Development of human single-chain antibodies against SARS-associated coronavirus

The outbreak of severe acute respiratory syndrome (SARS), caused by a distinct coronavirus, in 2003 greatly threatened public health in China, Southeast Asia as well as North America. Over 1,000 patients died of the SARS virus, representing 10% of infected people. Like other coronaviruses, the SARS virus also utilizes a surface glycoprotein, namely the spike protein, to infect host cells. The spike protein of SARS virus consists of 1,255 amino acid residues and can be divided into two sub-domains, S1 and S2. The S1 domain mediates the binding of the virus to its receptor angiotensin-converting enzyme 2, which is abundantly distributed on the surface of human lung cells. The S2 domain mediates membrane fusion between the virus and the host cell. Hence two strategies can be used to block the infection of the SARS virus, either by interfering with the binding of the S1 domain to the receptor or by blocking the fusion of the virus with the cell membrane mediated by the S2 domain. Several antibodies against the S1 domain have been generated and all of them are able to neutralize the virus in vitro and in vivo using animal models. Unfortunately, point mutations have been identified in the S1 domain, so that the virus isolated in the future may not be recognized by these antibodies. As no mutation has been found in the S2 domain indicating that this region is more conserved than the S1 domain, it may be a better target for antibody binding. After predicting the immunogenicity of the epitopes of the S2 domain, we chemically synthesized two peptides and also expressed one of them using a recombinant DNA method. We screened a phage displaying library of human single-chain antibodies (ScFv) against the predicted epitopes and obtained a human ScFv which can recognize the SARS virus in vitro.

AAV serotype 1 mediates more efficient gene transfer to pig myocardium than AAV serotype 2 and plasmid

Adeno-associated virus (AAV) has many properties of an ideal vector for delivery of therapeutic genes into the myocardium. Previous studies in a mouse model of myocardial infarction showed that AAV serotype 1 (AAV1) is superior to AAV serotypes 2-5 to transfer genes into the myocardium by direct injection. Since vectors may behave differently in humans and because the human and the pig hearts resemble each other closely, we tested whether AAV1 is also superior to AAV2 in transferring genes into the pig myocardium. We also compared gene transduction efficiency between AAV vectors and plasmid. We injected CMVLacZ and CMVVEGF (vectors with the cytomegalovirus (CMV) promoter driving LacZ and VEGF gene expression) unpackaged or packaged in AAV serotypes 1 or 2 capsids into pig myocardium. Hearts were collected 3, 14 and 28 days after the injection. Gene expression was analyzed by real-time reverse-transcription polymerase chain reaction (RT-PCR) and histological staining. Capillaries and smooth muscle alpha-actin (SMA)-positive vessels were quantified. Potential lymphocyte infiltration at the injection sites was analyzed by immunostaining using specific antibodies. As in the mouse, AAV1 mediated better gene transduction than AAV2. Plasmid mediated minimal gene expression only. More capillaries and SMA-positive vessels were detected at AAV1CMVVEGF- and AAV2CMVVEGF-injected than AAV1CMVLacZ-injected sites. We did not detect inflammatory cell infiltration at the injection sites. In conclusion, by direct injection, AAV1 is more efficient than AAV2, and plasmid is inefficient in mediating gene transfer into the pig myocardium. AAV-mediated VEGF gene transfer can also induce neovascular formation in the pig myocardium.

Fetal gene therapy of alpha-thalassemia in a mouse model

Fetuses with homozygous alpha-thalassemia usually die at the third trimester of pregnancy or soon after birth. Hence, the disease could potentially be a target for fetal gene therapy. We have previously established a mouse model of alpha-thalassemia. These mice mimic the human alpha-thalassemic conditions and can be used as preclinical models for fetal gene therapy. We tested a lentiviral vector containing the HS 2, 3, and 4 of the beta-LCR, a central polypurine tract element, and the beta-globin gene promoter directing either the EGFP or the human alpha-globin gene. We showed that the GFP expression was erythroid-specific and detected in BFU-E colonies and the erythroid progenies of CFU-GEMM. For in utero gene delivery, we did yolk sac vessel injection at midgestation of mouse embryos. The recipient mice were analyzed after birth for human alpha-globin gene expression. In the newborn, human alpha-globin gene expression was detected in the liver, spleen, and peripheral blood. The human alpha-globin gene expression was at the peak at 3-4 months, when it reached 20% in some recipients. However, the expression declined at 7 months. Colony-forming assays in these mice showed low abundance of the transduced human alpha-globin gene in their BFU-E and CFU-GEMM and the lack of its transcript. Thus, lentiviral vectors can be an effective vehicle for delivering the human alpha-globin gene into erythroid cells in utero, but, in the mouse model, delivery at late midgestation could not transduce hematopoietic stem cells adequately to sustain gene expression.

AAV serotype-1 mediates early onset of gene expression in mouse hearts and results in better therapeutic effect

Adeno-associated viral vectors (AAV) are attractive tool for gene therapy for coronary artery disease. However, gene expression in myocardium mediated by AAV serotype 2 (AAV2) does not peak until 4-6 weeks after gene transfer. This delayed gene expression may reduce its therapeutic potential for acute cardiac infarction. To determine whether earlier gene expression and better therapeutic effect could be achieved using a different serotype, CMV promoter driving the EPO gene (AAV-EPO) was packaged into AAV serotypes 1-5 capsids and injected into mouse myocardium. EPO expression was studied by measuring the hematocrits and EPO mRNA. After we found that AAV1 mediates the highest gene expression after 4 days of gene transduction, AAV-LacZ (CMV promoter driving LacZ gene expression) and MLCVEGF (hypoxia-inducible and cardiac-specific VEGF expression) were packaged into AAV1 and 2 capsids. LacZ expression was detected in AAV1-LacZ but not in AAV2-LacZ-injected hearts 1 day after vector injection. Compared to AAV2-MLCVEGF that mediated no significant VEGF expression, AAV1-MLCVEGF mediated 13.7-fold induction of VEGF expression in ischemic hearts 4 days after gene transduction and resulted in more neovasculatures, better cardiac function and less myocardial fibrosis. Thus, AAV1 mediates earlier and higher transgene expression in myocardium and better therapeutic effects.

