDP enables our filter-based techniques to produce accuracies better than those reported in previous studies which employed similarly realistic evaluation procedures.

Genes associated with the formation of germ cells from embryonic stem cells in cultures containing different glucose concentrations

In a previous study, we established a system for visualizing the development of germ cells from mouse embryonic stem (ES) cells in culture using knock-in ES clones in which visual reporter genes were expressed from the mouse vasa homolog, Mvh. While assessing various culture conditions, we found that germ-cell formation was markedly depressed in low glucose medium. Using a repeated polymerase chain reaction (PCR) subtraction method, we identified genes that were differentially expressed in low versus high glucose media. Three genes that were predominantly expressed in high glucose medium, thioredoxin-interacting protein (Txnip), pituitary tumor-transforming gene 1 (Pttg), and RuvB-like protein 2 (RuvBl2), were further investigated. These genes were also found to be highly expressed in adult and embryonic gonads, and RuvBl2 in particular, which encodes an ATP-dependent DNA helicase, was specifically detected in the spermatocytes and spermatids of the adult testis as well as in primordial germ cells. Furthermore, using a green fluorescent protein (GFP) fusion construct, we found that RuvBl2 was expressed in both the nucleus and cytoplasm of testicular germ cells. These findings suggest a possible relationship between glucose metabolism and germ-cell development.

Detection of msj-1 gene expression in the frog, Rana esculenta testis, brain, and spinal cord

MSJ-1 is member of the DnaJ/heat shock protein (Hsp) 40 chaperone protein family. It is present in mouse testis and spinal cord. In particular, MSJ-1 is localized in post-meiotic cells and in motoneurones of the ventral horns. To assess whether the role of this protein is evolutionarily conserved, we have investigated if msj-1 gene is expressed in the frog, Rana esculenta. Using reverse transcription-polymerase chain reaction (RT-PCR), a msj-1-like transcript was detected in testis, brain, and spinal cord. Homology ranging from 42.3 to 46.0% was found as compared with the mammalian counterparts. Muscle did not show any signal. By Western blot analysis, a signal of the predicted size of 30 kDa was evidenced in testis, brain, and spinal cord but not in ovary, heart, liver, kidney, and muscle. MSJ-1 fluctuations in the testis reveal that it appeared in concomitance with post-meiotic events during the annual sexual cycle, as shown in a previous study. The protein is localized in spermatids and is still retained in mature spermatozoa, where it has perinuclear and centriolar localization. MSJ-1 levels did not change in brain and spinal cord. Furthermore, in the brain MSJ-1 was mainly present in diencephalon and mesencephalon, while in spinal cord MSJ-1 was localized into several motoneurones of the cervical and thoracic tract. A putative role in vesicle trafficking is briefly discussed.

Human pituitary tumor transforming gene (hPTTG) inhibits human lung cancer A549 cell growth through activation of p21(WAF1/CIP1 )

Pituitary tumor transforming gene (PTTG) is a proto-oncogene cloned from rat GH4 cells. This gene was able to induce cell transformation in vitro and is also associated with p53-dependent and -independent apoptosis. In this study, we cloned human PTTG (hPTTG) from a pituitary tumor and then stably transfected the hPTTG into HeLa and A549 cells. An overexpression of hPTTG significantly inhibited cell growth, which was determined by the adherent cell growth properties, colony formation in soft agar and [3H] thymidine incorporation, respectively, in HeLa and A549 cells. The inhibitory effect on cell growth was associated with the activation of p21WAF1/CIP1 in A549 cells, but not in HeLa cells. The hPTTG overexpression increased both the p21WAF1/CIP1 mRNA and protein expression levels as determined by both Northern and Western blot analysis, respectively, in A549 cells. The increased expression of p21WAF1/CIP1 mRNA was regulated at the transcription level and was independent on p53 expression because the luciferase activity increased after the co-transfection of hPTTG and p21WAF1/CIP1 promoter fragments with and without a p53 binding sequence. The subcellular distribution of hPTTG was dependent on cell type, and was predominantly in the nucleus in HeLa, Cos-7 and DU145 cells, but showed a diffuse distribution in both the nucleus and cytoplasm in A549, DLD-1 and NIH3T3 cells. These results indicate that an overexpression of hPTTG inhibits the cell growth due to different mechanisms, which are p21WAF1/CIP1 -dependent and -independent.

Expression of PTTG and c-myc gene in human primary hepatocellular carcinoma

AIM

To investigate the relationship between expressions of PTTG and c-myc genes and oncogenesis in human hepatocellular carcinomas(HCC).

