Loss of ORP3 induces aneuploidy and promotes bladder cancer cell invasion through deregulated microtubule and actin dynamics

We have recently shown that loss of ORP3 leads to aneuploidy induction and promotes tumor formation. However, the specific mechanisms by which ORP3 contributes to ploidy-control and cancer initiation and progression is still unknown. Here, we report that ORP3 is highly expressed in ureter and bladder epithelium while its expression is downregulated in invasive bladder cancer cell lines and during tumor progression, both in human and in mouse bladder cancer. Moreover, we observed an increase in the incidence of N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN)-induced invasive bladder carcinoma in the tissue-specific Orp3 knockout mice. Experimental data demonstrate that ORP3 protein interacts with γ-tubulin at the centrosomes and with components of actin cytoskeleton. Altering the expression of ORP3 induces aneuploidy and genomic instability in telomerase-immortalized urothelial cells with a stable karyotype and influences the migration and invasive capacity of bladder cancer cell lines. These findings demonstrate a crucial role of ORP3 in ploidy-control and indicate that ORP3 is a bona fide tumor suppressor protein. Of note, the presented data indicate that ORP3 affects both cell invasion and migration as well as genome stability through interactions with cytoskeletal components, providing a molecular link between aneuploidy and cell invasion and migration, two crucial characteristics of metastatic cells.

TBX3 is dynamically expressed in pancreatic organogenesis and fine-tunes regeneration

BACKGROUND

The reactivation of genetic programs from early development is a common mechanism for injury-induced organ regeneration. T-box 3 (TBX3) is a member of the T-box family of transcription factors previously shown to regulate pluripotency and subsequent lineage commitment in a number of tissues, including limb and lung. TBX3 is also involved in lung and heart organogenesis. Here, we provide a comprehensive and thorough characterization of TBX3 and its role during pancreatic organogenesis and regeneration.

RESULTS

We interrogated the level and cell specificity of TBX3 in the developing and adult pancreas at mRNA and protein levels at multiple developmental stages in mouse and human pancreas. We employed conditional mutagenesis to determine its role in murine pancreatic development and in regeneration after the induction of acute pancreatitis. We found that Tbx3 is dynamically expressed in the pancreatic mesenchyme and epithelium. While Tbx3 is expressed in the developing pancreas, its absence is likely compensated by other factors after ablation from either the mesenchymal or epithelial compartments. In an adult model of acute pancreatitis, we found that a lack of Tbx3 resulted in increased proliferation and fibrosis as well as an enhanced inflammatory gene programs, indicating that Tbx3 has a role in tissue homeostasis and regeneration.

CONCLUSIONS

TBX3 demonstrates dynamic expression patterns in the pancreas. Although TBX3 is dispensable for proper pancreatic development, its absence leads to altered organ regeneration after induction of acute pancreatitis.

Npm1 haploinsufficiency in collaboration with MEIS1 is sufficient to induce AML in mice

NPM1 is among the most frequently mutated genes in acute myeloid leukemia (AML). Mutations in the NPM1 gene result in the increased export of NPM1 to the cytoplasm (NPM1c) and are associated with multiple transforming events including the aberrant upregulation of MEIS1 that maintains stem cell and cell cycle-associated pathways in NPM1c AML. However, another consequence of the NPM1c mutation is the inadequate levels of NPM1 wild-type in the nucleus and nucleolus, caused by the loss of one wild-type allele in addition to enforced NPM1 nuclear export. The contribution of NPM1 haploinsufficiency independently of the NPM1 mutation to AML development and its relationship with MEIS1 function is poorly understood. Using mouse models, our study shows that NPM1 haploinsufficiency paired with MEIS1 overexpression is sufficient to induce a fully penetrant AML in mice that transcriptionally resembles human NPM1c AML. NPM1 haploinsufficiency alters MEIS1-binding occupancies such that it binds the promoter of the oncogene structural maintenance of chromosome protein 4 (SMC4) in NPM1 haploinsufficient AML cells but not in NPM1 wild-type-harboring Hoxa9/Meis1-transformed cells. SMC4 is higher expressed in haploinsufficient and NPM1c+ AML cells, which are more vulnerable to the disruption of the MEIS1-SMC4 axis compared with AML cells with nonmutated NPM1. Taken together, our study underlines that NPM1 haploinsufficiency on its own is a key factor of myeloid leukemogenesis and characterizes the MEIS1-SMC4 axis as a potential therapeutic target in this AML subtype.

The Role of TKS5 in Chromosome Stability and Bladder Cancer Progression

TKS5 promotes invasion and migration through the formation of invadopodia in some tumour cells, and it also has an important physiological function in cell migration through podosome formation in various nontumour cells. To date, the role of TKS5 in urothelial cells, and its potential role in BC initiation and progression, has not yet been addressed. Moreover, the contribution of TKS5 to ploidy control and chromosome stability has not been reported in previous studies. Therefore, in the present study, we wished to address the following questions: (i) Is TKS5 involved in the ploidy control of urothelial cells? (ii) What is the mechanism that leads to aneuploidy in response to TKS5 knockdown? (iii) Is TKS5 an oncogene or tumour-suppressor gene in the context of BC? (iv) Does TKS5 affect the proliferation, migration and invasion of BC cells? We assessed the gene and protein expressions via qPCR and Western blot analyses in a set of nontumour cell strains (Y235T, HBLAK and UROtsa) and a set of BC cell lines (RT4, T24, UMUC3 and J82). Following the shRNA knockdown in the TKS5-proficient cells and the ectopic TKS5 expression in the cell lines with low/absent TKS5 expression, we performed functional experiments, such as metaphase, invadopodia and gelatine degradation assays. Moreover, we determined the invasion and migration abilities of these genetically modified cells by using the Boyden chamber and wound-healing assays. The TKS5 expression was lower in the bladder cancer cell lines with higher invasive capacities (T24, UMUC3 and J82) compared to the nontumour cell lines from human ureter (Y235T, HBLAK and UROtsa) and the noninvasive BC cell line RT4. The reduced TKS5 expression in the Y235T cells resulted in augmented aneuploidy and impaired cell division. According to the Boyden chamber and wound-healing assays, TKS5 promotes the invasion and migration of bladder cancer cells. According to the present study, TKS5 regulates the migration and invasion processes of bladder cancer (BC) cell lines and plays an important role in genome stability.

[Organoids as a milestone on the way to personalized treatment of urothelial carcinoma: a systematic review]

BACKGROUND

The treatment options for locally advanced and metastatic urothelial carcinoma (UC) are currently limited to established chemotherapy and immunotherapy protocols. Targeted treatment is so far restricted to a small subgroup of patients. Urothelial organoid systems could make a decisive contribution in establishing effective personalized treatment options by enabling drug response prediction through testing the sensitivity of individual patients. The aim of this article is to describe the state of the science of clinically applicable organoid systems for UC.

METHODOLOGY

A systematic literature search was conducted in several medical databases (Medline, Cochrane Library) and study registers (ClinicalTrials.gov, the EU Clinical Trials Register and the WHO International Clinical Trials Registry). The search terms and the search strategy were adapted to the databases used.

