Isolation and properties of cDNA clones encoding SRF, a transcription factor that binds to the c-fos serum response element

The serum response element (SRE) is a sequence required for transient transcriptional activation of genes in response to growth factors. We have isolated cDNA clones encoding serum response factor (SRF), a ubiquitous nuclear protein that binds to the SRE. The SRF gene is highly conserved through evolution, and in cultured cells its transcription is itself transiently increased following serum stimulation. A cDNA clone of SRF expressed in vitro generates protein that forms complexes indistinguishable from those formed with HeLa cell SRF, as judged by DNA binding specificity and the ability to promote SRE-dependent in vitro transcription. SRF binds DNA as a dimer, and the DNA binding/dimerization domain of the protein exhibits striking homology to two yeast regulatory proteins.

Selective killing of mixed lineage leukemia cells by a potent small-molecule DOT1L inhibitor

Mislocated enzymatic activity of DOT1L has been proposed as a driver of leukemogenesis in mixed lineage leukemia (MLL). The characterization of EPZ004777, a potent, selective inhibitor of DOT1L is reported. Treatment of MLL cells with the compound selectively inhibits H3K79 methylation and blocks expression of leukemogenic genes. Exposure of leukemic cells to EPZ004777 results in selective killing of those cells bearing the MLL gene translocation, with little effect on non-MLL-translocated cells. Finally, in vivo administration of EPZ004777 leads to extension of survival in a mouse MLL xenograft model. These results provide compelling support for DOT1L inhibition as a basis for targeted therapeutics against MLL.

MLL-rearranged leukemia is dependent on aberrant H3K79 methylation by DOT1L

The histone 3 lysine 79 (H3K79) methyltransferase Dot1l has been implicated in the development of leukemias bearing translocations of the Mixed Lineage Leukemia (MLL) gene. We identified the MLL-fusion targets in an MLL-AF9 leukemia model, and conducted epigenetic profiling for H3K79me2, H3K4me3, H3K27me3, and H3K36me3 in hematopoietic progenitor and leukemia stem cells (LSCs). We found abnormal profiles only for H3K79me2 on MLL-AF9 fusion target loci in LSCs. Inactivation of Dot1l led to downregulation of direct MLL-AF9 targets and an MLL translocation-associated gene expression signature, whereas global gene expression remained largely unaffected. Suppression of MLL translocation-associated gene expression corresponded with dependence of MLL-AF9 leukemia on Dot1l in vivo. These data point to DOT1L as a potential therapeutic target in MLL-rearranged leukemia.

A selective inhibitor of EZH2 blocks H3K27 methylation and kills mutant lymphoma cells

EZH2 catalyzes trimethylation of histone H3 lysine 27 (H3K27). Point mutations of EZH2 at Tyr641 and Ala677 occur in subpopulations of non-Hodgkin's lymphoma, where they drive H3K27 hypertrimethylation. Here we report the discovery of EPZ005687, a potent inhibitor of EZH2 (K(i) of 24 nM). EPZ005687 has greater than 500-fold selectivity against 15 other protein methyltransferases and has 50-fold selectivity against the closely related enzyme EZH1. The compound reduces H3K27 methylation in various lymphoma cells; this translates into apoptotic cell killing in heterozygous Tyr641 or Ala677 mutant cells, with minimal effects on the proliferation of wild-type cells. These data suggest that genetic alteration of EZH2 (for example, mutations at Tyr641 or Ala677) results in a critical dependency on enzymatic activity for proliferation (that is, the equivalent of oncogene addiction), thus portending the clinical use of EZH2 inhibitors for cancers in which EZH2 is genetically altered.