METHODS

In situ hybridization (DNA-RNA) and immunohistochemistry (SP method) methods were used to detect the expressions of PTTG and c-myc genes in 61 cases of human hepatocellular carcinomas.

RESULTS

The distributions of positive cells of PTTG mRNA and PTTG protein in HCC were diffuse, aggregate or scattered. The positive stainings of PTTG mRNA and PTTG protein were plasma and submembrane types. The positive rates of PTTG mRNA and PTTG protein were 72.1% (44/61) and 78.7% (48/61) in HCC, and 93.4% (57/61) and 91.8% (56/61) in pericarcinomatous liver tissues. The expressions of PTTG mRNA and PTTG protein in HCC were significantly lower than those in paracancerous tissues (P<0.005, P<0.05). The expression of PTTG gene was significantly correlated with that of c-myc gene (P<0.005).

CONCLUSION

Overexpression of PTTG is related to human hepatocellular carcinogenesis. C-myc gene activated by PTTG protein may play an important role in hepatocellular transformation and carcinogenesis.

Characterization of two isoforms of a human DnaJ homologue, HSJ2

Two cDNA forms were characterized for a human dnaJ homologue, HSJ2. Nucleotide sequencing showed that the gene product HSJ2 was longer than previously reported, extending its homology to other human DnaJ paralogues, and that the two cDNAs encoded two proteins as a result of alternative splicing. The products were 326 amino acids (designated as HSJ2a) and 241 amino acids (HSJ2b) in length, sharing the N-terminal 231 amino acids including the DnaJ homology region. When fused to green fluorescent protein and expressed in HeLa cells, HSJ2a was found to be localized to the nucleus, indicating that HSJ2a is a nuclear co-chaperone. HSJ2b, however, was observed throughout the cell, consistent with the elimination of a putative nuclear localization signal sequence as a result of the alternative splicing.

Identification of mRNAs that are up-regulated after fertilization in the murine zygote by suppression subtractive hybridization

Transcriptions occur in mouse preimplantation embryos as early as one-cell stage. However, our understanding on gene expression at this stage is lacking. The present study applied suppression subtractive hybridization (SSH) to compared gene expression profiles of mouse zygote and oocyte. Forty-four differentially expressed genes were selected and shown positive signals by reverse dot-blot hybridization. DNA sequences comparison of these putative clones with the GenBank/EMBL databases using BLAST search identified 38 clones with >90% identity to known genes and six novel clones with less than 70% homology to the databases. Eleven out of the 44 differentially expressed clones were either originally isolated from male embryo or testis-specific genes, suggesting that these genes may be derived from paternal genome. Five differentially expressed genes of interest, including bromodomain-containing protein BP75, spindlin, radixin, pituitary tumor-transforming gene (PTTG), and proteoglycan core protein (serglycin) were further studied by semi-quantitative RT-PCR. It is noted that spindlin which involves in cell division is highly expressed in zygote, suggesting that this protein may play an important role in zygotic gene activation (ZGA) and early stage development in 1-cell stage mouse embryos.

Characterization of a polyclonal antibody to human pituitary tumor transforming gene 1 (PTTG1) protein

Pituitary tumor transforming gene 1 (PTTG1), recently cloned from human testis, is a potent oncogene that is expressed in most tumors. However, assessment of its potential value as a prognostic marker is dependent on the development of a suitable antibody. We have developed a rabbit polyclonal antibody, SK601, that is highly specific for the PTTG1 gene product using recombinant PTTG1 protein (24 kD) containing an N-terminal His(6) tag as the immunogen. The antiserum is capable of detecting recombinant PTTG1 protein in ELISA assays at a titer of 1:100,000. Use of the antibody as the probe in Western blotting analyses revealed a single band with the anticipated relative molecular weights of 52 kD from E. coli expressing the GST-PTTG1 recombinant protein, and 56 kD from COS-7 cells transfected with the PTTG1-GFP chimeric construct. A single band with a relative molecular weight of 28 kD was observed in extract of COS-7 cells transfected with PTTG1 cDNA. The antiserum immunoprecipitated a protein of relative molecular weight of 56 kD from the extracts of COS-7 cells transfected with the PTTG1-GFP chimeric construct. Immunohistochemical analysis of COS-7 cells transfected with this construct confirmed that the antibody detected and was specific for expressing the PTTG1-GFP recombinant protein. Screening of various normal human tissues (testis, ovary, and breast) by immunohistochemistry indicated that these tissues did not exhibit staining with the exception of testis, a tissue that had previously been shown to express PTTG1 mRNA. In contrast all of the tumor tissues (testicular tumor, ovarian tumor, and breast tumor) that were assessed exhibited intense staining. The results suggest that antiserum SK601 is highly specific for the PTTG1 protein and therefore should prove useful in further analysis of the expression and interactions of this protein, including its potential application as an immunohistochemical marker of human tumors.

