Protein disulphide isomerase (PDI) is protective against amyotrophic lateral sclerosis (ALS)-related mutant Fused in Sarcoma (FUS) in in vitro models

Mutations in Fused in Sarcoma (FUS) are present in familial and sporadic cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). FUS is localised in the nucleus where it has important functions in DNA repair. However, in ALS/FTD, mutant FUS mislocalises from the nucleus to the cytoplasm where it forms inclusions, a key pathological hallmark of neurodegeneration. Mutant FUS also inhibits protein import into the nucleus, resulting in defects in nucleocytoplasmic transport. Fragmentation of the neuronal Golgi apparatus, induction of endoplasmic reticulum (ER) stress, and inhibition of ER-Golgi trafficking are also associated with mutant FUS misfolding in ALS. Protein disulphide isomerase (PDI) is an ER chaperone previously shown to be protective against misfolding associated with mutant superoxide dismutase 1 (SOD1) and TAR DNA-binding protein-43 (TDP-43) in cellular and zebrafish models. However, a protective role against mutant FUS in ALS has not been previously described. In this study, we demonstrate that PDI is protective against mutant FUS. In neuronal cell line and primary cultures, PDI restores defects in nuclear import, prevents the formation of mutant FUS inclusions, inhibits Golgi fragmentation, ER stress, ER-Golgi transport defects, and apoptosis. These findings imply that PDI is a new therapeutic target in FUS-associated ALS.

The expression of HMGB1 on microparticles from Jurkat and HL-60 cells undergoing apoptosis in vitro

HMGB1 is a highly conserved nuclear protein that displays important biological activities inside as well as outside the cell and serves as a prototypic alarmin to activate innate immunity. The translocation of HMGB1 from inside to outside the cell occurs with cell activation as well as cell death, including apoptosis. Apoptosis is also a setting for the release of cellular microparticles (MPs), which are small membrane-bound vesicles that represent an important source of extracellular nuclear molecules. To investigate whether HMGB1 released from cells during apoptosis is also present on MPs, we determined the presence of HMGB1 on particles released from Jurkat and HL-60 cells induced to undergo apoptosis in vitro by treatment with either etoposide or staurosporine; MPs released from cells undergoing necrosis by freeze-thaw were also characterized. As shown by both Western blot analysis and flow cytometry, MPs from apoptotic cells contain HMGB1, with binding by antibodies indicating an accessible location in the particle structure. These results indicate that HMGB1, like other nuclear molecules, can translocate into MPs during apoptosis and demonstrate another biochemical form of this molecule that may be immunologically active.

Inability of Petite Mutants of Industrial Yeasts to Utilize Various Sugars, and a Comparison with the Ability of the Parent Strains to Ferment the Same Sugars Microaerophilically

A number of industrial strains of Saccharomyces cerevisiae were converted to the petite form and tested for the ability to utilize galactose, maltose, sucrose, α-methyl glucoside and raffinose. The parent strains all metabolized these sugars aerobically. Twelve of the petite forms did not utilize galactose, six failed to utilize maltose, 17 did not utilize x-methyl glucoside, and 18 did not utilize raffinose. The petites of two distiller’s yeast strains did not utilize sucrose. The respiratory-competent parent strains nearly all fermented galactose, maltose, sucrose and raffinose, though 19 strains did not ferment α-methyl glucoside microaerophilically. Three strains did not ferment galactose, two fermented it only after several days adaptation, one did not ferment raffinose, and two did not ferment sucrose under microaerophilic conditions. Six respiratory-competent strains which did not utilize galactose when in the petite form fermented higher (10%) concentrations of glucose and maltose under microaerophilic conditions, but only three of these fermented galactose. The implications of these findings for the use of such strains in industry are discussed briefly.

Correlation of serum cytokines with clinical responses in patients treated with BPX-101, a drug-activated vaccine for metastatic castration-resistant prostate cancer (mCRPC)

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Background: We report the correlation of clinical and immune monitoring results for subjects enrolled in a phase I/IIa clinical trial of BPX-101, a drug-activated dendritic cell vaccine for mCRPC.

Methods: Men with progressive mCRPC were enrolled in a 3+3 dose escalation trial evaluating BPX-101 and activating agent AP1903. BPX-101 was administered intradermally every 2 weeks for 6 doses, during the induction phase, and for non-progressing patients, every 8 weeks for up to 5 doses during the maintenance phase. AP1903 (0.4 mg/kg) was infused 24 hours after each BPX-101 dose. Blood samples for immune monitoring were collected weekly during the induction phase, and before and one week after each maintenance dose. GM-CSF, TNF-α, IFN-γ, IP-10, MCP-1, MIP-1α, MIP-1β, and RANTES levels were measured by Luminex microspheres, and IL-6 by ELISA.

Results: Planned enrollment of 12 subjects is complete, including 3 each at 4 × 106 and 12.5 × 106 cells/dose, and 6 at 25 x 106 cells/dose. A pattern of spiking levels of serum cytokines one week after each dose, returning to baseline the following week, was observed in subjects with greater disease burden. In one low dose subject who experienced a PR after one year on study, panel cytokines spiked 4-fold on average after each induction phase dose, less than 2-fold after the first two boosters, and between 6-fold and 56-fold after the final three boosters. IL-6, which had declined during the induction phase to below 1 pg/mL through two boosters, spiked between 1,680-fold and 13,000-fold after each of the last three boosters. In a second, high dose subject (#1008), who experienced a near CR of multiple lung metastases with otherwise stable disease, panel cytokines spiked 150-fold on average during the induction phase. In both cases, TNF-α, MIP-1α and MIP-1β spiked the most, including a more than 1,000-fold average spike in TNF-α for subject 1008. Cytokine spikes were not associated with AEs.

Conclusions: BPX-101 induces a spiking pattern of cytokine elevations after each dose. In patients who experienced measurable disease reductions, more dramatic spikes in serum inflammatory cytokine levels were seen.

[Table: see text]

Antigen-specific immunity and tumor inflammation after vaccination with BPX-101, a drug-activated dendritic cell vaccine for metastatic castration-resistant prostate cancer (mCRPC)

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Background: We report evidence of antigen-specific immunity and severe prostate cancer inflammation and necrosis after vaccination in patients enrolled in a phase I-IIa clinical trial of BPX-101, a drug-activated DC vaccine for mCRPC.