Intracavernosal vascular endothelial growth factor (VEGF) injection and adeno-associated virus-mediated VEGF gene therapy prevent and reverse venogenic erectile dysfunction in rats

Penile veno-occlusive dysfunction (venogenic erectile dysfunction) is a common cause of erectile dysfunction (ED). We investigated whether vascular endothelial growth factor (VEGF) can be used to prevent and reverse venogenic ED in a rat model. Pharmacological cavernosometry was developed and validated using adult male rats with either arteriogenic or venogenic ED. Castrated animals were treated with intracavernous VEGF as either a recombinant protein (C+VEGF) or adeno-associated virus (AAV)-mediated VEGF gene therapy (C+VEGF gene) in an attempt to prevent the development of venogenic ED. Other animal groups received testosterone replacement (C+testosterone) or intracavernous AAV-LacZ gene (C+LacZ). Animals with documented venogenic ED were treated with intracavernous VEGF in an attempt to reverse their ED. Functional analysis (pharmacological infusion cavernosometry) was performed following treatment. Penile specimens were harvested for immunohistochemistry and electron microscopic evaluation. Castrated rats showed a decrease in papaverine-induced intracavernous pressure and an increase in maintenance and drop rates during pharmacological cavernosometry. These changes were prevented by systemic testosterone and intracavernous VEGF or AAV-VEGF therapy. Moreover, intracavernous VEGF was able to reverse the venogenic ED produced by castration. The quantity of penile smooth muscle detected by alpha actin staining decreased after castration but not in the C+T, C+VEGF, or C+VEGF gene groups. Transmission electron microscopy revealed atrophy of penile smooth muscle cells and nerves in the castrated rats. In VEGF-treated rats, regeneration of smooth muscle and nerves as well as endothelial cell hypertrophy and hyperplasia were the prominent features. In our animal model, systemic testosterone replacement or intracavernous VEGF (protein and VEGF gene) prevented the veno-occlusive dysfunction in castrated animals. In rats with established venous leakage, VEGF treatment reversed the cavernosometric findings of leakage. Intracavernous injection of either VEGF protein or VEGF gene may be a preferred therapy to preserve erectile function in patients in whom testosterone therapy is contraindicated.

The effect of adeno-associated virus mediated brain derived neurotrophic factor in an animal model of neurogenic impotence

PURPOSE

We tested the hypothesis that transfecting penile tissue with brain derived neurotrophic factor may facilitate neural recovery and erectile capability after cavernous nerve injury.

MATERIALS AND METHODS

Of the 34 Sprague-Dawley rats used 10 underwent sham operation and 24 underwent bilateral cavernous nerve freezing and intracavernous injection of adeno-associated virus-LacZ (12) or adeno-associated virus-brain derived neurotrophic factor (12). Erectile function was assessed by cavernous nerve electrostimulation at 4 and 8 weeks, and samples of penile tissue and the major pelvic ganglia were evaluated histologically.

RESULTS

In the brain derived neurotrophic factor group mean maximal intracavernous pressure plus or minus standard deviation was significantly higher than in the LacZ group at 4 and 8 weeks (58.5 +/- 11.7 cm. water versus 28.4 +/- 5.5 and 61.3 +/- 12.5 versus 37.7 +/- 7.9, respectively). In addition, in the brain derived neurotrophic factor group reduced nicotinamide adenine dinucleotide phosphate diaphorase staining and neuronal nitric oxide synthase immunostaining revealed significantly more positive nerve fibers in the dorsal nerves and cavernous tissue than in the LacZ group at each time point and the percent of neuronal nitric oxide synthase positive neurons in the major pelvic ganglia was also significantly greater. Moreover, in the LacZ group most neurons showed a light staining pattern with irregular contours and numerous vacuoles in the cytoplasm.

CONCLUSIONS

Intracavernous injection of adeno-associated virus-brain derived neurotrophic factor may prevent the degeneration of neuronal nitric oxide synthase containing neurons in the major pelvic ganglia and facilitate the regeneration of neuronal nitric oxide synthase containing nerve fibers in penile tissue, thus, enhancing the recovery of erectile function after bilateral cavernous nerve injury.

A hypoxia-regulated adeno-associated virus vector for cancer-specific gene therapy

The presence of hypoxic cells in human brain tumors is an important factor leading to resistance to radiation therapy. However, this physiological difference between normal tissues and tumors also provides the potential for designing cancer-specific gene therapy. We compared the increase of gene expression under anoxia (<0.01% oxygen) produced by 3, 6, and 9 copies of hypoxia-responsive elements (HRE) from the erythropoietin gene (Epo), which are activated through the transcriptional complex hypoxia-inducible factor 1 (HIF-1). Under anoxic conditions, nine copies of HRE (9XHRE) yielded 27- to 37-fold of increased gene expression in U-251 MG and U-87 MG human brain tumor cell lines. Under the less hypoxic conditions of 0.3% and 1% oxygen, gene activation by 9XHRE increased expression 11- to 18-fold in these cell lines. To generate a recombinant adeno-associated virus (rAAV) in which the transgene can be regulated by hypoxia, we inserted the DNA fragment containing 9XHRE and the LacZ reporter gene into an AAV vector. Under anoxic conditions, this vector produced 79- to 110-fold increase in gene expression. We believe this hypoxia-regulated rAAV vector will provide a useful delivery vehicle for cancer-specific gene therapy.

An important function of Nrf2 in combating oxidative stress: detoxification of acetaminophen

Nrf2, a member of the "cap 'n collar" group of transcription factors, is important for protecting cells against oxidative damage. We investigated its role in the detoxification of acetaminophen [N-acetyl-p-aminophenol (APAP)]-induced hepatotoxicity. When Nrf2 knockout (Nrf2(-/-)) and wild-type mice were given APAP by i.p. injection, the Nrf2(-/-) mice were highly susceptible to APAP treatment. With doses of APAP that were tolerated by wild-type mice, the Nrf2(-/-) mice died of liver failure. When hepatic glutathione was depleted after a dose of 400 mg/kg of APAP, the wild-type mice were able to compensate and regain the normal glutathione level. In contrast, the glutathione level in the Nrf2(-/-) mice was not compensated and remained low. This was because of the decrease in the gene expression of gcs(H) and gcs(L) as well as gss in the livers of the Nrf2(-/-) mice. In addition, the expression of ugt1a6 and gstpi that detoxify APAP by conjugation was also decreased. This increased susceptibility of the Nrf2(-/-) mice to APAP, because of an impaired capacity to replenish their glutathione stores, compounded with a decreased detoxification capability, highlights the importance of Nrf2 in the regulation of glutathione synthesis and cellular detoxification processes.

Antibodies to human fetal erythroid cells from a nonimmune phage antibody library

The ability to isolate fetal nucleated red blood cells (NRBCs) from the maternal circulation makes possible prenatal genetic analysis without the need for diagnostic procedures that are invasive for the fetus. Such isolation requires antibodies specific to fetal NRBCs. To generate a panel of antibodies to antigens present on fetal NRBCs, a new type of nonimmune phage antibody library was generated in which multiple copies of antibody fragments are displayed on each phage. Antibody fragments specific for fetal NRBCs were isolated by extensive predepletion of the phage library on adult RBCs and white blood cells (WBCs) followed by positive selection and amplification on fetal liver erythroid cells. After two rounds of selection, 44% of the antibodies analyzed bound fetal NRBCs, with two-thirds of these showing no binding of WBCs. DNA fingerprint analysis revealed the presence of at least 16 unique antibodies. Antibody specificity was confirmed by flow cytometry, immunohistochemistry, and immunofluorescence of total fetal liver and adult RBCs and WBCs. Antibody profiling suggested the generation of antibodies to previously unknown fetal RBC antigens. We conclude that multivalent display of antibodies on phage leads to efficient selection of panels of specific antibodies to cell surface antigens. The antibodies generated to fetal RBC antigens may have clinical utility for isolating fetal NRBCs from maternal circulation for noninvasive prenatal genetic diagnosis. Some of the antibodies may also have possible therapeutic utility for erythroleukemia.