MSJ-1, a mouse testis-specific DnaJ protein, is highly expressed in haploid male germ cells and interacts with the testis-specific heat shock protein Hsp70-2

The MSJ-1 gene encodes a murine DnaJ homologue that is expressed specifically in adult testis. DnaJ proteins act as cochaperones of Hsp70 proteins in promoting diverse cellular functions. In this study we used recombinant MSJ-1 proteins to produce MSJ-1 antiserum and to carry out in vitro binding assays. In a wide immunoscreening of mouse tissues, affinity-purified MSJ-1 antibodies recognize a unique protein of 30 kDa in male germ cells only. MSJ-1 is able to interact with the testis-specific Hsp70-2 protein and can be coimmunoprecipitated with Hsp70-2 from spermatogenic cells; binding of these two chaperones is consistent with the presence of a third component, which is so far unknown. MSJ-1 is weakly detected in early round spermatids, and its protein content increases in cytodifferentiating spermatids where it colocalizes with the developing acrosome and their postnuclear region. Hsp70-2, which is known to be highly expressed in meiotic cells, shows a subcellular localization in late differentiating spermatids that overlaps that of MSJ-1. MSJ-1 is also maintained in testicular and epididymal spermatozoa, where it sharply demarcates into two distinct cell areas; the outer surface of the acrosomal vesicle, and the centrosomal area. On the whole, our findings are consistent with a role for MSJ-1 in acrosome formation and centrosome adjustment during spermatid development, whereas its presence in mature spermatozoa suggests a special function during fertilization, shortly afterward, or both.

Cloning and expression of murine Hsp40 gene: differences in initiation sites between heat-induced and constitutive transcripts

We have isolated cDNA and genomic clones of murine Hsp40 (mmDjB1). The murine Hsp40 gene was expressed at a high level in testis and was induced by heat shock. The transcriptional initiation sites were different between heat-induced transcripts and constitutive ones. The heat-induced transcripts initiated 22 to 28 bp downstream of the TATA box, whereas constitutive transcripts initiated from multiple sites, many of which initiated upstream of the TATA box. To our knowledge, this is the first report on the heat shock-dependent usage of transcriptional start sites of a heat shock gene.

Identification of c-myc as a down-stream target for pituitary tumor-transforming gene

Pituitary tumor-transforming gene (PTTG) encodes a protein implicated in cellular transformation and transcriptional regulation. To identify downstream target genes, I established cell lines with tightly regulated inducible expression of PTTG. DNA arrays were used to analyze gene expression profiles after PTTG induction. I identified c-myc oncogene as a major PTTG target. Induction of PTTG resulted in increased cell proliferation through activation of c-myc. I showed that PTTG activates c-myc transcription in transfected cells. PTTG binds to c-myc promoter near the transcription initiation site in a protein complex containing the upstream stimulatory factor (USF1). I have defined the PTTG DNA-binding site and mapped PTTG DNA binding domain to a region between amino acids 61 and 118. Furthermore, I demonstrated that PTTG DNA binding is required for its transcriptional activation function. These results definitively established the role of PTTG as a transcription activator and indicate that PTTG is involved in cellular transformation and tumorigenesis through activation of c-myc oncogene.

Molecular cloning of pituitary tumor transforming gene 1 from ovarian tumors and its expression in tumors

Pituitary tumor transforming gene 1 (PTTG1) recently cloned from human testis is a potent oncogene and is highly expressed in all the tumors analyzed to date. However, primary structure of PTTG1 and the cell types that express PTTG1 in tumors remained undescribed. We have used the reverse transcriptase-polymerase chain reaction technique to clone PTTG1 from ovarian tumors. Nucleotide sequencing of the PTTG1 cDNAs from various ovarian tumors showed identity with that of the human testis PTTG1. To determine the cell types that express PTTG1 in normal and tumor tissues, we performed in situ hybridization using digoxigenin-labeled cRNA as a probe. Our studies revealed a high level of expression of PTTG1 mRNA in both seminomatous and non-seminomatous testicular tumors; epithelial, sex-cord and stromal cell, and germ cell tumors of the ovary; and invasive ductal, ductal in situ and infiltrating ductal carcinoma of the breast. In normal tissues, expression of PTTG1 mRNA was very low or undetectable except in testis, where PTTG1 mRNA was found to be localized to spermatocytes and spermatids. Tumors that expressed high levels of PTTG1 mRNA also exhibited high levels of expression of basic fibroblast growth factor (bFGF), suggesting a correlation between PTTG1 and bFGF expression, and further suggesting that the PTTG1 protein may be involved in tumor angiogenesis and mitogenesis.