Methods: Twelve men with progressive, mCRPC were enrolled in a 3+3 dose escalation trial evaluating BPX-101 and activating agent AP1903. BPX-101, which targets prostate-specific membrane antigen (PSMA), was administered intradermally every 2 weeks for 6 doses, followed 24 hours after each dose by infusion of AP1903 (0.4 mg/kg). Injection site skin biopsies were performed after the fourth vaccination. T cells cultured from the skin biopsy ex vivo were stimulated with PSMA protein or control antigens, and were analyzed using Luminex microspheres for 30 inflammatory cytokines/chemokines. One patient (#1007) with an intact prostate developed lower urinary tract bleeding after the fifth vaccination and underwent a transurethral resection of bleeding prostate cancer tissue. Paraffin-embedded blocks were stained for hematoxylin and eosin (H&E). Immunohistochemical stains for CD3, CD4, CD8 and CD34 were also performed.

Results: Of 5 subjects with evaluable injection site biopsy results, all exhibited PSMA-specific immunity (3 TH1-biased and 2 TH2- biased). Subject 1007's injection site biopsy demonstrated a significant >10-fold increase in IFN-gamma and IL-2 after stimulation by PSMA, compared to stimulation by ovalbumin, consistent with induction of a strong PSMA-specific CTL or TH1-biased immune response. H&E stained resected prostate tissue demonstrated Gleason 8 (4+4) prostate adenocarcinoma exhibiting a severe inflammatory response, consisting of infiltrating plasma cells and CD4+ and CD8+ T cells. Large areas of necrosis were seen adjacent to inflamed prostate cancer tissue.

Conclusions: Vaccination with BPX-101 followed by AP1903 can induce a strong, PSMA-specific immune response. Furthermore, evidence of severe prostate cancer-specific inflammation and necrosis, associated with a strong PSMA-specific immune response has been observed after multiple doses of BPX-101.

[Table: see text]

Results of a phase I/II clinical trial of BPX-101, a novel drug-activated dendritic cell (DC) vaccine for metastatic castration-resistant prostate cancer (mCRPC)

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Background: We report results of a phase I/II clinical trial of BPX-101, a drug- activated autologous DC vaccine targeting PSMA.

Methods: Men with progressive mCRPC following up to one prior chemotherapy regimen were enrolled in a 3+3 dose escalation trial evaluating BPX-101 and CD40 activating agent AP1903. BPX-101 was administered intradermally every 2 weeks for 6 doses, during the induction phase, and for nonprogressing patients, every 8 weeks for up to 5 doses during the maintenance phase. AP1903 (0.4 mg/kg) was infused 24 hours after each BPX-101 dose. Radiologic evaluation was performed every 12 weeks.

Results: Planned enrollment of 12 subjects has been completed, including 3 each at 4 × 106 and 12.5 × 106 cells/dose, and 6 at 25 × 106 cells/dose. All vaccine products were releasable. Median Halabi- predicted survival was 13.8 months. Two subjects went off protocol prior to the end of induction due to progression, 8 reached end of induction, and 2 are nearing completion of induction. Toxicities (e.g. injection site reactions) were generally mild. One high dose subject experienced a single acute cytokine reaction during infusion of AP1903 at the second vaccination, but continued induction without further drug-related adverse events. Notably, one post- docetaxel subject in the low dose cohort achieved a RECIST PR, and one chemo-naive subject in the mid-dose cohort with extensive visceral, nodal, and bone metastases experienced a RECIST CR with docetaxel-based chemotherapy after induction and maintains an undetectable ultrasensitive PSA (0.009 ng/mL) 10 months after enrollment. A third subject, in the high-dose cohort, experienced near complete elimination of multiple lung metastases with otherwise stable disease by the end of induction. Robust immune responses were seen in all three.

Conclusions: BPX-101 can be reliably manufactured and safely administered, followed by AP1903, at doses of at least 25 × 106 cells. Contrary to the observation that cancer vaccine therapy improves survival without short-term response, BPX-101-treated patients have experienced measurable disease responses, including near elimination of poor-risk visceral disease.

[Table: see text]

Death switch for gene therapy: application to erythropoietin transgene expression

The effectiveness of the caspase-9-based artificial "death switch" as a safety measure for gene therapy based on the erythropoietin (Epo) hormone was tested in vitro and in vivo using the chemical inducer of dimerization, AP20187. Plasmids encoding the dimeric murine Epo, the tetracycline-controlled transactivator and inducible caspase 9 (ptet-mEpoD, ptet-tTAk and pSH1/Sn-E-Fv'-Fvls-casp9-E, respectively) were used in this study. AP20187 induced apoptosis of iCasp9-modified C2C12 myoblasts. In vivo, two groups of male C57BI/6 mice, 8-12 weeks old, were injected intramuscularly with 5 microg/50 g ptet-mEpoD and 0.5 microg/50 g ptet-tTAk. There were 20 animals in group 1 and 36 animals in group 2. Animals from group 2 were also injected with the 6 microg/50 g iCasp9 plasmid. Seventy percent of the animals showed an increase in hematocrit of more than 65% for more than 15 weeks. AP20187 administration significantly reduced hematocrit and plasma Epo levels in 30% of the animals belonging to group 2. TUNEL-positive cells were detected in the muscle of at least 50% of the animals treated with AP20187. Doxycycline administration was efficient in controlling Epo secretion in both groups. We conclude that inducible caspase 9 did not interfere with gene transfer, gene expression or tetracycline control and may be used as a safety mechanism for gene therapy. However, more studies are necessary to improve the efficacy of this technique, for example, the use of lentivirus vector.

Lipid raft-targeted Akt promotes axonal branching and growth cone expansion via mTOR and Rac1, respectively

The molecular mechanisms by which extracellular guidance cues regulate axonal morphology are not fully understood. Recent findings suggest that increased activity of the protein kinase Akt promotes dendritic branching and elongation in hippocampal neurons. We tested whether expression of constitutively active Akt (CA-Akt) in primary sensory neurons would promote axonal branching and whether targeting CA-Akt to lipid rafts, common sites of Akt function, would differentially regulate axonal morphology. Biolistic transduction of sensory neurons induced a rapid expression of CA-Akt, resulting in increased axonal branching, cell hypertrophy, and growth cone expansion. Additionally, we found that targeting of CA-Akt to lipid rafts significantly potentiated growth cone expansion compared with expression of CA-Akt throughout the neuron. Because lipid rafts are concentrated within the growth cone, this finding suggests that signaling of expansion is likely regulated locally. We found that CA-Akt-mediated growth cone expansion, but not axonal branching, was attenuated by coexpression of dominant-negative Rac1. In contrast, blockade of mammalian target of rapamycin (mTOR) prevented axonal branching and hypertrophy in response to CA-Akt, but not growth cone expansion. These data indicate that Akt activity can regulate growth cone expansion via localized Rac1 signaling and regulate axonal branching and soma size via activation of mTOR.