Prospects for research in hematologic disorders: sickle cell disease and thalassemia

Sickle cell anemia and thalassemia constitute the most common genetic diseases in the world. Affected patients carry a heavy burden of morbidity and early mortality. With improved understanding of the pathophysiology and molecular basis of these diseases, treatment is evolving from management of symptoms to more effective strategies that aim to modify diseased red blood cells or replace them with normal cells. Available treatment options include red blood cell transfusions, pharmacologic interventions to increase fetal hemoglobin levels, and stem cell transplantation. Improvements in these approaches or the development of means to replace defective genes with normal ones using techniques of gene transfer offer hope for the future.

Adeno-associated viral vector-mediated vascular endothelial growth factor gene transfer induces neovascular formation in ischemic heart

Vascular endothelial growth factor (VEGF) plays important roles in physiological and pathological angiogenesis. Recent studies have demonstrated that direct injection of VEGF protein, plasmid DNA, or an adenoviral vector encoding the VEGF gene into ischemic myocardium or limb can induce collateral blood vessel formation and improve perfusion of the ischemic areas. However, these approaches have limitations ranging from a short-lasting effect to angioma formation. In this study, we investigated the feasibility of using adeno-associated viral (AAV) vectors to deliver VEGF genes to mouse myocardium. A cytomegalovirus promoter was used to drive genes for a human VEGF isoform, VEGF(165), and LacZ. A mouse myocardial ischemic model was generated by ligation of the anterior descending coronary artery. Approximately 10(11) copies of the AAV-VEGF vector mixed with 10(10) copies of AAV-LacZ were injected to one site of normal myocardium and a total of 10(11) copies of AAV-VEGF were injected to multiple sites of myocardium around the ischemic region. LacZ gene expression was observed up to 3 months after the vector inoculation. After AAV-VEGF inoculation, neoangiogenesis was observed in the ischemic heart model but not in normal heart tissue. An inflammatory-cell infiltration was not observed in the AAV-VEGF- and AAV-LacZ-inoculated hearts, and angioma-like structure was not observed. These results indicated that injection of the AAV vector directly to myocardium could mediate efficient gene transfer and transgene expression and that VEGF gene delivered by AAV vector can induce angiogenesis in ischemic myocardium.

Adeno-associated viral-mediated gene transfer to hepatoma: thymidine kinase/interleukin 2 is more effective in tumor killing in non-ganciclovir (GCV)-treated than in GCV-treated animals

Interleukin 2 (IL-2) enhancement of herpes simplex virus-thymidine kinase (HSV-TK)/ganciclovir (GCV)-induced tumor killing was studied by cloning the human interleukin 2 gene into an HSV-TK-bearing adeno-associated viral (AAV) vector (TK/IL-2). The mouse hepatocellular carcinoma cell line Hepa 1-6 was used as a model in this study. We found that TK/IL-2-transduced Hepa 1-6 cells were more susceptible to ganciclovir treatment than tumor cells transduced with only TK in both nude mice and immunocompetent C57L/J mice. TK/IL-2-transduced tumors also showed shrinkage without GCV treatment. The tumor-killing effect of AAV-mediated TK/IL-2 gene transfer was further studied by inoculating animals with TK/IL-2- or TK-transduced tumor cells mixed with unmodified cells with or without GCV treatment. Although tumor growth in each group was inhibited, the best result was obtained from the TK/IL-2-transduced group without GCV treatment. In this group, 10% of the transduced tumor cells could eradicate the whole tumor in 50% of the animals tested as well as provide long-term protection against tumor cell rechallenge. When this group was treated with GCV, the antitumor effect of TK/IL-2 was reduced. We attribute this to the early ablation of transgene-bearing tumor cells by GCV treatment, which thus reduces the duration of IL-2 expression. We conclude that (i) TK/IL-2 plus GCV treatment generates a stronger tumor-killing effect than HSV-TK plus GCV and (ii) tumor killing of TK/IL-2 is more effective in non-GCV-treated animals than in GCV-treated animals.

Dominant negative down-regulation of endotoxin-induced tumor necrosis factor alpha production by Lps(d)/Ran

We recently showed that adenoviral transfer and expression of the Lps(d)/Ran gene isolated from endotoxin-resistant C3H/HeJ mice could protect endotoxin-sensitive mice from endotoxic shock. Elevation of proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-alpha), is thought to be essential for the development of septic shock. To investigate the extent to which Lps(d)/Ran affects TNF-alpha production, we transduced primary macrophages from endotoxin-sensitive and -resistant mice with adenoviral vectors expressing the wild-type and the mutant Lps/Ran cDNAs and other control genes, and compared the amount of TNF-alpha produced by these various transduced macrophages. Successful transfer and expression of Lps(d)/Ran cDNA in endotoxin-sensitive C3H/HeOuJ macrophages reduced TNF-alpha production upon lipopolysaccharide (LPS) stimulation, as compared with macrophages transduced with vectors expressing the wild-type Lps(n)/Ran cDNA, the green fluorescent protein gene, or the lacZ gene. On the other hand, successful transfer and expression of the wild-type Lps(n)/Ran cDNA in primary macrophages from endotoxin-resistant C3H/HeJ mice failed to induce TNF-alpha production to any significant extent unless a very high LPS concentration was used. Given our previous demonstration that Lps(n)/Ran functions effectively in restoring LPS responsiveness in B cells from C3H/HeJ mice, we conclude that Lps/Ran is involved in a CD14-independent signal transduction pathway. This dominant negative down-regulation by Lps(d)/Ran on TNF-alpha production by macrophages and probably other innate immune responses may be key to the development of an effective gene therapy for endotoxic or septic shock.

The CNC basic leucine zipper factor, Nrf1, is essential for cell survival in response to oxidative stress-inducing agents. Role for Nrf1 in gamma-gcs(l) and gss expression in mouse fibroblasts

Nrf1 is a member of the CNC-basic leucine zipper (CNC-bZIP) family of transcription factors. CNC bZIP factors, together with small Maf proteins, bind as heterodimers to the NF-E2/AP-1 element. Similarity between the NF-E2/AP-1 element and the antioxidant response element identified in a number of promoters of genes involved in detoxification and antioxidant response raises the possibility that Nrf1 plays a role in mediating the antioxidant response element response. In this study, we exploited the availability of cells from Nrf1 knockout mice to study the role of Nrf1 transcription factor in the regulation of antioxidant gene expression and in cellular antioxidant response. Fibroblast cells derived from Nrf1 null embryos showed lower levels of glutathione and enhanced sensitivity to the toxic effects of oxidant compounds. Our results indicate that Nrf1 plays a role in the regulation of genes involved in glutathione synthesis and suggest a basis for a correspondingly low GSH concentration and reduced stress response.

