High-Level rAAV Vector Production by rAdV-Mediated Amplification of Small Amounts of Input Vector

The successful application of recombinant adeno-associated virus (rAAV) vectors for long-term transgene expression in clinical studies requires scalable production methods with genetically stable components. Due to their simple production scheme and the high viral titers achievable, first generation recombinant adenoviruses (rAdV) have long been taken into consideration as suitable tools for simultaneously providing both the helper functions and the AAV rep and cap genes for rAAV packaging. So far, however, such rAdV-rep/cap vectors have been difficult to generate and often turned out to be genetically unstable. Through ablation of cis and trans inhibitory function in the AAV-2 genome we have succeeded in establishing separate and stable rAdVs for high-level AAV serotype 2 Rep and Cap expression. These allowed rAAV-2 production at high burst sizes by simple coinfection protocols after providing the AAV-ITR flanked transgene vector genome either as rAAV-2 particles at low input concentrations or in form of an additional rAdV. With characteristics such as the ease of producing the required components, the straightforward adaption to other transgenes and the possible extension to further serotypes or capsid variants, especially the rAdV-mediated rAAV amplification system presents a very promising candidate for up-scaling to clinical grade vector preparations.

Acute retinol mobilization by retinol-binding protein 4 in mouse liver induces fibroblast growth factor 21 expression

Hepatocytes secrete retinol-binding protein 4 (RBP4) into circulation, thereby mobilizing vitamin A from the liver to provide retinol for extrahepatic tissues. Obesity and insulin resistance are associated with elevated RBP4 levels in the blood. However, in a previous study, we observed that chronically increased RBP4 by forced Rbp4 expression in the liver does not impair glucose homeostasis in mice. Here, we investigated the effects of an acute mobilization of hepatic vitamin A stores by hepatic overexpression of RBP4 in mice. We show that hepatic retinol mobilization decreases body fat content and enhances fat turnover. Mechanistically, we found that acute retinol mobilization increases hepatic expression and serum levels of fibroblast growth factor 21 (FGF21), which is regulated by retinol mobilization and retinoic acid in primary hepatocytes. Moreover, we provide evidence that the insulin-sensitizing effect of FGF21 is associated with organ-specific adaptations in retinoid homeostasis. Taken together, our findings identify a novel crosstalk between retinoid homeostasis and FGF21 in mice with acute RBP4-mediated retinol mobilization from the liver.

Hepatic p53 is regulated by transcription factor FOXO1 and acutely controls glycogen homeostasis

The tumor suppressor p53 is involved in the adaptation of hepatic metabolism to nutrient availability. Acute deletion of p53 in the mouse liver affects hepatic glucose and triglyceride metabolism. However, long-term adaptations upon the loss of hepatic p53 and its transcriptional regulators are unknown. Here we show that short-term, but not chronic, liver-specific deletion of p53 in mice reduces liver glycogen levels, and we implicate the transcription factor forkhead box O1 protein (FOXO1) in the regulation of p53 and its target genes. We demonstrate that acute p53 deletion prevents glycogen accumulation upon refeeding, whereas a chronic loss of p53 associates with a compensational activation of the glycogen synthesis pathway. Moreover, we identify fasting-activated FOXO1 as a repressor of p53 transcription in hepatocytes. We show that this repression is relieved by inactivation of FOXO1 by insulin, which likely mediates the upregulation of p53 expression upon refeeding. Strikingly, we find that high-fat diet–induced insulin resistance with persistent FOXO1 activation not only blunted the regulation of p53 but also the induction of p53 target genes like p21 during fasting, indicating overlapping effects of both FOXO1 and p53 on target gene expression in a context-dependent manner. Thus, we conclude that p53 acutely controls glycogen storage in the liver and is linked to insulin signaling via FOXO1, which has important implications for our understanding of the hepatic adaptation to nutrient availability.

Liver-secreted RBP4 does not impair glucose homeostasis in mice

Retinol-binding protein 4 (RBP4) is the major transport protein for retinol in blood. Recent evidence from genetic mouse models shows that circulating RBP4 derives exclusively from hepatocytes. Because RBP4 is elevated in obesity and associates with the development of glucose intolerance and insulin resistance, we tested whether a liver-specific overexpression of RBP4 in mice impairs glucose homeostasis. We used adeno-associated viruses (AAV) that contain a highly liver-specific promoter to drive expression of murine RBP4 in livers of adult mice. The resulting increase in serum RBP4 levels in these mice was comparable with elevated levels that were reported in obesity. Surprisingly, we found that increasing circulating RBP4 had no effect on glucose homeostasis. Also during a high-fat diet challenge, elevated levels of RBP4 in the circulation failed to aggravate the worsening of systemic parameters of glucose and energy homeostasis. These findings show that liver-secreted RBP4 does not impair glucose homeostasis. We conclude that a modest increase of its circulating levels in mice, as observed in the obese, insulin-resistant state, is unlikely to be a causative factor for impaired glucose homeostasis.

Comprehensive Small RNA-Seq of Adeno-Associated Virus (AAV)-Infected Human Cells Detects Patterns of Novel, Non-Coding AAV RNAs in the Absence of Cellular miRNA Regulation

Most DNA viruses express small regulatory RNAs, which interfere with viral or cellular gene expression. For adeno-associated virus (AAV), a small ssDNA virus with a complex biphasic life cycle miRNAs or other small regulatory RNAs have not yet been described. This is the first comprehensive Illumina-based RNA-Seq analysis of small RNAs expressed by AAV alone or upon co-infection with helper adenovirus or HSV. Several hotspots of AAV-specific small RNAs were detected mostly close to or within the AAV-ITR and apparently transcribed from the newly identified anti-p5 promoter. An additional small RNA hotspot was located downstream of the p40 promoter, from where transcription of non-coding RNAs associated with the inhibition of adenovirus replication were recently described. Parallel detection of known Ad and HSV miRNAs indirectly validated the newly identified small AAV RNA species. The predominant small RNAs were analyzed on Northern blots and by human argonaute protein-mediated co-immunoprecipitation. None of the small AAV RNAs showed characteristics of bona fide miRNAs, but characteristics of alternative RNA processing indicative of differentially regulated AAV promoter-associated small RNAs. Furthermore, the AAV-induced regulation of cellular miRNA levels was analyzed at different time points post infection. In contrast to other virus groups AAV infection had virtually no effect on the expression of cellular miRNA, which underscores the long-established concept that wild-type AAV infection is apathogenic.