Conditional activation of FGFR1 in the prostate epithelium induces angiogenesis with concomitant differential regulation of Ang-1 and Ang-2

The expression of fibroblast growth factor receptor (FGFR)-1 correlates with angiogenesis and is associated with prostate cancer (CaP) progression. To more precisely define the molecular mechanisms whereby FGFR1 causes angiogenesis in the prostate we exploited a transgenic mouse model, JOCK-1, in which activation of a conditional FGFR1 allele in the prostate epithelium caused rapid angiogenesis and progressive hyperplasia. By labeling the vasculature in vivo and applying a novel method to measure the vasculature in three dimensions, we were able to observe a significant increase in vascular volume 1 week after FGFR1 activation. Although vessel volume and branching both continued to increase throughout a 6-week period of FGFR1 activation, importantly, we discovered that continued activation of FGFR1 was not required to maintain the new vasculature. Exploring the molecular mediators of the angiogenic phenotype, we observed consistent upregulation of HIF-1alpha, vascular endothelial growth factor (VEGF) and angiopoietin 2 (Ang-2), whereas expression of Ang-1 was lost. Further analysis revealed that loss of Ang-1 expression occurred in the basal epithelium, whereas the increase in Ang-2 expression occurred in the luminal epithelium. Reporter assays confirmed that the Ang-2 promoter was regulated by FGFR1 signaling and a small molecule inhibitor of FGFR activity, PD173074, could abrogate this response. These findings establish a method to follow spontaneous angiogenesis in a conditional autochthonous system, implicate the angiopoietins as downstream effectors of FGFR1 activation in vivo, and suggest that therapies targeting FGFR1 could be used to inhibit neovascularization during initiation and progression of CaP.

Antiangiogenic gene therapy: disruption of neovascular networks mediated by inducible caspase-9 delivered with a transcriptionally targeted adenoviral vector

The activation of an inducible caspase (iCaspase-9) mediates apoptosis of neovascular endothelial cells, and overcomes the prosurvival effect of vascular endothelial growth factor or basic fibroblast growth factor. The potential utilization of direct activation of caspases as an antiangiogenic strategy for treatment of angiogenesis-dependent diseases (eg cancer) requires expression of the inducible caspase primarily in the tumor endothelium. The objective of this work was to develop and characterize a transcriptionally targeted adenoviral vector that mediates expression of iCaspase-9 specifically in neovascular endothelial cells. We observed that adenoviral vectors containing the human VEGFR2 promoter induced reporter gene expression primarily in proliferating human dermal microvascular endothelial cells (HDMEC). HDMEC transduced with recombinant adenoviral vectors containing iCaspase-9 under regulation of the VEGFR2 promoter (Ad-hVEGFR2-iCaspase-9) and exposed to a cell-permeable dimerizer drug (AP20187), presented higher caspase-3 activity and apoptosis than controls (P < or = 0.05). Using the SCID Mouse Model of Human Angiogenesis, we observed that local delivery of Ad-hVEGFR2-iCaspase-9 followed by intraperitoneal injection of AP20187 resulted in endothelial cell apoptosis and local ablation of microvessels. We believe that this constitutes the first report of a transcriptionally targeted antiangiogenic adenoviral vector that mediates neovascular disruption upon activation of a caspase-based artificial death switch.

Suicide genes as safety switches in T lymphocytes

Broader application of adoptive transfer of tumor-specific T-lymphocytes is accompanied by the need for effective suicide genes to ensure the safety of this cell-based therapy. In vivo elimination of T-lymphocytes expressing the herpes simplex virus-derived thymidine kinase gene has demonstrated the feasibility of this suicide gene as safety switch. However, improvements are required to overcome initial problems, such as immunogenicity. Here, newly developed suicide genes, including inducible Fas, inducible caspase and CD20 are discussed. In addition, problems of clinical application of marker genes and gene transfer techniques, which are prerequisites for suicide gene therapy, are addressed.

Ablation of microvessels in vivo upon dimerization of iCaspase-9

Anti-angiogenic therapies based on targeted disruption of the tumor microvascular network have been proposed for cancer treatment. Inhibitors of the endothelial cell pro-survival pathway mediated by VEGF were shown to activate caspases and cause microvascular regression, but the efficacy of this strategy can be hindered by the engagement of redundant survival pathways. Alternatively, if direct activation of an apical pro-apoptotic caspase is sufficient to disrupt microvessels in vivo, such a strategy could potentially override upstream endothelial cell survival inputs and disrupt tumor neovascular networks. Here, we fused caspase-9 to a mutated FKBP12 domain to express an inducible caspase-9 molecule (iCaspase-9) that can be activated by a cell-permeable dimerizer drug, and transduced this construct into primary endothelial cells. We found that drug-induced dimerization of iCaspase-9 is sufficient to activate endogenous caspase-3 and trigger apoptosis even when endothelial cells are treated with the pro-survival factors VEGF or bFGF. A single intraperitoneal injection of the dimerizer drug induced apoptosis of endothelial cells expressing iCaspase-9 and elimination of human microvessels engineered in immunodeficient mice. These results demonstrate that the activation of iCaspase-9 disrupts microvessels in vivo, and suggest a novel anti-angiogenic strategy based on the expression and controlled activation of an inducible death gene in neovascular endothelial cells.