Nrf2 is essential for protection against acute pulmonary injury in mice

Nrf2 is a member of the "cap 'n' collar" family of transcription factors. These transcription factors bind to the NF-E2 binding sites (GCTGAGTCA) that are essential for the regulation of erythroid-specific genes. Nrf2 is expressed in a wide range of tissues, many of which are sites of expression for phase 2 detoxification genes. Nrf2(-/-) mice are viable and have a normal phenotype under normal laboratory conditions. The NF-E2 binding site is a subset of the antioxidant response elements that have the sequence GCNNNGTCA. The antioxidant response elements are regulatory sequences found on promoters of several phase 2 detoxification genes that are inducible by xenobiotics and antioxidants. We report here that Nrf2(-/-) mice are extremely susceptible to the administration of the antioxidant butylated hydroxytoluene. With doses of butylated hydroxytoluene that are tolerated by wild-type mice, the Nrf2(-/-) mice succumb from acute respiratory distress syndrome. Gene expression studies show that the expression of several detoxification enzymes is altered in the Nrf2(-/-) mice. The Nrf2(-/-) mice may prove to be a good in vivo model for toxicological studies. As oxidative damage causes DNA breakage, these mice may also be useful for testing carcinogenic agents.

Lps(d)/Ran of endotoxin-resistant C3H/HeJ mice is defective in mediating lipopolysaccharide endotoxin responses

C3H/HeJ inbred mice are defective in that they are highly resistant to endotoxic shock as compared with normal responder mice. Their B cells and macrophages do not respond significantly when exposed to lipopolysaccharide (LPS), whereas cells from the responder mice do. Using a functional assay, we previously isolated a cDNA, which encodes for Ran/TC4 GTPase. We now show that this gene is mutated in C3H/HeJ mice, which accounts for their resistance to endotoxin stimulation. Sequence analysis of independent mutant Lps(d)/Ran cDNAs isolated from splenic B cells of C3H/HeJ mice reveals a consistent single base substitution at position 870, where a thymidine is replaced with a cytidine. In situ hybridization maps the Lps(d)/Ran cDNA to mouse chromosome 4. By retroviral gene transfer, the wild-type Lps(n)/Ran cDNA but not the mutant Lps(d)/Ran cDNA can restore LPS responsiveness of C3H/HeJ cells. Adenoviral gene transfer in vivo with the mutant Lps(d)/Ran cDNA but not the wild-type Lps(n)/Ran cDNA rescues endotoxin-sensitive mice from septic shock. Thus Lps/Ran is an important target for LPS-mediated signal transduction, and the Lps(d)/Ran gene may be useful as a therapeutic sequence in gene therapy for endotoxemia and septic shock.

Transgenic knockout mice exclusively expressing human hemoglobin S after transfer of a 240-kb betas-globin yeast artificial chromosome: A mouse model of sickle cell anemia

Sickle cell anemia (SCA) and thalassemia are among the most common genetic diseases worldwide. Current approaches to the development of murine models of SCA involve the elimination of functional murine alpha- and beta-globin genes and substitution with human alpha and betas transgenes. Recently, two groups have produced mice that exclusively express human HbS. The transgenic lines used in these studies were produced by coinjection of human alpha-, gamma-, and beta-globin constructs. Thus, all of the transgenes are integrated at a single chromosomal site. Studies in transgenic mice have demonstrated that the normal gene order and spatial organization of the members of the human beta-globin gene family are required for appropriate developmental and stage-restricted expression of the genes. As the cis-acting sequences that participate in activation and silencing of the gamma- and beta-globin genes are not fully defined, murine models that preserve the normal structure of the locus are likely to have significant advantages for validating future therapies for SCA. To produce a model of SCA that recapitulates not only the phenotype, but also the genotype of patients with SCA, we have generated mice that exclusively express HbS after transfer of a 240-kb betas yeast artificial chromosome. These mice have hemolytic anemia, 10% irreversibly sickled cells in their peripheral blood, reticulocytosis, and other phenotypic features of SCA.

Alterations in protein-DNA interactions in the gamma-globin gene promoter in response to butyrate therapy

The mechanisms by which pharmacologic agents stimulate gamma-globin gene expression in beta-globin disorders has not been fully established at the molecular level. In studies described here, nucleated erythroblasts were isolated from patients with beta-globin disorders before and with butyrate therapy, and globin biosynthesis, mRNA, and protein-DNA interactions were examined. Expression of gamma-globin mRNA increased twofold to sixfold above baseline with butyrate therapy in 7 of 8 patients studied. A 15% to 50% increase in gamma-globin protein synthetic levels above baseline gamma globin ratios and a relative decrease in beta-globin biosynthesis were observed in responsive patients. Extensive new in vivo footprints were detected in erythroblasts of responsive patients in four regions of the gamma-globin gene promoter, designated butyrate-response elements gamma 1-4 (BRE-G1-4). Electrophoretic mobility shift assays using BRE-G1 sequences as a probe demonstrated that new binding of two erythroid-specific proteins and one ubiquitous protein, alphaCP2, occurred with treatment in the responsive patients and did not occur in the nonresponder. The BRE-G1 sequence conferred butyrate inducibility in reporter gene assays. These in vivo protein-DNA interactions in human erythroblasts in which gamma-globin gene expression is being altered strongly suggest that nuclear protein binding, including alphaCP2, to the BRE-G1 region of the gamma-globin gene promoter mediates butyrate activity on gamma-globin gene expression.

Efficient expression of CFTR function with adeno-associated virus vectors that carry shortened CFTR genes

Adeno-associated virus (AAV)-based vectors have been shown to be effective in transferring the cystic fibrosis gene (CFTR) into airway epithelial cells in animal models and in patients. However, the level of CFTR gene expression has been low because the vector cannot accommodate the CFTR gene together with a promoter. In this study, we described a strategy to reduce the size of the CFTR cDNA to allow the incorporation of an effective promoter with the CFTR gene into AAV vectors. We engineered and tested 20 CFTR mini-genes containing deletions that were targeted to regions that may contain nonessential sequences. Functional analyses showed that four of the shortened CFTRs (one with combined deletions) retained the function and the characteristics of a wild-type CFTR, as measured by open probability, time voltage dependence, and regulation by cAMP. By using an AAV vector with a P5 promoter, we transduced these short forms of CFTR genes into target cells and demonstrated high levels of CFTR expression. We also demonstrated that smaller AAV/CFTR vectors with a P5 promoter expressed the CFTR gene more efficiently than larger vectors or a vector in which CFTR gene was expressed from the AAV inverted terminal repeat sequence. The CFTR mini-gene with combined deletions was packaged into AAV virions more efficiently, generated higher titers of transducing virions, and more effectively transferred CFTR function into target cells. These new vectors should circumvent the limitations of AAV vector for CFTR expression. Our strategy also may be applicable to other genes, the sizes of which exceed the packaging limit of an AAV vector.

Targeted disruption of the ubiquitous CNC-bZIP transcription factor, Nrf-1, results in anemia and embryonic lethality in mice

The CNC-basic leucine zipper (CNC-bZIP) family is a subfamily of bZIP proteins identified from independent searches for factors that bind the AP-1-like cis-elements in the beta-globin locus control region. Three members, p45-Nf-e2, Nrf-1 and Nrf-2 have been identified in mammals. Expression of p45-Nf-e2 is largely restricted to hematopoietic cells while Nrf-1 and Nrf-2 are expressed in a wide range of tissues. To determine the function of Nrf-1, targeted disruption of the Nrf-1 gene was carried out. Homozygous Nrf-1 mutant mice are anemic due to a non-cell autonomous defect in definitive erythropoiesis and die in utero.