RESULTS

Overall, 7 studies met the inclusion criteria on the topic of UC organoids. These studies describe the fundamental workflow in establishing organoid systems in patients with tumors of the urinary bladder or the renal pelvis. The success rates in generating organoids from non-muscle-invasive bladder cancer were 70-77% and for muscle-invasive bladder cancer 42%. For patient organoids systematic drug testing was carried out.

CONCLUSION

The generation of UC organoids is feasible and the ex vivo testing of individual treatment forms is possible. Due to the lack of a standardized methodology, their implementation remains experimental at the moment. The methodology has a high potential to provide a personalized treatment concept to patients with urothelial cancer.

Organoids at the PUB: The Porcine Urinary Bladder Serves as a Pancreatic Niche for Advanced Cancer Modeling

Despite intensive research and progress in personalized medicine, pancreatic ductal adenocarcinoma remains one of the deadliest cancer entities. Pancreatic duct-like organoids (PDLOs) derived from human pluripotent stem cells (PSCs) or pancreatic cancer patient-derived organoids (PDOs) provide unique tools to study early and late stage dysplasia and to foster personalized medicine. However, such advanced systems are neither rapidly nor easily accessible and require an in vivo niche to study tumor formation and interaction with the stroma. Here, the establishment of the porcine urinary bladder (PUB) is revealed as an advanced organ culture model for shaping an ex vivo pancreatic niche. This model allows pancreatic progenitor cells to enter the ductal and endocrine lineages, while PDLOs further mature into duct-like tissue. Accordingly, the PUB offers an ex vivo platform for earliest pancreatic dysplasia and cancer if PDLOs feature KRASG12D mutations. Finally, it is demonstrated that PDOs-on-PUB i) resemble primary pancreatic cancer, ii) preserve cancer subtypes, iii) enable the study of niche epithelial crosstalk by spiking in pancreatic stellate and immune cells into the grafts, and finally iv) allow drug testing. In summary, the PUB advances the existing pancreatic cancer models by adding feasibility, complexity, and customization at low cost and high flexibility.

A Comparative Assessment of Replication Stress Markers in the Context of Telomerase

Simple Summary

Genetic alterations such as oncogenic- or aneuploidy-inducing mutations can induce replication stress as a tumor protection mechansim. Previous data indicated that telomerase may ameliorate the cellular responses that induce replication stress. However, the mechanisms how this may occur are still unclear. In order to address this question, the accurate evaluation of replication stress in the presence and absence of telomerase is crucial. Therefore, we used telomerase negative normal human fibroblasts, as well as their telomerase positive counterparts to compare the suitability of three protein markers (pRPA2, γ-H2AX and 53BP1), which were previously reported to accumulate in response to harmful conditions leading to replication stress in cells. In summary, we find that pRPA2 is the most consistent and reliable marker for the detection of replication stress. Further, we demonstrated that the inhibition of the DNA-damage activated ATM and ATR kinases by specific small compounds impaired the accumulation of pRPA2 foci in the absence of telomerase. These data suggest that telomerase rescues the cells from replication stress upon supression of DNA damage induction by modulating the ATM and ATR signaling pathways, and may therefore support tumor formation of genetically unstable cells.

Abstract

Aberrant replication stress (RS) is a source of genome instability and has serious implications for cell survival and tumourigenesis. Therefore, the detection of RS and the identification of the underlying molecular mechanisms are crucial for the understanding of tumourigenesis. Currently, three protein markers—p33-phosphorylated replication protein A2 (pRPA2), γ-phosphorylated H2AX (γ-H2AX), and Tumor Protein P53 Binding Protein 1 (53BP1)—are frequently used to detect RS. However, to our knowledge, there is no report that compares their suitability for the detection of different sources of RS. Therefore, in this study, we evaluate the suitability of pRPA2, γ-H2AX, and 53BP1 for the detection of RS caused by different sources of RS. In addition, we examine their suitability as markers of the telomerase-mediated alleviation of RS. For these purposes, we use here telomerase-negative human fibroblasts (BJ) and their telomerase-immortalized counterparts (BJ-hTERT). Replication stress was induced by the ectopic expression of the oncogenic RAS mutant RAS^G12V (OI-RS), by the knockdown of ploidy-control genes ORP3 or MAD2 (AI-RS), and by treatment with hydrogen peroxide (ROS-induced RS). The level of RS was determined by immunofluorescence staining for pRPA2, γ-H2AX, and 53BP1. Evaluation of the staining results revealed that pRPA2- and γ-H2AX provide a significant and reliable assessment of OI-RS and AI-RS compared to 53BP1. On the other hand, 53BP1 and pRPA2 proved to be superior to γ-H2AX for the evaluation of ROS-induced RS. Moreover, the data showed that among the tested markers, pRPA2 is best suited to evaluate the telomerase-mediated suppression of all three types of RS. In summary, the data indicate that the choice of marker is important for the evaluation of RS activated through different conditions.

Telomerase and Pluripotency Factors Jointly Regulate Stemness in Pancreatic Cancer Stem Cells

To assess the role of telomerase activity and telomere length in pancreatic CSCs we used different CSC enrichment methods (CD133, ALDH, sphere formation) in primary patient-derived pancreatic cancer cells. We show that CSCs have higher telomerase activity and longer telomeres than bulk tumor cells. Inhibition of telomerase activity, using genetic knockdown or pharmacological inhibitor (BIBR1532), resulted in CSC marker depletion, abrogation of sphere formation in vitro and reduced tumorigenicity in vivo. Furthermore, we identify a positive feedback loop between stemness factors (NANOG, OCT3/4, SOX2, KLF4) and telomerase, which is essential for the self-renewal of CSCs. Disruption of the balance between telomerase activity and stemness factors eliminates CSCs via induction of DNA damage and apoptosis in primary patient-derived pancreatic cancer samples, opening future perspectives to avoid CSC-driven tumor relapse. In the present study, we demonstrate that telomerase regulation is critical for the "stemness" maintenance in pancreatic CSCs and examine the effects of telomerase inhibition as a potential treatment option of pancreatic cancer. This may significantly promote our understanding of PDAC tumor biology and may result in improved treatment for pancreatic cancer patients.

Modeling plasticity and dysplasia of pancreatic ductal organoids derived from human pluripotent stem cells

Personalized in vitro models for dysplasia and carcinogenesis in the pancreas have been constrained by insufficient differentiation of human pluripotent stem cells (hPSCs) into the exocrine pancreatic lineage. Here, we differentiate hPSCs into pancreatic duct-like organoids (PDLOs) with morphological, transcriptional, proteomic, and functional characteristics of human pancreatic ducts, further maturing upon transplantation into mice. PDLOs are generated from hPSCs inducibly expressing oncogenic GNAS, KRAS, or KRAS with genetic covariance of lost CDKN2A and from induced hPSCs derived from a McCune-Albright patient. Each oncogene causes a specific growth, structural, and molecular phenotype in vitro. While transplanted PDLOs with oncogenic KRAS alone form heterogenous dysplastic lesions or cancer, KRAS with CDKN2A loss develop dedifferentiated pancreatic ductal adenocarcinomas. In contrast, transplanted PDLOs with mutant GNAS lead to intraductal papillary mucinous neoplasia-like structures. Conclusively, PDLOs enable in vitro and in vivo studies of pancreatic plasticity, dysplasia, and cancer formation from a genetically defined background.