Activation of mitogen-activated protein kinase cascade regulates pituitary tumor-transforming gene transactivation function

Pituitary tumor-transforming gene (PTTG) is a recently characterized oncogene that can act as a transcriptional activator. In this study, we have characterized the transactivation domain of PTTG. Transient transfection of fusion constructs containing GAL4 DNA-binding domain and different parts of PTTG indicated the transactivation domain of PTTG is located between amino acids 119 and 164. Mitogen-activated protein (MAP) kinase cascade is important in the regulation of cell growth, apoptosis, and differentiation. Therefore, we have explored the possibility that this kinase cascade plays a role in regulating PTTG transactivation function. Activation of the MAP kinase cascade by epidermal growth factor or an expression vector for a constitutively active form of the MAP kinase kinase (MEK1) led to stimulation of PTTG transactivation activity. We showed that PTTG is phosphorylated in vitro on Ser(162) by MAP kinase and that this phosphorylation site plays an essential role in PTTG transactivation function. We demonstrated that PTTG interacts directly with MEK1 through a putative SH3 domain-binding site located between amino acids 51 and 54 and that this interaction is crucial for PTTG transactivation function. In addition, we showed that activation of MAP kinase phosphorylation cascade resulted in nuclear translocation of PTTG. Together, our data establish that a growth factor-stimulated MAP kinase plays an important role in modulating PTTG function.

A novel binding factor facilitates nuclear translocation and transcriptional activation function of the pituitary tumor-transforming gene product

Pituitary tumor-transforming gene (PTTG) is a recently characterized oncogene whose expression product contains a transcriptional activation domain at the C terminus. To understand the mechanisms involved in PTTG biological functions, we used yeast two-hybrid screening to identify proteins that interact with PTTG. This study reports the isolation and characterization of a novel PTTG-binding factor (PBF). PBF contains an open reading frame of 179 amino acids with a predicted molecular mass of 22 kDa. In Northern blot analyses, PBF mRNA was ubiquitously expressed in human tissues. Glutathione S-transferase pull-down and co-immunoprecipitation assays demonstrate that PBF interacts specifically with PTTG under both in vitro and in vivo conditions. The PTTG binding domain in PBF was located within the C-terminal 30-amino acid region that contain a nuclear localization signal. Immunofluorescence and subcellular fractionation studies showed that PTTG is predominantly expressed in the cytoplasm with partial nuclear localization, whereas PBF is localized both in the cytoplasm and the nucleus. The interaction between PBF and PTTG facilitated PTTG translocation from the cytoplasm to the nucleus. Furthermore, PBF is required for transcriptional activation of basic fibroblast growth factor by PTTG. In summary, we have characterized a novel PTTG-binding protein that facilitates PTTG nuclear translocation and potentiates its transcriptional activation function.

Down-regulated RPS3a/nbl expression during retinoid-induced differentiation of HL-60 cells: a close association with diminished susceptibility to actinomycin D-stimulated apoptosis

The efficacy of anticancer agents significantly depends on the differential susceptibility of undifferentiated cancer cells and differentiated normal cells to undergo apoptosis. We previously found that enhanced expression of RPS3a/nbl, which apparently encodes a ribosomal protein, seems to prime cells for apoptosis, while suppressing such enhanced expression triggers cell death. The present study found that HL-60 cells induced to differentiate by all-trans retinoic acid did not undergo apoptosis following treatment with actinomycin D whereas undifferentiated HL-60 cells were highly apoptosis-susceptible, confirming earlier suggestions that differentiated cells have diminished apoptosis-susceptibility. Undifferentiated HL-60 cells highly expressed RPS3a/nbl whereas all-trans retinoic acid -induced differentiated cells exhibited markedly reduced levels, suggesting that apoptosis-resistance of differentiated cells could be due to low RPS3a/nbl expression. Down-regulation of enhanced RPS3a/nbl expression was also observed in cells induced to differentiate with the retinoid 4-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-napthalenyl)-1- propenyl]benzoic acid without any significant induction of cell death. While down-regulation of RPS3a/nbl expression during differentiation did not apparently induce apoptosis, RPS3a/nbl antisense oligomers triggered death of undifferentiated HL-60 cells, but not of retinoid-induced differentiated cells. It therefore seems that while down-regulation of enhanced RPS3a/nbl expression can induce apoptosis in undifferentiated cells, down-regulation of enhanced RPS3a/nbl expression during differentiation occurs independently of apoptosis, and could be regarded as reverting the primed condition to the unprimed (low RPS3a/nbl) state.