Vasopressinergic control of stress-related behavior: studies in Brattleboro rats

Vasopressin, a nonapeptide, signaling both as hormone in the blood and neuromodulator/neurotransmitter in the brain is considered to be causally involved in the pathological changes underlying anxiety and depression. In the present review we summarize experimental data obtained with Brattleboro rats as a model of congenital vasopressin-deficiency to test the hypothesis that central vasopressin signaling contributes to anxiety- and depression-like behavior. Male, female and lactating rats were studied. We focused on the paraventricular nucleus of the hypothalamus (PVN) and the septum, two brain areas in which vasopressin is proposed to control the endocrine and behavioral stress response, respectively. The presented data support the hypothesis that the behavioral changes seen in these rats are brought about by an altered vasopressin signaling at the brain level. Whereas vasopressin synthesized and released within the hypothalamus is primarily involved in endocrine regulation, vasopressin signaling in other brain areas may contribute to anxiety- and depression-like behavioral parameters. Further studies in this context might focus particularly on the interplay between extra-hypothalamic brain areas such as the septum and the medial amygdala.

Hepatitis E Virus Seroprevalence in Free-Ranging Deer in Canada

Hepatitis E virus infection (HEV) is an important public health concern not only in traditional endemic areas, but also in some industrialized countries where both domesticated and wild animals have been recognized as potential zoonotic reservoirs implicated in HEV transmission. While the prevalence of infection in the deer population in Europe and Asia has been thoroughly investigated, it remains largely undetermined in North America. We assessed the presence of HEV in three different species of free-range deer in Canada. The seroprevalence of HEV among deer in Canada was 8.8% in white-tailed deer, 4.5% in mule deer and 3.2% in caribou. Hepatitis E virus RNA was not detected. Overall, data indicate that HEV infection occurs in deer in Canada. The absence of viraemia and the low seroprevalence especially in barren-ground caribou which is an important part of the diet in many northern communities suggests that the risk of zoonotic transmission may be less pronounced compared to other countries.

NPY Y2 receptors in the central amygdala reduce cued but not contextual fear

The amygdala is fundamental for associative fear and extinction learning. Recently, also the central nucleus of the amygdala (CEA) has emerged as a site of plasticity actively controlling efferent connections to downstream effector brain areas. Although synaptic transmission is primarily mediated by glutamate and GABA, neuropeptides critically influence the overall response. While neuropeptide Y (NPY) acting via postsynaptic Y1 receptors exerts an important anxiolytic and fear-reducing action, the role of the predominantly presynaptic Y2 receptors is less defined. To investigate the role of Y2 receptors in the CEA we employed viral-vector mediated over-expression of the Y2 selective agonist NPY3-36 in fear conditioning and extinction experiments. NPY3-36 over-expression in the CEA resulted in reduced fear expression during fear acquisition and recall. Interestingly, this effect was blocked by intraperitoneal injection of a brain-penetrant Y2 receptor antagonist. Furthermore, over-expression of NPY3-36 in the CEA also reduced fear expression during fear extinction of CS-induced but not context-related fear. Again, fear extinction appeared delayed by peripheral injection of a Y2 receptor antagonist JNJ-31020028. Importantly, mice with over-expression of NPY3-36 in the CEA also displayed reduced spontaneous recovery and reinstatement, suggesting that Y2 receptor activation supports a permanent suppression of fear. Local deletion of Y2 receptors in the CEA, on the other hand, increased the expression of CS-induced freezing during fear recall and fear extinction. Thus, NPY inhibits fear learning and promotes cued extinction by reducing fear expression also via activation of presynaptic Y2 receptors on CEA neurons.

OneBac 2.0: Sf9 Cell Lines for Production of AAV5 Vectors with Enhanced Infectivity and Minimal Encapsidation of Foreign DNA

Scalable production of recombinant adeno-associated virus vectors (rAAV) in baculovirus-infected Sf9 cells yields high burst sizes but variable infectivity rates per packaged AAV vector genome depending on the chosen serotype. Infectivity rates are particularly low for rAAV5 vectors, based on the genetically most divergent AAV serotype. In this study we describe key improvements of the OneBac system for the generation of rAAV5 vectors, whose manufacturing has been unsatisfactory in all current insect cell-based production systems. The Sf9 cell-based expression strategy for AAV5 capsid proteins was modified to enhance relative AAV5 VP1 levels. This resulted in a 100-fold boost of infectivity per genomic AAV5 particle with undiminished burst sizes per producer cell. Furthermore, the issue of collateral packaging of helper DNA into AAV capsids was approached. By modifications of the AAV rep and cap expression constructs used for the generation of stable Sf9 cell lines, collateral packaging of helper DNA sequences during rAAV vector production was dramatically reduced down to 0.001% of packaged rAAV genomes, while AAV5 burst sizes and infectivity rates were maintained. OneBac 2.0 represents the first insect cell-based scalable production system for high per-particle AAV5 infectivity rates combined with minimal collateral packaging of helper DNA, allowing the manufacturing of safe AAV5-based gene therapies for clinical application.

Interactions of cullin3/KCTD5 complexes with both cytoplasmic and nuclear proteins: Evidence for a role in protein stabilization

Based on its specific interaction with cullin3 mediated by an N-terminal BTB/POZ homologous domain, KCTD5 has been proposed to function as substrate adapter for cullin3 based ubiquitin E3 ligases. In the present study we tried to validate this hypothesis through identification and characterization of additional KCTD5 interaction partners. For the replication protein MCM7, the zinc finger protein ZNF711 and FAM193B, a yet poorly characterized cytoplasmic protein, we could demonstrate specific interaction with KCTD5 both in yeast two-hybrid and co-precipitation studies in mammalian cells. Whereas trimeric complexes of cullin3 and KCTD5 with the respective KCTD5 binding partner were formed, KCTD5/cullin3 induced polyubiquitylation and/or proteasome-dependent degradation of these binding partners could not be demonstrated. On the contrary, KCTD5 or Cullin3 overexpression increased ZNF711 protein stability.

Definition of herpes simplex virus helper functions for the replication of adeno-associated virus type 5

Adeno-associated virus (AAV) type 5 represents the genetically most distant AAV serotype and the only one isolated directly from human tissue. Seroepidemiological evidence suggests herpes simplex virus (HSV) as a helper virus for human AAV5 infections, underlining the in vivo relevance of the AAV-herpesvirus relationship. In this study we analysed, for the first time, HSV helper functions for productive AAV5 replication, and compared these to AAV2. Using a combination of HSV strains and plasmids for individual genes, the previously defined HSV helper functions for AAV2 replication were shown to induce AAV5 gene expression, DNA replication and production of infectious progeny. The helper functions comprise the replication genes for ICP8 (UL29), helicase-primase (UL5/8/52), and DNA polymerase (UL30/42). HSV immediate-early genes for ICP0 and ICP4 further enhanced AAV5 replication, mainly by induction of rep gene expression. In the presence of HSV helper functions, AAV5 Rep co-localized with ICP8 in nuclear replication compartments, and HSV alkaline exonuclease (UL12) enhanced AAV5 replication, similarly to AAV2. UL12, in combination with ICP8, was shown to induce DNA strand exchange on partially double-stranded templates to resolve and repair concatemeric HSV replication intermediates. Similarly, concatemeric AAV replication intermediates appeared to be processed to yield AAV unit-length molecules, ready for AAV packaging. Taken together, our findings show that productive AAV5 replication is promoted by the same combination of HSV helper functions as AAV2.