Tissue-specific expression of herpes simplex virus thymidine kinase gene delivered by adeno-associated virus inhibits the growth of human hepatocellular carcinoma in athymic mice

About 70% of hepatocellular carcinomas are known to express alpha-fetoprotein, which is normally expressed in fetal but not in adult livers. To induce herpes simplex virus-thymidine kinase expression in these cancer cells, we constructed an adeno-associated viral vector containing the HSV-TK gene under the control of the alpha-fetoprotein enhancer and albumin promoter. We previously demonstrated in vitro that although this vector can transduce a variety of human cells, only transduced AFP and albumin-expressing hepatocellular carcinoma cell lines were sensitive to killing by ganciclovir (GCV). In the present study, we explored the effect of this vector on hepatocellular carcinoma cells in vivo. Subcutaneous tumors generated in nude mice by implanting hepatocellular carcinoma cells previously transduced with this vector shrank dramatically after treatment with GCV. Bystander effect was also observed on the tumors generated by mixing transduced and untransduced cells. To test whether the tumor cells can be transduced by the virus in vivo, we injected the recombinant adeno-associated virus into tumors generated by untransduced hepatocarcinoma cell line. Tumor growth were retarded after treatment with GCV. These experiments demonstrate the feasibility of in vivo transduction of tumor cell with rAAV.

hMAF, a small human transcription factor that heterodimerizes specifically with Nrf1 and Nrf2

A 1.6-kilobase pair full-length cDNA encoding a transcription factor homologous to the Maf family of proteins was isolated by screening a K562 cDNA library with the NFE2 tandem repeat probe derived from the globin locus control region. The protein, which was designated hMAF, contains a basic DNA binding domain and an extended leucine zipper but lacks any recognizable activation domain. Expressed in vitro, the hMAF protein is able to homodimerize in solution and band-shift the NFE2 tandem repeat probe. In addition to homodimers, hMAF can also form high affinity heterodimers with two members of the NFE2/CNC-bZip family (Nrf1 and Nrf2) but not with a third family member, p45-NFE2. Although hMAF/hMAF homodimers and hMAF/Nrf1 and hMAF/Nrf2 heterodimers bind to the same NFE2 site, they exert functionally opposite effects on the activity of a linked gamma-globin gene. In fact, whereas all hMAF/CNC-bZip heterodimers stimulate the activity of a gamma-promoter reporter construct in K562 cells, the association into homodimers that is induced by overexpressing hMAF inhibits the activity of the same construct. Thus variations in the expression of hMAF may account for the modulation in the activity of the genes that bear NFE2 recognition sites.

NRF2, a member of the NFE2 family of transcription factors, is not essential for murine erythropoiesis, growth, and development

The locus control region of the beta-globin gene is composed of four erythroid-specific hypersensitive sites. Hypersensitive site 2 has been shown to be a powerful enhancer and contains a tandem repeat sequence for the transcription factors AP1 and NFE2 (activating protein 1 and nuclear factor erythroid 2, respectively). The human NRF2 (NFE2 related factor 2) has been isolated by bacterial expression screening using this core sequence as a probe. p45-NFE2, NRF1, and NRF2 belong to the CNC ("cap 'n' collar") subfamily of the basic region-leucine zipper transcription factors, which exhibits strong homology at specific regions such as the "CNC" and the DNA binding and leucine zipper domains. Although the erythroid-specific p45-NFE2 has been implicated in globin gene regulation, p45-NFE2 null mice succumb to bleedings due to lack of platelets and those that survive exhibit only a mild anemia. To determine the function of NRF2, which we found to be widely expressed in vivo, we have characterized the genomic structure of the mouse NRF2 gene, disrupted the Nrf2 gene by homologous recombination in mouse embryonic stem cells (ES cells), and generated NRF2-/- mice. Homozygous mutant mice developed normally, were not anemic, reached adulthood, and reproduced. Our studies indicate that NRF2 is dispensable for mouse development.

Prenatal diagnosis of sickle cell anaemia and thalassaemia by analysis of fetal cells in maternal blood

Currently, amniocentesis, chorionic villus sampling (CVS) and fetal blood sampling are used to obtain fetal cells for genetic diagnosis. These invasive procedures pose a small but not negligible risk for the fetus. Efforts have been directed towards the enrichment of fetal cells, such as erythroblasts, from maternal blood and progress has been made in the diagnosis of some chromosomal disorders and in sex determinations. We now report the detection of point mutations in single gene disorders using this method of prenatal diagnosis by enriching fetal cells from maternal blood by magnetic cell sorting followed by isolation of pure fetal cells by microdissection. In two pregnancies at risk for sickle cell anaemia and beta-thalassaemia, we successfully identified the fetal genotypes. Thus, prenatal diagnosis of single gene disorders by recovering fetal cells from maternal circulation appears to be a feasible approach.

Inactivation of mouse alpha-globin gene by homologous recombination: mouse model of hemoglobin H disease

We have disrupted the 5' locus of the duplicated adult alpha-globin genes by gene targeting in the mouse embryonic stem cells and created mice with alpha-thalassemia syndromes. The heterozygous knockout mice (.alpha/alpha alpha) are asymptomatic like the silent carriers in humans whereas the homozygous knockout mice (.alpha/.alpha) show hemolytic anemia. Mice with three dysfunctional alpha-globin genes generated by breeding the 5' alpha-globin knockouts (.alpha/alpha alpha) and the deletion type alpha-thalassemia mice (../alpha alpha) produce severe hemoglobin H disease and they die in utero. These results indicate that the 5' alpha-globin gene is the predominant locus in mice, and suggest that it is even more dominant than its human homologue.

Globin gene switching. In vivo protein-DNA interactions of the human beta-globin locus in erythroid cells expressing the fetal or the adult globin gene program

To characterize the protein-DNA interactions important for the developmental control of the human beta-globin locus, we analyzed by in vivo dimethyl sulfate footprinting erythroid cells expressing either the fetal or the adult globin developmental program. In the locus control region (LCR) of the beta-globin locus, in vivo footprints on NF-E2 (or AP-1) and GATA-1 motifs remained the same regardless of whether the fetal or the adult globin genes are expressed. In contrast, in vivo footprints on GT (CACCC) motifs differed between the cells expressing the fetal or the adult globin program. In promoter regions, the actively transcribed genes demonstrated extensive and consistent footprints over the canonical elements, such as CACCC and CCAAT motifs. The adult globin expressing cells displayed more extensive footprints than the fetal globin expressing cells in the 3' regulatory sequences of both the Agamma- and the beta-globin genes, suggesting a role of these 3' elements in beta-globin gene expression. Our results suggest that the bulk of protein-DNA interactions that underlies the developmental control of globin genes takes place in the gamma- and beta-globin gene promoters, and that GT motifs of the beta-globin locus LCR may play a role in the developmental regulation of human beta-globin gene expression, perhaps by increasing the probability of interaction of the LCR holocomplex with the fetal or the adult globin gene.

