Cloning and characterization of TDD5, an androgen target gene that is differentially repressed by testosterone and dihydrotestosterone

Species differences in hormonally mediated gene expression underlie the evolutionary loss of sexually dimorphic coloration in Sceloporus lizards

Phenotypic sexual dimorphism often involves the hormonal regulation of sex-biased expression for underlying genes. However, it is generally unknown whether the evolution of hormonally mediated sexual dimorphism occurs through upstream changes in tissue sensitivity to hormone signals, downstream changes in responsiveness of target genes, or both. Here, we use comparative transcriptomics to explore these possibilities in 2 species of Sceloporus lizards exhibiting different patterns of sexual dichromatism. Sexually dimorphic S. undulatus develops blue and black ventral coloration in response to testosterone, while sexually monomorphic S. virgatus does not, despite exhibiting similar sex differences in circulating testosterone levels. We administered testosterone implants to juveniles of each species and used RNAseq to quantify gene expression in ventral skin. Transcriptome-wide responses to testosterone were stronger in S. undulatus than in S. virgatus, suggesting species differences in tissue sensitivity to this hormone signal. Species differences in the expression of genes for androgen metabolism and sex hormone-binding globulin were consistent with this idea, but expression of the androgen receptor gene was higher in S. virgatus, complicating this interpretation. Downstream of androgen signaling, we found clear species differences in hormonal responsiveness of genes related to melanin synthesis, which were upregulated by testosterone in S. undulatus, but not in S. virgatus. Collectively, our results indicate that hormonal regulation of melanin synthesis pathways contributes to the development of sexual dimorphism in S. undulatus, and that changes in the hormonal responsiveness of these genes in S. virgatus contribute to the evolutionary loss of ventral coloration.

Crystal and solution structure of NDRG1, a membrane-binding protein linked to myelination and tumour suppression

N-myc downstream-regulated gene 1 (NDRG1) is a tumour suppressor involved in vesicular trafficking and stress response. NDRG1 participates in peripheral nerve myelination, and mutations in the NDRG1 gene lead to Charcot-Marie-Tooth neuropathy. The 43-kDa NDRG1 is considered as an inactive member of the α/β hydrolase superfamily. In addition to a central α/β hydrolase fold domain, NDRG1 consists of a short N terminus and a C-terminal region with three 10-residue repeats. We determined the crystal structure of the α/β hydrolase domain of human NDRG1 and characterised the structure and dynamics of full-length NDRG1. The structure of the α/β hydrolase domain resembles the canonical α/β hydrolase fold with a central β sheet surrounded by α helices. Small-angle X-ray scattering and CD spectroscopy indicated a variable conformation for the N- and C-terminal regions. NDRG1 binds to various types of lipid vesicles, and the conformation of the C-terminal region is modulated upon lipid interaction. Intriguingly, NDRG1 interacts with metal ions, such as nickel, but is prone to aggregation in their presence. Our results uncover the structural and dynamic features of NDRG1, as well as elucidate its interactions with metals and lipids, and encourage studies to identify a putative hydrolase activity of NDRG1. DATABASES: The coordinates and structure factors for the crystal structure of human NDRG1 were deposited to PDB (PDB ID: 6ZMM).

Identification of candidate genes in regulation of spermatogenesis in sheep testis following dietary vitamin E supplementation

Dietary vitamin E supplementation is beneficial to semen quality in different sheep and goat breeds. The aim of this research was to further investigate the effect of vitamin E in sheep on spermatogenesis and its regulatory mechanisms using RNA-seq. Thirty male Hu lambs were randomly divided into three groups. The animals received 0, 200 or 2000 IU/day vitamin E dietary supplementation for 105 days, and its effects were subsequently evaluated. The results indicate vitamin E supplementation increased the number of germ cells in the testes and epididymides. The positive effects were reduced, however, in animals that received 2000 IU/d vitamin E. Using the RNA-seq procedure, there was detection of a number of differentially expressed genes such as NDRG1, FSCN3 and CYP26B1 with these genes being mainly related to the regulation of spermatogenesis. Supplementation with 2000 IU/d vitamin E supplementation resulted in a lesser abundance of skeleton-related transcripts such as TUBB, VIM and different subtypes of collagen, and there was also an effect on the ECM-receptor interaction pathway. These changes appear to be responsible for the lesser beneficial effect of the greater vitamin E concentrations. The results provide a novel insight into the regulation of spermatogenesis by vitamin E at the molecular level, however, for a precise understanding of functions of the affected genes there needs to be further study.

Overexpression of N-myc downstream-regulated gene 1 inhibits human glioma proliferation and invasion via phosphoinositide 3-kinase/AKT pathways

N-myc downstream-regulated gene 1 (NDRG1) was previously shown to exhibit low expression in glioma tissue as compared with that in normal brain tissue; however, the role of NDRG1 in human glioma cells has remained to be elucidated. The present study used the U87 MG and SHG-44 human glioma cell lines as well as the normal human astrocyte cell line 1800, which are known to have differential NDRG1 expression. Small interfering (si)RNA targeting NDRG1, and NDRG1 overexpression vectors were transfected into the SHG-44 and U87 MG glioma cells, respectively. Cell proliferation, invasion, apoptosis and cell cycle arrest were subsequently examined by MTT assay, transwell chamber assay, flow cytometry and western blot analysis, respectively. Furthermore, a subcutaneous tumor mouse model was used to investigate the effects of NDRG1 on the growth of glioma cells in vivo. Overexpression of NDRG1 was shown to inhibit cell proliferation and invasion, and induce apoptosis in the U87 MG glioma cells, whereas NDRG1 downregulation increased proliferation, suppressed apoptosis and promoted invasion of the SHG-44 glioma cells. In addition, in the subcutaneous tumor mouse model, overexpression of NDRG1 in U-87 MG cells suppressed tumorigenicity in vivo. The findings of the present study indicated that NDRG1 is required for the inhibition of gliomagenesis; therefore, targeting NDRG1 and its downstream targets may represent novel therapies for the treatment of glioma.

Improving intermittent androgen deprivation therapy: lessons learned from basic and translational research

Intermittent androgen deprivation therapy (IADT) is an alternative to continuous androgen deprivation therapy (ADT) in prostate cancer patients with nonmetastatic disease. ADT is associated with numerous side effects such as hot flashes, sexual dysfunction, anemia, fatigue, loss of muscle mass, osteoporosis, metabolic syndrome and premature cardiovascular disease. IADT was developed with the intention of improving the quality of life and to delay progression of prostate cancer to castration resistance. The benefits of slightly improved quality of life by IADT compared to ADT were demonstrated in multiple clinical trials. IADT was noted to be noninferior to ADT in patients with biochemical recurrence of prostate cancer but in studies performed in patients with metastatic prostate cancer, the results were inconclusive. Our recent studies suggested that the administration of 5 alpha-reductase inhibitors during the off-cycle of IADT can significantly prolong the survival of mice bearing androgen-sensitive prostate tumors when off-cycle duration was short. This review discusses the survival benefit of 5 alpha-reductase inhibition in IADT in animal models and the potential translation of this finding into clinic.

Molecular functions of the iron-regulated metastasis suppressor, NDRG1, and its potential as a molecular target for cancer therapy

N-myc down-regulated gene 1 (NDRG1) is a known metastasis suppressor in multiple cancers, being also involved in embryogenesis and development, cell growth and differentiation, lipid biosynthesis and myelination, stress responses and immunity. In addition to its primary role as a metastasis suppressor, NDRG1 can also influence other stages of carcinogenesis, namely angiogenesis and primary tumour growth. NDRG1 is regulated by multiple effectors in normal and neoplastic cells, including N-myc, histone acetylation, hypoxia, cellular iron levels and intracellular calcium. Further, studies have found that NDRG1 is up-regulated in neoplastic cells after treatment with novel iron chelators, which are a promising therapy for effective cancer management. Although the pathways by which NDRG1 exerts its functions in cancers have been documented, the relationship between the molecular structure of this protein and its functions remains unclear. In fact, recent studies suggest that, in certain cancers, NDRG1 is post-translationally modified, possibly by the activity of endogenous trypsins, leading to a subsequent alteration in its metastasis suppressor activity. This review describes the role of this important metastasis suppressor and discusses interesting unresolved issues regarding this protein.