Selective inhibition of EZH2 by EPZ-6438 leads to potent antitumor activity in EZH2-mutant non-Hodgkin lymphoma

Mutations within the catalytic domain of the histone methyltransferase EZH2 have been identified in subsets of patients with non-Hodgkin lymphoma (NHL). These genetic alterations are hypothesized to confer an oncogenic dependency on EZH2 enzymatic activity in these cancers. We have previously reported the discovery of EPZ005678 and EPZ-6438, potent and selective S-adenosyl-methionine-competitive small molecule inhibitors of EZH2. Although both compounds are similar with respect to their mechanism of action and selectivity, EPZ-6438 possesses superior potency and drug-like properties, including good oral bioavailability in animals. Here, we characterize the activity of EPZ-6438 in preclinical models of NHL. EPZ-6438 selectively inhibits intracellular lysine 27 of histone H3 (H3K27) methylation in a concentration- and time-dependent manner in both EZH2 wild-type and mutant lymphoma cells. Inhibition of H3K27 trimethylation (H3K27Me3) leads to selective cell killing of human lymphoma cell lines bearing EZH2 catalytic domain point mutations. Treatment of EZH2-mutant NHL xenograft-bearing mice with EPZ-6438 causes dose-dependent tumor growth inhibition, including complete and sustained tumor regressions with correlative diminution of H3K27Me3 levels in tumors and selected normal tissues. Mice dosed orally with EPZ-6438 for 28 days remained tumor free for up to 63 days after stopping compound treatment in two EZH2-mutant xenograft models. These data confirm the dependency of EZH2-mutant NHL on EZH2 activity and portend the utility of EPZ-6438 as a potential treatment for these genetically defined cancers.

A humanized system for pharmacologic control of gene expression

Gene therapy was originally conceived as a medical intervention to replace or correct defective genes in patients with inherited disorders. However, it may have much broader potential as an alternative delivery platform for protein therapeutics, such as cytokines, hormones, antibodies and novel engineered proteins. One key technical barrier to the widespread implementation of this form of therapy is the need for precise control over the level of protein production. A suitable system for pharmacologic control of therapeutic gene expression would permit precise titration of gene product dosage, intermittent or pulsatile treatment, and ready termination of therapy by withdrawal of the activating drug. We set out to design such a system with the following properties: (1) low baseline expression and high induction ratio; (2) positive control by an orally bioavailable small-molecule drug; (3) reduced potential for immune recognition through the exclusive use of human proteins; and (4) modularity to allow the independent optimization of each component using the tools of protein engineering. We report here the properties of this system and demonstrate its use to control circulating levels of human growth hormone in mice implanted with engineered human cells.

Human SRF-related proteins: DNA-binding properties and potential regulatory targets

Serum response factor (SRF) is a transcription factor that binds the sequence CC(A/T)6GG found in a number of growth factor-inducible and muscle-specific promoters. We describe the isolation and characterization of cDNA clones encoding a family of three human SRF-related DNA-binding proteins. Each of these RSRF (related to SRF) proteins contains an 86-amino-acid amino-terminal region related to the SRF DNA-binding domain: In RSRFC4 and RSRFC9, this region is identical, whereas that present in RSRFR2 differs by seven conservative amino acid substitutions. The DNA-binding specificity of the RSRF proteins, which recognize the consensus sequence CTA(A/T)4TAG, is distinct from that of SRF. The entire RSRF common region is required for DNA binding, and the differential sequence specificity of the RSRFs and SRF is the result of differences in the basic amino-terminal part of this domain. The RSRF proteins bind DNA as dimers and can dimerize with one another but not with SRF. Although the RSRF mRNAs are expressed in many cell types, RSRFR2 mRNA is expressed at elevated levels in several B-cell lines. Consistent with this, extracts from many cell types form CTA(A/T)4TAG-binding complexes that contain RSRF proteins, and oligonucleotides containing RSRF-binding sites function as promoter elements in transfection assays. Like SRF-binding sites, RSRF-binding sites are found in the regulatory sequences of a number of growth factor-inducible and muscle-specific genes, and we show that RSRF polypeptides are components of previously characterized binding activities that interact with these elements. We discuss the potential role of RSRF proteins in the regulation of these genes.