Grainyhead-Like 3 Influences Migration and Invasion of Urothelial Carcinoma Cells

Invasive urothelial carcinomas of the bladder (UCB) characteristically show a loss of differentiation markers. The transcription factor Grainyhead-like 3 (GRHL3) plays an important role in the development and differentiation of normal urothelium. The contribution to UCB progression is still elusive. Differential expression of GRHL3 was assessed in normal human urothelium and in non-invasive and invasive bladder cancer cell lines. The contribution of GRHL3 to cell proliferation, viability and invasion in UCB cell lines was determined by gain- and loss-of-function assays in vitro and in an organ culture model using de-epithelialized porcine bladders. GRHL3 expression was detectable in normal human urothelial cells and showed significantly higher mRNA and protein levels in well-differentiated, non-invasive RT4 urothelial carcinoma cells compared to moderately differentiated RT112 cells. GRHL3 expression was absent in anaplastic and invasive T24 cells. Ectopic de novo expression of GRHL3 in T24 cells significantly impaired their migration and invasion properties in vitro and in organ culture. Its downregulation improved the invasive capacity of RT4 cells. The results indicate that GRHL3 may play a role in progression and metastasis in UCB. In addition, this work demonstrates that de-epithelialized porcine bladder organ culture can be a useful, standardized tool to assess the invasive capacity of cancer cells.

Bladder cancer-derived interleukin-1 converts the vascular endothelium into a pro-inflammatory and pro-coagulatory surface

Background

Bladder cancer cells orchestrate tumour progression by pro-inflammatory cytokines. Cytokines modulate the local tumour microenvironment and increase the susceptibility of tumour distant tissues for metastasis. Here, we investigated the impact of human bladder cancer cell derived factors on the ability to modulate and activate human vascular endothelial cells.

Methods

The pro-inflammatory and pro-coagulatory potential of four different bladder cancer cell lines was accessed by qRT-PCR arrays and ELISA. Modulation and activation of endothelial cells was studied in microfluidic devices. Clinical relevance of our findings was confirmed by immune histology in tissue samples of bladder cancer patients and public transcriptome data.

Results

The unbalanced ratio between interleukin (IL)-1 and IL-1 receptor antagonist (IL-1ra) in the secretome of bladder cancer cells converted the quiescent vascular endothelium into a pro-adhesive, pro-inflammatory, and pro-coagulatory surface. Microfluidic experiments showed that tumour cell induced endothelial cell activation promoted leukocyte recruitment and platelet adhesion. Human bladder cancer tissue analysis confirmed that loss of IL-1ra and elevated IL-1 expression was associated with enhanced cancer progression.

Conclusions

Our data indicate that IL-1 and IL-1ra were dysregulated in bladder cancer and could facilitate tumour dissemination through endothelial cell activation. Targeting the IL-1/IL-1ra axis might attenuate tumour-mediated inflammation and metastasis formation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-020-07548-z.

Establishment of Real-Time Multispectral Imaging for the Detection of Bladder Cancer Using a Preclinical in Vivo Model

BACKGROUND: Emerging imaging technologies such as real-time multispectral imaging (rMSI) hold great potential for simultaneous visualization of multiple target structures using fluorophores on various tumours including bladder cancer (BC). These technologies, however, require a multi-step preclinical evaluation process, including mouse models. OBJECTIVE: To demonstrate the suitability of the new rMSI technology for the detection of premalignant lesions and malignant BC in a preclinical mouse model using contrast agents. METHODS: Tumours were induced by N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN), which is known to induce BC in rodent models. In total, 30 mice (C57BL/6) were fed with 0.1% BBN ad libitum in drinking water for up to 5 months. Bladders were excised at 3 (n = 6) and 5 months (n = 24) of treatment and incubated ex vivo with Hexaminolevulinat (HAL, Hexvix®), CD47-FITC, CD90.2-FITC or a combination of CD90.2-FITC/CD47-FITC and HAL. The bladders were analyzed by an endoscopic rMSI prototype system equipped with a spectral filter (Chroma), a 4 mm endoscope (Karl Storz) with 30° optic, a LED light source and a PC with a microcontroller board. RESULTS: 5-month treatment of mice with 0.1% BBN led to the formation of squamous carcinoma (46%, n = 11) while urothelial carcinoma was observed only in one mouse (4%, n = 1). Carcinoma in situ (CIS) was detectable in twelve out of twenty-four mice (50%, n = 12) treated for 5 month and in three out of six mice (50%, n = 3) treated for 3 months.The metabolite of HAL, protoporphyrin IX (PpIX), could be reliably and specifically detected in all of mouse bladder tumours and CIS. However, detection of the CD90.2 surface marker was less reliable, potentially due to species- or tumour-subtype specificity. CONCLUSIONS: This model offers the potential for preclinical imaging studies with combined fluorescence targets, e.g. HAL, in combination with BC-specific antibodies.

Telomeres and Telomerase in the Development of Liver Cancer

Liver cancer is one of the most common cancer types worldwide and the fourth leading cause of cancer-related death. Liver carcinoma is distinguished by a high heterogeneity in pathogenesis, histopathology and biological behavior. Dysregulated signaling pathways and various gene mutations are frequent in hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA), which represent the two most common types of liver tumors. Both tumor types are characterized by telomere shortening and reactivation of telomerase during carcinogenesis. Continuous cell proliferation, e.g., by oncogenic mutations, can cause extensive telomere shortening in the absence of sufficient telomerase activity, leading to dysfunctional telomeres and genome instability by breakage-fusion-bridge cycles, which induce senescence or apoptosis as a tumor suppressor mechanism. Telomerase reactivation is required to stabilize telomere functionality and for tumor cell survival, representing a genetic risk factor for the development of liver cirrhosis and liver carcinoma. Therefore, telomeres and telomerase could be useful targets in hepatocarcinogenesis. Here, we review similarities and differences between HCC and iCCA in telomere biology.

Drug targeting CYP2E1 for the treatment of early-stage alcoholic steatohepatitis

Background and aims

Alcoholic steatohepatitis (ASH)—the inflammation of fatty liver—is caused by chronic alcohol consumption and represents one of the leading chronic liver diseases in Western Countries. ASH can lead to organ dysfunction or progress to hepatocellular carcinoma (HCC). Long-term alcohol abstinence reduces this probability and is the prerequisite for liver transplantation—the only effective therapy option at present. Elevated enzymatic activity of cytochrome P450 2E1 (CYP2E1) is known to be critically responsible for the development of ASH due to excessively high levels of reactive oxygen species (ROS) during metabolization of ethanol. Up to now, no rational drug discovery process was successfully initiated to target CYP2E1 for the treatment of ASH.

Methods

In this study, we applied a rational drug design concept to develop drug candidates (NCE) including preclinical studies.