OneBac: platform for scalable and high-titer production of adeno-associated virus serotype 1-12 vectors for gene therapy

Scalable and genetically stable recombinant adeno-associated virus (rAAV) production systems combined with facile adaptability for an extended repertoire of AAV serotypes are required to keep pace with the rapidly increasing clinical demand. For scalable high-titer production of the full range of rAAV serotypes 1-12, we developed OneBac, consisting of stable insect Sf9 cell lines harboring silent copies of AAV1-12 rep and cap genes induced upon infection with a single baculovirus that also carries the rAAV genome. rAAV burst sizes reach up to 5 × 10(5) benzonase-resistant, highly infectious genomic particles per cell, exceeding typical yields of current rAAV production systems. In contrast to recombinant rep/cap baculovirus strains currently employed for large-scale rAAV production, the Sf9rep/cap cell lines are genetically stable, leading to undiminished rAAV burst sizes over serial passages. Thus, OneBac combines full AAV serotype options with the capacity for stable scale-up production, the current bottleneck for the transition of AAV from gene therapy trials to routine clinical treatment.

Arcuate NPY controls sympathetic output and BAT function via a relay of tyrosine hydroxylase neurons in the PVN

Neuropepetide Y (NPY) is best known for its powerful stimulation of food intake and its effects on reducing energy expenditure. However, the pathways involved and the regulatory mechanisms behind this are not well understood. Here we demonstrate that NPY derived from the arcuate nucleus (Arc) is critical for the control of sympathetic outflow and brown adipose tissue (BAT) function. Mechanistically, a key change induced by Arc NPY signaling is a marked Y1 receptor-mediated reduction in tyrosine hydroxylase (TH) expression in the hypothalamic paraventricular nucleus (PVN), which is also associated with a reduction in TH expression in the locus coeruleus (LC) and other regions in the brainstem. Consistent with this, Arc NPY signaling decreased sympathetically innervated BAT thermogenesis, involving the downregulation of uncoupling protein 1 (UCP1) expression in BAT. Taken together, these data reveal a powerful Arc-NPY-regulated neuronal circuit that controls BAT thermogenesis and sympathetic output via TH neurons.

Transactivation of human parvovirus B19 gene expression in endothelial cells by adenoviral helper functions

Human parvovirus B19 (B19V) DNA is highly prevalent in endothelial cells lining up intramyocardial arterioles and postcapillary venules of patients with chronic myocarditis and cardiomyopathies. We addressed the question of a possible stimulation of B19V gene expression in endothelial cells by infection with adenoviruses. Adenovirus infection led to a strong augmentation of B19V structural and nonstructural proteins in individual endothelial cells infected with B19V or transfected with an infectious B19V genome. Transactivation was mostly mediated at the level of transcription and not due to adenovirus-mediated induction of second-strand synthesis from the single-stranded parvoviral genome. The main adenoviral functions required were E1A and E4orf6, which displayed synergistic effects. Furthermore, a limited B19V genome replication could be demonstrated in endothelial cells and adenovirus infection induced the appearance of putative dimeric replication intermediates. Thus the almost complete block in B19V gene expression seen in endothelial cells can be abrogated by infection with other viruses.

Long-term cardiac-targeted RNA interference for the treatment of heart failure restores cardiac function and reduces pathological hypertrophy

BACKGROUND

RNA interference (RNAi) has the potential to be a novel therapeutic strategy in diverse areas of medicine. Here, we report on targeted RNAi for the treatment of heart failure, an important disorder in humans that results from multiple causes. Successful treatment of heart failure is demonstrated in a rat model of transaortic banding by RNAi targeting of phospholamban, a key regulator of cardiac Ca(2+) homeostasis. Whereas gene therapy rests on recombinant protein expression as its basic principle, RNAi therapy uses regulatory RNAs to achieve its effect.

METHODS AND RESULTS

We describe structural requirements to obtain high RNAi activity from adenoviral and adeno-associated virus (AAV9) vectors and show that an adenoviral short hairpin RNA vector (AdV-shRNA) silenced phospholamban in cardiomyocytes (primary neonatal rat cardiomyocytes) and improved hemodynamics in heart-failure rats 1 month after aortic root injection. For simplified long-term therapy, we developed a dimeric cardiotropic adeno-associated virus vector (rAAV9-shPLB) to deliver RNAi activity to the heart via intravenous injection. Cardiac phospholamban protein was reduced to 25%, and suppression of sacroplasmic reticulum Ca(2+) ATPase in the HF groups was rescued. In contrast to traditional vectors, rAAV9 showed high affinity for myocardium but low affinity for liver and other organs. rAAV9-shPLB therapy restored diastolic (left ventricular end-diastolic pressure, dp/dt(min), and tau) and systolic (fractional shortening) functional parameters to normal ranges. The massive cardiac dilation was normalized, and cardiac hypertrophy, cardiomyocyte diameter, and cardiac fibrosis were reduced significantly. Importantly, no evidence was found of microRNA deregulation or hepatotoxicity during these RNAi therapies.

CONCLUSIONS

Our data show for the first time the high efficacy of an RNAi therapeutic strategy in a cardiac disease.

The E3 ligase Topors induces the accumulation of polysumoylated forms of DNA topoisomerase I in vitro and in vivo

Human Topors has originally been identified as binding partner of p53 and DNA topoisomerase I (TOP1). It can function as both an ubiquitin and SUMO-1 E3 ligase for p53. Here we demonstrate that Topors enhances the formation of high-molecular weight SUMO-1 conjugates of TOP1 in a reconstituted in vitro system and also in human osteosarcoma cells, similar to treatment with CPT. In contrast to the situation observed with p53, overall sumoylation levels were rather unaffected. Experiments with TOP1 point mutants strongly suggest that the high-molecular weight conjugates represent SUMO-1 chains formed on a limited number of SUMO-1 acceptor sites.