A sensitive method for the determination of protein-DNA binding specificities

We describe a sensitive and rapid method for determination of the sequence specificity of DNA binding proteins. The method allows recovery of specific sites using the small amounts of protein present in crude cell extracts or produced by cell-free translation reactions. Extract proteins are incubated with a pool of random sequence oligonucleotides, complexes purified by immunoprecipitation, and bound DNA amplified by the Polymerase Chain Reaction (PCR). This DNA is then used in further rounds of binding, immunoprecipitation, and amplification, until specific binding is detectable. With the transcription factor SRF as a model system, we demonstrate that authentic high affinity binding sites are recovered, and show that epitope tagging can be used to allow recovery of sites when specific antibodies are unavailable. We also show that specific sites bound by the Fos protein, which binds DNA with high affinity only when complexed with other polypeptides, are easily recovered by this technique.

Content and organization of the human Ig VH locus: definition of three new VH families and linkage to the Ig CH locus

We present a detailed analysis of the content and organization of the human immunoglobulin VH locus. Human VH genes representing five distinct families were isolated, including novel members belonging to two out of three of the known VH gene families (VH1 and VH3) as well as members of three new families (VH4, VH5, and VH6). We report the nucleotide sequence of 21 novel human VH genes, many of which belong to the three new VH gene families. In addition, we provide a preliminary analysis of the organization of these gene segments over the full extent of the locus. We find that the five multi-segment families (VH1-5) have members interspersed over nearly the full 1500-2000 kb of the VH locus, and estimate that the entire heavy chain locus covers 2500 kb or less. Finally, we provide the first report of the physical linkage of the variable and constant loci of a human Ig gene family by demonstrating that the most proximal known human VH segments lie within 100 kb of the constant region locus.

Mitogen- and IL-4-regulated expression of germ-line Ig gamma 2b transcripts: evidence for directed heavy chain class switching

Treatment of murine B cells with bacterial lipopolysaccharide (LPS) in the presence or absence of different lymphokines results in cell populations that differentially express particular immunoglobulin heavy chain constant region (CH) genes. This class switch involves recombination between switch regions located upstream of the germ-line CH genes. We have treated Abelson murine leukemia virus-transformed pre-B cells and normal splenic B cells with LPS or LPS plus the lymphokine IL-4 and examined the effect on the germ-line gamma 2b locus and gamma 2b class switching. In both cell types, LPS induces transcription specifically through the germ-line gamma 2b locus before gamma 2b class switching. Furthermore, IL-4 inhibits LPS induction of germ-line gamma 2b transcripts in spleen cells and correspondingly abrogates switching to this CH gene. Thus treatment with mitogens and lymphokines can alter transcription of germ-line CH genes in B lineage cells and thereby directly regulate class switching in the context of a recombinase accessibility mechanism.

A versatile synthetic dimerizer for the regulation of protein-protein interactions

The use of low molecular weight organic compounds to induce dimerization or oligomerization of engineered proteins has wide-ranging utility in biological research as well as in gene and cell therapies. Chemically induced dimerization can be used to activate intracellular signal transduction pathways or to control the activity of a bipartite transcription factor. Dimerizer systems based on the natural products cyclosporin, FK506, rapamycin, and coumermycin have been described. However, owing to the complexity of these compounds, adjusting their binding or pharmacological properties by chemical modification is difficult. We have investigated several families of readily prepared, totally synthetic, cell-permeable dimerizers composed of ligands for human FKBP12. These molecules have significantly reduced complexity and greater adaptability than natural product dimers. We report here the efficacies of several of these new synthetic compounds in regulating two types of protein dimerization events inside engineered cells--induction of apoptosis through dimerization of engineered Fas proteins and regulation of transcription through dimerization of transcription factor fusion proteins. One dimerizer in particular, AP1510, proved to be exceptionally potent and versatile in all experimental contexts tested.