Selective killing of AFP-positive hepatocellular carcinoma cells by adeno-associated virus transfer of the herpes simplex virus thymidine kinase gene

The use of viral thymidine kinase (TK) gene coupled with the administration of ganciclovir to render cancer cell death has been studied extensively. Many of these experiments utilized retrovirus to transfer the TK gene under the control of a nonspecific promoter. Because nonspecific expression of the viral TK gene may cause death of proliferating cells, other than cancer cells, we explored the use of a liver-specific promoter and a tumor-specific AFP enhancer to achieve regulated viral TK gene expression for treatment of hepatocellular carcinoma. We also used the adeno-associated virus (AAV) as vector for the delivery of the TK gene because this virus is not associated with any pathological consequences in humans. Because it can infect nondividing S-phase cells, AAV can transfer genes into noncycling tumor cells. A recombinant AAV virus was constructed to include the selectable marker neoR gene and the herpes simplex virus (HSV)-TK gene driven by the human AFP enhancer and the albumin promoter. The liver-predominant expression pattern of the TK gene was observed when this construct was tested in transgenic mice. When human hepatocellular carcinoma cell lines displaying different levels of AFP and albumin and nonhepatocyte tumor cell lines were infected with the recombinant AAV virus, ganciclovir treatment caused only AFP and albumin-positive hepatocellular carcinoma cells death, but not nonhepatocyte tumor cells or AFP and albumin-negative hepatic tumor cells. Moreover, the dose required to kill the cancer cells was inversely proportional to the level of AFP expression in the cells.

Thymic epithelial neoplasms in transgenic mice expressing SV40 T antigen under the control of an erythroid-specific enhancer

The beta-globin locus control region is known to be a powerful erythroid-specific enhancer. In an attempt to produce immortalized erythroid percursor cells, transgenic mice have been generated with the simian virus (SV) 40 T antigen gene under the control of the locus control region. As previously reported, transgenic mice did not develop erythroleukaemia, but rather succumbed to insulinomas and poorly differentiated rhabdomyosarcomas. This paper describes additional mice containing this transgene that developed thymomas of the mixed epithelial/lymphocytic type, in which only the epithelial component expressed the T antigen. Epithelial cell lines have been established from these tumours. This system may be useful in future studies on the pathogenesis of thymomas and the function of thymic epithelial cells.

Ligand-directed retroviral targeting of human breast cancer cells

We explored the feasibility of designing retroviral vectors that can target human breast cancer cells with characteristic receptors via ligand-receptor interaction. The ecotropic Moloney murine leukemia virus envelope was modified by insertion of sequences encoding human heregulin. Ecotropic virus, which normally does not infect human cells, when pseudotyped with the modified envelope protein now crosses species to infect human breast cancer cell lines that overexpress HER-2 (human epidermal growth factor receptor; also called ERBB2) and HER-4 (also called ERBB4), while human breast cancer cell lines expressing low levels of these receptors remain resistant to infection. Since about 20% of human breast cancers overexpress HER-2 and some of breast cancer cell lines overexpress both HER-2 and HER-4, cell-specific targeting of retroviral vectors may provide a different approach for in vivo gene therapy of this type of breast cancer.

Isolation of a differentially regulated splicing isoform of human NF-E2

The transcription factor NF-E2 (nuclear factor erythroid 2), interacting via DNA motifs within regulatory regions of several hematopoietic genes, is thought to mediate the enhancer activity of the globin locus control regions. By screening a human fetal liver cDNA library with probes derived from mouse NF-E2, we have isolated a splicing variant of the NF-E2 gene (fNF-E2) that differs in the 5' untranslated region from the previously reported cDNA (aNF-E2). The fNF-E2 isoform is transcribed from an alternative promoter located in the 3' end of the first intron and joined by alternative splicing to the second and third exons, which are shared by both RNA isoforms. Although the two forms produce the same protein, they are expressed in different ratios during development. fNF-E2 is more abundant in the fetal liver and less abundant in the adult bone marrow compared to the previously described form. Their distribution apparently follows the differential expression of fetal and adult hemoglobins.

Chromosomal localization of the human NF-E2 family of bZIP transcription factors by fluorescence in situ hybridization

A family of human genes encoding basic-leucine zipper (bZIP) transcription factors, p45-NF-E2, Nrf1 and Nrf2, have been isolated independently. Whereas the encoded proteins of the three genes share highly conserved regions distinct from other bZIP families such as Jun or Fos, remaining regions diverged considerably from each other. Chromosomal localization by fluorescence in situ hybridization demonstrates that these genes are non-syntenic. p45-NF-E2 mapped to chromosome 12q13.1-13.3, whereas Nrf1 and 2 mapped to 17q21.3 and 2q31, respectively. However, these three genes were probably derived from a single ancestor by chromosomal duplication as other genes that also map in these regions are related to one another.

Tissue-specific targeting of retroviral vectors through ligand-receptor interactions

The development of retroviral vectors that target specific cell types could have important implications for the design of gene therapy strategies. A chimeric protein containing the polypeptide hormone erythropoietin and part of the env protein of ecotropic Moloney murine leukemia virus was engineered into the virus. This murine virus became several times more infectious for murine cells bearing the erythropoietin receptor, and it also became infectious for human cells bearing the erythropoietin receptor. This type of tissue-specific targeting by means of ligand-receptor interactions may have broad applications to a variety of gene delivery systems.

Isolation of NF-E2-related factor 2 (Nrf2), a NF-E2-like basic leucine zipper transcriptional activator that binds to the tandem NF-E2/AP1 repeat of the beta-globin locus control region

Hypersensitive site 2 located in the beta-globin locus control region confers high levels of expression to the genes of the beta-globin cluster. A tandem repeat of the consensus sequence for the transcription factors AP1 and NF-E2 (activating protein 1 and nuclear factor erythroid 2, respectively) is present within hypersensitive site 2 and is absolutely required for strong enhancer activity. This sequence binds, in vitro and in vivo, to ubiquitous proteins of the AP1 family and to the recently cloned erythroid-specific transcription factor NF-E2. Using the tandem repeat as a recognition site probe to screen a lambda gt11 cDNA expression library from K562 cells, we isolated several DNA binding proteins. Here, we report the characterization of one of the clones isolated. The gene, which we named Nrf2 (NF-E2-related factor 2), is encoded within a 2.2-kb transcript and predicts a 66-kDa protein with a basic leucine zipper DNA binding domain highly homologous to that of NF-E2. Although Nrf2 is expressed ubiquitously, a role of this protein in mediating enhancer activity of hypersensitive site 2 in erythroid cells cannot be excluded. In this respect, Nrf2 contains a powerful acidic activation domain that may participate in the transcriptional stimulation of beta-globin genes.

Amplification of a SV40 T antigen transgene is associated with sarcomagenesis in mice

Transgenic mice harboring simian virus 40 large T antigen (Tag) gene fused to an erythroid-specific enhancer developed soft tissue sarcomas which expressed very high levels of T antigen. The Tag expression was not detectable in the animals' non-transformed tissues. While mice bearing several copies of the transgene developed tumors at an early age of 4-6 months, those with a single copy had a delayed onset of 10-16 months, and DNA analysis of their tumors showed amplification of the Tag transgene. Amplification of a Tag transgene has also been described previously in brain tumors. Our studies demonstrate that Tag transgene amplification is not restricted to a particular construct or a single tumor type. Therefore, this may be a general mechanism for Tag-mediated carcinogenesis, and our transgenic mouse system can be useful for elucidating the mechanisms that govern the amplification process of Tag sequences in vivo.