The expression and localization of N-myc downstream-regulated gene 1 in human trophoblasts

The protein N-Myc downstream-regulated gene 1 (NDRG1) is implicated in the regulation of cell proliferation, differentiation, and cellular stress response. NDRG1 is expressed in primary human trophoblasts, where it promotes cell viability and resistance to hypoxic injury. The mechanism of action of NDRG1 remains unknown. To gain further insight into the intracellular action of NDRG1, we analyzed the expression pattern and cellular localization of endogenous NDRG1 and transfected Myc-tagged NDRG1 in human trophoblasts exposed to diverse injuries. In standard conditions, NDRG1 was diffusely expressed in the cytoplasm at a low level. Hypoxia or the hypoxia mimetic cobalt chloride, but not serum deprivation, ultraviolet (UV) light, or ionizing radiation, induced the expression of NDRG1 in human trophoblasts and the redistribution of NDRG1 into the nucleus and cytoplasmic membranes associated with the endoplasmic reticulum (ER) and microtubules. Mutation of the phosphopantetheine attachment site (PPAS) within NDRG1 abrogated this pattern of redistribution. Our results shed new light on the impact of cell injury on NDRG1 expression patterns, and suggest that the PPAS domain plays a key role in NDRG1’s subcellular distribution.

5α-reductase inhibition suppresses testosterone-induced initial regrowth of regressed xenograft prostate tumors in animal models

Androgen deprivation therapy (ADT) is the standard treatment for patients with prostate-specific antigen progression after treatment for localized prostate cancer. An alternative to continuous ADT is intermittent ADT (IADT), which allows recovery of testosterone during off-cycles to stimulate regrowth and differentiation of the regressed prostate tumor. IADT offers patients a reduction in side effects associated with ADT, improved quality of life, and reduced cost with no difference in overall survival. Our previous studies showed that IADT coupled with 5α-reductase inhibitor (5ARI), which blocks testosterone conversion to DHT could prolong survival of animals bearing androgen-sensitive prostate tumors when off-cycle duration was fixed. To further investigate this clinically relevant observation, we measured the time course of testosterone-induced regrowth of regressed LuCaP35 and LNCaP xenograft tumors in the presence or absence of a 5ARI. 5α-Reductase inhibitors suppressed the initial regrowth of regressed prostate tumors. However, tumors resumed growth and were no longer responsive to 5α-reductase inhibition several days after testosterone replacement. This finding was substantiated by bromodeoxyuridine and Ki67 staining of LuCaP35 tumors, which showed inhibition of prostate tumor cell proliferation by 5ARI on day 2, but not day 14, after testosterone replacement. 5α-Reductase inhibitors also suppressed testosterone-stimulated proliferation of LNCaP cells precultured in androgen-free media, suggesting that blocking testosterone conversion to DHT can inhibit prostate tumor cell proliferation via an intracrine mechanism. These results suggest that short off-cycle coupled with 5α-reductase inhibition could maximize suppression of prostate tumor growth and, thus, improve potential survival benefit achieved in combination with IADT.

Molecular classification of prostate cancer progression: foundation for marker-driven treatment of prostate cancer

Recently, many therapeutic agents for prostate cancer have been approved that target the androgen receptor and/or the prostate tumor microenvironment. Each of these therapies has modestly increased patient survival. A better understanding of when in the course of prostate cancer progression specific therapies should be applied, and of what biomarkers would indicate when resistance arises, would almost certainly improve survival due to these therapies. Thus, applying the armamentarium of therapeutic agents in the right sequences in the right combination at the right time is a major goal in prostate cancer treatment. For this to occur, an understanding of prostate cancer evolution during progression is required. In this review, we discuss the current understanding of prostate cancer progression, but challenge the prevailing view by proposing a new model of prostate cancer progression, with the goal of improving biologic classification and treatment strategies. We use this model to discuss how integrating clinical and basic understanding of prostate cancer will lead to better implementation of molecularly targeted therapeutics and improve patient survival.

Association of Differentiation-Related Gene-1 (DRG1) with Breast Cancer Survival and in Vitro Impact of DRG1 Suppression

Differentiation-related gene-1, DRG1, is a metastasis suppressor gene whose expression has been shown to be dysregulated in a number of malignancies. The current study examines the expression of DRG1 in a clinical breast cohort and its association with a number of clinical pathological factors using quantitative polymerase chain reaction. Additionally, DRG1 expression is targeted in vitro using ribozyme transgene technology to explore the function of DRG1 in two human breast cancer cell lines. Low levels of DRG1 were found in patients who developed metastasis (p = 0.036) and who died of breast cancer (p = 0.0048) compared to disease free patients. Knockdown of DRG1 also resulted in significantly increased invasion and motility, but decreased matrix-adhesion in MCF7 cells. Knockdown of DRG1 seemed to have minimal impact on the cellular functions of the MDA-MB-231 breast cancer cell line causing no significant differences in cell growth, invasion, motility or matrix-adhesion. Thus, DRG1 appears to be linked to development of metastasis and death in patients who died as a result of breast cancer and may be useful as a prognostic factor as its knockdown appears to be linked with increased invasion and motility and decreased adhesion in MCF7 breast cancer cells.

Testosterone, not 5α-dihydrotestosterone, stimulates LRH-1 leading to FSH-independent expression of Cyp19 and P450scc in granulosa cells

Androgens are crucial for normal folliculogenesis and female fertility as evidenced in androgen receptor-null and granulosa cell conditional knockout mice. It is thought, however, that the multiple effects of androgens in the ovary are mainly complementary to the actions of gonadotropins. Using primary rat granulosa cells, we demonstrated that in the absence of gonadotropins, testosterone (T) increases aromatase (Cyp19) and P450 side-change cleavage expression, two enzymes crucial for normal ovarian function. T can be converted into estradiol, a classical estrogen, by Cyp19 and into 5α-dihydrotestosterone, a pure androgen, by 5α-reductase. However, inhibition of Cyp19 and/or 5α-reductase did not prevent the stimulatory effects of T. In contrast, the effect of this steroid was potentiated by blocking 5α-reductase. Additionally, T, not 5α-dihydrotestosterone, stimulates liver receptor homolog-1 (LRH-1) expression, whereas the expression of steroidogenic factor-1 (SF-1) was not affected by either steroid. LRH-1 and SF-1 are transcription factors known to be involved in the regulation of Cyp19. Accordingly, small interference RNA against LRH-1 prevented Cyp19 and P450 side-change cleavage up-regulation whereas anti-SF-1 small interference RNA had no effects. Chromatin immunoprecipitation demonstrated that T stimulation of LRH-1 leads to the recruitment of LRH-1 to the native Cyp19 promoter, which was not affected by cotreatment with 5α-reductase and Cyp19 inhibitors. Finally, gel shift and supershift analysis demonstrated that the androgen receptor binds to an androgen response element located within the LRH-1 promoter. These results provide novel evidence that T has a direct effect on the expression of genes involved in granulosa cell differentiation.

Metastasis suppressors in human benign prostate, intraepithelial neoplasia, and invasive cancer: their prospects as therapeutic agents

Despite advances in diagnosis and treatment of prostate cancer, development of metastases remains a major clinical challenge. Research efforts are dedicated to overcome this problem by understanding the molecular basis of the transition from benign cells to prostatic intraepithelial neoplasia (PIN), localized carcinoma, and metastatic cancer. Identification of proteins that inhibit dissemination of cancer cells will provide new perspectives to define novel therapeutics. Development of antimetastatic drugs that trigger or mimic the effect of metastasis suppressors represents new therapeutic approaches to improve patient survival. This review focuses on different biochemical and cellular functions of metastasis suppressors known to play a role in prostate carcinogenesis and progression. Ten putative metastasis suppressors implicated in prostate cancer are discussed. CD44s is decreased in both PIN and cancer; Drg-1, E-cadherin, KAI-1, RKIP, and SSeCKS show similar expression between benign epithelia and PIN, but are downregulated in invasive cancer; whereas, maspin, MKK4, Nm23 and PTEN are upregulated in PIN and downregulated in cancer. Moreover, the potential role of microRNA in prostate cancer progression, the understanding of the cellular distribution and localization of metastasis suppressors, their mechanism of action, their effect on prostate invasion and metastasis, and their potential use as therapeutics are addressed.

Differentiation-related gene-1 decreases Bim stability by proteasome-mediated degradation

Drg1 was identified as a differentiation-related, putative metastatic suppressor gene in human colon and prostate cancer. Its expression is associated with resistance to irinotecan (CPT-11) therapy in preclinical colorectal cancer models both in vitro and in vivo. However, the functional significance of Drg1 in these processes is unknown. We have shown for the first time that Drg1 directly binds to the BH3-only proapoptotic protein Bim. Depletion of Drg1 by small interfering RNA induced up-regulation of Bim and its accumulation in the mitochondria, which correlated with loss of mitochondrial membrane potential and induction of apoptosis in cells exposed to SN-38. Further analyses revealed that Drg1 promotes degradation of Bim through the Cullin2/ElonginB-CIS ubiquitin-protein ligase complex. Conversely, in the absence of Drg1, Bim was stabilized and bound more abundantly to Hsp70. These results show that Drg1 renders cancer cells more resistant to chemotherapy through enhanced proteasome-mediated Bim degradation.