Inhibition of wild-type and mutant Bcr-Abl by AP23464, a potent ATP-based oncogenic protein kinase inhibitor: implications for CML

The deregulated, oncogenic tyrosine kinase Bcr-Abl causes chronic myeloid leukemia (CML). Imatinib mesylate (Gleevec, STI571), a Bcr-Abl kinase inhibitor, selectively inhibits proliferation and promotes apoptosis of CML cells. Despite the success of imatinib mesylate in the treatment of CML, resistance is observed, particularly in advanced disease. The most common imatinib mesylate resistance mechanism involves Bcr-Abl kinase domain mutations that impart varying degrees of drug insensitivity. AP23464, a potent adenosine 5'-triphosphate (ATP)-based inhibitor of Src and Abl kinases, displays antiproliferative activity against a human CML cell line and Bcr-Abl-transduced Ba/F3 cells (IC(50) = 14 nM; imatinib mesylate IC(50) = 350 nM). AP23464 ablates Bcr-Abl tyrosine phosphorylation, blocks cell cycle progression, and promotes apoptosis of Bcr-Abl-expressing cells. Biochemical assays with purified glutathione S transferase (GST)-Abl kinase domain confirmed that AP23464 directly inhibits Abl activity. Importantly, the low nanomolar cellular and biochemical inhibitory properties of AP23464 extend to frequently observed imatinib mesylate-resistant Bcr-Abl mutants, including nucleotide binding P-loop mutants Q252H, Y253F, E255K, C-terminal loop mutant M351T, and activation loop mutant H396P. AP23464 was ineffective against mutant T315I, an imatinib mesylate contact residue. The potency of AP23464 against imatinib mesylate-refractory Bcr-Abl and its distinct binding mode relative to imatinib mesylate warrant further investigation of AP23464 for the treatment of CML.

Babesiosis in Washington State: a new species of Babesia?

OBJECTIVE

To characterize the etiologic agent (WA1) of the first reported case of babesiosis acquired in Washington State.

DESIGN

Case report, and serologic, molecular, and epizootiologic studies.

SETTING

South-central Washington State.

PATIENT

A 41-year-old immunocompetent man with an intact spleen who developed a moderately severe case of babesiosis.

MEASUREMENTS

Serum specimens from the patient were assayed by indirect immunofluorescent antibody (IFA) testing for reactivity with seven Babesia species and with WA1, which was propagated in hamsters inoculated with his blood. A Babesia-specific, ribosomal-DNA (rDNA) probe was hybridized to Southern blots of restriction-endonuclease-digested preparations of DNA from WA1, Babesia microti, and Babesia gibsoni. Serum specimens from 83 family members and neighbors were assayed for IFA reactivity with WA1 and B. microti. Small mammals and ticks were examined for Babesia infection.

RESULTS

The patient's serum had very strong IFA reactivity with WA1, strong reactivity with B. gibsoni (which infects dogs), but only weak reactivity with B. microti. DNA hybridization patterns with the rDNA probe clearly differentiated WA1 from B. gibsoni and B. microti. Four of the patient's neighbors had IFA titers to WA1 of 256. The tick vector and animal reservoir of WA1 have not yet been identified, despite trapping 83 mammals and collecting 235 ticks.

CONCLUSIONS

WA1 is morphologically indistinguishable but antigenically and genotypically distinct from B. microti. Some patients elsewhere who were assumed to have been infected with B. microti may have been infected with WA1. Improved serodiagnostic and molecular techniques are needed for characterizing Babesia species and elucidating the epidemiology of babesiosis, an emergent zoonosis.

Conformational adaptation drives potent, selective and durable inhibition of the human protein methyltransferase DOT1L

DOT1L is the human protein methyltransferase responsible for catalyzing the methylation of histone H3 on lysine 79 (H3K79). The ectopic activity of DOT1L, associated with the chromosomal translocation that is a universal hallmark of MLL-rearranged leukemia, is a required driver of leukemogenesis in this malignancy. Here, we present studies on the structure-activity relationship of aminonucleoside-based DOT1L inhibitors. Within this series, we find that improvements in target enzyme affinity and selectivity are driven entirely by diminution of the dissociation rate constant for the enzyme-inhibitor complex, leading to long residence times for the binary complex. The biochemical K(i) and residence times measured for these inhibitors correlate well with their effects on intracellular H3K79 methylation and MLL-rearranged leukemic cell killing. Crystallographic studies reveal a conformational adaptation mechanism associated with high-affinity inhibitor binding and prolonged residence time; these studies also suggest that conformational adaptation likewise plays a critical role in natural ligand interactions with the enzyme, hence, facilitating enzyme turnover. These results provide critical insights into the role of conformational adaptation in the enzymatic mechanism of catalysis and in pharmacologic intervention for DOT1L and other members of this enzyme class.