SV40 T antigen directed by a powerful erythroid enhancer-promoter produced sarcomas and pancreatic tumors but not erythroid-specific tumors in transgenic mice

We have expressed the simian virus 40 (SV40) large T antigen oncogene in erythroid tissues of mice to test its ability to immortilize erythroid cells. A transgene construct was built in which the SV40 large T antigen structural gene was linked to erythroid-specific enhancer and promoter sequences. The enhancer employed was the human beta-globin family microlocus control region, and the promoter sequences were derived from the human beta-globin promoter. Transgenic mice were generated and they expressed T antigen in the bone marrow and spleen cells. Yet, no hematopoietic neoplasia arose in these mice. Instead, after a lag period of 2-6 months, the mice developed soft tissue sarcomas and pancreatic islet-cell tumors that expressed high levels of T antigen.

Characterization of beta-thalassemia mutations by denaturing gradient gel electrophoresis: patterns in the Mediterranean mutations

Of the many methods which have been devised to detect point mutations, we use reverse dot blot for beta-thalassemia in our laboratory. In any mutation detection program, rare or new mutations outside of a laboratory's repertoire will be encountered. Denaturing gradient gel electrophoresis (DGGE) is one of the methods used to localize such mutations. We describe the DGGE electrophoresis pattern of eight common Mediterranean beta-thalassemia mutations and the beta S and beta C mutations, and the definition of two rare mutations outside of these ten. We believe that DGGE is a useful adjunct for mutation detection.

Reverse dot blot probes for the screening of beta-thalassemia mutations in Asians and American blacks

We have optimized a battery of reverse dot blot oligonucleotide probes for detecting the most common beta-globin gene mutations in Asians and American Blacks. These probes allow a high degree of coverage of mutant chromosomes in these two populations and are useful in mutation screening and prenatal diagnosis. When coupled with the Mediterranean subset of probes, a 95% worldwide coverage of beta-thalassemia mutations should be possible. The use of these probes in the reverse dot blot system should allow the distribution of premade strips and application to automated screening.

Isolation of cDNA encoding the human NF-E2 protein

The human homolog of mouse NF-E2 was isolated from the K562 cell line and found to encode a member of the basic leucine-zipper family of DNA-binding regulatory proteins. The deduced amino acid sequence of the mouse and human proteins exhibited near identity. Comparison to the related protein, Nrf1, revealed significant homologies at isolated regions, particularly within the basic domain, suggesting that NF-E2 and Nrf1 are members of a distinct subfamily of basic leucine-zipper proteins that share similar DNA-binding properties. High levels of human NF-E2 mRNA were observed in human erythroleukemic cell lines examined. Extensive survey of human tissue samples found NF-E2 expression not limited to erythropoeitic organs. Expression in the colon and testis suggests that NF-E2 may participate in the regulation of genes other than globin.

Germ-line transmission and developmental regulation of a 150-kb yeast artificial chromosome containing the human beta-globin locus in transgenic mice

Sequential expression of the genes of the human beta-globin locus requires the formation of an erythroid-specific chromatin domain spanning > 200 kb. Regulation of this gene family involves both local interactions with proximal cis-acting sequences and long-range interactions with control elements upstream of the locus. To make it possible to analyze the interactions of cis-acting sequences of the human beta-globin locus in their normal spatial and sequence context, we characterized two yeast artificial chromosomes (YACs) 150 and 230 kb in size, containing the entire beta-globin locus. We have now successfully integrated the 150-kb YAC into the germ line of transgenic mice as a single unrearranged fragment that includes the locus control region, structural genes, and 30 kb of 3' flanking sequences present in the native locus. Expression of the transgenic human beta-globin locus is tissue- and developmental stage-specific and closely follows the pattern of expression of the endogenous mouse beta-globin locus. By using homology-directed recombination in yeast and methods for the purification and transfer of YACs into transgenic mice, it will now be feasible to study the physiological role of cis-acting sequences in specifying an erythroid-specific chromatin domain and directing expression of beta-globin genes during ontogeny.

Cloning of Nrf1, an NF-E2-related transcription factor, by genetic selection in yeast

We have devised a complementation assay in yeast to clone mammalian transcriptional activators and have used it to identify a human basic leucine-zipper transcription factor that we have designated Nrf1 for NF-E2-related factor 1. Nrf1 potentially encodes a 742-aa protein and displays marked homology to the mouse and human NF-E2 transcription factors. Nrf1 activates transcription via NF-E2 binding sites in yeast cells. The ubiquitous expression pattern of Nrf1 and the range of promoters containing the NF-E2 binding motif suggest that this gene may play a role in the regulation of heme synthesis and ferritin genes.

Rhabdomyosarcoma arising in transgenic mice harboring the beta-globin locus control region fused with simian virus 40 large T antigen gene

The beta-globin locus control region (LCR) confers a high level of erythroid-specific and copy-number-dependent expression to human globin genes in transgenic mice. Simian virus 40 T (tumor) antigen (Tag) with its own natural enhancer causes choroid plexus tumors in mice. We investigated the effect of the LCR on Tag gene expression, reasoning that mice harboring a LCR-Tag fusion gene might develop hematopoietic malignancies. To test this hypothesis we introduced an enhancerless Tag gene downstream of a LCR cassette into the germ lines of mice. The phenotypes of the transgenic mice depended on the copy number of the transgene. While mice with 1-2 copies matured normally, those with 3-7 copies developed rhabdomyosarcomas in different anatomic sites at high frequency and showed hyperplasia of the pancreatic islet cells which progressed to pancreatic islet tumors. In addition, the mice bearing 7 copies of the transgene had hypoglycemia and were stunted in growth. Mice with more than 10 copies were markedly stunted in growth and died within 2-4 weeks. Tag expression was detected at high levels in the mouse tumors but not in any other tissues, including the hematopoietic cells.

An isoform-specific mutation in the protein 4.1 gene results in hereditary elliptocytosis and complete deficiency of protein 4.1 in erythrocytes but not in nonerythroid cells

Multiple protein 4.1 isoforms are expressed in a variety of tissues through complex alternative pre-mRNA splicing events, one function of which is to regulate use of two alternative translation initiation signals. Late erythroid cells express mainly the downstream initiation site for synthesis of prototypical 80-kD isoforms; nonerythroid cells in addition use an upstream site to encode higher molecular mass isoform(s). In this study, we examined the effects of a 5' gene rearrangement in a family with hereditary elliptocytosis and complete deficiency of erythrocyte 4.1 protein on 4.1 isoform expression in erythroid vs. nonerythroid cells. Patient 4.1 mRNAs from reticulocytes, fibroblasts, and B lymphocytes were amplified by reverse transcriptase/polymerase chain reaction techniques and shown to exhibit a 318-nucleotide deletion that encompasses the downstream AUG, but leaves intact the upstream AUG. Immunoblot analysis revealed a total deficiency of 4.1 in patient red cells and a selective deficiency of 80-kD isoform(s) but not high molecular weight 4.1 in patient nonerythroid cells. Thus, the 4.1 gene mutation in this family produces an isoform-specific deficiency that is manifested clinically in tissue-specific fashion, such that red cells are affected but other cell types are unaffected because of tissue-specific differences in RNA splicing and translation initiation.