Role of the herpes simplex virus helicase-primase complex during adeno-associated virus DNA replication

A subset of DNA replication proteins of herpes simplex virus (HSV) comprising the single-strand DNA-binding protein, ICP8 (UL29), and the helicase-primase complex (UL5, UL8, and UL52 proteins) has previously been shown to be sufficient for the replication of adeno-associated virus (AAV). We recently demonstrated complex formation between ICP8, AAV Rep78, and the single-stranded DNA AAV genome, both in vitro and in the nuclear HSV replication domains of coinfected cells. In this study the functional role(s) of HSV helicase and primase during AAV DNA replication were analyzed. To differentiate between their necessity as structural components of the HSV replication complex or as active enzymes, point mutations within the helicase and primase catalytic domains were analyzed. In two complementary approaches the remaining HSV helper functions were either provided by infection with HSV mutants or by plasmid transfection. We show here that upon cotransfection of the minimal four HSV proteins (i.e., the four proteins constituting the minimal requirements for basal AAV replication), UL52 primase catalytic activity was not required for AAV DNA replication. In contrast, UL5 helicase activity was necessary for fully efficient replication. Confocal microscopy confirmed that all mutants retained the ability to support formation of ICP8-positive nuclear replication foci, to which AAV Rep78 colocalized in a manner strictly dependent on the presence of AAV single-stranded DNA (ssDNA). The data indicate that recruitment of AAV Rep78 and ssDNA to nuclear replication sites by the four HSV helper proteins is maintained in the absence of catalytic primase or helicase activities and suggest an involvement of the HSV UL5 helicase activity during AAV DNA replication.

Differential internalization and nuclear uncoating of self-complementary adeno-associated virus pseudotype vectors as determinants of cardiac cell transduction

Recently it was shown that several new pseudotyped adeno-associated virus (AAV) vectors support cardioselective expression of transgenes. The molecular mechanisms underlying this propensity for cardiac cell transduction are not well understood. We comparatively analyzed AAV vector attachment, internalization, intracellular trafficking, and nuclear uncoating of recombinant self-complementary (sc) AAV2.2 versus pseudotyped scAAV2.6 vectors expressing green fluorescence protein (GFP) in cells of cardiac origin. In cardiac-derived HL-1 cells and primary neonatal rat cardiomyocytes (PNCMs), expression of GFP increased rapidly after incubation with scAAV2.6-GFP, but remained low after scAAV2.2-GFP. Internalization of scAAV2.6-GFP was more efficient than that of scAAV2.2-GFP. Nuclear translocation was similarly efficient for both, but differential nuclear uncoating rates emerged as a key additional determinant of transduction: 30% of all scAAV2.6-GFP genomes translocated to the nucleus became uncoated within 48 h, but only 16% of scAAV2.2-GFP genomes. In contrast to this situation in cells of cardiac origin, scAAV2.2-GFP displayed more efficient internalization and similar (tumor cell line HeLa) or higher (human microvascular endothelial cell (HMEC)) uncoating rates than scAAV.2.6-GFP in non-cardiac cell types. In summary, both internalization and nuclear uncoating are key determinants of cardiac transduction by scAAV2.6 vectors. Any in vitro screening for the AAV pseudotype most suitable for cardiac gene therapy - which is desirable since it may allow significant reductions in vector load in upcoming clinical trials--needs to quantitate both key steps in transduction.

SUMOylation modulates transcriptional repression by TRPS1

Mutations or deletions of the TRPS1 gene on human chromosome 8q.24.1 cause the tricho-rhino-phalangeal syndromes (TRPS), which are characterized by craniofacial and skeletal malformations. The gene encodes a transcription factor that functions as a repressor for GATA-mediated transcription. The activity of transcription factors is often controlled by posttranslational modifications. We show here that TRPS1 is SUMOylated at multiple sites, both in vivo and in vitro, through interaction with UBC9. Overexpression of wild-type UBC9 enhances TRPS1-mediated transcriptional repression. In contrast, a SUMOylation-deficient UBC9 mutant, which nevertheless still binds TRPS1, has no effect. Of the five potential TRPS1 SUMO-target sites, which were predicted based on a minimal SUMOylation consensus sequence (MCS), two are located within the C-terminal repression domain (RD) at lysine residues 1192 (termed S4) and 1201 (S5). S5 was identified as the major acceptor site within this region, and a point mutation of S5 strongly decreases TRPS1-RD-mediated transcriptional repression. Additional mutation of S4 results in abrogation of SUMOylation at the TRPS1-RD and almost complete loss of the repressive properties of TRPS1. These results identify SUMOylation at the TRPS1-RD as a major mechanism that regulates the function of TRPS1.

Identification of a cytoplasmic interaction partner of the large regulatory proteins Rep78/Rep68 of adeno-associated virus type 2 (AAV-2)

Through yeast two-hybrid analysis and coimmunoprecipitation studies, we have identified a novel cellular AAV-2 Rep78/Rep68 interaction partner located predominantly in the cytoplasm. In public databases, it has been assigned as KCTD5, because of a region of high similarity to the cytoplasmic tetramerization domain of voltage-gated potassium channels. Whereas Rep/KCTD5 interaction relied on the region surrounding the Rep nuclear localization signal, nuclear accumulation of Rep was not required. Wildtype Rep78/Rep68 proteins induced the translocation of large portions of KCTD5 into the nucleus pointing to functional interactions both in the cytoplasm and the nucleus. In line with an anticipated functional interference in the cytoplasm, KCTD5 overexpression completely abrogated Rep68-mediated posttranscriptional activation of a HIV-LTR driven luciferase reporter gene. Our study expands the panel of already identified nuclear Rep interaction partners to a cytoplasmic protein, which raises the awareness that important steps in the AAV life cycle may be regulated in this compartment.

A bidirectional Tet-dependent promotor construct regulating the expression of E1A for tight control of oncolytic adenovirus replication

Tight regulation of oncolytic adenoviruses (oAdV) represents an important requirement for their safe application. Here we describe a new doxycycline (Dox)-dependent oAdV with a bidirectional expression cassette, which drives the expression of the reverse tetracycline-controlled transactivator (rtTA(s)-M2) from a lung tumor-specific promoter and, in the opposite direction, the expression of the adenoviral E1A gene from a second generation TetO(7) sequence linked to an isolated TATA box. In H441 lung cancer cells, this oAdV showed a strictly Dox-dependent E1A expression, adenoviral replication, cell killing activity and a 450-fold induction of progeny virus production. The virus could be shut off again by withdrawal of Dox and, in contrast to a control oAdV expressing E1A directly from the SP-B promoter, did not replicate in non-target cells. However, the absolute values of virus production and the cell killing activity in the presence of the inducer were still reduced as compared to the control oAdV. The results demonstrate, for the first time, Dox-dependent oAdV replication from a single adenoviral vector genome. Future improvement of the Dox-dependent E1A regulation cassette should lead to the generation of an oAdV well suited to meet the demands for a highly regulated and efficient oncolytic virus for in vivo applications.

