Vacuolar H+-ATPase is down-regulated by the angiogenesis-inhibitory pigment epithelium-derived factor in metastatic prostate cancer cells

The Vacuolar H+-ATPases (V-ATPases), a multi-subunits nanomotor present in all eukaryotic cells resides in the endomembranes of exocytotic and endocytotic pathways. Plasmalemmal V-ATPases have been shown to be involved in tumor cell metastasis. Pigment epithelium-derived factor (PEDF), a potent endogenous inhibitor of angiogenesis, is down-regulated in prostate cancer cells. We hypothesized that the transduction of PEDF in prostate cancer cells will down-regulate V-ATPase function; that in turn will decrease the expression of the V-ATPase accessory protein ATP6ap2 and a-subunit isoforms that target V-ATPase to the cell surface. To test these hypotheses, we used the human androgen-sensitive prostate cancer cells LNCaP, and its castration-refractory-derivative CL1 that were engineered to stably co-express the DsRed Express Fluorescent Protein with or without PEDF. To determine if PEDF down-regulates the function of V-ATPase, we measured the rate of proton fluxes (JH+) of the cytosolic and endosome/lysosome compartments. The mRNA levels for subunit-a isoforms and the ATP6ap2 were measured using quantitative reverse transcription-PCR. The results showed that PEDF expression decreased the rate of JH+ in metastatic CL1 cells without affecting JH+ in non-metastatic LNCaP cells, when studying pH(cyt). Interestingly, PEDF did not affect JH+ in endosomes/lysosomes either in metastatic cells or in non-metastatic cells. We also showed that PEDF significantly decreases the levels of a4 isoform and ATP6ap2 in metastatic CL1 cells, without affecting the levels of a4 isoform in the non-metastatic LNCaP cells. These data identify PEDF as a novel regulator of V-ATPase suggesting a new way by which PEDF may inhibit prostate tumor growth.

Pigment epithelium-derived factor expression prolongs survival and enhances the cytotoxicity of low-dose chemotherapy in castration-refractory prostate cancer

There is currently no cure for advanced castration-refractory prostate cancer (CRPC) despite the recent approval of several new therapeutic agents. We report here the anti-tumor effect of the angio-inhibitory pigment epithelium-derived factor (PEDF) in the metastatic LNCaP-derivative CRPC CL1 model and explore PEDF anti-neoplasic efficacy in combination with low-dose chemotherapy. Androgen-sensitive LNCaP and CRPC PC3 cell lines were examined as comparison. Using a retroviral expression system, we showed that PEDF limited the proliferation of all prostatic cell lines tested; an effect attributed to interleukin 8 (IL8)-CXCR1/IL8RA inhibition. PEDF also reduced the number and size of 3D tumor spheroids in vitro, but only induced cell differentiation in CRPC spheroids. Similarly, PEDF inhibited the migration of CRPC cells suggesting both anti-proliferative and anti-migratory functions. In vivo, PEDF decreased by 85% and 65% the growth of subcutaneous (s.c.) PC3 and CL1 tumors, respectively. In the CL1 orthotopic model, tumor intake with lethal metastases was found in all animals; nevertheless, PEDF prolonged the median survival of tumor-bearing mice (95% confidence interval: 53±0.001 to 57±1 days). Accordingly, PEDF delayed the emergence of skeletal-related event in intra-tibial xenografts. Next, we evaluated low-dose docetaxel (DTX; 5, 1, 0.5 mg/kg) or cyclophosphamide (CTX; 10–20 mg/kg) on established s.c. PC3 tumors that conditionally express PEDF anti-tumoral epitope/NT3. Although NT3–DTX-5 mg/kg combination was inefficient, NT3–DTX-1 mg/kg and -0.5 mg/kg inhibited by 95% and 87.8%, respectively, tumor growth compared with control and induced tumor stasis. Both NT3–CTX combinations were advantageous. Inversely, PEDF–DTX-5 mg/kg and PEDF–CTX-10 mg/kg delayed the most CL1 tumor growth (15, 11 and 5 days for PEDF–DTX-5 mg/kg, PEDF–CTX-10 mg/kg and single treatments, respectively) with elevated apoptosis and serum thrombospondin-1 as possible mechanism and marker, respectively. As well, both PEDF–CTX-10 mg/kg and PEDF–DTX-5 mg/kg prolonged significantly the survival of tumor-bearing mice compared with single treatments. Metastases were reduced in PEDF–DTX-5 mg/kg compared with other treatments, suggesting that PEDF–DTX delayed metastases formation. Our results advocate that PEDF/low-dose chemotherapy may represent a new therapeutic alternative for CRPC.