Results

A new class of drug candidates was generated successfully. Two of the most promising small compounds named 12-Imidazolyl-1-dodecanol (abbr.: I-ol) and 1-Imidazolyldodecane (abbr.: I-an) were selected at the end of this process of drug discovery and developability. These new ω-imidazolyl-alkyl derivatives act as strong chimeric CYP2E1 inhibitors at a nanomolar range. They restore redox balance, reduce inflammation process as well as the fat content in the liver and rescue the physiological liver architecture of rats consuming continuously a high amount of alcohol.

Conclusions

Due to its oral application and therapeutic superiority over an off-label use of the hepatoprotector ursodeoxycholic acid (UDCA), this new class of inhibitors marks the first rational, pharmaceutical concept in long-term treatment of ASH.

Urothelial Carcinoma of the Bladder Induces Endothelial Cell Activation and Hypercoagulation

Cancer-related venous thromboembolisms (VTE) are associated with metastasis and reduced survival in patients with urothelial cancer of the bladder. Although previous reports suggest the contribution of tissue factor and podoplanin, the mechanistic linkage between VTE and bladder cancer cell-derived molecules is unknown. Therefore, we compared distinct procoagulant pathways in four different cell lines. In vitro findings were further confirmed by microfluidic experiments mimicking the pathophysiology of tumor blood vessels and in tissue samples of patients with bladder cancer by transcriptome analysis and immunohistology. In vitro and microfluidic experiments identified bladder cancer-derived VEGF-A as highly procoagulant because it promoted the release of von Willebrand factor (VWF) from endothelial cells and thus platelet aggregation. In tissue sections from patients with bladder cancer, we found that VWF-mediated blood vessel occlusions were associated with a poor outcome. Transcriptome data further indicate that elevated expression levels of enzymes modulating VEGF-A availability were significantly connected to a decreased survival in patients with bladder cancer. In comparison with previously postulated molecular players, we identified tumor cell-derived VEGF-A and endothelial VWF as procoagulant mediators in bladder cancer. Therapeutic strategies that prevent the VEGF-A-mediated release of VWF may reduce tumor-associated hypercoagulation and metastasis in patients with bladder cancer. IMPLICATIONS: We identified the VEGF-A-mediated release of VWF from endothelial cells to be associated with bladder cancer progression.

[The development of real-time multispectral imaging for the diagnostics of bladder cancer]

The performance of white light (WL) cystoscopy in the diagnostics of bladder cancer can be optimized by the use of modern imaging modalities, such as photodynamic diagnostics (PDD) and narrow band imaging (NBI). Real-time multispectral imaging (rMSI) enables simultaneous imaging of reflectance and fluorescence modalities in multiple spectral bands. We created a multiparametric cystoscopy image by digital overlapping of several modalities, e.g. WL, enhanced vascular contrast (EVC), raw fluorescence mode, protoporphyrin IX and autofluorescence (AF). The technical development and the subsequent clinical implementation of rMSI required a structured preclinical evaluation process, including both ex vivo and in vivo trials before the technology can be applied in patients. This review article presents the phases of testing, validation and the first clinical application of rMSI in urological endoscopy.

Aneuploidy-inducing gene knockdowns overlap with cancer mutations and identify Orp3 as a B-cell lymphoma suppressor

Aneuploidy can instigate tumorigenesis. However, mutations in genes that control chromosome segregation are rare in human tumors as these mutations reduce cell fitness. Screening experiments indicate that the knockdown of multiple classes of genes that are not directly involved in chromosome segregation can lead to aneuploidy induction. The possible contribution of these genes to cancer formation remains yet to be defined. Here we identified gene knockdowns that lead to an increase in aneuploidy in checkpoint-deficient human cancer cells. Computational analysis revealed that the identified genes overlap with recurrent mutations in human cancers. The knockdown of the three strongest selected candidate genes (ORP3, GJB3, and RXFP1) enhances the malignant transformation of human fibroblasts in culture. Furthermore, the knockout of Orp3 results in an aberrant expansion of lymphoid progenitor cells and a high penetrance formation of chromosomal instable, pauci-clonal B-cell lymphoma in aging mice. At pre-tumorous stages, lymphoid cells from the animals exhibit deregulated phospholipid metabolism and an aberrant induction of proliferation regulating pathways associating with increased aneuploidy in hematopoietic progenitor cells. Together, these results support the concept that aneuploidy-inducing gene deficiencies contribute to cellular transformation and carcinogenesis involving the deregulation of various molecular processes such as lipid metabolism, proliferation, and cell survival.

Multiparametric Cystoscopy for Detection of Bladder Cancer Using Real-time Multispectral Imaging

BACKGROUND

Various imaging modalities can be used in addition to white light (WL) to improve detection of bladder cancer (BC).

OBJECTIVE

To use real-time multispectral imaging (rMSI) during urethrocystoscopy to combine different imaging modalities to achieve multiparametric cystoscopy (MPC).

DESIGN, SETTING, AND PARTICIPANTS

The rMSI system consisted of a camera with a spectral filter, a multi-LED light source, a microcontroller, and a computer for display and data acquisition. MSI with this system was achieved via temporal multiplexing.

SURGICAL PROCEDURE

MPC was performed in ten patients with a diagnosed bladder tumor.

MEASUREMENTS

We gathered evidence to prove the feasibility of our approach. In addition, experienced urologists performed post-interventional evaluation of images of individual lesions. Images were independently rated in a semiquantitative manner for each modality. A statistical model was built for pairwise comparisons across modalities.

RESULTS AND LIMITATIONS

Overall, 31 lesions were detected using the rMSI set-up. Histopathology revealed malignancy in 27 lesions. All lesions could be visualized simultaneously in five modalities: WL, enhanced vascular contrast (EVC), blue light fluorescence, protoporphyrin IX fluorescence, and autofluorescence. EVC and photodynamic diagnosis images were merged in real time into one MP image. Using the recorded images, two observers identified all malignant lesions via MPC, whereas the single modalities did not arouse substantial suspicion for some lesions. The MP images of malignant lesions were rated significantly more suspicious than the images from single imaging modalities.

CONCLUSIONS

We demonstrated for the first time the application of rMSI in endourology and we established MPC for detection of BC. This approach allows existing imaging modalities to be combined, and it may significantly improve the detection of bladder cancer.

PATIENT SUMMARY

Real-time multispectral imaging was successfully used to combine different imaging aids for more comprehensive illustration of bladder tumors for surgeons. In the future, this technique may allow better detection of bladder tumors and more complete endoscopic resection in cases of cancer.

Implications of TERT promoter mutations and telomerase activity in urothelial carcinogenesis

Telomerase activity imparts eukaryotic cells with unlimited proliferation capacity, one of the cancer hallmarks. Over 90% of human urothelial carcinoma of the bladder (UCB) tumours are positive for telomerase activity. Telomerase activation can occur through several mechanisms. Mutations in the core promoter region of the human telomerase reverse transcriptase gene (TERT) cause telomerase reactivation in 60-80% of UCBs, whereas the prevalence of these mutations is lower in urothelial cancers of other origins. TERT promoter mutations are the most frequent genetic alteration across all stages of UCB, indicating a strong selection pressure during neoplastic transformation. TERT promoter mutations could arise during regeneration of normal urothelium and, owing to consequential telomerase reactivation, might be the basis of UCB initiation, which represents a new model of urothelial cancer origination. In the future, TERT promoter mutations and telomerase activity might have diagnostic and therapeutic applications in UCB.