Highly efficient and specific modulation of cardiac calcium homeostasis by adenovector-derived short hairpin RNA targeting phospholamban

Impaired function of the phospholamban (PLB)-regulated sarcoplasmic reticulum Ca(2+) pump (SERCA2a) contributes to cardiac dysfunction in heart failure (HF). PLB downregulation may increase SERCA2a activity and improve cardiac function. Small interfering (si)RNAs mediate efficient gene silencing by RNA interference (RNAi). However, their use for in vivo gene therapy is limited by siRNA instability in plasma and tissues, and by low siRNA transfer rates into target cells. To address these problems, we developed an adenoviral vector (AdV) transcribing short hairpin (sh)RNAs against rat PLB and evaluated its potential to silence the PLB gene and to modulate SERCA2a-mediated Ca(2+) sequestration in primary neonatal rat cardiomyocytes (PNCMs). Over a period of 13 days, vector transduction resulted in stable > 99.9% ablation of PLB-mRNA at a multiplicity of infection of 100. PLB protein gradually decreased until day 7 (7+/-2% left), whereas SERCA, Na(+)/Ca(2+) exchanger (NCX1), calsequestrin and troponin I protein remained unchanged. PLB silencing was associated with a marked increase in ATP-dependent oxalate-supported Ca(2+) uptake at 0.34 microM of free Ca(2+), and rapid loss of responsiveness to protein kinase A-dependent stimulation of Ca(2+) uptake was maintained until day 7. In summary, these results indicate that AdV-derived PLB-shRNA mediates highly efficient, specific and stable PLB gene silencing and modulation of active Ca(2+) sequestration in PNCMs. The availability of the new vector now enables employment of RNAi for the treatment of HF in vivo.

An improved Tet-On regulatable FasL-adenovirus vector system for lung cancer therapy

Gene therapy is a new therapeutic approach for the treatment of human cancers. Gene expression systems that can be regulated by drugs have been developed to improve the safety and efficacy of therapeutic transgene delivery. One of the most promising systems is the tetracycline (Tet)-responsive system in the Tet-On configuration. A major problem of the Tet-On system if used in viral vectors is the high basal activity of the Tet response element (TRE) promoter leading to leaky expression of transgenes under uninduced conditions. We therefore evaluated novel TRE promoters for controlling gene expression in an adenovirus vector (AdV) Tet-On system and further investigated them for expression of the pro-apoptotic CD95/Fas ligand (FasL) in human epithelial carcinoma cell line (HeLa) and lung cancer cells. Plasmid-based reporter gene assays showed that modifications within the tetO (7) and minimal immediate early cytomegalovirus promoter (CMV)(min) sequence of the TRE promoter reduced its leakiness and led to a markedly improved regulatability by doxycycline. Among several TRE promoters tested, a new construct (TRE-Tight1) containing modifications of both the tetO (7) sequence and the CMV(min) showed 11-fold reduced leakiness and 1.5-fold increased absolute transgene expression levels after induction, as compared to the original TRE. Under induced conditions, a TRE-Tight1 promoter-dependent AdV expressing the pro-apoptotic CD95L/FasL induced apoptosis and cell lysis in HeLa cells as efficiently as an AdV containing the original TRE promoter. In contrast to the latter, however, the vector with the modified TRE promoter left cells totally unaffected in the absence of the inducer. Stringently regulated induction of apoptosis and cell death by TRE-Tight1-AdV was also demonstrated in three human lung cancer cell lines. These data show that the novel TRE-Tight1 promoter has a high potential for closely controlled and efficient expression of cytotoxic genes in AdV-based anti-cancer approaches.

Topors acts as a SUMO-1 E3 ligase for p53 in vitro and in vivo

Human Topors, which was originally identified as cellular binding partner of DNA topoisomerase I and of p53, has recently been shown to function as an ubiquitin E3 ligase for p53 in a manner dependent on its N'-terminally located RING finger. Here, we demonstrate that Topors also enhances the conjugation of the small ubiquitin-like modifier 1 (SUMO-1) to p53 in vivo and in a reconstituted in vitro system. The Topors SUMO-1 E3 ligase activity does not depend upon its RING finger motif. In HeLa cells, Topors induced p53 sumoylation was accompanied by an increase in endogenous p53 protein levels. Furthermore, Topors enhances the sumoylation of a variety of other, yet unidentified, cellular proteins.

Tamoxifen-regulated adenoviral E1A chimeras for the control of tumor selective oncolytic adenovirus replication in vitro and in vivo

Pharmacological control is a desirable safety feature of oncolytic adenoviruses (oAdV). It has recently been shown that oAdV replication may be controlled by drug-dependent transcriptional regulation of E1A expression. Here, we present a novel concept that relies on tamoxifen-dependent regulation of E1A activity through functional linkage to the mutated hormone-binding domain of the murine estrogen receptor (Mer). Four different E1A-Mer chimeras (ME, EM, E(DeltaNLS)M, MEM) were constructed and inserted into the adenoviral genome under control of a lung-specific surfactant protein B promoter. The highest degree of regulation in vitro was seen for the corresponding oAdVs Ad.E(DeltaNLS)M and Ad.MEM, which exhibited an up to 100-fold higher oAdV replication in the presence as compared with the absence of 4-OH-tamoxifen. Moreover, destruction of nontarget cells was six- and 13-fold reduced for Ad.E(DeltaNLS)M and Ad.MEM, respectively, as compared with Ad.E. Further investigations supported tamoxifen-dependent regulation of Ad.E(DeltaNLS)M and Ad.MEM in vivo. Induction of Ad.E(DeltaNLS)M inhibited growth of H441 lung tumors as efficient as a control oAdV expressing E1A. E(DeltaNLS)M and the MEM chimeras can be easily inserted into a single vector genome, which extends their application to existing oAdVs and strongly facilitates in vivo application.

SUMO-1 modification regulates the protein stability of the large regulatory protein Rep78 of adeno associated virus type 2 (AAV-2)

The large Rep proteins Rep78 and Rep68 of the helper-dependent adeno associated virus type 2 (AAV-2) are essential for both site-specific integration of AAV DNA in the absence of helpervirus and productive AAV replication in the presence of helpervirus. We have identified UBC9, the E2 conjugating enzyme for the small ubiquitin-related polypeptide SUMO-1, as binding partner of the large Rep proteins in yeast two-hybrid analysis and in GST pulldown assays. Modification of the large Rep proteins with SUMO-1 could be demonstrated in immunoblot analysis and in immunoprecipitations, with the lysine residue at amino acid position 84 serving as the major attachment site. The largely sumolation-deficient Rep78 lysine to arginine point mutant showed a strongly reduced half-life as compared to the wild-type protein. This finding implicates a role for sumolation in the regulation of Rep78 protein stability that is assumed to be critical for the establishment and maintenance of AAV latency.