NDRG3 is an androgen regulated and prostate enriched gene that promotes in vitro and in vivo prostate cancer cell growth

NDRG3 belongs to the N-myc down-regulated gene (NDRG) family that contains 4 paralogs: NDRG1, -2, -3 and -4. The function of NDRG3 and its relationship to cancer has not been studied. We herein report our examination of the expression and biological roles of NDRG3 in prostate cancers. We showed that NDRG3 expression is enriched in testis and prostate using gene expression data derived from massively parallel signature sequencing from 33 different human organs. We further showed that NDRG3 is expressed in both epithelial prostate cancer cells and prostatic stromal cells at both mRNA and proteins levels. We demonstrated that NDRG1 is significantly up-regulated by androgen in LNCaP cells. Over-expression of NDRG3 in stably transfected PC-3 cells increased their growth rates and migration capabilities when compared to parental or mock empty vector transfected PC-3 cells. In addition, we found that overexpresson of NDRG3 promoted the growth of xenograft tumors in nude mice. Finally, we found that NDRG3 expression was detected in 58.6% (41/70) of prostate cancer specimens compared to 13.2% (5/38) of benign prostatic hyperplasia specimens by immunohistochemistry. We showed by microarray and by RT-PCR that NDRG3 overexpression up-regulates the expression of many angiogenic chemokines including CXCL1 (chemokine ligand 1), CXCL3 (chemokine ligand 3) and CXCL5 (chemokine ligand 5), which may increase angiogenesis of tumors. Taken together, these results demonstrate that NDRG3 is a tumor promoter, the overexpression of which may contribute to the malignant phenotype of tumors.

Impaired Mast Cell Maturation and Degranulation and Attenuated Allergic Responses inNdrg1-Deficient Mice

We have previously reported that N-myc downstream regulated gene-1 (NDRG1) is an early inducible protein during the maturation of mouse bone marrow-derived mast cells (BMMCs) toward a connective tissue mast cell-like phenotype. To clarify the function of NDRG1 in mast cells and allergic responses, we herein analyzed mast cell-associated phenotypes of mice lacking the Ndrg1 gene. Allergic responses including IgE-mediated passive systemic and cutaneous anaphylactic reactions were markedly attenuated in Ndrg1-deficient mice as compared with those in wild-type mice. In Ndrg1-deficient mice, dermal and peritoneal mast cells were decreased in number and morphologically abnormal with impaired degranulating ability. Ex vivo, Ndrg1-deficient BMMCs cocultured with Swiss 3T3 fibroblasts in the presence of stem cell factor, a condition that facilitates the maturation of BMMCs toward a CTMC-like phenotype, displayed less exocytosis than replicate wild-type cells after the cross-linking of FcepsilonRI or stimulation with compound 48/80, even though the exocytotic response of IL-3-maintained, immature BMMCs from both genotypes was comparable. Unlike degranulation, the production of leukotriene and cytokines by cocultured BMMCs was unaffected by NDRG1 deficiency. Taken together, the altered phenotypes of Ndrg1-deficient mast cells both in vivo and ex vivo suggest that NDRG1 has roles in the terminal maturation and effector function (degranulation) of mast cells.

Proteomics analysis of the interactome of N-myc downstream regulated gene 1 and its interactions with the androgen response program in prostate cancer cells

NDRG1 is known to play important roles in both androgen-induced cell differentiation and inhibition of prostate cancer metastasis. However, the proteins associated with NDRG1 function are not fully enumerated. Using coimmunoprecipitation and mass spectrometry analysis, we identified 58 proteins that interact with NDRG1 in prostate cancer cells. These proteins include nuclear proteins, adhesion molecules, endoplasmic reticulum (ER) chaperons, proteasome subunits, and signaling proteins. Integration of our data with protein-protein interaction data from the Human Proteome Reference Database allowed us to build a comprehensive interactome map of NDRG1. This interactome map consists of several modules such as a nuclear module and a cell membrane module; these modules explain the reported versatile functions of NDRG1. We also determined that serine 330 and threonine 366 of NDRG1 were phosphorylated and demonstrated that the phosphorylation of NDRG1 was prominently mediated by protein kinase A (PKA). Further, we showed that NDRG1 directly binds to beta-catenin and E-cadherin. However, the phosphorylation of NDRG1 did not interrupt the binding of NDRG1 to E-cadherin and beta-catenin. Finally, we showed that the inhibition of NDRG1 expression by RNA interference decreased the ER inducible chaperon GRP94 expression, directly proving that NDRG1 is involved in the ER stress response. Intriguingly, we observed that many members of the NDRG1 interactome are androgen-regulated and that the NDRG1 interactome links to the androgen response network through common interactions with beta-catenin and heat shock protein 90. Therefore we overlaid the transcriptomic expression changes in the NDRG1 interactome in response to androgen treatment and built a dual dynamic picture of the NDRG1 interactome in response to androgen. This interactome map provides the first road map for understanding the functions of NDRG1 in cells and its roles in human diseases, such as prostate cancer, which can progress from androgen-dependent curable stages to androgen-independent incurable stages.

N-Myc Down-regulated Gene 1 Modulates the Response of Term Human Trophoblasts to Hypoxic Injury

The placenta is susceptible to diverse insults during human pregnancy. The expression of the protein N-myc down-regulated gene 1 (NDRG1) is regulated during cell proliferation, differentiation, and in response to stress. Nevertheless, the function of this protein in humans remains unknown. We tested the hypothesis that NDRG1 is up-regulated in hypoxic primary human trophoblasts and that NDRG1 modulates trophoblast response to hypoxia. We initially demonstrated that the expression of NDRG1 is enhanced in primary human trophoblasts exposed to hypoxia. Importantly, we found a similar increase in NDRG1 expression in placental samples derived from either singleton gestations complicated by intrauterine growth restriction or from dizygotic twin gestation where one twin exhibited growth restriction. Having established efficient lentivirus-mediated transfection of primary human trophoblasts, we overexpressed NDRG1 in trophoblasts, which resulted in enhanced trophoblast differentiation. In contrast, lentivirus-driven short interfering RNA-mediated silencing of NDRG1 diminished trophoblast viability and differentiation. Consistent with these results, NDRG1 reduced the expression level of p53 in trophoblasts cultured in standard or hypoxic conditions. Furthermore, NDRG1 expression was regulated by the activity of SIRT1 (Sir2-like protein 1), which promotes cell survival. Together, our data indicate that NDRG1 interacts with SIRT1/p53 signaling to attenuate hypoxic injury in human trophoblasts.

Expression of androgen receptor and androgen regulation of NDRG2 in the rat renal collecting duct

Androgens are known to regulate gene expression in the renal proximal tubule. Whether the distal parts of the nephron, in particular the cortical collecting duct (CCD), where sodium reabsorption is controlled tightly by aldosterone, are also targets for these hormones is unknown. Real-time PCR on rat isolated renal tubules showed that androgen receptor mRNA is not only, as expected, expressed in the proximal tubule, but also in the CCD. We examined the effects of adrenalectomy (ADX) plus castration and in-vivo administration of the active metabolite of testosterone, dihydrotestosterone (DHT), on the intrarenal expression of N-myc downstream regulated gene 2 (NDRG2), an early aldosterone-induced gene located specifically in the CCD. NDRG2 belongs to a newly identified family of differentiation-related genes; although the function of these genes remains elusive, regulation of NDRG1 by androgens has been suggested. Castration plus ADX increased NDRG2 expression (RNase protection assay) significantly in the whole kidney, and a single i.p. injection of DHT caused a significant decrease in NDRG2 expression 4 h afterwards (up to 24 h). Furthermore, real-time PCR on microdissected tubules revealed that the decrease in NDRG2 expression caused by DHT is restricted to the CCD. Thus, aldosterone and androgens have opposite effects on NDRG2 expression in the renal CCD. These results are the first demonstration of androgen-dependent gene regulation in the rat renal CCD.