A multicenter round robin test of PD-L1 expression assessment in urothelial bladder cancer by immunohistochemistry and RT-qPCR with emphasis on prognosis prediction after radical cystectomy

Background

Immunohistochemical PD-L1 assessment is currently used to identify responders towards checkpoint inhibitors although it is limited by inter-observer effects. Here, we conducted a multi-center round robin test to prove the possibility of assessing the PD-L1 status by gene expression to avoid inter-observer effects.

Patients and methods

Gene expression of PD-L1 was analyzed in a total of 294 samples (14 cases non-muscle invasive and muscle-invasive bladder cancer; MIBC) in seven centers by a RT-qPCR kit and compared with immunohistochemical scoring of three pathologists (DAKO, 22c3). Both assays were compared towards prognosis prediction in a cohort of 88 patients with MIBC.

Results

PD-L1 gene expression revealed very high inter center correlation (centrally extracted RNA: r = 0.68–0.98, p ≤ 0.0076; locally extracted RNA: r = 0.81–0.98, p ≤ 0.0014). IHC Inter-observer concordance was moderate to substantial for immune cells (IC), fair for combined IC/ tumor cell (TC) (IC: κ = 0.50–0.61; IC + TC: κ = 0.50), and fair for TC scoring (κ = 0.26–0.35). Gene expression assessment resulted in more positive cases (9/14 cases positive vs. 6/14 cases [IHC]) which could be validated in the independent cohort. Positive mRNA status was associated with significantly better overall and disease-specific survival (5-year OS: 50% vs. 26%, p = 0.0042, HR = 0.48; 5 year DSS: 65% vs. 40%, p = 0.012, HR = 0.49). The 1% IHC IC cut-off also revealed significant better OS (5 year OS: 58% vs. 31%, p = 0.036, HR = 0.62).

Conclusion

Gene expression showed very high inter-center agreement. Gene expression assessment also resulted in more positive cases and revealed better prognosis prediction. PD-L1 mRNA expression seems to be a reproducible and robust tool for PD-L1 assessment.

Decreased Invasion of Urothelial Carcinoma of the Bladder by Inhibition of Matrix-Metalloproteinase 7

Objectives:

To measure and to modulate the invasive potential of urothelial carcinoma of the bladder (UCB) cells in a standardized preclinical setting using broad-spectrum matrix-metalloproteinase (MMPs) inhibitors and specific targeting of MMP7.

Materials and Methods:

MMP expression levels in UCB cells were determined by quantitative real-time PCR (qRT-PCR) and gel zymographies of cell supernatants (MMP9, MMP2 and MMP1) and cell lysates (MMP7). The invasiveness of human UCB cells (HT1197 and T24/83) and human benign urothelial cells (UROtsa) was modulated by a broad-spectrum MMP inhibitor (4-Aminobenzoyl-Gly-Pro-D-Leu-D-Ala hydroxamic acid; AHA) and by MMP7 specific siRNAs. MMP7 knockdown efficiency was assessed by qRT-PCR and western blot. Invasive potential of UCB cells was measured by a standardized trans-epithelial electrical resistance (TEER) assay.

Results:

Different MMP secretion profiles were measured in UCB cells. The active form of MMP7 was exclusively detected in HT1197 cells. Characteristic TEER breakdown patterns were observed in UCB cells when compared to benign cells. Invasive potentials were significantly higher in HT1197 cells than in T24/83 and in UROtsa cells [14.8±5.75 vs. 1.5±0.56 and 1.2±0.15, respectively; p < 0.01]. AHA treatment reduced the invasive potential of HT1197 cells. Also the specific downregulation of MMP7 by siRNA lowered the HT1197 cell invasiveness [20±1.0 vs. 16±2.8; p < 0.05]. Neither AHA nor MMP-7 siRNA transfection altered the invasive potential of T24/83 cells.

Conclusions:

Invasion of UCB is partially dependent on MMPs. Specific targeting of MMP7 by siRNA reduces the invasive potential in a subgroup of UCB cells. Therefore, MMP7 represents a potential therapeutic target which warrants further investigation.

Characterization of SKAP/kinastrin isoforms: the N-terminus defines tissue specificity and Pontin binding

Small Kinetochore-Associated Protein (SKAP)/Kinastrin is a multifunctional protein with proposed roles in mitosis, apoptosis and cell migration. Exact mechanisms underlying its activities in these cellular processes are not completely understood. SKAP is predicted to have different isoforms, however, previous studies did not differentiate between them. Since distinct molecular architectures of protein isoforms often influence their localization and functions, this study aimed to examine the expression profile and functional differences between SKAP isoforms in human and mouse. Analyses of various human tissues and cells of different origin by RT-PCR, and by Western blotting and immunocytochemistry applying newly generated anti-SKAP monoclonal antibodies revealed that human SKAP exists in two protein isoforms: ubiquitously expressed SKAP16 and testis/sperm-specific SKAP1. In mouse, SKAP1 expression is detectable in testis at 4 weeks postnatally, when the first wave of spermatogenesis in mice is complete and the elongated spermatids are present in the testes. Furthermore, we identified Pontin as a new SKAP1 interaction partner. SKAP1 and Pontin co-localized in the flagellar region of human sperm suggesting a functional relevance for SKAP1-Pontin interaction in sperm motility. Since most previous studies on SKAP were performed with the testis-specific isoform SKAP1, our findings provide a new basis for future studies on the role of SKAP in both human somatic cells and male germ cells, including studies on male fertility.

Telomerase abrogates aneuploidy-induced telomere replication stress, senescence and cell depletion

The causal role of aneuploidy in cancer initiation remains under debate since mutations of euploidy-controlling genes reduce cell fitness but aneuploidy strongly associates with human cancers. Telomerase activation allows immortal growth by stabilizing telomere length, but its role in aneuploidy survival has not been characterized. Here, we analyze the response of primary human cells and murine hematopoietic stem cells (HSCs) to aneuploidy induction and the role of telomeres and the telomerase in this process. The study shows that aneuploidy induces replication stress at telomeres leading to telomeric DNA damage and p53 activation. This results in p53/Rb-dependent, premature senescence of human fibroblast, and in the depletion of hematopoietic cells in telomerase-deficient mice. Endogenous telomerase expression in HSCs and enforced expression of telomerase in human fibroblasts are sufficient to abrogate aneuploidy-induced replication stress at telomeres and the consequent induction of premature senescence and hematopoietic cell depletion. Together, these results identify telomerase as an aneuploidy survival factor in mammalian cells based on its capacity to alleviate telomere replication stress in response to aneuploidy induction.