A novel conditional Akt 'survival switch' reversibly protects cells from apoptosis

The anti-apoptotic Akt kinase is commonly activated by survival factors following plasma membrane relocalization attributable to the interaction of its pleckstrin homology (PH) domain with phosphatidylinositol 3-kinase (PI3K)-generated PI3,4-P(2) and PI3,4,5-P(3). Once activated, Akt can prevent or delay apoptosis by phosphorylation-dependent inhibition or activation of multiple signaling molecules involved in apoptosis, such as BAD, caspase-9, GSK3, and NF-kappaB and forkhead family transcription factors. Here, we describe and characterize a novel, conditional Akt controlled by chemically induced dimerization (CID). In this approach, the Akt PH domain has been replaced with the rapamycin (and FK506)-binding domain, FKBP12, to make F3-DeltaPH.Akt. To effect membrane recruitment, a myristoylated rapamycin-binding domain from FRAP/mTOR, called M-FRB, binds to lipid permeable rapamycin (and non-bioactive synthetic 'rapalogs'), leading to reversible heterodimerization of M-FRB with FKBP-DeltaPH.Akt. Like endogenous c-Akt, we show that the kinase activity of membrane-localized F3-DeltaPH.Akt correlates strongly with phosphorylation at T308 and S473; however, unlike c-Akt, phosphorylation and activation of inducible Akt (iAkt) is largely PI3K independent. CID-mediated activation of iAkt results in phosphorylation of GSK3, and contributes to NF-kappaB activation in vivo in a dose-sensitive manner. Finally, in Jurkat T cells stably expressing iAkt, CID-induced Akt activation rescued cells from apoptosis triggered by multiple apoptotic stimuli, including staurosporine, anti-Fas antibodies, PI3K inhibitors and the DNA damaging agent, etoposide. This novel inducible Akt should be useful for identifying new Akt substrates and for reversibly protecting tissue from apoptosis due to ischemic injury or immunological attack.

Caspase-10 is an initiator caspase in death receptor signaling

A role for caspase-10, previously implicated in the autoimmune lymphoproliferative syndrome, in death receptor signaling has not been directly shown. Here we show that caspase-10 can function independently of caspase-8 in initiating Fas- and tumor necrosis factor-related apoptosis-inducing ligand-receptor-mediated apoptosis. Moreover, Fas crosslinking in primary human T cells leads to the recruitment and activation of caspase-10. Fluorescent resonance energy transfer analysis indicates that the death-effector domains of caspase-8 and -10 both interact with the death-effector domain of FADD. Nonetheless, we find that caspase-8 and -10 may have different apoptosis substrates and therefore potentially distinct roles in death receptor signaling or other cellular processes.

Adenovirus-mediated tissue-targeted expression of a caspase-9-based artificial death switch for the treatment of prostate cancer

Clinical experience with suicide gene therapy for prostate cancer using first-generation approaches has provided a basis for developing improved strategies. Given the low proliferation rate exhibited by prostate cancer, one improvement would be to develop suicide genes that effectively kill both dividing and nondividing cells. A second improvement would be to restrict cytotoxicity to prostate cancer cells, limiting injury of nondiseased tissue. Here we describe a novel approach to achieving both goals based on: (a) the use of a small, but potent, prostate-specific composite promoter, ARR(2)PB, based on the rat probasin gene; and (b) the use of a powerful artificial death switch, called inducible caspase-9 (iCaspase-9). ARR(2)PB includes two copies of the androgen response region (ARR), each containing two androgen receptor (AR)-binding sites, placed upstream of the probasin promoter elements necessary for basal transcription. Because iCaspase-9 contains two binding sites for the dimeric ligand, AP20187, administration of chemical inducers of dimerization leads to aggregation and caspase activation, followed by rapid apoptosis in both dividing and nondividing cells. Using both reagents, we constructed two novel adenoviruses (ADVs), ADV.ARR(2)PB-iCasp9 expressing iCaspase-9 and control ADV.ARR(2)PB-EGFP expressing enhanced green fluorescent protein (EGFP). We demonstrate that tissue specificity is not sacrificed in an ADV backbone because the marker protein, EGFP, is expressed in R1881-stimulated ADV.ARR(2)PB-EGFP-transduced LNCaP cells but not in AR(-) PC-3, 293, HuH-7, U-87, and MCF-7 cells. Similarly, Pro-iCaspase-9 is expressed in ADV.ARR(2)PB-iCasp9-infected LNCaP cells after R1881 administration and is activated after AP20187 administration. In vitro experiments revealed rapid and efficient iCaspase-9-induced apoptosis of LNCaP cells in both an R1881- and AP20187-dependent manner. Only 28, 8, and 0.5% survival of LNCaP cells was seen at multiplicities of infection of 2, 10, and 25, respectively. Furthermore, at a multiplicity of infection of 10, extraordinary sensitivity to AP20187 was seen (IC(50), approximately 3 pM). In vivo experiments showed that ADV.ARR(2)PB-iCasp9 induced apoptosis in LNCaP but not in HuH-7 xenograft tumors in an AP20187-dependent manner. Furthermore, a simple i.p. injection of AP20187 dramatically suppressed LNCaP tumor growth in nude mice and led to a significantly increased host survival. This study demonstrates the feasibility of using tissue-specific expression of cell cycle-independent iCaspases as a nonmutagenic alternative modality for prostate cancer suicide gene therapy.

Intracellular Calcium Signals Regulating Cytosolic Phospholipase A2 Translocation to Internal Membranes

Increased intracellular Ca(2+) concentrations ([Ca(2+)](i)) promote cytosolic phospholipase A(2) (cPLA(2)) translocation to intracellular membranes. The specific membranes to which cPLA(2) translocates and the [Ca(2+)](i) signals required were investigated. Plasmids of EGFP fused to full-length cPLA(2) (EGFP-FL) or to the cPLA(2) C2 domain (EGFP-C2) were used in Ca(2+)/EGFP imaging experiments of cells treated with [Ca(2+)](i)-mobilizing agonists. EGFP-FL and -C2 translocated to Golgi in response to sustained [Ca(2+)](i) greater than approximately 100-125 nm and to Golgi, ER, and perinuclear membranes (PNM) at [Ca(2+)](i) greater than approximately 210-280 nm. In response to short duration [Ca(2+)](i) transients, EGFP-C2 translocated to Golgi, ER, and PNM, but EGFP-FL translocation was restricted to Golgi. However, EGFP-FL translocated to Golgi, ER, and PNM in response to long duration transients. In response to declining [Ca(2+)](i), EGFP-C2 readily dissociated from Golgi, but EGFP-FL dissociation was delayed. Agonist-induced arachidonic acid release was proportional to the [Ca(2+)](i) and to the extent of cPLA(2) translocation. In summary, we find that the differential translocation of cPLA(2) to Golgi or to ER and PNM is a function of [Ca(2+)](i) amplitude and duration. These results suggest that the cPLA(2) C2 domain regulates differential, Ca(2+)-dependent membrane targeting and that the catalytic domain regulates both the rate of translocation and enzyme residence.