Modulation of differentiation-related gene 1 expression by cell cycle blocker mimosine, revealed by proteomic analysis

L-mimosine, a plant amino acid, can reversibly block mammalian cells at late G1 phase and has been found to affect translation of mRNAs of the cyclin-dependent kinase inhibitor p27, eIF3a (eIF3 p170), and ribonucleotide reductase M2. The effect of mimosine on the expression of these genes may be essential for the G1 phase arrest. To determine additional genes that may be early respondents to the mimosine treatment, we performed two-dimensional gel electrophoretic analysis of [35S]methionine-labeled cell lysates followed by identification of the altered protein spots by LC-tandem mass spectrometry. In this study, the synthesis of two protein spots (MIP42 and MIP17) was found to be enhanced by mimosine, whereas the formation of another protein spot (MSP17) was severely blocked following mimosine treatment. These protein spots, MIP42, MIP17, and MSP17, were identified to be differentiation-related gene 1 (Drg-1; also called RTP, cap43, rit42, Ndrg-1, and PROXY-1), deoxyhypusine-containing eIF5A intermediate, and mature hypusine-containing eIF5A, respectively. The effect of mimosine on eIF5A maturation was due to inhibition of deoxyhypusine hydroxylase, the enzyme catalyzing the final step of hypusine biosynthesis in eIF5A. The mimosine-induced expression of Drg-1 was mainly attributable to increased transcription likely by the c-Jun/AP-1 transcription factor. Because induction of Drg-1 is an early event after mimosine treatment and is observed before a notable reduction in the steady-state level of mature eIF5A, eIF5A does not appear to be involved in the modulation of Drg-1 expression.

PTEN up-regulates the tumor metastasis suppressor gene Drg-1 in prostate and breast cancer

PTEN (phosphatase and tensin homologue deleted on chromosome 10) has been shown to be inactivated in a wide variety of cancers, and the role of this gene as a tumor suppressor has been well established. On the other hand, results of recent animal studies as well as clinical evidence indicate that PTEN is also involved in tumor metastasis suppression. Although PTEN is known to play a key role in controlling cell growth and apoptosis, how PTEN exerts the metastasis suppressor function remains largely unknown. Recently, a microarray analysis identified the Drg-1 gene (differentiation related gene 1) as one of the potential targets of PTEN. The Drg-1 gene has been shown to suppress tumor metastasis in animal models of prostate and colon cancer, and the expression of this gene is significantly reduced with advancement of prostate and breast cancers in clinical setting. In this study, we explored the possibility that PTEN controls tumor metastasis by regulating the expression of the Drg-1 gene. Our results indicate that overexpression of PTEN significantly augments the endogenous expression of Drg-1 protein, whereas inhibition of PTEN by small interfering RNA decreases Drg-1 in a dose- and time-dependent manner. We also found that the control of the Drg-1 gene by PTEN seems to be at the transcriptional level, and that a phospho-Akt inhibitor restores the Drg-1 expression, indicating that PTEN controls Drg-1 by an Akt-dependent pathway. Consistent with these results, our immunohistochemical analysis revealed that PTEN expression correlates significantly with Drg-1 in both prostate and breast cancer cases. Furthermore, combination of the two markers, PTEN and Drg-1, emerged as a significantly better predictor of prostate and breast cancer patient survival than either marker alone.

Iron chelators with high antiproliferative activity up-regulate the expression of a growth inhibitory and metastasis suppressor gene: a link between iron metabolism and proliferation

Iron (Fe) is critical for proliferation, but its precise role in cell cycle progression remains unclear. In this study, we examined the mechanisms involved by assessing the effects of Fe chelators on the expression of molecules that play key roles in this process. In initial studies, gene arrays were used to assess gene expression after incubating cells with 2 Fe chelators, namely, desferrioxamine (DFO) and 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311), or the DNA-damaging agent, actinomycin D. From the genes assessed, only the N-myc downstream-regulated gene 1 (Ndrg1) was specifically up-regulated by Fe chelation. Although the function of Ndrg1 is unclear, previous studies showed it markedly slows tumor growth and acts as a potent metastasis suppressor. Incubation of cells with chelators markedly increased Ndrg1 mRNA and protein expression, but this was not found with their Fe complexes or when the Fe-binding site had been inactivated. Increased Ndrg1 expression following Fe chelation was related to the permeability and antiproliferative activity of chelators and could be reversed by Fe repletion. Moreover, Ndrg1 up-regulation after chelation occurred at the transcriptional level and was mediated by hypoxia inducible factor-1α (HIF-1α)-dependent and -independent mechanisms. Our investigation suggests Ndrg1 is a novel link between Fe metabolism and the control of proliferation.

Role of the putative tumor metastasis suppressor gene Drg-1 in breast cancer progression

The differentiation-related gene-1 (Drg-1) was first identified as a gene strongly upregulated by induction of differentiation in colon carcinoma cells in vitro, and later the same gene was shown to suppress tumorigenicity of human bladder cancer cells in vivo. On the other hand, we and others have demonstrated that the Drg-1 gene suppresses prostate and colon cancer metastases in mouse models. In the context of such potential organ-specific differential function of the Drg-1 gene, the present study was designed to clarify the expression status, regulation and function of Drg-1 in the case of human breast cancer. We found that the expression of the Drg-1 protein was significantly reduced in breast tumor cells, particularly in patients with lymph node or bone metastasis as compared to those with localized breast cancer. Drg-1 expression also exhibited significant inverse correlation with the disease-free survival rate of patients and emerged as an independent prognostic factor. The downregulation of the Drg-1 gene appeared to be largely at the RNA level, and the DNA methylation inhibitor, 5-Azacytidine, significantly elevated the Drg-1 gene expression in various breast tumor cell lines. Furthermore, we found that overexpression of the Drg-1 gene suppresses the invasiveness of breast cancer cells in vitro, and this suppression was also achieved by treatment of cells with 5-Azacytidine. Together, our results strongly suggest functional involvement of the Drg-1 gene in suppressing the metastatic advancement of human breast cancer.

Ndrg1-deficient mice exhibit a progressive demyelinating disorder of peripheral nerves

NDRG1 is an intracellular protein that is induced under a number of stress and pathological conditions, and it is thought to be associated with cell growth and differentiation. Recently, human NDRG1 was identified as a gene responsible for hereditary motor and sensory neuropathy-Lom (classified as Charcot-Marie-Tooth disease type 4D), which is characterized by early-onset peripheral neuropathy, leading to severe disability in adulthood. In this study, we generated mice lacking Ndrg1 to analyze its function and elucidate the pathogenesis of Charcot-Marie-Tooth disease type 4D. Histological analysis showed that the sciatic nerve of Ndrg1-deficient mice degenerated with demyelination at about 5 weeks of age. However, myelination of Schwann cells in the sciatic nerve was normal for 2 weeks after birth. Ndrg1-deficient mice showed muscle weakness, especially in the hind limbs, but complicated motor skills were retained. In wild-type mice, NDRG1 was abundantly expressed in the cytoplasm of Schwann cells rather than the myelin sheath. These results indicate that NDRG1 deficiency leads to Schwann cell dysfunction, suggesting that NDRG1 is essential for maintenance of the myelin sheaths in peripheral nerves. These mice will be used for future analyses of the mechanisms of myelin maintenance.

Correlation of N-myc downstream-regulated gene 1 overexpression with progressive growth of colorectal neoplasm

AIM

To study the function of N-myc downstream-regulated gene 1 (NDRG1) in colorectal carcinogenesis and its correlation with tumor lymph node metastasis.

METHODS

NDRG1 was detected at its protein level by immunohistochemistry (IHC) and image analysis (IA), and NDRG1 mRNA was detected by in situ hybridization (ISH) in formalin-fixed and paraffin-embedded sections with a total of 190 specimens including 38 normal colorectal mucosae, 31 colorectal adenomas, 45 non-metastatic colorectal carcinomas (CRCs), 38 metastatic primary CRC and subsequently regional lymph nodes respectively. At the same time, the correlations of NDRG1 with sex, age of patients and histological types of colorectal carcinomas were observed.

RESULTS

NDRG1 proteins were gradually increased in colorectal carcinogenesis (P<0.05 or P<0.01). There was a significant difference in the expression of NDRG1 between non-metastatic and metastatic CRCs (P<0.05), and the correlation was positive (P<0.01, r(s)=0.329). However, there was no obvious difference in the expression of NDRG1 between the primary sites of CRCs and that in the metastatic sites of corresponding regional lymph nodes, nor was there an apparent difference in sex, age, and histological types. The expression of NDRG1 mRNA was generally in concordance with that of NDRG1 protein.

CONCLUSION

NDRG1 gene may play an important role in colorectal carcinogenesis. In addition, NDRG1 may be a putative tumor metastasis promoter gene and is regarded as one of the molecular biological markers that can forecast early metastasis of CRCs. NDRG1 gene in the metastatic sites of regional lymph nodes may preserve its expression characteristics in the primary sites of CRCs to some extent. The expression of NDRG1 is not affected by sex, age and histological types. The role of NDRG1 in tumor metastatic process can be demonstrated by in vivo and in vitro.