Structure and Property Guided Design in the Identification of PRMT5 Tool Compound EPZ015666

The recent publication of a potent and selective inhibitor of protein methyltransferase 5 (PRMT5) provides the scientific community with in vivo-active tool compound EPZ015666 (GSK3235025) to probe the underlying pharmacology of this key enzyme. Herein, we report the design and optimization strategies employed on an initial hit compound with poor in vitro clearance to yield in vivo tool compound EPZ015666 and an additional potent in vitro tool molecule EPZ015866 (GSK3203591).

Delivery of a stringent dimerizer-regulated gene expression system in a single retroviral vector

Small molecule-regulated transcription has broad utility and would benefit from an easily delivered self-contained regulatory cassette capable of robust, tightly controlled target gene expression. We describe the delivery of a modified dimerizer-regulated gene expression system to cells on a single retrovirus. A transcription factor cassette responsive to the natural product dimerizer rapamycin was optimized for retroviral delivery by fusing a highly potent chimeric activation domain to the rapamycin-binding domain of FKBP-rapamycin-associated protein (FRAP). This improvement led to an increase in both the potency and maximal levels of gene expression induced by rapamycin, or nonimmunosuppressive rapamycin analogs. The modified transcription factor cassette was incorporated along with a target gene into a single rapamycin-responsive retrovirus. Cell pools stably transduced with the single virus system displayed negligible basal expression and gave induction ratios of at least three orders of magnitude in the presence of rapamycin or a nonimmunosuppressive rapamycin analog. Levels of induced gene expression were comparable to those obtained with the constitutive retroviral long terminal repeat and the single virus system performed well in four different mammalian cell lines. Regulation with the dimerizer-responsive retrovirus was tight enough to allow the generation of cell lines displaying inducible expression of the highly toxic diphtheria toxin A chain gene. The ability to deliver the tightly inducible rapamycin system in a single retrovirus should facilitate its use in the study of gene function in a broad range of cell types.

Ridaforolimus (AP23573; MK-8669), a potent mTOR inhibitor, has broad antitumor activity and can be optimally administered using intermittent dosing regimens

The mTOR pathway is hyperactivated through oncogenic transformation in many human malignancies. Ridaforolimus (AP23573; MK-8669) is a novel rapamycin analogue that selectively targets mTOR and is currently under clinical evaluation. In this study, we investigated the mechanistic basis for the antitumor activity of ridaforolimus in a range of human tumor types, exploring potential markers of response, and determining optimal dosing regimens to guide clinical studies. Administration of ridaforolimus to tumor cells in vitro elicited dose-dependent inhibition of mTOR activity with concomitant effects on cell growth and division. We showed that ridaforolimus exhibits a predominantly cytostatic mode of action, consistent with the findings for other mTOR inhibitors. Potent inhibitory effects on vascular endothelial growth factor secretion, endothelial cell growth, and glucose metabolism were also observed. Although PTEN and/or phosphorylated AKT status have been proposed as potential mTOR pathway biomarkers, neither was predictive for ridaforolimus responsiveness in the heterogeneous panel of cancer cell lines examined. In mouse models, robust antitumor activity was observed in human tumor xenografts using a series of intermittent dosing schedules, consistent with pharmacodynamic observations of mTOR pathway inhibition for at least 72 hours following dosing. Parallel skin-graft rejection studies established that intermittent dosing schedules lack the immunosuppressive effects seen with daily dosing. Overall these findings show the broad inhibitory effects of ridaforolimus on cell growth, division, metabolism, and angiogenesis, and support the use of intermittent dosing as a means to optimize antitumor activity while minimizing systemic effects.