ssDNA-dependent colocalization of adeno-associated virus Rep and herpes simplex virus ICP8 in nuclear replication domains

The subnuclear distribution of replication complex proteins is being recognized as an important factor for the control of DNA replication. Herpes simplex virus (HSV) single-strand (ss)DNA-binding protein, ICP8 (infected cell protein 8) accumulates in nuclear replication domains. ICP8 also serves as helper function for the replication of adeno-associated virus (AAV). Using quantitative 3D colocalization analysis we show that upon coinfection of AAV and HSV the AAV replication protein Rep and ICP8 co-reside in HSV replication domains. In contrast, Rep expressed by a recombinant HSV, in the absence of AAV DNA, displayed a nuclear distribution pattern distinct from that of ICP8. Colocal ization of Rep and ICP8 was restored by the reintroduction of single-stranded AAV vector genomes. In vitro, ICP8 displayed direct binding to Rep78. Single-stranded recombinant AAV DNA strongly stimulated this interaction, whereas double-stranded DNA was ineffective. Our findings suggest that ICP8 by its strong ssDNA-binding activity exploits the unique single-strandedness of the AAV genome to form a tripartite complex with Rep78 and AAV ssDNA. This novel mechanism for recruiting components of a functional replication complex directs AAV to subnuclear HSV replication compartments where the HSV replication complex can replicate the AAV genome.

The DNA topoisomerase I binding protein topors as a novel cellular target for SUMO-1 modification: characterization of domains necessary for subcellular localization and sumolation

Over the past years, modification by covalent attachment of SUMO (small ubiquitin-like modifier) has been demonstrated for of a number of cellular and viral proteins. While increasing evidence suggests a role for SUMO modification in the regulation of protein-protein interactions and/or subcellular localization, most SUMO targets are still at large. In this report we show that Topors, a Topoisomerase I and p53 interacting protein of hitherto unknown function, presents a novel cellular target for SUMO-1 modification. In a yeast two-hybrid system, Topors interacted with both SUMO-1 and the SUMO-1 conjugating enzyme UBC9. Multiple SUMO-1 modified forms of Topors could be detected after cotransfection of exogenous SUMO-1 and Topors induced the colocalization of a YFP tagged SUMO-1 protein in a speckled pattern in the nucleus. A subset of these Topors' nuclear speckles were closely associated with the PML nuclear bodies (POD, ND10). A central domain comprising Topors residues 437 to 574 was sufficient for both sumolation and localization to nuclear speckles. One SUMO-1 acceptor site at lysine residue 560 could be identified within this region. However, sumolation-deficient Topors mutants showed that sumolation obviously is not required for localization to nuclear speckles.

Packaging of human chromosome 19-specific adeno-associated virus (AAV) integration sites in AAV virions during AAV wild-type and recombinant AAV vector production

Adeno-associated virus type 2 (AAV-2) establishes latency by site-specific integration into a unique locus on human chromosome 19, called AAVS1. During the development of a sensitive real-time PCR assay for site-specific integration, AAV-AAVS1 junctions were reproducibly detected in highly purified AAV wild-type and recombinant AAV vector stocks. A series of controls documented that the junctions were packaged in AAV capsids and were newly generated during a single round of AAV production. Cloned junctions displayed variable AAV sequences fused to AAVS1. These data suggest that packaged junctions represent footprints of AAV integration during productive infection. Apparently, AAV latency established by site-specific integration and the helper virus-dependent, productive AAV cycle are more closely related than previously thought.

Kinetics and frequency of adeno-associated virus site-specific integration into human chromosome 19 monitored by quantitative real-time PCR

Adeno-associated virus type 2 (AAV-2) integrates specifically into a site on human chromosome 19 (chr-19) called AAVS1. To study the kinetics and frequency of chr-19-specific integration after AAV infection, we developed a rapid, sensitive, and quantitative real-time PCR assay for AAV inverted terminal repeat-chr-19-specific junctions. Despite the known variability of junction sites, conditions were established that ensured reliable quantification of integration rates within hours after AAV infection. The overall integration frequency was calculated to peak at between 10 and 20% of AAV-infected, unselected HeLa cells. At least 1 in 1,000 infectious AAV-2 particles was found to integrate site specifically up to day 4 postinfection in the absence of selection. Chromosomal breakpoints within AAVS1 agreed with those found in latently infected clonal cell lines and transgenic animals. Use of this quantitative real-time PCR will greatly facilitate the study of the early steps of wild-type and recombinant AAV vector integration.

Topors, a p53 and topoisomerase I binding protein, interacts with the adeno-associated virus (AAV-2) Rep78/68 proteins and enhances AAV-2 gene expression

The adeno-associated virus type 2 (AAV-2) Rep proteins are essential for AAV DNA replication and regulation of AAV gene expression. We have identified a cellular protein interacting with Rep78 and Rep68 in yeast two-hybrid analysis and in GST pull-down assays. This protein has recently been described as both a p53 (p53BP3) and a topoisomerase I interacting protein (Topors). It contains an arginine/serine-rich domain, a RING finger domain and five PEST sequences. A minimal sequence sufficient for interaction with Rep was mapped to Topors amino acids 871 to 917. We show that the same region is also involved in the interaction with p53. Rep sequences involved in interaction with Topors were mapped to Rep amino acids 172 to 481. Overexpression of Topors stimulated AAV gene expression in the absence of helper virus, suggesting a function of Topors as a transcriptional regulator.

Adeno-associated virus type 2 protein interactions: formation of pre-encapsidation complexes

The nonstructural adeno-associated virus type 2 Rep proteins are known to control viral replication and thus provide the single-stranded DNA genomes required for packaging into preformed capsids. In addition, complexes between Rep proteins and capsids have previously been observed in the course of productive infections. Such complexes have been interpreted as genome-linked Rep molecules associated with the capsid upon successful DNA encapsidation. Here we demonstrate via coimmunoprecipitation, cosedimentation, and yeast two-hybrid analyses that the Rep-VP association also occurs in the absence of packageable genomes, suggesting that such complexes could be involved in the preparation of empty capsids for subsequent encapsidation steps. The Rep domain responsible for the observed Rep-VP interactions is situated within amino acids 322 to 482. In the presence of all Rep proteins, Rep52 and, to a lesser extent, Rep78 are most abundantly recovered with capsids, whereas Rep68 and Rep40 vary in association depending on their expression levels. Rep78 and Rep52 are bound to capsids to roughly the same extent as the minor capsid protein VP2. Complexes of Rep78 and Rep52 with capsids differ in their respective detergent stabilities, indicating that they result from different types of interactions. Rep-VP interaction studies suggest that Rep proteins become stably associated with the capsid during the assembly process. Rep-capsid complexes can reach even higher complexity through additional Rep-Rep interactions, which are particularly detergent labile. Coimmunoprecipitation and yeast two-hybrid data demonstrate the interaction of Rep78 with Rep68, of Rep68 with Rep52, and weak interactions of Rep40 with Rep52 and Rep78. We propose that the large complexes arising from these interactions represent intermediates in the DNA packaging pathway.