N-myc downregulated gene 1 is a phosphorylated protein in mast cells

We previously demonstrated that the in vitro maturation of mouse immature bone marrow-derived mast cells into a mature connective tissue mast cell-like phenotype is accompanied by a marked induction of N-myc downregulated gene (NDRG) 1, a cytosolic protein with unknown function. Here we show that NDRG1 undergoes phosphorylation in mast cells. Recombinant NDRG1 was phosphorylated by calmodulin kinase-II, protein kinase (PK) A and PKC in vitro. Deletion of the C-terminal tandem repeats of NDRG1 resulted in increased phosphorylation by PKA and PKC, but not by calmodulin kinase-II. Furthermore, NDRG1 was phosphorylated on serine and threonine residues in mast cells, a process that was accelerated transiently following cell activation. Pharmacologic studies using kinase-specific inhibitors demonstrated that this NDRG1 phosphorylation in mast cells depended on calmodulin kinase-II and PKA, but not PKC. Collectively, our results indicate that NDRG1 is a multiphosphorylated protein in mast cells, and that the kinetics of increased NDRG1 phosphorylation parallels signaling events leading to exocytosis.

Ndrg2, a novel gene regulated by adrenal steroids and antidepressants, is highly expressed in astrocytes

Previously, we cloned a gene from rat hippocampus that now shows homology to Ndrg2, a member of the N-myc downregulated gene (NDRG) family with putative roles in neural differentiation, synapse formation, and axon survival. Following adrenalectomy, hippocampal Ndrg2 mRNA increased in response to glucocorticoids. Ndrg2 mRNA was also upregulated by corticosterone in cerebral cortex and heart. Since Ndrg2 mRNA increased in response to glucocorticoid treatment of cultured astrocytes, we examined its cellular localization in adult brain by in situ hybridization. Ndrg2 mRNA is a prevalent message that is widely expressed throughout the brain, but is more abundant in gray matter than in white matter. Predominant mRNA expression was found in neurogenic regions of the adult brain. Furthermore, Ndrg2 mRNA in these regions was localized to GFAP-positive astrocytes or radial glia. In one of these regions, the subgranular zone of the dentate gyrus, Ndrg2 expression was decreased after adrenalectomy, and was restored to sham-operated levels by corticosterone, indicating that it is under positive regulation by glucocorticoids in vivo. Recently, another group reported that Ndr2/Ndrg2 transcripts in rat frontal cortex were decreased by chronic antidepressant treatment. Because antidepressants may alleviate symptoms of depression by reversing the effects of glucocorticoids, these data suggest that further study of Ndrg2 regulation and function in glia could contribute to understanding the pathogenesis and treatment of depression.

Correlation of N-myc downstream-regulated gene 1 overexpression with progressive growth of colorectal neoplasm

AIM: To study the function of N-myc downstream-regulated gene 1 (NDRG1) in colorectal carcinogenesis and its correlation with tumor lymph node metastasis.

METHODS: NDRG1 was detected at its protein level by immunohistochemistry (IHC) and image analysis (IA), and NDRG1 mRNA was detected by in situ hybridization (ISH) in formalin-fixed and paraffin-embedded sections with a total of 190 specimens including 38 normal colorectal mucosae, 31 colorectal adenomas, 45 non-metastatic colorectal carcinomas (CRCs), 38 metastatic primary CRC and subsequently regional lymph nodes respectively. At the same time, the correlations of NDRG1 with sex, age of patients and histological types of colorectal carcinomas were observed.

RESULTS: NDRG1 proteins were gradually increased in colorectal carcinogenesis (P < 0.05 or P < 0.01). There was a significant difference in the expression of NDRG1 between non-metastatic and metastatic CRCs (P < 0.05), and the correlation was positive (P < 0.01, r_s = 0.329). However, there was no obvious difference in the expression of NDRG1 between the primary sites of CRCs and that in the metastatic sites of corresponding regional lymph nodes, nor was there an apparent difference in sex, age, and histological types. The expression of NDRG1 mRNA was generally in concordance with that of NDRG1 protein.

CONCLUSION: NDRG1 gene may play an important role in colorectal carcinogenesis. In addition, NDRG1 may be a putative tumor metastasis promoter gene and is regarded as one of the molecular biological markers that can forecast early metastasis of CRCs. NDRG1 gene in the metastatic sites of regional lymph nodes may preserve its expression characteristics in the primary sites of CRCs to some extent. The expression of NDRG1 is not affected by sex, age and histological types. The role of NDRG1 in tumor metastatic process can be demonstrated by in vivo and in vitro.

Association of <i>N-myc</i> Downregulated Gene 1 with Heat-Shock Cognate Protein 70 in Mast Cells

N-Myc downregulated gene (NDRG) 1 is markedly induced during in vitro maturation of mouse immature bone marrow-derived mast cells (BMMCs) into a mature connective tissue mast cell (CTMC)-like phenotype. However, cellular function of this unique cytosolic protein is currently obscure. In this study, we sought potential NDRG1-binding proteins using yeast two-hybrid analysis and found that NDRG1 is capable of binding to heat-shock cognate protein 70 (Hsc70) both in vitro and in mast cells. The expression of Hsc70 was markedly elevated during the in vitro maturation of BMMCs into CTMC-like cells in accordance with the increased expression of NDRG1. Deletion of the C-terminal hydrophilic tandem repeats from NDRG1 facilitated the interaction with Hsc70 in vitro. Interaction between NDRG1 and Hsc70 was constitutive in mast cells and was not altered following cell activation. Although NDRG1 undergoes phosphorylation (accompanying paper), the binding of NDRG1 to Hsc70 was not affected by this event. Interestingly, the NDRG1-Hsc70 complex transiently appeared in the nuclear fraction of activated mast cells.

Identification and characterization of Xenopus NDRG1

NDRG1 is a member of the N-myc downstream-regulated gene (NDRG) family and is involved in cellular differentiation, activation of p53, cell cycle arrest, metastasis, and hypoxia. Expression of NDRG1 is repressed by the proto-oncogene, N-myc during mouse development, although the exact functional role of NDRG1 in development remains unknown. Here, we report the characterization of Xenopus laevis NDRG1 (xNDRG1) during X. laevis development. Expression of xNDRG1 transcript was first detected at stage 15, and was localized to the presumptive pronephric anlagen at stage 26 and to pronephros, eye, branchial arches, and tail-bud at stage 32. Overexpression of xNDRG1 results in a reduced pronephros and disorganized somites. Depletion of xNDRG1, using morpholinos, causes failure of pronephros development. These results suggest that xNDRG1 is required for pronephros development in X. laevis.

The growth-inhibitory Ndrg1 gene is a Myc negative target in human neuroblastomas and other cell types with overexpressed N- or c-myc

A major prognostic marker for neuroblastoma (Nb) is N-myc gene amplification, which predicts a poor clinical outcome. We sought genes differentially expressed on a consistent basis between multiple human Nb cell lines bearing normal versus amplified N-myc, in hopes of finding target genes that might clarify how N-myc overexpression translates into poor clinical prognosis. Using differential display, we find the previously described growth-inhibitory gene Ndrg1 is strongly repressed in all tested Nb cell lines bearing N-myc amplification, as well as in a neuroepithelioma line with amplified c-myc. Overexpression of N-myc in non-amplified Nb cells leads to repression of Ndrg1, as does activation of an inducible c-myc transgene in fibroblasts. Conversely, N-myc downregulation in N-myc-amplified Nb cells results in re-expression of the Ndrg1, and stimuli known to induce Ndrg1 do so in Nb cells while simultaneously down-regulating N-myc. Relevant to these results, we demonstrate an in vitro interaction of Myc protein with the Ndrg1 core promoter. We also find that Ndrg1 levels increase dramatically during in vitro differentiation of two cell lines modeling neural and glial development, while c- and N-myc levels decline. Our results combined with previous information on the Ndrg1 gene product suggest that downregulation of this gene is an important component of N-Myc effects in neuroblastomas with poor clinical outcome. In support of this notion, we find that re-expression of Ndrg1 in high-Myc Nb cells results in smaller cells with reduced colony size in soft-agar assays, further underscoring the functional significance of this gene in human neuroblastoma cells.