Extraluminal colonic carcinoma invading into kidney: a case report and review of the literature

Renal metastasis from primary colon cancer is very rare, comprising less than 3% of secondary renal neoplasms. There are just 11 cases reported in the medical literature of colonic adenocarcinoma metastatic to the kidney. Of these cases, none occurred via direct invasion. We report a unique case of a 51-year-old female with extraluminal colonic adenocarcinoma which directly invaded into the kidney. Additionally, we investigate the causal relationship between the site of invasion and a previous stab injury by reviewing the role of the peritoneum and Gerota's fascia in preventing the spread of metastatic cancer into the perirenal space. Due to the rarity of this event, we present this case including a review of the existing literature relative to the diagnosis and treatment.

[Self-inflicted penile strangulation]

INTRODUCTION

Constricting devices or misappropriated means are either used to increase sexual performance or for autoerotic actions. They can lead to edema, maceration, to local infections up to Fournier gangrene or penile necrosis with or without involvement of the urethra. Injuries by these means are often challenging for the treating urologist.

CASE REPORT

A 22-year-old patient presented to the urological emergency clinic with strong penile pain and voiding difficulties. Within the scope of the clinical investigation a foreign body (frying pan handle) was found around the penis. The penis appeared to be edematous, and necrosis of the distal superficial penis segments was noted. Under local anesthesia the frying pan handle, after procurement of suitable instruments, was removed. Subsequently, a suprapubic catheter was inserted and a broad antibiotic therapy was initiated. An antiseptic local therapy completed the primary treatment. Eight weeks after the event an orthograde urethrogram was performed. The urethra appeared to behave a normal caliber without evidence for strictures or other patho-morphological changes. The final examination showed a nearly completely epithelialized glans penis, with an approximately 1-cent piece small epithelial defect.

CONCLUSIONS

Constricting devices for the penis are used to increase the sexual performance or with autoerotic intentions. Removal of the constricting devices can become impossible secondary to a hefty swelling of the penis. The treatment consists, primarily, of an immediate decompression of the strangulated penis to ensure a free blood flow and an uninhibited micturition. The removal of the various objects requires in part craft instruments. A supplementary therapy must be selected based on existing additional complications.

PSA surge/flare-up in patients with castration-refractory prostate cancer during the initial phase of chemotherapy

BACKGROUND

Docetaxel-based chemotherapy has shown great promise for the treatment of CRPC and is considered the current standard of care. PSA is mainly used as marker to monitor the treatment response. Several articles were published reporting an initial PSA surge/flare-up after starting chemotherapy. The cause and the impact of this phenomenon are discussed controversially. The intention of this review is to define the significance of initial PSA surge/flare-up and to increase awareness to this phenomenon in the urological community.

MATERIALS AND METHODS

A comprehensive literature search was performed in different data bases using various key words. Relevant articles and references between 1999 and 2009 were reviewed and analyzed for data on the association between chemotherapy and initial PSA surge/flare.

RESULTS

The incidence of a PSA surge/flare-up ranges according to the reported studies between 7.6% and 13.6%. A PSA surge/flare-up was reported up to 404% from baseline PSA level followed by PSA response. The median duration of a PSA surge/flare-up is 2-3 weeks and can last up to 6-8 weeks. However, the occurrence of a PSA surge/flare-up did not impact outcome and survival negatively compared to patients with an immediate PSA response.