Glucose substitution prolongs maintenance of energy homeostasis and lifespan of telomere dysfunctional mice

DNA damage and telomere dysfunction shorten organismal lifespan. Here we show that oral glucose administration at advanced age increases health and lifespan of telomere dysfunctional mice. The study reveals that energy consumption increases in telomere dysfunctional cells resulting in enhanced glucose metabolism both in glycolysis and in the tricarboxylic acid cycle at organismal level. In ageing telomere dysfunctional mice, normal diet provides insufficient amounts of glucose thus leading to impaired energy homeostasis, catabolism, suppression of IGF-1/mTOR signalling, suppression of mitochondrial biogenesis and tissue atrophy. A glucose-enriched diet reverts these defects by activating glycolysis, mitochondrial biogenesis and oxidative glucose metabolism. The beneficial effects of glucose substitution on mitochondrial function and glucose metabolism are blocked by mTOR inhibition but mimicked by IGF-1 application. Together, these results provide the first experimental evidence that telomere dysfunction enhances the requirement of glucose substitution for the maintenance of energy homeostasis and IGF-1/mTOR-dependent mitochondrial biogenesis in ageing tissues.

Shortened telomeres and reduced mitochondrial biogenesis are cellular hallmarks of ageing. Here, Missios et al. show that old mice with telomere dysfunction have an increased energetic demand that cannot be met unless mice are fed a glucose-rich diet, which improves energy metabolism and extends lifespan.

The role of telomeres in stem cells and cancer

Telomere shortening impairs proliferation of transformed cells but also leads to cancer initiation by inducing chromosomal instability. Here, we discuss recent developments in our understanding of the role of telomeres in replication stress and how telomerase expression in somatic stem cells may affect genome integrity control and carcinogenesis.

CEBP factors regulate telomerase reverse transcriptase promoter activity in whey acidic protein-T mice during mammary carcinogenesis

Telomerase is activated in the majority of invasive breast cancers, but the time point of telomerase activation during mammary carcinogenesis is not clear. We have recently presented a transgenic mouse model to study human telomerase reverse transcriptase (TERT) gene expression in vivo (hTERTp-lacZ). In the present study, hTERTp-lacZxWAP-T bitransgenic mice were generated to analyze the mechanisms responsible for human and mouse TERT upregulation during tumor progression in vivo. We found that telomerase activity and TERT expression were consistently upregulated in SV40-induced invasive mammary tumors compared to normal and hyperplastic tissues and ductal carcinoma in situ (DCIS). Human and mouse TERT genes are regulated similarly in the breast tissue, involving the CEBP transcription factors. Loss of CEBP-α and induction of CEBP-β expression correlated well with the activation of TERT expression in mouse mammary tumors. Transfection of CEBP-α into human or murine cells resulted in TERT repression, whereas knockdown of CEBP-α in primary human mammary epithelial cells resulted in reactivation of endogenous TERT expression and telomerase activity. Conversely, ectopic expression of CEBP-β activated endogenous TERT gene expression. Moreover, ChIP and EMSA experiments revealed binding of CEBP-α and CEBP-β to human TERT-promoter. This is the first evidence indicating that CEBP-α and CEBP-β are involved in TERT gene regulation during carcinogenesis.

Impaired CK1 delta activity attenuates SV40-induced cellular transformation in vitro and mouse mammary carcinogenesis in vivo

Simian virus 40 (SV40) is a powerful tool to study cellular transformation in vitro, as well as tumor development and progression in vivo. Various cellular kinases, among them members of the CK1 family, play an important role in modulating the transforming activity of SV40, including the transforming activity of T-Ag, the major transforming protein of SV40, itself. Here we characterized the effects of mutant CK1δ variants with impaired kinase activity on SV40-induced cell transformation in vitro, and on SV40-induced mammary carcinogenesis in vivo in a transgenic/bi-transgenic mouse model. CK1δ mutants exhibited a reduced kinase activity compared to wtCK1δ in in vitro kinase assays. Molecular modeling studies suggested that mutation N172D, located within the substrate binding region, is mainly responsible for impaired mutCK1δ activity. When stably over-expressed in maximal transformed SV-52 cells, CK1δ mutants induced reversion to a minimal transformed phenotype by dominant-negative interference with endogenous wtCK1δ. To characterize the effects of CK1δ on SV40-induced mammary carcinogenesis, we generated transgenic mice expressing mutant CK1δ under the control of the whey acidic protein (WAP) gene promoter, and crossed them with SV40 transgenic WAP-T-antigen (WAP-T) mice. Both WAP-T mice as well as WAP-mutCK1δ/WAP-T bi-transgenic mice developed breast cancer. However, tumor incidence was lower and life span was significantly longer in WAP-mutCK1δ/WAP-T bi-transgenic animals. The reduced CK1δ activity did not affect early lesion formation during tumorigenesis, suggesting that impaired CK1δ activity reduces the probability for outgrowth of in situ carcinomas to invasive carcinomas. The different tumorigenic potential of SV40 in WAP-T and WAP-mutCK1δ/WAP-T tumors was also reflected by a significantly different expression of various genes known to be involved in tumor progression, specifically of those involved in wnt-signaling and DNA repair. Our data show that inactivating mutations in CK1δ impair SV40-induced cellular transformation in vitro and mouse mammary carcinogenesis in vivo.

The promoter of human telomerase reverse transcriptase is activated during liver regeneration and hepatocyte proliferation

BACKGROUND & AIMS

Telomerase activity has not been detected in healthy human liver biopsy samples, but it is up-regulated in most human liver tumors. It is not clear whether telomerase is activated in response to acute or chronic liver injury. Telomerase activity is closely associated with expression of its catalytic subunit, telomerase reverse transcriptase (TERT). We analyzed the activity of the human TERT (hTERT) promoter during liver regeneration in vivo and hepatocyte proliferation in vitro.

METHODS

We used hTERTp-lacZ transgenic mice, which contain an 8.0-kilobase pair fragment of the hTERT gene promoter, to study the role of TERT in liver regeneration following partial hepatectomy. As an in vitro model, we used the HepaRG cell line as a new model system for human hepatocyte proliferation and differentiation.

RESULTS

Activity of the hTERT promoter increased significantly after partial hepatectomy; it was also induced in hepatocytes, based on immunohistologic analysis. Similar to the in vivo results, telomerase activity and hTERT expression were up-regulated in proliferating HepaRG cells and repressed in response to growth arrest and differentiation. Promoter mapping revealed that a proximal 0.3-kilobase pair fragment contains all elements necessary for regulation of hTERT in HepaRG cells. We identified E2F2 and E2F7 as transcription factors that control the differential expression of hTERT in proliferating hepatocytes, in vitro and in vivo.

CONCLUSIONS

hTERT is induced in hepatocytes during liver regeneration, indicating a functional role for telomerase in human liver.