Identification of NDRG1 as an early inducible gene during in vitro maturation of cultured mast cells

Coculture of mouse bone marrow-derived mast cells (BMMC) with fibroblasts in the presence of stem cell factor (SCF) facilitates morphological and functional maturation toward a connective tissue mast cell (CTMC)-like phenotype. By means of cDNA subtraction, we identified several inducible genes during this mast cell maturation process. Of approximately 100 sequenced clones induced, nearly 50% were chromosome 14-associated serine proteases. Approximately 14% encoded NDRG1, a 43-kDa cytosolic protein that has been implicated in cell differentiation. NDRG1 was distributed in the cytosol of cultured mast cells and CTMC in rat skin. Overexpression of NDRG1 in RBL-2H3 cells resulted in enhanced degranulation in response to various stimuli. Thus, NDRG1 may be a mast cell maturation-associated inducible protein that allows the cells to be susceptible to extracellular stimuli leading to degranulation. Additionally, several unique maturation-associated inducible genes were identified, molecular and functional characterization of which will provide new insights into mast cell biology.

A novel homocysteine-responsive gene, smap8, modulates mitogenesis in rat vascular smooth muscle cells

We isolated the cDNA of a gene, designated smooth muscle-associated protein 8 (smap8), during a search for new genes expressed in human aortic smooth muscle cells. The full-length smap8 cDNA is 3241 bp long and contains an open reading frame of 1113 bp encoding an approximately 45 kDa soluble protein identical to NDRG4 protein. Smap8 mRNA was expressed predominantly in the brain and heart, and moderately in vascular smooth muscle cells. Expression of smap8 mRNA was induced within 3-12 h by treatment with 10 mm homocysteine in rat aortic smooth muscle cells (A10 cells). Expression of exogenous smap8 markedly reduced both the proliferation and migration rates of rat A10 cells, however, PDGF-induced proliferation was significantly enhanced in smap8-expressed cells compared with mock-transfected cells. To ascertain the involvement of smap8 in mitogenesis, we tested the effects of stimulation of smap8, MEK1/2 or ERK1/2, which is known as a proliferation relating intermediate, by various growth factors and cytokines. PDGF was the most prominent in promoting phosphorylation of the smap8 protein. PDGF-dependent phosphorylation of smap8 was induced prior to ERK1/2 activation, and was repressed by staurosporine, a general inhibitor of serine/threonine kinases. Furthermore, activation of both MEK1/2 and ERK1/2 was markedly enhanced in these cells. Smap8 might therefore regulate the potentiation of ERK1/2 signalling induced by PDGF treatment. Our results imply that smap8 is involved in the regulation of mitogenic signalling in vascular smooth muscle cells, possibly in response to a homocysteine-induced injury.

Differentially expressed transcripts in neoplastic hepatic nodules and neonatal rat liver studied by cDNA microarray analysis

The molecular mechanisms underlying hepatocarcinogenesis remain unclear. Wistar rats treated with 2-AAF develop hepatocarcinoma in histologically well-characterised stages. In our study, cDNA microarrays were used to measure the expression of 3,000 genes during the progression of liver carcinogenesis in persistent neoplastic nodules. Because tumours frequently revert into a more poorly differentiated phenotype, we also studied the expression of the same set of transcripts in neonatal rat liver. Approximately 2,000 transcripts gave a detectable signal in experiments comparing gene expression in nodules and control tissue. Approximately 8% of these were identified as differentially expressed in liver nodules. The differentially expressed genes fell into several categories with putative or demonstrated roles in signal transduction, metabolism, detoxification, cell-structure and transport. Many of the differentially expressed genes in nodules were not previously known to be regulated during liver carcinogenesis. A universal transcript profile for gene expression in hepatic liver nodules and neonatal liver has been created.

Characterization of rat NDRG2 (N-Myc downstream regulated gene 2), a novel early mineralocorticoid-specific induced gene

The early phase of the stimulatory action of aldosterone on sodium reabsorption in tight epithelia involves hormone-regulated genes that remain to be identified. Using a subtractive hybridization technique on isolated renal cortical collecting ducts from rats injected with a physiological dose of aldosterone, we have identified an early response cDNA highly homologous to human and murine NDRG2 (N-Myc downstream regulated gene 2), which consists of four isoforms and belongs to a new family of differentiation-related genes. NDRG2 mRNA was expressed in classical aldosterone target epithelia, and in the kidney, it was specifically located in the collecting duct, the site of aldosterone-regulated sodium absorption. NDRG2 mRNA was increased within 45 min by aldosterone in the kidney and distal colon, whereas it was unaffected in the heart. In the RCCD2 collecting duct cell line, NDRG2 mRNA was enhanced as early as 15 min after aldosterone addition by transcription-dependent effects. NDRG2 was induced by aldosterone concentrations as low as 10(-9) M, and a maximal effect was observed at 10(-8) M. In contrast, the glucocorticoid dexamethasone was ineffective in NDRG2 expression, whereas the glucocorticoid-regulated gene sgk was induced. Taken together, these results indicate that NDRG2 regulation by aldosterone is an early mineralocorticoid-specific effect. Interestingly, NDRG2 is homologous to Drosophila MESK2, a component of the Ras pathway, suggesting that activation of the Ras cascade may play a significant role in mineralocorticoid signaling.

Characterization and expression of three novel differentiation-related genes belong to the human NDRG gene family

NDRG1 (N-Myc downstream regulated) is upregulated during cell differentiation, repressed by N-myc and c-myc in embryonic cells, and suppressed in several tumor cells. A nonsense mutation in the NDRG1 gene has been reported to be causative for hereditary motor and sensory neuropathy-Lom (HMSNL), indicating that NDRG1 functions in the peripheral nervous system necessary for axonal survival. Here, we cloned three human cDNAs encoding NDRG2 (371aa), NDRG3 (375aa) and NDRG4 (339aa), which are homologous to NDRG1. These three genes, together with NDRG1, constitute the NDRG gene family. The phylogenetic analysis of the family demonstrated that human NDRG1 and NDRG3 belong to a subfamily, and NDRG2 and NDRG4 to another. At amino acid (aa) level, the four members share 53-65% identity. Each of the four proteins contains an alpha/beta hydrolase fold as in human lysosomal acid lipase. Expression of the fusion proteins NDRG2/GFP, NDRG3/GFP and NDRG4/GFP in COS-7 cells showed that all of them are cytosolic proteins. Based on UniGene cluster analysis, the genes NDRG2, NDRG3 and NDRG4 are located at chromosome 14q11.1-11.2, 20q12-11.23 and 16q21-22.1, respectively. Northern and dot blot analysis shows that all of the three genes are highly expressed in adult brain and almost not detected in the eight human cancer lines. In addition, in contrast to the relatively ubiquitous expression of NDRG1, NDRG2 is highly expressed in adult skeletal muscle and brain, NDRG3 highly expressed in brain and testis, and NDRG4 specifically expressed in brain and heart, suggesting that they might display different specific functions in distinct tissues.

Regulation of the differentiation-related gene Drg-1 during mouse skin carcinogenesis

Differentiation-related gene-1 (Drg-1) has been identified as a gene whose expression is increased in several processes related to differentiation, but its function is currently unknown. In this report, we show that Drg-1 was expressed in keratinocytes, this expression being rapidly increased as a result of induction by 12-O-tetradecanoylphorbol-13-acetate (TPA) or the presence of an activating form of Ha-ras. Induction by TPA occurred both in cultured cell lines and primary keratinocytes as well as in mouse skin after a single TPA application. Overexpression of Drg-1 was also observed in TPA-induced hyperplastic skin. In agreement, mouse skin papillomas and carcinomas also overexpressed Drg-1. In addition, Drg-1 was induced when keratinocytes were forced to differentiate by calcium switch or serum starvation. Analysis of the expression of Drg-1 during the keratinocyte cell cycle demonstrated relatively high levels of Drg-1 mRNA in G(0), which increased in early G(1) and decreased afterwards in late G(1)/S. In situ analysis showed an accumulation of Drg-1 in the suprabasal layers of the skin, as well as in the more differentiated areas of mouse skin papillomas. These results suggest that, in addition to being upregulated during keratinocyte differentiation, the Drg-1 gene might have a complex function in skin tumorigenesis.