CONCLUSIONS

A considerable portion of CRPC patients experience an initial PSA surge/flare-up under systemic chemotherapy. The definitions used for PSA surge/flare-up differ slightly in the literature. This issue needs to be solved since it might impact defining treatment response. As a PSA surge/flare-up did not impact outcome and survival negatively, chemotherapy should be continued according to the literature addressing specifically the phenomenon of a PSA surge/flare-up for a minimum of 8 weeks or 3 rounds of a 3-weekly cycle chemotherapy regimen before further decisions are made about efficacy. However, Scher et al. recommended a 12-week period drug exposure based on their results on PSA progression-free survival and overall survival. This dilemma needs to be addressed in further data analysis in order to establish a general rule regarding when to stop chemotherapy. Physicians should be aware of this effect to avoid inadequate early discontinuation of chemotherapy. The underlying mechanisms of a PSA surge/flare-up are still elusive and need further clarification.

Characterization of PEDF: a multi-functional serpin family protein

Pigment epithelium-derived factor (PEDF) is a 50 kDa secreted glycoprotein that belongs to the non-inhibitory serpin family group. PEDF has been described as a natural angiogenesis inhibitor with neurotrophic and immune-modulation properties; it balances angiogenesis in the eye and blocks tumor progression. The mechanisms underlying most of these events are not completely clear; however, it appears that PEDF acts via multiple high affinity ligands and cell receptors. In this review article, we will summarize the current knowledge on the biochemical properties of PEDF and its receptors, the multimodal activities of PEDF and finally address the therapeutic potential of PEDF in treating angiogenesis-, neurodegeneration- and inflammation-related diseases.

Deleted in cancer 1: Search for a function in prostate cancer

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Background: Deleted In Cancer 1 (DICE1/INTS6) gene was recently identified to colocalize with the microsatellite marker D13S284 in 13q14.3, a region frequently affected by allelic deletion in many solid tumors including prostate cancer (PrCa). DICE1 missense mutations have been previously detected in PrCa cell line LNCap, and reduced DICE1 expression appears to be associated with CpG promoter hypermethylation in PrCa cells. DICE1 is a highly conserved nuclear protein suggesting its involvement in DNA repair, transcription, or RNA splicing. In mouse, the DICE1 homologue interferes with the response to insulin-like growth factor 1 and suppresses anchorage-independent growth of transformed mouse cells. The totality of these results suggests that DICE1 is a tumor suppressor gene and insist on the need to better characterize DICE1 function in PrCa. Methods: Expression of DICE1 was evaluated by Northern Blot in PrCa cell lines LNCap, DU145, PC3, PC3ml and CPTX1532 and compared to expression level in normal prostate cell line NPTX1532. DICE1 growth inhibitory effects were analyzed by colony formation assay on PC3 and DU145 cells transfected with DICE1 expression plasmid or control vector. Apoptosis was assessed by visualization of genomic DNA fragmentation on agarose gel. PCR arrays (SABiosciences) were used to identify specific signaling pathways modulated in response to DICE1 expression. Results: Markedly decreased DICE1 mRNA levels were detected in PrCa cell lines LNCap, DU145, PC3 and PC3ml as well as CPTX1532 as compared to NPTX1532, a cell line derived from normal prostate tissue. Ectopic expression of DICE1 cDNA in DU145 and PC3 cells substantially suppressed their ability to form colonies in vitro. This growth inhibition was not due to immediate induction of apoptosis suggesting growth suppression by other pathways. Expression profiling identified multiple pathways, such as Wnt, Hedgehog, PI-3 Kinase, NFκB and Insulin pathways, regulated in response to ectopic DICE1 expression. Furthermore, various transcription factors including Fos, Jun, CEBPA and PPAR-γ were up-regulated in response to DICE1. Conclusions: These results clearly illustrate the growth inhibitory ability of DICE1 in PrCa. Expression profiling links DICE1 function to growth factor signaling and cell-cell communication.

No significant financial relationships to disclose.