The adeno-associated virus type 2 regulatory proteins rep78 and rep68 interact with the transcriptional coactivator PC4

The adeno-associated virus type 2 (AAV-2) Rep78/Rep68 regulatory proteins are pleiotropic effectors of viral and cellular DNA replication, of cellular transformation by viral and cellular oncogenes, and of homologous and heterologous gene expression. To search for cellular proteins involved in mediating these functions, we used Rep68 as bait in the yeast two-hybrid system and identified the transcriptional coactivator PC4 as a Rep interaction partner. PC4 has been shown to mediate transcriptional activation by a variety of sequence-specific transcription factors in vitro. Rep amino acids 172 to 530 were sufficient and amino acids 172 to 224 were absolutely necessary for the interaction with PC4. The PC4 domains required for interaction were mapped to the C-terminal single-stranded DNA-binding domain of PC4. In glutathione S-transferase (GST) pull-down assays, in vitro-transcribed and -translated Rep78 or Rep68 proteins were bound specifically by GST-PC4 fusion proteins. Similarly, PC4 expressed in Escherichia coli was bound by GST-Rep fusion proteins, confirming the direct interaction between Rep and PC4 in vitro. Rep was found to have a higher affinity for the nonphosphorylated, transcriptionally active form of PC4 than for the phosphorylated, transcriptionally inactive form. The latter is predominant in nuclear extracts of HeLa or 293 cells. In the yeast system, but not in vitro, Rep-PC4 interaction was disrupted by a point mutation in the putative nucleotide-binding site of Rep68, suggesting that a stable interaction between Rep and PC4 in vivo is ATP dependent. This mutation has also been shown to impair Rep function in AAV-2 DNA replication and in inhibition of gene expression and inducible DNA amplification. Cytomegalovirus promoter-driven overexpression of PC4 led to transient accumulation of nonphosphorylated PC4 with concomitant downregulation of all three AAV-2 promoters in the absence of helper virus. In the presence of adenovirus, this effect was relieved. These results imply an involvement of the transcriptional coactivator PC4 in the regulation of AAV-2 gene expression in the absence of helper virus.

Control of adeno-associated virus type 2 cap gene expression: relative influence of helper virus, terminal repeats, and Rep proteins

Adeno-associated virus type 2 (AAV-2) gene expression is tightly controlled by functions of the helper virus as well as by the products of its own viral rep gene. Double-immunofluorescence studies of Rep and VP protein expression in cells coinfected with AAV-2 and adenovirus type 2 showed that a large proportion of these cells expressed Rep78 and Rep52 but no capsid proteins. The percentage of Rep78/Rep52- and capsid protein-positive cells was strongly influenced by the relative ratio of AAV-2 to adenovirus type 2. In contrast, nearly all cells positive for Rep68/Rep40 were also positive for capsid protein expression. Examination of p40 promoter transactivation by individual Rep proteins in the presence of adenovirus, however, showed that both Rep78 and Rep68 efficiently stimulated p40 mRNA accumulation and capsid protein expression. This strong transactivation was reliant upon the presence of terminal repeats and correlated with template amplification. In replication-deficient expression constructs, transactivation was observed only with Rep68 and was dependent on the linear Rep binding site within the left terminal repeat which was detected in the presence of high adenovirus concentrations. In the absence of any terminal repeat sequences, Rep68 expression again led to a minor transactivation of capsid protein expression which was detectable only at low adenovirus concentrations. This low level of transactivation of capsid protein expression by Rep proteins in the absence of terminal repeats resulted in a lower efficiency of capsid assembly. The data show a dominant influence of adenovirus type 2 functions on AAV-2 gene expression, a requirement for terminal repeats for strong transactivation of the p40 promoter by Rep proteins, and differential influences of Rep78 and Rep68 on AAV-2 promoters. Implications for the production of recombinant AAV-2 vectors are discussed.

Subcellular compartmentalization of adeno-associated virus type 2 assembly

Using immunofluorescence and in situ hybridization techniques, we studied the intracellular localization of adeno-associated virus type 2 (AAV-2) Rep proteins, VP proteins, and DNA during the course of an AAV-2/adenovirus type 2 coinfection. In an early stage, the Rep proteins showed a punctate distribution pattern over the nuclei of infected cells, reminiscent of replication foci. At this stage, no capsid proteins were detectable. At later stages, the Rep proteins were distributed more homogeneously over the nuclear interior and finally became redistributed into clusters slightly enriched at the nuclear periphery. During an intermediate stage, they also appeared at an interior part of the nucleolus for a short period, whereas most of the time the nucleoli were Rep negative. AAV-2 DNA colocalized with the Rep proteins. All three capsid proteins were strongly enriched in the nucleolus in a transient stage of infection, when the Rep proteins homogeneously filled the nucleoplasm. Thereafter, they became distributed over the whole nucleus and colocalized in nucleoplasmic clusters with the Rep proteins and AAV-2 DNA. While VP1 and VP2 strongly accumulated in the nucleus, VP3 was almost equally distributed between the nucleus and cytoplasm. Capsids, visualized by a conformation-specific antibody, were first detectable in the nucleoli and then spread over the whole nucleoplasm. This suggests that nucleolar components are involved in initiation of capsid assembly whereas DNA packaging occurs in the nucleoplasm. Expression of a transfected full-length AAV-2 genome followed by adenovirus infection showed all stages of an AAV-2/adenovirus coinfection, whereas after expression of the cap gene alone, capsids were restricted to the nucleoli and did not follow the nuclear redistribution observed in the presence of the whole AAV-2 genome. Coexpression of Rep proteins released the restriction of capsids to the nucleolus, suggesting that the Rep proteins are involved in nuclear redistribution of AAV capsids during viral infection. Capsid formation was dependent on the concentration of expressed capsid protein.