Characterization of the human NDRG gene family: a newly identified member, NDRG4, is specifically expressed in brain and heart

RTP/Drg1/Cap43/rit42/TDD5/Ndr1/NDRG1 (referred to as NDRG1 hereafter) is a cytoplasmic protein involved in stress responses, hormone responses, cell growth, and differentiation. Recently, the mutation of this gene was reported to be causative for hereditary motor and sensory neuropathy-Lom. Here, we cloned two human cDNAs encoding NDRG3 and NDRG4, which are homologous to NDRG1. These two genes, together with NDRG1 and a previously deposited cDNA (designated NDRG2), constitute the NDRG gene family. The four members share 57-65% amino acid identity. NDRG4 was further characterized because its mRNA expression was quite specific in brain and heart, in contrast to the relatively ubiquitous expression of the other three members. NDRG4 mRNA consists of three isoforms, NDRG4-B, NDRG4-B(var), and NDRG4-H. Northern and Western blot analyses showed that NDRG4-B was expressed only in the brain, whereas NDRG4-H was expressed in both brain and heart. NDRG4-B(var) was a minor product. NDRG4 expression was more abundant in adult than fetal brain and heart and was markedly decreased in the Alzheimer's diseased brain. In situ hybridization showed that NDRG4 was localized in neurons of the brain and spinal cord. The NDRG4 gene contains 17 exons. mRNA expression of the three NDRG4 isoforms is regulated by alternative splicing and possibly by alternative promoter usage. The finely tuned expression of the NDRG gene family members suggests that they have different specific functions.

The leukemogenic transcription factor E2a-Pbx1 induces expression of the putative N-myc and p53 target gene NDRG1 in Ba/F3 cells

The chimeric transcription factor E2a-Pbx1 is expressed as a result of the 1;19 chromosomal translocation in some 5% of cases of pediatric acute lymphoblastic leukemia. We investigated the biological and transcriptional consequences of forced expression of E2a-Pbx1 in the interleukin-3 (IL-3) dependent, bone marrow-derived cell line Ba/F3. We show that forced expression of E2a-Pbx1 induces apoptosis in Ba/F3 cells without apparent effects on cell cycle progression. This pro-apoptotic effect is enhanced on cytokine deprivation. Furthermore, using cDNA representational difference analysis (RDA), we show that these cellular effects are associated with marked induction of the gene NDRG1, which was previously identified as a target of transcriptional repression by N-myc and induction by the tumor suppressor protein p53. We identify a portion of the NDRG1 promoter capable of mediating transcriptional induction by E2a-Pbx1 and show that NDRG1 is also induced on simple IL-3 deprivation of BaF3 cells. Although we show that E2a-Pbx1 induction of NDRG1 is not impaired as a result of targeting p53 using HPV E6, and therefore does not appear to be p53-dependent, our results overall are consistent with the notion that induction of NDRG1 by E2a-Pbx1 may represent part of an apoptotic or cytostatic cellular response to oncogene activation.

Inhibition of 5alpha-reductase in rat prostate reveals differential regulation of androgen-response gene expression by testosterone and dihydrotestosterone

The growth and development of some of the male sex accessory organs such as the prostate requires the conversion of testosterone to dihydrotestosterone (DHT) by 5alpha-reductase. To provide insights into the role of testosterone versus DHT in the prostate, we studied the impact of finasteride, a potent and specific inhibitor of 5alpha-reductase, on the expression of prostatic androgen-response genes in testis-intact rats and in 7-day castrated rats. Finasteride inhibition of the conversion of testosterone to DHT was confirmed by measuring serum and intraprostatic androgens. As expected, finasteride treatment caused a reduction in the wet weight of the prostate in the testis-intact rats and inhibited the testosterone-stimulated prostatic regrowth in the 7-day castrated rats. Although finasteride treatment had little or no effect on the expression of the surveyed androgen-response genes in testis-intact rats, its administration enhanced the expression of many androgen-response genes during the testosterone-stimulated regrowth of the regressed prostate in castrated rats. These observations suggest that testosterone is more potent than DHT in stimulating the expression of many androgen-response genes in the regressed prostate. The expression of androgen-response genes is mainly prostate specific and thus is likely to be associated with androgen-dependent prostatic differentiation. Therefore, testosterone is more potent than DHT in inducing differentiation and weaker in stimulating proliferation during prostate regrowth. The fact that testosterone is a strong inducer of prostatic differentiation has potential clinical implications.

Hypoxia induces the expression of a 43-kDa protein (PROXY-1) in normal and malignant cells

This study was designed to determine the expression of cellular factors that may participate in phenotypic changes that occur under conditions of hypoxia. Using the RT-PCR differential display method, we isolated a cDNA fragment corresponding to a gene whose expression was induced in trophoblast and breast carcinoma cells cultured under 1 or 2% oxygen vs 4% oxygen or higher. This gene encodes a 43-kDa protein initially identified in homocysteine-treated endothelial cells and later shown to be upregulated in various human and mouse cell types (termed RTP, Drg1, Cap43, rit42, Ndr1). Herein we refer to this gene product as PROXY-1, for Protein Regulated by OXYgen-1. Elevated mRNA and protein levels were first observed in cells cultured in 1% oxygen for 8 h. Although PROXY-1 mRNA levels returned to near-control values within 2 h of reexposure to 20% oxygen, protein levels remained high 72 h after reexposure to 20% oxygen. Treatment of cells with hypoxia mimics such as cobalt or iron chelators also increased PROXY-1 expression. Moreover, presence of 30% carbon monoxide in the hypoxic atmosphere abrogated the upregulation of PROXY-1 expression. These findings suggest that hypoxia upregulates PROXY-1 levels through a heme protein-dependent pathway and that assessment of PROXY-1 expression may be of potential use in evaluating tissue hypoxia.

The p53/retinoblastoma-mediated repression of testicular orphan receptor-2 in the rhesus monkey with cryptorchidism

Whereas the linkage of infertility to cryptorchidism, the failure of the testis to descend into the scrotum at birth, has been well documented, the detailed molecular mechanism remains unclear. Here we report that the testicular orphan receptor-2 (TR2) expression, which modulates many signal pathways, was completely repressed in the surgery-induced cryptorchidism of the rhesus monkey. Further studies link TR2 repression to the induction of p53 and results suggest that induced p53 could repress TR2 expression via the p53-->p21-->CDK-->Rb-->E2F signal pathway. In return, TR2 could also control the expression of p53 and Rb through the regulation of human papillomavirus 16 E6/E7 genes. Together, our data suggest a feedback control mechanism between TR2 and p53/Rb tumor suppressors, which might play important roles in male infertility associated with cryptorchidism.

Phosphorylation of RTP, an ER stress-responsive cytoplasmic protein

RTP, also called Drg1/Cap43/rit42/TDD5/Ndr1, was originally identified as a homocysteine-responsive gene product, and is now considered to be involved in stress responses, atherosclerosis, carcinogenesis, differentiation, androgen responses, hypoxia, and N-myc pathways. We raised an antiserum against a recombinant human RTP. Western blot analysis showed that RTP expression was induced in human umbilical vein endothelial cells under conditions causing endoplasmic reticulum stress. RTP was partially phosphorylated at seven or more sites. The phosphorylation was reversible, and was enhanced by an increased level of intracellular cAMP and inhibited by both a protein kinase A inhibitor and a calmodulin kinase inhibitor. Protein kinase A directly phosphorylated recombinant RTP in vitro. The phosphorylated forms were abundant in cells at the early log phase, and then decreased with increasing cell density. These data demonstrated that RTP is a phosphorylated stress-responsive protein, and its phosphorylation may be related to cell growth.

Identification of new genes ndr2 and ndr3 which are related to Ndr1/RTP/Drg1 but show distinct tissue specificity and response to N-myc

Ndr1 was isolated as a gene upregulated in N-myc mutant mouse embryos and is repressed by N-myc and c-myc. Consistent with Myc regulation, the same gene was also isolated as one sensitive to transformation (Drg1), and in addition as one induced under a few stress conditions (RTP). Two new genes, Ndr2 and Ndr3, were identified which encode proteins highly related to Ndr1/RTP/Drg1 and constitute the Ndr gene family. Ndr2 and Ndr3 are under spatio-temporal regulations distinct from Ndr1, and are not activated in N-myc mutants. When whole embryo RNA was analyzed, Ndr3 expression was already high at 9.5 days postcoitus (dpc), while expression of Ndr2 and Ndr1 became significant after 12.5 dpc and 13. 5 dpc, respectively. At 14.5 dpc, expression of these genes partially overlaps, but many tissues are unique to one of them. For instance, Ndr1 is strongly expressed in the liver and gut epithelium, Ndr2 in the ventricular zone throughout the CNS, and Ndr3 in the spinal cord and the thymus rudiment. Genes of the Ndr family probably have tissue-dependent allotments of the possibly related functions.