Clinical outcome of patients (pts) with taxane-resistant (TR) hormone-refractory prostate cancer (HRPC) treated with second-line cyclophosphamide (CP) -based metronomic chemotherapy

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Background: For pts with TR HRPC no standard chemotherapeutic treatment exist. In this study we evaluate the efficacy of CP-based metronomic chemotherapy in this pt population. Methods: Pts with metastatic HRPC with disease progression under docetaxel-based chemotherapy were eligible. The primary endpoint was PSA response. Secondary endpoints were time to progression (TTP), survival and toxicity. Low dose CP (50 mg/d) and dexamethasone (1 mg/d) were administered orally in a metronomic manner. Treatment was continued until disease progression. Results: Between February 2005 and May 2006 17 pts were enrolled in this study. The median follow-up was 12 weeks (range: 4–60). Median Age was 68 years (range: 42–85). Median PSA at study entry was 134 ng/ml (range: 46.0–6554). 9 pts had a PSA response (medium 44.4%), 4 pts = 50% and 5 pts < 50%. 8 pts had a PSA progression. The medium time to maximal response was 12 weeks (range: 4–36). TTP/survival for pts with PSA response and PSA progression was 24/60 weeks and 4/4 weeks, respectively. 3 pts of the progression group showed a decrease in PSA doubling time. 5 pts reported a decrease in bone pain after 4 weeks treatment. No grade 3 and 4 toxicities were noted. Conclusions: In this study, low-dose metronomic administered CP demonstrated efficacy as second line treatment in pts with TR HRPC. The treatment was well tolerated and almost without toxicity. The mechanism of action of low dose CP involves inhibition of tumor angiogenesis secondary to inhibition of dividing endothelial cells in tumor associated blood vessels. Dexamethasone may also have antiangiogenic properties by inhibiting the production of vascular endothelial growth factor. Further investigation regarding an antiangiogenic treatment strategy for HRPC are therefore of great interest.

No significant financial relationships to disclose.

Deleted In Cancer 1 (DICE1): Search for a function in prostate carcinoma (PCa)

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Background: Recently, DICE1 gene (MIM 604331 ) was identified to colocalize with the microsatellite marker D13S284 in 13q14.3, a region frequently affected by allelic deletion in PCa. We previously showed that DICE1 mRNA expression is down-regulated in PCa cell lines compared to normal prostate tissue, due to DICE1 promoter hypermethylation; suggesting that DICE1 is a tumor suppressor gene. Methods: Human PCa cell lines PC3 and DU145 were lipo-transfected with mammalian expression plasmids encoding for the full length DICE1 gene or for its N- (APAI construct) and C-terminal (DEAD construct) fragments. The constructs expression was determined by semi-quantitative PCR and quantified by Real-time PCR. Clonogenic formation and apoptotic assays were performed. Results: The PCR analysis showed that the expression of DICE1, APAI and DEAD domains in transfected PC3 and DU145 cell lines was increased 30.6, 75.2 and 27.9 fold in PC3 cells and 4.3, 5 and 2.5 fold in DU145 cells, respectively, compared to non-transfected cells. The function analysis showed that the ectopic expression of DICE1 suppressed clonogenic growth of PC3 and DU145 cell lines. Surprisingly, we showed that like DICE1, DEAD and APAI inhibit the PC3 and DU145 clonogenic growth suggesting that both regions are involved in prostate tumor growth inhibition. The apoptosis assay could not show any DNA fragmentation activity for DICE1. Conclusions: We demonstrated that DICE1 is a tumor suppressor in PCa. DICE1 mRNA expression is down-regulated in PCa cell lines compared to normal prostate tissue and its ectopic expression in PCa cell lines inhibits their capacity to form clonogenic colonies in vitro. The functional analysis could not reveal any role of DICE1 in PCa apoptosis, suggesting that other molecular mechanisms are involved.

No significant financial relationships to disclose.