Cell proliferation through forced engagement of c-Kit and Flt-3

To investigate the potential for functional interactions between heterologous receptors, the cytoplasmic domains of 2 different receptors (c-Kit and Flt-3) were coexpressed in the interleukin-3–dependent cell line Ba/F3. The receptor signaling domains were presented in the context of fusion proteins, with c-Kit linked to the FK506 binding protein (FKBP12) and Flt-3 linked to the FRB domain of the FKBP12–rapamycin-associated protein. The fusions were brought into apposition with the use of chemical inducers of dimerization (CIDs). Two classes of CID were employed. FK1012 and its synthetic analogue AP1510 bring together 2 copies of the FKBP12 domain, thereby inducing homodimerization of the c-KitFKBP12fusion. A second type of CID, rapamycin, brings together one FKBP12 domain and one FRB domain, resulting in heterodimerization of the c-KitFKBP12 and Flt-3FRB fusions. Ba/F3 cell growth was promoted not only by FK1012- or AP1510-induced homodimerization of the c-KitFKBP12 fusion (as reported previously), but also by rapamycin-induced c-KitFKBP12–Flt-3FRB heterodimerization. These findings demonstrate the potential for a direct functional interaction between c-Kit and Flt-3.

Robust prostate-specific expression for targeted gene therapy based on the human kallikrein 2 promoter

Tissue-specific transcriptional regulatory elements can increase the safety of gene therapy vectors. Unlike prostate-specific antigen (PSA/hK3), whose expression displays an inverse correlation with prostate cancer grade and stage, human glandular kallikrein 2 (hK2) is upregulated in higher grade and stage disease. Therefore, our goal was to develop a strong and prostate-specific hK2-based promoter for targeted gene therapy. We identified the minimum "full-strength" hK2 enhancer and built transcriptional regulatory elements composed of multiple tandem copies of this 1.2-kb enhancer, fused to the hK2 minimal promoter. Relative to the weak induction of the minimal hK2 promoter by androgen analog (R1881) in androgen receptor (AR)-positive LNCaP cells, transcriptional activity was increased by 25-, 44-, 81-, and 114-fold when one to four enhancers were spliced to the hK2 promoter, respectively. In contrast, the enhancer/promoter elements were inactive in the AR(-) prostate cancer line PC-3 and in a panel of nonprostate lines, including 293, U87, MCF-7, HuH-7, and HeLa cells. Furthermore, we generated a recombinant adenovirus, ADV.hK2-E3/P-EGFP, expressing enhanced green fluorescent protein (EGFP) under the control of the hK2 triplicate enhancer/promoter, and compared its properties with ADV.CMV-EGFP expressing EGFP under the control of the cytomegalovirus (CMV) enhancer/promoter. Unlike the CMV promoter, the hK2-E3/P promoter was at least 100-fold inducible by R1881 in the adenoviral backbone. Compared with in situ injection of subcutaneous LNCaP tumors with ADV.CMV-EGFP, which led to detectable EGFP expression in tumor, liver, and brain tissue, ADV.hK2-E3/P-EGFP injection led to robust but tumor-restricted EGFP expression. These results suggest that the hk2 multienhancer/promoter should be a powerful novel reagent for safer targeted gene therapy of prostate cancer.

Adenovirus-mediated transfer of inducible caspases: a novel "death switch" gene therapeutic approach to prostate cancer

In patients with localized prostate cancer, radical prostatectomy and radiation therapy, although effective in controlling localized disease, are often associated with significant side effects attributable to injury of adjacent tissues. Moreover, patients with metastatic disease eventually fail systemic hormonal or chemotherapy because of the development of progressive, refractory disease. In this study, we evaluated the safety and efficacy of a novel suicide gene therapy that could potentially spare normal tissue while bypassing molecular mechanisms of apoptosis resistance by using chemically inducible effector caspases to trigger apoptosis in prostate cancer cells. Initially, we compared the ability of a panel of inducible Fas signaling intermediates to kill human and murine prostate cancer cell lines. On the basis of the superior killing by downstream caspase-1 and caspase-3, replication-deficient adenoviral vectors expressing conditional caspase-1 (Ad-G/iCasp1) or caspase-3 (Ad-G/iCasp3), regulated by nontoxic, lipid-permeable, chemical inducers of dimerization (CID), were constructed. Upon vector transduction followed by CID administration, aggregation and activation of these recombinant caspases occur, leading to rapid apoptosis. In vitro, both human (LNCaP and PC-3) and murine (TRAMP-C2 and TRAMP-C2G) prostate cancer cell lines were efficiently transduced and killed in a CID-dependent fashion. In vivo, direct injection of Ad-G/iCasp1 into s.c. TRAMP-C2 tumors caused focal but extensive apoptosis without evidence for a bystander effect at the maximal viral dose (i.e., 2.5 x 10(10) viral particles/25 microl) in host animals that also received CID compared with control animals. Treatment with Ad-G/iCasp1 plus CID resulted in a transient, yet significant, reduction both in tumor growth and volume compared with tumors treated with vector but not CID (P < 0.035) or vector-diluent plus CID (P < 0.022), both of which grew more rapidly. These results demonstrate that CID-regulated, caspase-based suicide gene therapy is safe and can inhibit the growth of experimental prostate cancer in vitro and in vivo through potent induction of apoptosis, providing a rationale for further development.

Developments in suicide genes for preclinical and clinical applications

The graduation of gene therapy from unfulfilled dreams to conventional therapy for genetic and acquired disorders will require a mastery of multiple disparate components including gene delivery vectors, regulated tissue-specific gene expression, control of immunity and manipulation of cell viability. Improvements in suicide genes have opened up a whole new treatment modality for treating hyperproliferative disorders and for designing animal models for disease. Along with herpes simplex virus-1 thymidine kinase, a host of additional suicide genes have been developed. A critical comparison of these will follow along with progress in utilizing these reagents for therapeutic benefits.