Roles of testosterone in the growth of keratinocytes through bald frontal dermal papilla cells

A coculture of dermal papilla cells (DPCs) from the bald frontal scalp of stumptailed macaques with keratinocytes derived from human neonatal foreskin revealed that testosterone inhibited keratinocyte proliferation, and that the antiandrogen RU58841 abolished this response. This testosterone-induced keratinocyte growth inhibition was not observed when either type of cells was cultured alone. We also examined conditioned media from the coculture system and demonstrated the identical testosterone-induced growth inhibition on keratinocytes, and this inhibitory effect was conditioned media concentration-dependent. These results suggested that the testosterone-mediated suppression on keratinocyte proliferation might proceed through some diffusible growth mediators in conditioned media. Differential display reverse transcriptase polymerase chain reaction allowed us to isolate several genes from frontal DPCs that can be either suppressed or induced by testosterone. Supervillin, a membrane-associated, F-actin-binding protein, was identified as one of the testosterone downregulated genes in frontal DPCs. Further characterization of these testosterone-target genes may reveal the mechanism by which testosterone inhibits the growth of follicular cells in androgenetic alopecia.

Androgen-induced regrowth in the castrated rat ventral prostate: role of 5alpha-reductase

Testosterone (T), the major circulating androgen, must be converted to dihydrotestosterone (DHT) by the enzyme 5alpha-reductase (5alpha-R) to be maximally active in the prostate. The present study was designed to determine the relative potency of T and DHT on regrowth of the involuted prostate and to elucidate the role of 5alpha-R in the growing prostate. To create dose-response curves for intraprostatic T or DHT, rats were castrated for 2 weeks to allow their prostates to fully regress and then given T implants of various sizes in the presence or absence of the 5alpha-R inhibitor, finasteride. Markers for androgen effects on regrowth of the prostate were prostate weight, duct mass (a measure of secretory activity) and DNA content (a measure of cell number). To assess the relative uptake of T and DHT by the prostate, a comparison was made of intraprostatic DHT levels resulting from T and DHT implants. In the prostate, 1.6-1.9 times more T than DHT was required to achieve a half-maximal response for each of the three markers of prostate regrowth. The dose-response curves revealed that thresholds for intraprostatic T and DHT had to be attained before significant growth was observed. The threshold for T was 2- to 3-fold greater than that for DHT. However, at high intraprostatic concentrations, the effects of T mimicked those of DHT. When the relationship between serum T levels and prostate regrowth was considered, 13 times more serum T was required for half-maximal prostate regrowth when its conversion to DHT was blocked by finasteride. This is partly due to decreased androgen accumulation in the prostate when T was the major intraprostatic androgen. Finally, T or DHT implants in the absence of finasteride resulted in similar intraprostatic DHT levels, indicating that uptake of each serum androgen into the prostate was similar. However, to achieve similar levels of DHT or T in serum, much larger DHT pellets were needed, suggesting more rapid metabolism of DHT in tissues other than the prostate. We conclude that the role of 5alpha-R is 2-fold: it converts testosterone into a modestly more potent androgen and enhances prostatic accumulation of androgen. DHT, in principle, could serve equally well as T as the circulating androgen, although the rate of DHT production would have to be considerably higher to counter the apparent rapid clearance from serum. In addition, we hypothesize that T has arisen as the major circulating androgen instead of DHT because it can be aromatized to estradiol, which itself has important roles in male reproductive function and bone physiology.

The differentiation-related gene 1, Drg1, is markedly upregulated by androgens in LNCaP prostatic adenocarcinoma cells

A differential display technique was used to identify androgen-regulated genes in LNCaP prostatic adenocarcinoma cells. One of the genes markedly upregulated by androgens proved to be identical to differentiation-related gene 1 (Drg1; also described as RTP, Cap43 and rit42), a gene whose expression has recently been shown to be diminished in colon, breast and prostate tumors. We show that Drg1 is abundantly expressed in the (androgen-exposed) human prostate and that its expression is stimulated some 14-fold in androgen-treated LNCaP cells. The ligand specificity of the induction reflects the altered specificity of the mutated androgen receptor in LNCaP. In androgen receptor negative tumor lines basal expression is slightly higher than in LNCaP but inducibility is absent. These data suggest that Drg1 is a novel marker of androgen-induced differentiation in the human prostate.

Molecular cloning and characterization of a novel developmentally regulated gene, Bdm1, showing predominant expression in postnatal rat brain

Postnatal development, such as synapse refinement, is necessary for the establishment of a mature and functional central nervous system (CNS). Using differential display analysis, we identified a novel gene, termed Bdm1, that is more abundantly expressed in the adult brain than in the embryonic brain. The full-length Bdm1 cDNA is 2718 base pairs long and contains an open reading frame of 1059 base pairs encoding a 38-kDa protein. Northern blot analysis revealed that expression of Bdm1 mRNA in the brain was weak on embryonic days and increased in the early postnatal period. Bdm1 mRNA was significantly expressed in the brain and heart, but there was no or little expression in other tissues. During the differentiation of mouse carcinoma cells P19 to neuron-like cells by retinoic acid, Bdm1 mRNA was up-regulated almost parallel to neurofilament mRNA. Expression of Bdm1 mRNA was observed appreciably in PC12 cells after neuronal differentiation but not in the nonneural cell lines examined. In situ hybridization demonstrated that Bdm1 was expressed widely in the olfactory bulb, cerebral cortex, hippocampus, cerebellum, thalamus, and medulla oblongata. Taken together, these data suggest that Bdm1 gene plays a role in the early postnatal development and function of neuronal cells.

N-myc-dependent repression of ndr1, a gene identified by direct subtraction of whole mouse embryo cDNAs between wild type and N-myc mutant

To identify genes regulated by N-myc, subtraction of whole embryo cDNA was carried out between wild type and N-myc-deficient mutant mice. Six cDNA clones were isolated as representing genes expressed higher in the mutant embryos and two as those expressed lower. One of them, Ndr1, coding for 43 kDa cytoplasmic protein was studied in detail. The Ndr1 gene was augmented 20-fold in the mutant embryos at 10.5 days post coitus which is indicative of repression by N-myc. An inverse relationship actually existed between the expression of N-myc and Ndr1 in various developing tissues of the wild type embryos. In the early stage of differentiation of these tissues when N-myc expression was high Ndr1 expression was low or undetectable, and later when N-myc activity diminished Ndr1 expression was augmented concomitantly with the occurrence of terminal differentiation. To establish the direct link between N-myc activity and the Ndr1 regulation, the Ndr1 gene was cloned and analyzed. The Ndr1 promoter activity was down-regulated by N-myc, and more strongly by the combination of N-myc and Max in the cotransfection assay. This repressive effect was mediated by the promoter region within 52 base pairs from the transcription start site but direct binding of N-myc:Max to the promoter sequence was not demonstrated, which is analogous to the cases recently reported for transcriptional repression by c-myc. c-myc also repressed Ndr1 promoter activity similarly to N-myc. The effect of N-myc:Max was sensitive to Trichostatin A, indicating involvement of histone deacetylase activity in repression of the Ndr1 promoter. The strategy we adopted in identifying target genes of a transcription factor should prove widely applicable when mutant animals are available.

Nonradioactive differential display cloning of genes induced by homocysteine in vascular endothelial cells

Hyperhomocysteinemia is known to be a risk factor for arteriosclerosis and thrombosis. To elucidate the mechanisms by which homocysteine may promote vascular diseases, we have applied a modified nonradioactive differential display analysis that evaluates changes in gene expression induced by homocysteine treatment of cultured human umbilical vein endothelial cells (HUVECs). We identified six upregulated and one downregulated gene. One upregulated gene was GRP78/BiP, an endoplasmic reticulum (ER)-resident molecular chaperone, suggesting that unfolded proteins would accumulate in the ER because of redox potential changes caused by homocysteine. Another upregulated gene encoded a bifunctional enzyme with activities of methylenetetrahydrofolate dehydrogenase and methenyltetrahydrofolate cyclohydrolase, which is involved in homocysteine metabolism. A third upregulated gene encoded activating transcription factor 4. Homology searches of the remaining four clones failed to retrieve any similar sequences with a known function. We isolated a full-length cDNA of one of the upregulated genes from a HUVEC library. It encoded a novel protein with 394 amino acids, which was termed RTP (reducing agent and tunicamycin-responsive protein). Northern blot analysis revealed that RTP mRNA expression was induced in HUVECs treated with not only homocysteine but also 2-mercaptoethanol and tunicamycin, both of which are known to induce ER stress. RTP mRNA was ubiquitously expressed in human adult organs, and seemed to be regulated in mouse embryogenesis. Consequently, our differential display analysis revealed that homocysteine alters the expressivity of multiple proteins, especially ER stress-responsive ones. This potential ability of homocysteine may be involved in atherogenesis.