Telomerase gene mutations are associated with cirrhosis formation

Telomere shortening impairs liver regeneration in mice and is associated with cirrhosis formation in humans with chronic liver disease. In humans, telomerase mutations have been associated with familial diseases leading to bone marrow failure or lung fibrosis. It is currently unknown whether telomerase mutations associate with cirrhosis induced by chronic liver disease. The telomerase RNA component (TERC) and the telomerase reverse transcriptase (TERT) were sequenced in 1,121 individuals (521 patients with cirrhosis induced by chronic liver disease and 600 noncirrhosis controls). Telomere length was analyzed in patients carrying telomerase gene mutations. Functional defects of telomerase gene mutations were investigated in primary human fibroblasts and patient-derived lymphocytes. An increased incidence of telomerase mutations was detected in cirrhosis patients (allele frequency 0.017) compared to noncirrhosis controls (0.003, P value 0.0007; relative risk [RR] 1.859; 95% confidence interval [CI] 1.552-2.227). Cirrhosis patients with TERT mutations showed shortened telomeres in white blood cells compared to control patients. Cirrhosis-associated telomerase mutations led to reduced telomerase activity and defects in maintaining telomere length and the replicative potential of primary cells in culture.

CONCLUSION

This study provides the first experimental evidence that telomerase gene mutations are present in patients developing cirrhosis as a consequence of chronic liver disease. These data support the concept that telomere shortening can represent a causal factor impairing liver regeneration and accelerating cirrhosis formation in response to chronic liver disease.

Functional p53 is required for effective execution of telomerase inhibition in BCR-ABL-positive CML cells

OBJECTIVE

In chronic myeloid leukemia (CML), increased cellular turnover of hematopoietic cells driven by the oncogene BCR-ABL leads to accelerated telomere shortening despite increased telomerase activity. It has been postulated that shortened telomeres, particularly in the context of increased telomerase activity, might facilitate accumulation of genetic aberrations and, consequently, disease progression from chronic phase to accelerated phase and blast crisis. Therefore, inhibition of telomerase might be a promising approach in CML therapy.

MATERIAL AND METHODS

To investigate the therapeutic potential of telomerase inhibition in this model disorder, we used a small molecule telomerase inhibitor, BIBR1532 as well as expression of a dominant-negative mutant of hTERT (DNhTERT-IRES-GFP) in the p53-negative CML blast crisis cell line K562 and characterized the effects in long-term culture. Furthermore, we expressed an inducible p53 construct (vector pBabe-p53ER(tam)) via retroviral transduction in cells with critically short telomeres and in cells with a normal telomere length to explain the role of the tumor suppressor in response to critical telomere shortening in BCR-ABL-positive cells.

RESULTS

BIBR1532-treated bulk cultures did not show altered growth kinetics despite significant telomere shortening to a critical length of approximately 5 kb. In comparison, DNhTERT-expressing clones either lost telomere length, leading to a significant but transient slow down in proliferation but eventually all escaped senescence/crisis (group I) or, alternatively, remained virtually unaffected despite measurable telomerase inhibition (group II). Further analyses of group I clones revealed impaired DNA damage response and an accumulation of dicentric chromosomes. However, upon restoration of p53 in telomerase-negative K562 clones with critically short telomeres, immediate reinduction of apoptosis and complete eradication of cells was observed, whereas vector control cells continued to escape from crisis.

CONCLUSIONS

These results suggest that the success of strategies aimed at telomerase inhibition in CML is highly dependent on the presence of functional p53 and should be explored preferentially in chronic phase CML.

Genome-wide microarray gene expression, array-CGH analysis, and telomerase activity in advanced ovarian endometriosis: a high degree of differentiation rather than malignant potential

The aim of the present study was to investigate whether endometriosis and cancer share common molecular characteristics. Tissue samples were collected prospectively during diagnostic laparoscopy of patients with primary infertility. Using high-density oligonucleotide microarrays, (Affymetrix Gene Chip HG-U133 Set) the genome-wide gene expression profile of advanced ovarian endometriosis was analyzed compared with matched normal endometrium. Expression of TERT, the gene encoding the telomerase reverse transcriptase subunit, and telomerase activity were analyzed in eutopic and ectopic endometrium. Genome-wide, high-resolution array-CGH was used to screen for genomic aberrations in endometriosis. Expression microarray data were validated quantitatively with RT-PCR. The genes RARRES1 and RARRES2 (retinoic acid receptor responder 1 and 2) were found to be up-regulated in endometriosis, suggesting a high degree of differentiation. Consistently, down-regulated genes included those involved in the cell cycle, cell metabolism and homeostasis. Expression of TERT and telomerase activity were present in eutopic but absent in ectopic endometrium. Array-CGH revealed a normal genomic pattern without gross amplifications and deletions. In conclusion, these data suggest that advanced ovarian endometriosis represents a highly differentiated tissue with minimal or no malignant potential.

Telomeres and telomerase. A survey about methods and recent advances in cancer diagnostic and therapy

Since the discovery that telomerase is repressed in most normal human somatic cells but strongly expressed in most human tumours, telomerase emerged as an attractive target for diagnostic, prognostic and therapeutic purposes to combat human cancer. In this review, a synopsis of methods detecting telomerase is presented evaluating their potential for diagnostic and prognostic use. Also, the most promising telomerase therapeutics are discussed in the light of recent advances in the field.

A novel transgenic mouse model reveals humanlike regulation of an 8-kbp human TERT gene promoter fragment in normal and tumor tissues

Telomerase activity is repressed in most human somatic tissues during differentiation processes but strongly up-regulated in most human tumors. Regulation of human telomerase activity primarily occurs at the level of transcriptional initiation of the TERT gene, which encodes the catalytic subunit of telomerase. We have generated a novel transgenic mouse model to study the regulation of the human TERT gene promoter in an in vivo system. For this purpose, we have cloned an 8.0-kbp human TERT promoter fragment in front of the bacterial lacZ reporter gene (hTERTp-lacZ), which encodes the beta-galactosidase enzyme. Expression of the reporter gene was monitored by reverse transcription-PCR analysis, 5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside staining of whole mount preparations, and histologic sections. We find that the activity of the human TERT promoter in most normal mouse tissues recapitulates the expression of the hTERT gene in normal human tissues and is under tighter control when compared with the endogenous mouse TERT gene expression. In testis, where highest lacZ expression was observed, the expression of the reporter gene was restricted to the spermatogonial stem cells and the spermatocytes. Intriguingly, we find increased levels of lacZ expression in mammary tumors of hTERTp-lacZ x p53(+/-) bitransgenic mouse mammary tumor model. Thus, this transgenic mouse model provides a suitable in vivo system to analyze the expression of the human TERT gene under physiologic conditions and during tumorigenesis.