[Idiopathic retroperitoneal fibrosis (Ormond's disease)]

INTRODUCTION

Idiopathic retroperitoneal fibrosis (RPF) represents a rare inflammatory disease, which leads to extensive fibrosis of the retroperitoneal space. In the course of the progressive fibrosis, fibrous tissue compresses the retroperitoneal structures with the development of consecutive ureteral obstruction. Because of the unknown aetiology, no consensus between conservative and surgical treatment exists.

CASE REPORT

A 60-year-old patient was admitted to hospital with left-sided flank pain, hydronephrosis, and retroperitoneal tumour. A CT scan-guided biopsy revealed RPF. The hydronephrosis was treated by endoluminal urinary diversion. Under simultaneous administration of steroids, an almost complete regression of the RPF was noted.

CONCLUSIONS

First goal in the treatment of RPF is urinary diversion to protect the renal function. A simultaneous therapy with steroids can cause a complete regression of the RPF. Surgical intervention is only recommended in refractory cases.

Randomized study of docetaxel (D) and dexamethasone (DX) with low or high dose estramustine (E) for patients with advanced hormone-refractory prostate cancer (HRPC)

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Background: D-based chemotherapy is a burgeoning option for men with advanced HRPC. Alone or in combination with E, D has been shown to improve median survival. In this study we tested the combination of D with two different doses of E in patients (pts) with HRPC to improve response rates and to lower side effects. Methods: 72 metastatic HRPC pts were randomly assigned to receive D (70 mg/m2 IV, d2, q3w) and E (3 × 280 mg/d PO starting 1 day prior to D, for 5 consecutive days) for arm A or E (3 x 140 mg/d PO starting 1 day prior to D, for 3 consecutive days) for arm B. Premedication with oral DX at a total daily dose of 16 mg, in divided doses two times a day was administered in arm A on day 1 to 5 and in arm B on day 1 to 3. Initially, 6 cycles were administered and repeated after significant PSA rise. Pts were monitored for PSA response, time to progression (TTP), survival and toxicity. Results: PSA declines of ≥75%, ≥50% and ≤50% were 36.8%, 55.3% and 44.7% in arm A and 38.2%, 67.6% and 32.4% in arm B, respectively (P = .442). TTP in Arm A and Arm B were 11 months (95% CI, 7–14) versus 14 months (95% CI, 8–19), P = .6911) and overall survival 21 months (95% CI, 6–35) versus 22 months (95% CI, 18–27), respectively, (P = .4149). The primary treatment-related side effects observed in arm A and arm B were granulocytopenia (34% and 29%, P = .663) and thrombotic complications caused by E (four pts (11%) and one pt (3%), respectively, P = .206). Associated baseline factors with overall survival in univariate analysis were ECOG performance status (P < .001), hemoglobin level (P < .001), bone pain (P < .001), and PSA (P < .097) and in multivariate analysis ECOG performance status (95% CI, 2.9–13.9) and bone pain (95% CI, 3.2–20.1), (P < .001). Conclusions: In this randomized phase II study the combination of D and E had substantial activity in HRPC. We did not find a statistically significant difference of higher dose of E in combination with D compared to a lower dose of E and D regarding PSA response, TTP and survival. However, there was a tendency of higher toxicity in the high dose E group. These treatment-related toxicities were mainly hematologic and manageable. The results of this study support the assertion that estramustine is not necessary in docetaxel-based treatment regimens.

No significant financial relationships to disclose.

In vivo upregulation of CD95 and CD95L causes synergistic inhibition of angiogenesis by TSP1 peptide and metronomic doxorubicin treatment

Antiangiogenic thrombospondin-1 (TSP1) induces endothelial cell death via a CD95-mediated cascade. We used this signaling pathway, where CD95/Fas is a rate-limiting intermediate, as a target to optimize the efficacy of TSP1 active peptide, DI-TSP. Like TSP1, DI-TSP upregulated endothelial CD95L in vivo. To modulate CD95 levels, we chose chemotherapy agent doxorubicin (DXR). DXR caused sustained upregulation of CD95 in the activated endothelium at 1/100 of the maximal tolerated dose. DI-TSP and DXR synergistically induced endothelial apoptosis in vitro, and in vivo, in developing murine vessels. Fas decoy, TSP1 receptor antibody and Pifithrin, a p53 inhibitor, severely decreased apoptosis and restored angiogenesis by DXR-DI-TSP combination, evidencing critical roles of CD95 and TSP1. Combined therapy synergistically blocked neovascularization and progression of the bladder and prostate carcinoma. Such informed design of a complex antiangiogenic therapy based on the rate-limiting molecular targets is a novel concept, which may yield new approaches to cancer treatment.