Cytosolic phospholipase A2 is required for macrophage arachidonic acid release by agonists that Do and Do not mobilize calcium. Novel role of mitogen-activated protein kinase pathways in cytosolic phospholipase A2 regulation

The 85-kDa cytosolic phospholipase A(2) (cPLA(2)) mediates agonist-induced arachidonic acid release and eicosanoid production. Calcium and phosphorylation on Ser-505 by mitogen-activated protein kinases (MAPKs) regulate cPLA(2). Arachidonic acid release and eicosanoid production induced by stimuli that do (A23187, zymosan) or do not (phorbol myristate acetate (PMA), okadaic acid) mobilize calcium were quantitatively suppressed in cPLA(2)-deficient mouse peritoneal macrophages. The contribution of MAPKs to cPLA(2)-mediated arachidonic acid release was investigated. Both extracellular signal-regulated kinases (ERKs) and p38 contributed to cPLA(2) phosphorylation on Ser-505. However, although ERK inhibition did not affect A23187-induced arachidonic acid release, it suppressed zymosan-, PMA-, and okadaic acid-induced arachidonic acid release under conditions where phosphorylation of cPLA(2) on Ser-505 was unaffected. This indicates an additional regulatory mechanism for the ERK pathway. A role for transcriptional regulation is suggested by data showing that cycloheximide and actinomycin D inhibited arachidonic acid release induced by zymosan, PMA and, okadaic acid but not by A23187. Our results show that MAPK pathways contribute to arachidonic acid release in macrophages through alternative mechanisms in addition to their ability to phosphorylate cPLA(2) on Ser-505 and suggest a role for new protein synthesis.

Improved artificial death switches based on caspases and FADD

A number of "suicide genes" have been developed as safety switches for gene therapy vectors or as potential inducible cytotoxic agents for hyperproliferative disorders, such as cancer or restenosis. However, most of these approaches have relied on foreign proteins, such as HSV thymidine kinase, that primarily target rapidly dividing cells. In contrast, novel artificial death switches based on chemical inducers of dimerization (CIDs) and endogenous proapoptotic molecules function efficiently in both dividing and nondividing cells. In this approach, lipid-permeable, nontoxic CIDs are used to conditionally cross-link target proteins that are fused to CID-binding domains (CBDs), thus activating signaling cascades leading to apoptosis. In previous reports, CID-regulated Fas and caspases 1, 3, 8, and 9 were described. Since the maximum efficacy of these artificial death switches requires low basal and high specific activity, we have optimized these death switches for three parameters: (1) extent of oligomerization, (2) spacing between CBDs and target proteins, and (3) intracellular localization. We describe improved conditional Fas and caspase 1, 3, 8, and 9 alleles that function at subnanomolar levels of the CID AP1903 to trigger apoptosis. Further, we demonstrate for the first time that oligomerization of the death effector domain of the Fas-associated protein, FADD, is sufficient to trigger apoptosis, suggesting that the primary function of FADD, like that of Apaf-1, is oligomerization of associated caspases. Finally, we demonstrate that nuclear-targeted caspases 1, 3, and 8 can trigger apoptosis efficiently, implying that the cleavage of nuclear targets is sufficient for apoptosis.

Role of phosphorylation sites and the C2 domain in regulation of cytosolic phospholipase A2

Cytosolic phospholipase A2 (cPLA2) mediates agonist-induced arachidonic acid release, the first step in eicosanoid production. cPLA2 is regulated by phosphorylation and by calcium, which binds to a C2 domain and induces its translocation to membrane. The functional roles of phosphorylation sites and the C2 domain of cPLA2 were investigated. In Sf9 insect cells expressing cPLA2, okadaic acid, and the calcium-mobilizing agonists A23187 and CryIC toxin induce arachidonic acid release and translocation of green fluorescent protein (GFP)-cPLA2 to the nuclear envelope. cPLA2 is phosphorylated on multiple sites in Sf9 cells; however, only S505 phosphorylation partially contributes to cPLA2 activation. Although okadaic acid does not increase calcium, mutating the calcium-binding residues D43 and D93 prevents arachidonic acid release and translocation of cPLA2, demonstrating the requirement for a functional C2 domain. However, the D93N mutant is fully functional with A23187, whereas the D43N mutant is nearly inactive. The C2 domain of cPLA2 linked to GFP translocates to the nuclear envelope with calcium-mobilizing agonists but not with okadaic acid. Consequently, the C2 domain is necessary and sufficient for translocation of cPLA2 to the nuclear envelope when calcium is increased; however, it is required but not sufficient with okadaic acid.

WD-40 repeat region regulates Apaf-1 self-association and procaspase-9 activation

The casp9 protein plays a critical role in apoptosis induced by a variety of death stimuli. A regulator of apoptosis, Apaf-1, binds to and activates pro-casp9 in the presence of cytochrome c and dATP, a requirement that is bypassed by deletion of the WD-40 repeats located in the C-terminal half of Apaf-1. In this report, we used constitutively active Apaf-1 mutant lacking the WD-40 repeat region to study the mechanism and regulation of pro-casp9 activation. Mutational analysis revealed that only a small portion of the CED-4 homologous region (residues 456-559) could be deleted without destroying the ability of Apaf-1-(1-559) to activate pro-casp9. Apaf-1 can self-associate to form oligomers. Disruption of Apaf-1 self-association by deletion (Delta109-559) or mutation of the P-loop region (K149R) abrogated Apaf-1-mediated pro-casp9 activation. Forced oligomerization of the caspase recruitment domain of Apaf-1 was sufficient for pro-casp9 activation. Dimerization of chimeric Fpk-pro-casp9 protein with the dimerizer drug FK1012 induced pro-casp9 processing and apoptosis in cells. Significantly, the C-terminal region containing WD-40 repeats interacted with its N-terminal CED-4 homologous region, as determined by immunoprecipitation experiments. Importantly, expression of the WD-40 repeat region inhibited Apaf-1 self-association and proteolytic activation of pro-casp9. These studies provide a mechanism by which Apaf-1 promotes autoactivation of pro-casp9 through Apaf-1 self-association, a process that is negatively regulated by the WD-40 repeats.