DOT1L inhibitor EPZ-5676 displays synergistic antiproliferative activity in combination with standard of care drugs and hypomethylating agents in MLL-rearranged leukemia cells

EPZ-5676 [(2R,3R,4S,5R)-2-(6-amino-9H-purin-9-yl)-5-((((1r,3S)-3-(2-(5-(tert-butyl)-1H-benzo[d]imidazol-2-yl)ethyl)cyclobutyl)(isopropyl)amino)methyl)tetrahydrofuran-3,4-diol], a small-molecule inhibitor of the protein methyltransferase DOT1L, is currently under clinical investigation for acute leukemias bearing MLL-rearrangements (MLL-r). In this study, we evaluated EPZ-5676 in combination with standard of care (SOC) agents for acute leukemias as well as other chromatin-modifying drugs in cellular assays with three human acute leukemia cell lines: MOLM-13 (MLL-AF9), MV4-11 (MLL-AF4), and SKM-1 (non-MLL-r). Studies were performed to evaluate the antiproliferative effects of EPZ-5676 combinations in a cotreatment model in which the second agent was added simultaneously with EPZ-5676 at the beginning of the assay, or in a pretreatment model in which cells were incubated for several days in the presence of EPZ-5676 prior to the addition of the second agent. EPZ-5676 was found to act synergistically with the acute myeloid leukemia (AML) SOC agents cytarabine or daunorubicin in MOLM-13 and MV4-11 MLL-r cell lines. EPZ-5676 is selective for MLL-r cell lines as demonstrated by its lack of effect either alone or in combination in the nonrearranged SKM-1 cell line. In MLL-r cells, the combination benefit was observed even when EPZ-5676 was washed out prior to the addition of the chemotherapeutic agents, suggesting that EPZ-5676 sets up a durable, altered chromatin state that enhances the chemotherapeutic effects. Our evaluation of EPZ-5676 in conjunction with other chromatin-modifying drugs also revealed a consistent combination benefit, including synergy with DNA hypomethylating agents. These results indicate that EPZ-5676 is highly efficacious as a single agent and synergistically acts with other chemotherapeutics, including AML SOC drugs and DNA hypomethylating agents in MLL-r cells.

Non-invasive distal femoral expandable endoprosthesis for limb-salvage surgery in paediatric tumours

We report our early experience with the use of a non-invasive distal femoral expandable endoprosthesis in seven skeletally immature patients with osteosarcoma of the distal femur. The patients had a mean age of 12.1 years (9 to 15) at the time of surgery. The prosthesis was lengthened at appropriate intervals in outpatient clinics, without anaesthesia, using the principle of electromagnetic induction. The patients were functionally evaluated using the Musculoskeletal Tumour Society scoring system. The mean follow-up was 20.2 months (14 to 30). The prostheses were lengthened by a mean of 25 mm (4.25 to 55) and maintained a mean knee flexion of 110° (100° to 120°). The mean Musculoskeletal Tumour Society score was 68% (11 to 29). Complications developed in two patients; one developed a flexion deformity of 25° at the knee joint, which was subsequently overcome and one died of disseminated disease. The early results from patients treated with this device have been encouraging. The implant avoids multiple surgical procedures, general anaesthesia and assists in maintaining leg-length equality.

Dimerizer-regulated gene expression

Control of gene expression using small molecules is a powerful research tool and has clinical utility in the context of regulated gene therapy. Use of chemical inducers of dimerization, or dimerizers, for this purpose has several advantages, including tight regulation, modularity to facilitate iterative improvements, and assembly from human proteins to minimize immune responses in clinical applications. Recent developments include the use of the rapamycin-based dimerizer system to regulate the expression of endogenous genes, the generation of new chemical dimerizers based on FK506, dexamethasone and methotrexate, and progress towards the clinical use of adeno-associated virus and adenovirus vectors regulated by rapamycin analogs.