Nitrate and glutamate sensing by plant roots

The architecture of a root system plays a major role in determining how efficiently a plant can capture water and nutrients from the soil. Growth occurs at the root tips and the process of exploring the soil volume depends on the behaviour of large numbers of individual root tips at different orders of branching. Each root tip is equipped with a battery of sensory mechanisms that enable it to respond to a range of environmental signals, including nutrients, water potential, light, gravity and touch. We have previously identified a MADS (MCM1, agamous, deficiens and SRF) box gene (ANR1) in Arabidopsis thaliana that is involved in modulating the rate of lateral root growth in response to changes in the external NO3− supply. Transgenic plants have been generated in which a constitutively expressed ANR1 protein can be post-translationally activated by treatment with dexamethasone (DEX). When roots of these lines are treated with DEX, lateral root growth is markedly stimulated but there is no effect on primary root growth, suggesting that one or more components of the regulatory pathway that operate in conjunction with ANR1 in lateral roots may be absent in the primary root tip. We have recently observed some very specific effects of low concentrations of glutamate on root growth, resulting in significant changes in root architecture. Experimental evidence suggests that this response involves the sensing of extracellular glutamate by root tip cells. We are currently investigating the possible role of plant ionotropic glutamate receptors in this sensory mechanism.

Major alterations of the regulation of root NO(3)(-) uptake are associated with the mutation of Nrt2.1 and Nrt2.2 genes in Arabidopsis

The role of AtNrt2.1 and AtNrt2.2 genes, encoding putative NO(3)(-) transporters in Arabidopsis, in the regulation of high-affinity NO(3)(-) uptake has been investigated in the atnrt2 mutant, where these two genes are deleted. Our initial analysis of the atnrt2 mutant (S. Filleur, M.F. Dorbe, M. Cerezo, M. Orsel, F. Granier, A. Gojon, F. Daniel-Vedele [2001] FEBS Lett 489: 220-224) demonstrated that root NO(3)(-) uptake is affected in this mutant due to the alteration of the high-affinity transport system (HATS), but not of the low-affinity transport system. In the present work, we show that the residual HATS activity in atnrt2 plants is not inducible by NO(3)(-), indicating that the mutant is more specifically impaired in the inducible component of the HATS. Thus, high-affinity NO(3)(-) uptake in this genotype is likely to be due to the constitutive HATS. Root (15)NO(3)(-) influx in the atnrt2 mutant is no more derepressed by nitrogen starvation or decrease in the external NO(3)(-) availability. Moreover, the mutant also lacks the usual compensatory up-regulation of NO(3)(-) uptake in NO(3)(-)-fed roots, in response to nitrogen deprivation of another portion of the root system. Finally, exogenous supply of NH(4)(+) in the nutrient solution fails to inhibit (15)NO(3)(-) influx in the mutant, whereas it strongly decreases that in the wild type. This is not explained by a reduced activity of NH(4)(+) uptake systems in the mutant. These results collectively indicate that AtNrt2.1 and/or AtNrt2.2 genes play a key role in the regulation of the high-affinity NO(3)(-) uptake, and in the adaptative responses of the plant to both spatial and temporal changes in nitrogen availability in the environment.