Activity of metal-responsive transcription factor 1 by toxic heavy metals and H2O2 in vitro is modulated by metallothionein

Metallothioneins are small, cysteine-rich proteins that avidly bind heavy metals such as zinc, copper, and cadmium to reduce their concentration to a physiological or nontoxic level. Metallothionein gene transcription is induced by several stimuli, notably heavy metal load and oxidative stress. Transcriptional induction of metallothionein genes is mediated by the metal-responsive transcription factor 1 (MTF-1), an essential zinc finger protein that binds to specific DNA motifs termed metal-response elements. In cell-free DNA binding reactions with nuclear extracts, MTF-1 requires elevated zinc concentrations for efficient DNA binding but paradoxically is inactivated by other in vivo inducers such as cadmium, copper, and hydrogen peroxide. Here we have developed a cell-free, MTF-1-dependent transcription system which accurately reproduces the activation of metallothionein gene promoters not only by zinc but also by these other inducers. We found that while transcriptional induction by zinc can be achieved by elevated zinc concentration alone, induction by cadmium, copper, or H2O2 additionally requires the presence of zinc-saturated metallothionein. This is explained by the preferential binding of cadmium or copper to metallothionein or its oxidation by H2O2; the concomitant release of zinc in turn leads to the activation of transcription factor MTF-1. Conversely, thionein, the metal-free form of metallothionein, inhibits activation of MTF-1. The release of zinc from cellular components, including metallothioneins, and the sequestration of zinc by newly produced apometallothionein might be a basic mechanism to regulate MTF-1 activity upon cellular stress.

Characterization of the mouse gene for the heavy metal-responsive transcription factor MTF-1

MTF-1 is a zinc finger transcription factor that mediates the cellular response to heavy metal stress; its targeted disruption in the mouse leads to liver decay and embryonic lethality at day E14. Recently, we have sequenced the entire MTF-1 gene in the compact genome of the pufferfish Fugu rubripes. Here we have defined the promoter sequences of human and mouse MTF-1 and the genomic structure of the mouse MTF-1 locus. The transcription unit of MTF-1 spans 42 kb (compared to 8.5 kb in Fugu) and is located downstream of the gene for a phosphatase (INPP5P) in mouse, human, and fish. In all of these species, the MTF promoter region has the features of a CpG island. In both mouse and human, the 5' untranslated region harbors conserved short reading frames of unknown function. RNA mapping experiments revealed that in these two species, MTF-1 mRNA is transcribed from a cluster of multiple initiation sites from a TATA-less promoter without metal-responsive elements. Transcription from endogenous and transfected MTF-1 promoters was not affected by heavy metal load or other stressors, in support of the notion that MTF-1 activity is regulated at the posttranscriptional level. Tissue Northern blots normalized for poly A+ RNA indicate that MTF-1 is expressed at similar levels in all tissues, except in the testes, that contain more than 10-fold higher mRNA levels.

Expression of the hTERT gene is regulated at the level of transcriptional initiation and repressed by Mad1

Telomerase, an enzymatic activity responsible for the replication of chromosome end structures, is strongly upregulated in most human cancers. In contrast, most differentiated tissues are telomerase negative. The rate-limiting step for telomerase activity seems to be the expression of the catalytic subunit of the enzyme, encoded by the human telomerase reverse transcriptase (hTERT) gene. The precise mechanism of how hTERT is regulated has not been elucidated yet. We show here that the down-regulation of hTERT mRNA during 12-O-tetradecanoylphorbol-13-acetate-induced differentiation of human U937 cells is a consequence of a fast decrease in the rate of transcription rather than changes in its half-life. The only transcription factor that has so far been implicated in the regulation of hTERT expression is the c-Myc oncoprotein. Our analysis shows that another member of the myc/marx/mad network, mad1, encoding a transcriptional repressor that is significantly increased by 12-O-tetra-decanoylphorbol-13-acetate treatment, represses hTERT promoter-driven reporter gene activity in transient transfection assays. This effect is dependent on the NH2 terminal domain of Madl, which mediates the association with the transcriptional corepressor mSin3. Our findings suggest the involvement of an additional transcription factor in the regulation of hTERT expression and may provide a model for how hTERT activity is controlled during the differentiation process in human somatic tissues.

Embryonic lethality and liver degeneration in mice lacking the metal-responsive transcriptional activator MTF-1

We have shown previously that the heavy metal-responsive transcriptional activator MTF-1 regulates the basal and heavy metal-induced expression of metallothioneins. To investigate the physiological function of MTF-1, we generated null mutant mice by targeted gene disruption. Embryos lacking MTF-1 die in utero at approximately day 14 of gestation. They show impaired development of hepatocytes and, at later stages, liver decay and generalized edema. MTF-1(-/-) embryos fail to transcribe metallothionein I and II genes, and also show diminished transcripts of the gene which encodes the heavy-chain subunit of the gamma-glutamylcysteine synthetase, a key enzyme for glutathione biosynthesis. Metallothionein and glutathione are involved in heavy metal homeostasis and detoxification processes, such as scavenging reactive oxygen intermediates. Accordingly, primary mouse embryo fibroblasts lacking MTF-1 show increased susceptibility to the cytotoxic effects of cadmium or hydrogen peroxide. Thus, MTF-1 may help to control metal homeostasis and probably cellular redox state, especially during liver development. We also note that the MTF-1 null mutant phenotype bears some similarity to those of two other regulators of cellular stress response, namely c-Jun and NF-kappaB (p65/RelA).

Mutants in position 69 of the Trp repressor of Escherichia coli K12 with altered DNA-binding specificity

Structural analysis by X-ray crystallography has indicated that direct contact occurs between Arg69, the second residue of the first helix of the helix-turnhelix (HTH) motif of the Trp repressor, and guanine in position 9 of the alpha-centred consensus trp operator. We therefore replaced residue 69 of the Trp repressor with Gly, Ile, Leu or Gln and tested the resultant repressor mutants for their binding to synthetic symmetrical alpha- or beta-centred trp operator variants, in vivo and in vitro. We present genetic and biochemical evidence that Ile in position 69 of the Trp repressor interacts specifically with thymine in position 9 of the alpha-centred trp operator. There are also interactions with other bases in positions 8 and 9 of the alpha-centred trp operator. In vitro, the Trp repressor of mutant RI69 binds to the consensus alpha-centred trp operator and a similar trp operator variant that carries a T in position 9. In vivo analysis of the interactions of Trp repressor mutant RI69 with symmetrical variants of the beta-centred trp operator shows a change in the specificity of binding to a beta-centred symmetrical trp operator variant with a gua-nine to thymine substitution in position 5, which corresponds to position 9 of the alpha-centred trp operator.

Co-operative binding of two Trp repressor dimers to alpha- or beta-centred trp operators

The alpha-centred trp operator binds one dimer of the Trp repressor, whereas the beta-centred trp operator binds two dimers of the Trp repressor (Carey et al., 1991; Haran et al., 1992). The Trp repressor with a Tyr-Gly-7 substitution binds almost as well as the wild-type Trp repressor to the alpha-centred trp operator, but it does not bind to the beta-centred trp operator. This confirms that Tyr-7 is involved in the interaction between Trp repressor dimers, as seen in the crystal structure (Lawson and Carey, 1993). Further experiments with alpha-centred trp operator variants showed that positions +/-1 of the alpha-centred trp operators play a crucial role in tetramerisation. The two innermost base pairs of the alpha-centred trp operator are not involved in contacts with the dimer of the Trp repressor binding to it. However, substitutions in these positions (T-A to G-T) effectively transform the alpha-centred trp operator into a beta-centred trp operator, and thus encourage the binding of two Trp repressor dimers to this operator. Finally, we demonstrate, with suitable heterodimers, that one subunit of each dimer suffices to bind to a beta-centred trp operator.