Differentiation-associated switches in protein 4.1 expression. Synthesis of multiple structural isoforms during normal human erythropoiesis

Erythroid differentiation is accompanied by dramatic alterations in morphology and membrane mechanical properties resulting, in large part, from reorganization of the membrane skeletal protein network. The 80-kD protein 4.1 is an important organizational component of this membrane skeleton. Recently, it has been recognized that multiple structural isoforms of 4.1 are encoded by a single gene via alternative pre-mRNA splicing, and that an upstream ATG can be spliced in and used for translation of high molecular weight 4.1. We are exploring the hypothesis that differentiation-associated switches in protein 4.1 structure play an important role in membrane reorganization. To study changes in 4.1 gene expression during normal human differentiation, we analyzed 4.1 protein and mRNA structure at various developmental stages. Using immunofluorescence microscopy, we observed high molecular weight 4.1 isoforms in preproerythroblasts producing punctate, predominantly cytoplasmic staining with a perinuclear area of intense fluorescence, while mature red cells expressed very little high molecular weight 4.1. Isoforms containing an alternatively expressed 102-nucleotide exon near the COOH terminus were abundant in both preproerythroblasts and mature cells but produced a punctate distribution of fluorescence over the entire preproerythroblast and intense membrane-associated fluorescence in the erythrocyte. Characterization of RNA by polymerase chain reaction and nuclease protection assays revealed a differentiation-associated switch in pre-mRNA splicing in the spectrin-actin binding domain. Since this domain plays a critical role in regulating membrane material properties, we speculate that this switch may be crucial to reorganization of the skeletal network during erythropoiesis. We conclude that 4.1 isoforms are differentially expressed and differentially localized during erythropoiesis, and that this isoform family is likely to have diverse functions during terminal differentiation.

Rapid and simultaneous typing of hemoglobin S, hemoglobin C, and seven Mediterranean beta-thalassemia mutations by covalent reverse dot-blot analysis: application to prenatal diagnosis in Sicily

The molecular lesions causing beta-thalassemia in Sicily can be subdivided into two groups. One that occurs at a 71% frequency and consists of the beta 39, IVS 1,110 and IVS 1,6 mutations and the other group at a 20% frequency comprising the -87, beta s, IVS 1,1 and IVS 2,745 mutations. The identification of all these mutations by polymerase chain reaction (PCR) and conventional dot-blot hybridization has been time consuming and expensive. In this article, we describe the implementation of the reverse dot-blot (RDB) hybridization as a rapid nonradioactive method for the identification of the nine most frequent molecular lesions in the beta-globin gene (-87, beta s, beta c, IVS 1,1, IVS 1,6, IVS 1,110, beta 39, IVS 2,1, IVS 2,745) in Sicily. Sixty prenatal diagnoses were performed by this RDB assay, each of which was confirmed by dot-blot/ASO hybridization; thus demonstrating the accuracy of the RDB. The main advantage of this assay is the rapid typing of an individual's DNA for many mutations in a single working day. Because the mutations in this assay are representative for the Mediterranean region, this mutational panel can also be extended to the screening of beta-thalassemia from other Mediterranean regions.

Evidence implicating heterozygous deletion of chromosome 7 in the pathogenesis of familial leukemia associated with monosomy 7

Complete or partial monosomy 7 is a recurring cytogenetic abnormality in acute myelogenous leukemia (AML) and myeloproliferative syndromes (MPS) and is particularly common in patients with Fanconi's anemia and in secondary AML. A familial form of monosomy 7 has been recognized in which two or more siblings develop MPS or AML before age 20. We tested the hypothesis that a recessive cancer susceptibility locus on chromosome 7 was important in the pathogenesis of leukemia in familial monosomy 7 by determining the parental origins of the chromosome 7 retained in the bone marrows of three pairs of affected siblings. We found no overlapping region where all three pairs retained DNA derived from the same paternal or maternal chromosome. These data suggest that inactivation of a single allele of a putative tumor-suppressor gene may be sufficient to contribute to leukemic transformation in familial monosomy 7.

Dissection of the enhancer activity of beta-globin 5' DNase I-hypersensitive site 2 in transgenic mice

The beta-globin locus control region (LCR) consists of four erythroid-specific DNase I-hypersensitive sites, which are necessary for high-level expression of the beta-like globin genes in erythroid tissues. One of these sites, designated 5'HS-2, functions as an erythroid-specific enhancer element in transfection and transgenic mouse experiments. Recent transfection experiments and studies of DNA-protein interactions have localized the 5'HS-2 enhancer to 18 nucleotides that contain a binding site for both the erythroid-specific factor nuclear factor erythroid 2 (NFE-2) and for activator protein 1 (AP-1). To define the sequences necessary for in vivo enhancer activity, several deletion mutants of 5'HS-2 were linked to the human beta-globin gene and their activity was tested in transgenic mice. Three upstream fragments of 5'HS-2 [341, 374, and 412 base pairs (bp)], each of which contained the NFE-2/AP-1 sequences, resulted in beta-globin expression at levels equivalent to or higher than those observed with the entire 732-bp 5'HS-2 fragment. In contrast, a 358-bp downstream portion of 5'HS-2, which lacked the NFE-2/AP-1 sequences, resulted in beta-globin expression at the low levels seen with the beta-globin gene alone. Removal of the NFE-2/AP-1 sequences by a 67-bp internal deletion resulted in similar low levels of beta-globin expression. A 100-bp 5' fragment that contained the NFE-2/AP-1 sequences resulted in beta-globin expression that was higher than the beta-globin gene alone but lower than the entire 5'HS-2 fragment or the three larger upstream fragments. These studies demonstrate that the NFE-2/AP-1 sequences are essential for enhancer activity of 5'HS-2 but that other sequences are required for full activity in vivo.

A 36-base-pair core sequence of locus control region enhances retrovirally transferred human beta-globin gene expression

The locus control region of the human beta-globin cluster consists of four major DNase I hypersensitive sites (HS). When linked to globin genes, the locus control region confers a high level of erythroid-specific expression of these genes in transgenic mice or transfected erythroid cell lines. We have examined the effect of one of these sites, HS2, on human beta-globin gene expression in a murine erythroleukemia cell line (MEL) after retrovirus-mediated gene transfer. We incorporated a 732- or 412-base-pair (bp) segment of HS2 in the retroviral construct carrying the human beta-globin gene. These fragments rendered the viruses unstable as the human beta-globin gene was rearranged or deleted in all the packaging cell lines examined. On the other hand, when a 36-bp fragment containing the NFE-2/AP-1 binding consensus in this region was inserted into the retroviral construct, we recovered 6 stable packaging cell lines of 12 examined, similar in percentage to the construct with the beta-globin gene alone. The virus titers of the packaging cell lines from these two constructs were similar. We infected MEL cells with viruses produced from three packaging cell lines of each of the two constructs and measured the ratio of human beta-globin to mouse alpha-globin mRNA after hexamethylenebisacetamide induction. The overall level of expression increased 2-fold from 6.0% to 12.7% with the addition of this 36-bp enhancer.