Mutational analysis of adeno-associated virus Rep protein-mediated inhibition of heterologous and homologous promoters

The four Rep proteins encoded by adeno-associated virus type 2 (AAV-2) inhibit transcription of their own promoters and of several heterologous promoters. To gain insight into the molecular mechanism of Rep-mediated transcription repression, we studied the effects of the four Rep proteins on the accumulation of mRNA transcribed from the human papillomavirus type 18 upstream regulatory region HPV18 URR, the human immunodeficiency virus long terminal repeat, and the AAV-2 p5 and p19 promoters by transient transfection experiments in HeLa cells. We observed a distinct contribution of the C- and N-terminal sequences in which the four Rep proteins (Rep78, Rep68, Rep52, and Rep40) differ from each other. While Rep78 showed a more than 10-fold inhibition of the four promoters studied, transcriptional repression mediated by Rep68 and Rep52 was reduced and nearly completely abolished for Rep40. The contribution of the C terminus of Rep78 was reduced with respect to the inhibition of the AAV-2 p5 and p19 promoters. Point mutations and deletions showed that a C-terminal zinc binding motif is required for zinc binding in vitro but plays no obvious role in the inhibition of homologous and heterologous promoters. Overall, inhibition of the four different promoters was dependent on the identical Rep protein domains with the exception of the AAV-2 p5 promoter. Expression of the AAV-2 p5 promoter was inhibited by a Rep78 protein with a mutation in the nucleotide binding motif, whereas expression of the AAV-2 p19 promoter, the human immunodeficiency virus long terminal repeat, and the HPV18 URR was not. Mutational analysis of the HPV18 URR showed that several, but not a single, cis regulatory elements are involved in the inhibition process. This finding suggests that transcriptional repression is mediated by protein-protein interactions of the Rep proteins either with multiple transcription factors or with target proteins of sequence-specific transcription factors of the basal transcription machinery.

Intermediates of adeno-associated virus type 2 assembly: identification of soluble complexes containing Rep and Cap proteins

The proteins encoded by the adeno-associated virus type 2 (AAV-2) rep and cap genes obtained during a productive infection of HeLa cells with AAV-2 and adenovirus type 2 were fractionated according to solubility, cellular localization, and sedimentation properties. The majority of Rep and Cap proteins accumulated in the nucleus, where they distributed into a soluble and an insoluble fraction. Analysis of the soluble nuclear fraction of capsid proteins by sucrose density gradients showed that they formed at least three steady-state pools: a monomer pool sedimenting at about 6S, a pool of oligomeric intermediates sedimenting between 10 and 15S, and a broad pool of assembly products with a peak between 60 and 110S, the known sedimentation positions of empty and full capsids. While the soluble nuclear monomer and oligomer pool contained predominantly only two capsid proteins, the 30 to 180S assembly products contained VP1, VP2, and VP3 in a stoichiometry similar to that of purified virions. They probably represent different intermediates in capsid assembly, DNA encapsidation, and capsid maturation. In contrast, the cytoplasmic fraction of capsid proteins showed a pattern of oligomers continuously increasing in size without a defined peak, suggesting that assembly of 60S particles occurs in the nucleus. Soluble nuclear Rep proteins were distributed over the whole sedimentation range, probably as a result of association with AAV DNA. Subfractions of the Rep proteins with defined sedimentation values were obtained in the soluble nuclear and cytoplasmic fractions. We were able to coimmunoprecipitate capsid proteins sedimenting between 60 and 110S with antibodies against Rep proteins, suggesting that they exist in common complexes possibly involved in AAV DNA packaging. Antibodies against the capsid proteins, however, precipitated Rep78 and Rep68 predominantly with a peak around 30S representing a second complex containing Rep and Cap proteins.

Mdr1/P-glycoprotein expression in natural killer (NK) cells enriched from peripheral or umbilical cord blood

The sensitivity to antineoplastic agents of subpopulations of haematopoietic cells during cancer chemotherapy is an open question. The performance of natural killer (NK) cells, possibly assisting the elimination of tumour cells under drug treatment might be of particular interest. We examined the expression of the transmembrane multidrug transporter mdr1/P-glycoprotein in NK-cells (CD56+) enriched from the peripheral blood or the umbilical cord blood from healthy donors by indirect immunocytofluorescence using the monoclonal P-glycoprotein antibody C219 and a polymerase chain reaction (PCR) approach with amplimers specific for the human mdr1 cDNA. As the antibody C219 apparently cross-reacts with the human mdr3 gene product whose functions are as yet unclear we also checked expression of this gene by PCR using mdr3 specific amplimers. Distinct, but rather inhomogeneous mdr1/P-glycoprotein expression was found in NK-cells enriched from the peripheral blood. NK-cells enriched from the umbilical cord blood showed quite strong mdr1 expression levels throughout, exceeding the values found in the moderately multidrug-resistant cell line CCRF VCR 100 which is permanently cultivated in the presence of 100 ng/ml vincristine. Mdr1/P-glycoprotein expression was mirrored by lowered sensitivities of the cultivated NK-cells towards actinomycin D or adriamycin. The drug sensitivity could be modulated by treatment of the cells with the immunosuppressive drug cyclosporin A. Expression of the mdr3 gene was low or absent in all NK-cell samples examined so far.

mdr1/P-glycoprotein gene segments analyzed from various human leukemic cell lines exhibiting different multidrug resistance profiles

Three high-level multidrug-resistant sublines of the human T-lymphoblastoid cell line CCRF-CEM were selected independently with either actinomycin D, vincristine or adriamycin. They exhibited distinct quantitative differences of cross-resistance profiles, and showed amplification and marked expression of the mdrl/P-glycoprotein gene. DNA and RNA were prepared from the cell lines, and additionally from three cell samples of patients suffering from acute lymphatic leukemia. Applying the polymerase chain reaction (PCR) for amplification, we cloned and sequenced from these sources segments of the mdrl/P-glycoprotein gene around the codon 185 which codes for an amino acid residue possibly influencing the drug binding function of the P-glycoprotein. Altogether, only 2 single nucleotide differences in an intron were found in 2 out of 40 recombinants each harboring a 209 bp genomic or a 269 bp cDNA fragment of the mdrl/P-glycoprotein gene. Our result does not support the idea of clustered point mutations in this segment of the P-glycoprotein gene as a cause of different multidrug resistance profiles. We additionally examined another segment of the P-glycoprotein gene in its second half, essentially delivering the same negative result, though.

Computer-controlled discontinuous rotating gel electrophoresis for separation of very large DNA molecules

The newly designed equipment for alternating field gel electrophoresis which permits the separation of very large DNA molecules and the simultaneous analysis of up to 35 samples is described. The field alternation is effected by intermittently rotating the submerged agarose gel by optitional angles. The time intervals between changes of position are controlled by a computer program driving a simple switching device which was designed to suit any technique using periodic switching or inversion of the electrical field. Because the electrophoresis unit provides an absolutely homogeneous electrical field, no distortion of migration lanes occurs and the resolution is very good. Moreover, by using a switching time interval gradient an almost perfect linear relationship between migration distances and molecule sizes in the range of about 100-1250 kilobase pairs is observed. In two-dimensional separations, different switching time programs for the first and second dimension allow maximum resolution of selected size ranges. Field inversion gel electrophoresis is possible as well. The performance of the method is demonstrated by comparing the chromosome sizes of different yeast strains.