In vivo mechanisms by which tumors producing thrombospondin 1 bypass its inhibitory effects

Thrombospondin 1 (TSP1) is a multifunctional protein able to activate TGFbeta and to inhibit angiogenesis in vivo. Although usually thought of as an inhibitor of tumor growth, TSP1 may sometimes be present at high levels during tumor progression, suggesting that tumors can eventually overcome their anti-tumor effects. Using a tet-repressible expression system, we demonstrate that murine TSP1 delayed the onset of tumor growth when produced in the tumor bed by rat fibrosarcoma tumor cells or by stromal fibroblasts coinjected with unmodified C6 glioma tumor cells. Yet upon prolonged exposure to TSP1, tumors came to grow at the same rate in the presence as in the absence of TSP1 and transplantation experiments showed that they had become insensitive to inhibition by TSP1 in both syngeneic and immune compromised hosts. Tumor resistance to TSP1 developed as a result of the in vivo outgrowth of pre-existing tumor cell variants that (1) secreted increased amounts of angiogenic factors that counterbalanced the inhibitory effect of TSP1 on neovascularization and (2) grew more efficiently in the presence of TSP1-activated TGFbeta. These results indicate that prolonged and continuous local delivery of a single multifunctional angiogenesis inhibitor like TSP1 to fast-growing tumors can lead to tumor resistance in vivo by fostering the outgrowth of subpopulations that are a by-product of the genetic instability of the tumor cells themselves.

An arabidopsis T-DNA mutant affected in Nrt2 genes is impaired in nitrate uptake

Expression analyses of Nrt2 plant genes have shown a strict correlation with root nitrate influx mediated by the high-affinity transport system (HATS). The precise assignment of NRT2 protein function has not yet been possible due to the absence of heterologous expression studies as well as loss of function mutants in higher plants. Using a reverse genetic approach, we isolated an Arabidopsis thaliana knock-out mutant where the T-DNA insertion led to the complete deletion of the AtNrt2.1 gene together with the deletion of the 3' region of the AtNrt2.2 gene. This mutant is impaired in the HATS, without being modified in the low-affinity system. Moreover, the de-regulated expression of a Nicotiana plumbaginifolia Nrt2 gene restored the mutant nitrate influx to that of the wild-type. These results demonstrate that plant NRT2 proteins do have a role in HATS.

CBP/p300 histone acetyl-transferase activity is important for the G1/S transition

Transforming viral proteins such as E1A which force quiescent cells into S phase have two essential cellular target proteins, Rb and CBP/p300. Rb regulates the G1/S transition by controlling the transcription factor E2F. CBP/p300 is a transcriptional co-activator with intrinsic histone acetyl-transferase activity. This activity is regulated in a cell cycle dependent manner and shows a peak at the G1/S transition, suggesting a function for CBP/p300 in this crucial step of the cell cycle. Here, we have artificially modulated CBP/p300 levels in individual cells through microinjection of specific antibodies and expression vectors. We show that CBP/p300 is required for cell proliferation and has an essential function during the G1/S transition. Using the same microinjection system and GFP-reporter vectors, we demonstrate that CBP/p300 is essential for the activity of E2F, a transcription factor that controls the G1/S transition. In addition, our results suggest that CBP HAT activity is required both for the G1/S transition and for E2F activity. Thus CBP/p300 seems to be a versatile protein involved in opposing cellular processes, which raises the question of how its multiple activities are regulated.

Molecular and functional regulation of two NO3- uptake systems by N- and C-status of Arabidopsis plants