Regulation of endogenous gene expression with a small-molecule dimerizer

Artificial transcription factors containing designer zinc-finger DNA-binding domains (DBDs) have been used to activate or repress expression of a growing number of endogenous genes. We have combined targeted zinc-finger DBD technology with a dimerizer-regulated gene expression system to permit the small-molecule control of endogenous gene transcription. We constructed a dimerizer-responsive transcription factor that incorporates an artificial zinc-finger DBD targeted to the promoter of the human VEGF gene. Introduction of this activator into human cells allowed expression of the chromosomal VEGF gene to be induced by a small-molecule dimerizer compound consisting of a nonimmunosuppressive rapamycin analog. We found that by directly regulating zinc-finger protein (ZFP) activity, we could circumvent difficulties encountered in the generation of cell lines stably expressing conventional unregulated activators. Dimerizer-dependent VEGF induction was rapid, tight, and dose dependent, and resulted in VEGF protein expression levels several-fold greater than those produced by the natural hypoxic response.

Apparent biliary pseudolithiasis during ceftriaxone therapy

Biliary pseudolithiasis has been reported in patients who received ceftriaxone therapy. To examine this phenomenon further, serial gallbladder sonograms were evaluated in 44 adult patients who received intravenous ceftriaxone at 2 g or a placebo daily for 14 days in a double-blind controlled study. Ultrasound examinations of gallbladders were performed on days 1 and 14 of therapy and 2 weeks posttherapy if abnormalities were observed on day 14. Eight patients were unevaluable because of abnormal base-line gallbladder sonograms. Thirty-six patients (ceftriaxone, n = 28; placebo, n = 8) demonstrated normal baseline gallbladder sonograms and were evaluated for the development of change. A total of 6 of 28 (21.4%) ceftriaxone-treated patients and 1 of 8 (12.5%) patients who received the placebo demonstrated abnormal gallbladder sonograms on day 14 (P = 0.491). Four of the six ceftriaxone-treated patients demonstrating abnormal sonograms were clinically asymptomatic, while two patients reported vomiting. The abnormal sonograms of gallbladders of patients treated with ceftriaxone returned to normal between 9 and 26 days posttherapy. These data suggest an association between ceftriaxone treatment and the development of gallbladder abnormalities on ultrasound examination which resolve spontaneously on discontinuation of ceftriaxone therapy.

The Pax-5 gene is alternatively spliced during B-cell development

The transcription factor Pax-5 is expressed during the early stages of B-cell differentiation and influences the expression of several B-cell-specific genes. In addition to the existing isoform (Pax-5, which we have named Pax-5a), we have isolated three new isoforms, Pax-5b, Pax-5d, and Pax-5e, from murine spleen and B-lymphoid cell lines using library screenings and polymerase chain reaction amplification. Isoforms Pax-5b and Pax-5e have spliced out their second exon, resulting in proteins with only a partial DNA-binding domain. Isoforms Pax-5d and Pax-5e have deleted the 3'-region, which encodes the transactivating domain, and replaced it with a novel sequence. The existence of alternative Pax-5 transcripts was confirmed using RNase protection assays. Furthermore, Pax-5a and Pax-5b proteins were detected using Western blot analysis. Pax-5a was detectable in pro-, pre-, and mature B-cell lines, but not in two plasmacytomas; Pax-5b was shown to be present at low levels in mature B-cell lines and, unexpectedly, in one plasma cell line, but not in pro-B-cell or T-cell lines. Mobility shift assays showed that in vitro translated Pax-5a and Pax-5d, but not Pax-5b or Pax-5e, could interact with a B-cell-specific activator protein-binding site on the blk promoter. Using this assay, we also showed that Pax-5d was present in nuclear extracts of some (but not all) B-lymphoid lines and interacts with the B-cell-specific activator protein-binding site. The pattern of differential expression of alternatively spliced Pax-5 isoforms suggests that they may be important regulators of transcription during B-cell maturation.