The role of calcium and phosphorylation of cytosolic phospholipase A2 in regulating arachidonic acid release in macrophages

Arachidonic acid release is induced in macrophages with diverse agonists including calcium ionophores, phorbol myristate acetate (PMA), okadaic acid, and the phagocytic particle, zymosan, and correlates with activation of cytosolic phospholipase A2 (cPLA2). The role of calcium and phosphorylation of cPLA2 in regulating arachidonic acid release was investigated. Zymosan induced a rapid and transient increase in [Ca2+]i. This in itself is not sufficient to induce arachidonic acid release since ATP and platelet activating factor (PAF), agonists that induce transient calcium mobilization in macrophages, induced little arachidonic acid release. Unlike zymosan, which is a strong activator of mitogen-activated protein kinase (MAPK), ATP and PAF were weak MAPK activators and induced only a partial and transient increase in cPLA2 phosphorylation (gel shift). However, ATP or PAF together with colony stimulating factor-1 (CSF-1) synergistically stimulated arachidonic acid release. CSF-1 is a strong MAPK activator that induces a rapid and complete cPLA2 gel shift but not calcium mobilization or arachidonic acid release. Arachidonic acid release was more rapid in response to CSF-1 plus ATP or PAF than zymosan and correlated with the time course of the cPLA2 gel shift. Although low concentrations of ionomycin induced a lower magnitude of calcium mobilization than ATP, the response was more sustained resulting in arachidonic acid release. A23187 and ionomycin induced weak MAPK activation, and a partial and transient cPLA2 gel shift. The MAPK kinase inhibitor, PD 98059 suppressed A23187-induced MAPK activation and cPLA2 gel shift but had little effect on arachidonic acid release. These results indicate that in macrophages a transient increase in [Ca2+]i and sustained phosphorylation of cPLA2 can act together to promote arachidonic acid release but neither alone is sufficient. A sustained increase in calcium is sufficient for inducing arachidonic acid release. However, PMA and okadaic acid induce arachidonic acid release without increasing [Ca2+]i, although resting levels of calcium are required, suggesting alternative mechanisms of regulation.

Synthetic activation of caspases: artificial death switches

The development of safe vectors for gene therapy requires fail-safe mechanisms to terminate therapy or remove genetically altered cells. The ideal "suicide switch" would be nonimmunogenic and nontoxic when uninduced and able to trigger cell death independent of tissue type or cell cycle stage. By using chemically induced dimerization, we have developed powerful death switches based on the cysteine proteases, caspase-1 ICE (interleukin-1beta converting enzyme) and caspase-3 YAMA. In both cases, aggregation of the target protein is achieved by a nontoxic lipid-permeable dimeric FK506 analog that binds to the attached FK506-binding proteins, FKBPs. We find that intracellular cross-linking of caspase-1 or caspase-3 is sufficient to trigger rapid apoptosis in a Bcl-xL-independent manner, suggesting that these conditional proapoptotic molecules can bypass intracellular checkpoint genes, such as Bcl-xL, that limit apoptosis. Because these chimeric molecules are derived from autologous proteins, they should be nonimmunogenic and thus ideal for long-lived gene therapy vectors. These properties should also make chemically induced apoptosis useful for developmental studies, for treating hyperproliferative disorders, and for developing animal models to a wide variety of diseases.

A proliferation switch for genetically modified cells

Receptor dimerization is the key signaling event for many cytokines, including erythropoietin. A system has been recently developed that permits intracellular protein dimerization to be reversibly activated in response to a lipid-soluble dimeric form of the drug FK506, called FK1012. FK1012 is used as a pharmacological mediator of dimerization to bring together FK506 binding domains, taken from the endogenous protein FKBP12. In experiments reported herein, FK1012-induced dimerization of a fusion protein containing the intracellular portion of the erythropoietin receptor allowed cells normally dependent on interleukin 3 to proliferate in its absence. FK506 competitively reversed the proliferative effect of FK1012 but had no influence on the proliferative effect of interleukin 3. Signaling pathways activated by FK1012 mimicked those activated by erythropoietin, because both JAK2 and STAT5 were phosphorylated in response to FK1012. This approach may provide a means to specifically and reversibly stimulate the proliferation of genetically modified cell populations in vitro or in vivo.

Fas signal transduction triggers either proliferation or apoptosis in human fibroblasts

Although shown to be highly expressed by the epidermis in inflammatory skin disease, the ability of the Fas protein to trigger apoptosis in the distinct cell subpopulations of cutaneous tissue, particularly with regard to receptor density and the degree of crosslinking, has not been fully characterized. We therefore determined the effect of Fas cross-linking in primary human dermal fibroblasts at both high and low levels of Fas receptor expression. First, we examined the effects of the anti-Fas monoclonal antibody, CH-11, on fibroblasts expressing low basal levels of Fas. In these cells Fas aggregation stimulated proliferation by 160 +/- 10% over untreated controls. In contrast, the same concentration of CH-11 had an inhibitory effect on epidermal keratinocyte growth. Because Fas is upregulated in inflamed skin, we next examined the effects of Fas cross-linking on fibroblasts expressing augmented levels ofFas. Fibroblasts were either transfected with plasmids for overexpression of full length or bioengineered Fas receptors or were transduced with a retroviral Fas expression vector. In these cells Fas oligomerization triggered the morphologic changes indicative of apoptosis regardless of whether or not the Fas-signaling domain was tethered to the plasma membrane. These studies indicate that Fas oligomerization in dermal fibroblasts may initiate dual signaling programs, either proliferation or apoptosis, and that the chosen outcome may depend upon the magnitude of Fas aggregation.

Specific triggering of the Fas signal transduction pathway in normal human keratinocytes

The epidermis is continually exposed to genotoxic injury and requires an efficient mechanism to eliminate genetically altered cells. The membrane receptor, Fas, initiates apoptosis in many cell types, including keratinocytes. Receptor cross-linking is the vital post-ligand binding step in Fas signal transduction, and we have utilized FK1012, capable of oligomerizing proteins engineered to contain the FK506 binding protein (FKBP), to trigger Fas via FKBP-linked receptor cytoplasmic domains in human keratinocytes. An FKBP chimera containing the Fas cytoplasmic domain targeted to the plasma membrane induced an up to 89% decrease in viability of keratinocytes, as reflected by the activity of constitutive promoters, in response to FK1012. Oligomerization of Fas, either with engineered Fas.FKBP by FK1012 or via antibody cross-linking of full-length Fas-induced cellular changes consistent with apoptosis. The lpr Fas point mutation abolished this effect. A Fas.FKBP construct unlinked to the membrane was fully active in this assay. Early developmental age or pre-treatment of cells with GM-CSF, TGF-beta, EGF, KGF, IFN-gamma, or phorbol ester failed to protect against Fas effects. These findings reveal that the Fas signal transduction pathway is active in keratinocytes, requires no induction, and dominantly overrides growth stimuli.