Mammalian HSP40/DNAJ homologs: cloning of novel cDNAs and a proposal for their classification and nomenclature

We have cloned 10 novel full-length cDNAs of mouse and human HSP40/DNAJ homologs using expressed sequence tag (EST) clones found in the DDBJ/GenBank/EMBL DNA database. In this report, we tentatively designated them mHsp40, mDj3, mDj4, mDj5, mDj6, mDj7, mDj8, hDj9, mDj10, and mDj11. Based on the identity of the deduced amino acid sequences, mHsp40, mDj3, and mDj11 are orthologs of human Hsp40, rat Rdj2, and human Tpr2, respectively. We determined that mDj4 is identical with the recently isolated mouse Mrj (mammalian relative of DnaJ). PSORT analysis (a program that predicts the subcellular localization site of a given protein from its amino acid sequences) revealed that hDj9 has an N-terminal signal peptide; hence, its localization might be extracellular, suggesting that there may be a partner Hsp70 protein that acts together with the hDj9 outside of the cell. The same analysis indicated that mDj7 and mDj10 may have transmembrane domains. In order to simplify the complicated and confusing nomenclature of recently identified mammalian HSP40/DNAJ homologs, we propose here some new rules for their nomenclature. This proposed nomenclature includes the name of species with 2 lowercase letters such as hs (Homo sapiens), mm (Mus musculus) and rn (Rattus norvegicus); Dj standing for DnaJ; the name of types with A, B, and C, which were previously classified as type I, II, and III according to the domain structure of the homologs; and finally Arabic numerals according to the chronological order of registration of the sequence data into the database.

Cell cycle regulated expression and phosphorylation of hpttg proto-oncogene product

We recently isolated a cDNA for hpttg, the human homolog of rat pituitary tumor transforming gene. Now we have analysed the expression of hpttg as a function of cell proliferation. hPTTG protein level is up-regulated in rapidly proliferating cells, is down-regulated in response to serum starvation or cell confluence, and is regulated in a cell cycle-dependent manner, peaking in mitosis. In addition, we show that hPTTG is phosphorylated during mitosis. Immunodepletion and in vitro phosphorylation experiments, together with the use of a specific inhibitor, indicate that Cdc2 is the kinase that phosphorylates hPTTG. These results suggest that hpttg is induced by, and may have a role in, regulatory pathways involved in the control of cell proliferation.

Hsc40, a new member of the hsp40 family, exhibits similar expression profile to that of hsc70 in mammalian cells

Here, we report the identification and characterization of a new hsp40 family member, heat shock cognate 40 (hsc40), which may be a specific functional partner for hsc70. The hsc40 gene consists of five exons and four introns. The previously characterized hsp40 gene contains only three exons and two introns. Despite this difference in the numbers of exons and introns, the structures of these two genes are actually quite similar. If the first two exons and introns of the hsc40 gene are excluded, the rest is essentially the same as the whole hsp40 gene. The intron/exon boundaries of the hsc40 and hsp40 genes are conserved with respect to amino acid coding, indicating that the hsp40 gene might have arisen from a duplicated hsc40 gene, which developed a new transcription-regulatory mechanism in the second intron. Hsc40 is evolutionally conserved. There is over 95% sequence identity between the putative mouse and human hsc40 proteins. However, there is only 60% sequence identity between the hsc40 and hsp40 proteins from either human or mouse cells. Northern blot analysis of various tissues and cells in culture revealed that this gene was expressed under normal conditions, and its expression was further increased after various stress treatments. The expression pattern of the hsc40 gene is very similar to that of the hsc70 gene under both normal and stress conditions, whereas the hsp40 gene exhibited an expression pattern more similar to that of hsp70 genes on the same Northern blots. These results, considered along with the high rate of sequence conservation between the same proteins from different species and high rate of variation between the two different proteins from the same species, strongly suggest that hsc40 and hsp40 may perform different functions and/or have different specificities in the cell.