Root NO3- uptake and expression of two root NO3- transporter genes (Nrt2;1 and Nrt1) were investigated in response to changes in the N- or C-status of hydroponically grown Arabidopsis thaliana plants. Expression of Nrt2;1 is up-regulated by NO3 - starvation in wild-type plants and by N-limitation in a nitrate reductase (NR) deficient mutant transferred to NO3- as sole N source. These observations show that expression of Nrt2;1 is under feedback repression by N-metabolites resulting from NO3- reduction. Expression of Nrt1 is not subject to such a repression. However, Nrt1 is over-expressed in the NR mutant even under N-sufficient conditions (growth on NH4NO3 medium), suggesting that expression of this gene is affected by the presence of active NR, but not by N-status of the plant. Root 15NO3- influx is markedly increased in the NR mutant as compared to the wild-type. Nevertheless, both genotypes have similar net 15NO3- uptake rates due to a much larger 14NO3- efflux in the mutant than in the wild-type. Expressions of Nrt2;1 and Nrt1 are diurnally regulated in photosynthetically active A. thaliana plants. Both increase during the light period and decrease in the first hours of the dark period. Sucrose supply prevents the inhibition of Nrt2;1 and Nrt1 expressions in the dark. In all conditions investigated, Nrt2;1 expression is strongly correlated with root 15NO3- influx at 0.2 mM external concentration. In contrast, changes in the Nrt1 mRNA level are not always associated with similar changes in the activities of high- or low-affinity NO3- transport systems.

The Wilms' tumor gene product represses the transcription of thrombospondin 1 in response to overexpression of c-Jun

Thrombospondin 1 (TSP1) is known for its significant anti-angiogenic properties. In a previous study, we have shown that transient or stable overexpression of the transcription factor c-Jun, in rat fibroblasts, leads to repression of TSP1. We now demonstrate that the c-Jun-induced repression of TSP1 does not occur directly and does not require binding of c-Jun to the TSP1 promoter. Instead, repression involves a factor secreted by c-Jun-overexpressing cells. This secreted factor triggers a signal transduction pathway from the membrane to the nucleus, and these signals lead to the binding of the product of the Wilms' tumor suppressor gene, WT1, to the -210 region of the TSP1 promoter. This region binds WT1 and SP1, but not EGR1, although its sequence fits the consensus binding site for this transcription factor. WT1 overexpression in transfected cells inhibits endogenous TSP1 gene expression and TSP1 transcription in experiments using TSP1 promoter-reporter constructs. The WT1 - KTS isoform is more active in repressing TSP1 transcription than WT1 + KTS, while EGR1 is inactive. Enhancement of WT1 binding to DNA in response to c-Jun does not require de novo protein synthesis. The above mechanism for TSP1 repression could apply to other genes, thus coordinating their regulation in the vicinity of a c-Jun-overexpressing cell. We conclude that WT1, which was discovered as a result of its tumor suppressor properties, may also possess oncogenic characteristics in the c-Jun transformation process, and thus repress the anti-angiogenic protein, TSP1.

Expression analysis of a high-affinity nitrate transporter isolated from Arabidopsis thaliana by differential display

We used the differential display technique on total RNAs from roots of Arabidopsis thaliana (L.) Heynh. plants which had or had not been induced for 2 h by nitrate. One isolated cDNA clone, designated Nrt2:1At, was found to code for a putative high-affinity nitrate transporter. Two genomic sequences homologous to Nrt2:1At were found to be localized on the same fragment of chromosome 1 in the Arabidopsis genome. Expression analyses of both low- and high-affinity nitrate transporter genes, respectively Nrt1:1At (previously named Chl1) and Nrt2:1At, were carried out on plants grown under different nitrogen regimes. In this paper, we show that both genes are induced by very low levels of nitrate (50 microM KNO3). However, stronger induction was observed with Nrt2:1At than with Nrt1:1At. Moreover, these two genes, although both over-expressed in a nitrate-reductase-deficient mutant, were differently regulated when N-sufficient wild-type or mutant plants were transferred to an N-free medium. Indeed, the steady-state amounts of Nrt1:1At mRNA declined whereas the amount of Nrt2:1At mRNA increased, probably reflecting the de-repression of the high-affinity transport system during N-starvation.

Nitrate transport: a key step in nitrate assimilation

The nitrate assimilation pathway has been the matter of intensive research during the past decade. Many genes involved in low and high affinity nitrate uptake have been identified in fungi, algae and, more recently, in plants. The plant genes so far isolated are transcriptionally regulated; their inducibility by nitrate seems to be a common feature, shared by their homologs in fungi and algae. A number of questions remain to be elucidated regarding the physiological roles of these transporters and the regulation of their expression.