Controlling programmed cell death with a cyclophilin-cyclosporin-based chemical inducer of dimerization

BACKGROUND

Cell death can occur either from physical damage (necrosis) or cellular suicide (apoptosis). Apoptosis is essential for the development of multicellular organisms and disregulated apoptosis underlies many human diseases. The Fas receptor (Fas) is a membrane signaling protein that mediates a death signal following its aggregation by the Fas ligand. We have described methods to induce the association of proteins using cell-permeable molecules called chemical inducers of dimerization (CIDs). Here we describe the synthesis of a novel CID, (CsA)2, that has two identical protein-binding surfaces derived from the immunosuppressant cyclosporin A (CsA). We use this CID to deliver a death signal to cells expressing a fusion protein containing cyclophilin (CyP, the protein receptor for cyclosporin) and the cytoplasmic signaling domain of Fas.

RESULTS

(CsA)2 was synthesized in six synthetic steps and 30% overall yield from cyclosporin. It binds to two CyP proteins simultaneously, but does not inhibit T-cell signaling, presumably because the (CsA)2-CyP complex does not bind to calcineurin. Jurkat cells stably transfected with constructs encoding myristoylated CyP-Fas fusion proteins undergo apoptosis in response to nanomolar quantities of (CsA)2. Constructs containing a mutation in the myristoylation signal are defective for signaling.

CONCLUSIONS

The Fas signaling pathway can be activated with a cell-permeable CID derived from CsA in cells expressing an appropriately engineered Fas construct, which must be localized at the membrane. This new class of homodimerizing CIDs will be useful for in-depth analysis of protein association events in complex systems, including transgenic animals. Now that several CIDs with distinct dimerization characteristics are available, it should be possible to induce the activation of multiple pathways with complete specificity.

Dimeric ligands define a role for transcriptional activation domains in reinitiation

Eukaryotic transcriptional activators mediate transcriptional induction through stabilization of the preinitiation complex, probably through direct interactions with basal transcription factors. In vitro studies on the role of an activator in the maintenance of on-going transcription (reinitiation) have been contradictory, suggesting that, after formation of a preinitiation complex, an activator may or may not be necessary for transcription to be maintained. We have developed a means of regulating transcription in living cells through the use of both homodimeric and heterodimerizing synthetic ligands that allow the ligand-dependent association and disassociation of a transcriptional activation domain with a promoter. Here we report that maintaining the transcription of endogenous genes in vivo, in both yeast and human cells, requires the continuous presence of the activation domain. The use of synthetic ligands as a transcriptional on-off switch represents a powerful means of controlling the transcription in vitro and in vivo for both experimental and therapeutic purposes.

Functional analysis of Fas signaling in vivo using synthetic inducers of dimerization

BACKGROUND

Genetic abnormalities in the Fas receptor or its trimeric ligand, FasL, result in massive T-cell proliferation and a lupus-like autoimmune syndrome, which was initially attributed to excessive lymphoproliferation but is now ascribed to the absence of Fas-mediated cell death. Although Fas is normally expressed on most thymocytes, negative selection seems to be unperturbed in Fas-deficient (lpr) mice. This suggests that Fas has an important function in peripheral, but not thymic, T cells.

RESULTS

To explore the Fas-mediated cell death pathway both in vitro and in vivo, we used conditional alleles of the Fas receptor that can be triggered by an intracellularly active chemical inducer of dimerization known as FK1012. We found that membrane attachment is important for Fas function and, unlike previous results with anti-Fas monoclonal antibodies, we show that dimerization is sufficient to trigger apoptosis. Finally, the administration of FK1012 in vivo to transgenic animals expressing the conditional FAS receptor in thymocytes demonstrates that sensitivity to FAS-mediated apoptosis is restricted to CD4+CD8+ thymocytes.

CONCLUSIONS

Here, we describe the first in vivo application of non-toxic, cell-permeable synthetic ligands to regulate signal transduction in transgenic mice expressing a conditional receptor. Using this system, we show that the Fas pathway is restricted to double-positive thymocytes in vivo, consistent with recent in vitro findings with thymocytes. This method promises to be more useful not only for developmental studies involving cell ablation, but also for studies involving the regulation of a wide variety of signaling molecules.

Creating conditional mutations in mammals

For many years geneticists have relied on conditional activation to study the roles of cytolytic or cytostatic proteins in lower eukaryotes or to elucidate the epistatic relationships of proteins in a signaling pathway. Regardless of their merits, conditional mutants have only been available to mammalian geneticists within the past few years. Moreover, the approaches that exist are still limited to a subset of signaling molecules and are not reliable for in vivo studies. Now, added to the biologist's toolbox is a versatile new approach based on chemically induced dimerization that should allow for the reversible regulation of proteins at the cell surface, intracellularly, in the nucleus and in vivo.

Treatment of deformity of the lower limb in adults who have osteogenesis imperfecta

The Ilizarov method of lengthening was used to correct deformities of the lower extremity in six patients who had type-1 osteogenesis imperfecta, as categorized by Silence et al. The average age was thirty-one years (range, fourteen to fifty-one years). The deformities included shortening of four tibiae and three femora as well as an angular malalignment (average, 28 degrees; range, 20 to 40 degrees) of all four tibiae and one femur. One patient also had a non-union of the right femur. The average angular correction was 23 degrees (range, 20 to 30 degrees). The seven limb segments gained an average of 6.6 centimeters (range, two to eleven centimeters) in length. All limb-length discrepancies were corrected to within two centimeters of the length of the contralateral limb. At an average of three years and four months (range, one year and seven months to six years), the roentgenographic appearance of the fully matured bone was comparable with that of the original bone. There was no fractures or increases in the angulation of the segment of new bone. Two patients had pain when walking; it was related to a chronic pin-track infection in one and to osteoarthrosis of the ankle in the other. The functional status of four patients was improved and that of the other two patients was unchanged. All six patients were pleased with the outcome of the procedure. There was eighteen complications: stiffness of the knee in two patients; a peroneal nerve palsy in two; a superficial pin-track infection in three; and a deep pin-track infection, greater-than-normal loss of blood intraoperatively, loosening of two pins, worsening of the instability of the knee, and an infection in the knee in one patient each. In another patient, a Rush rod that had been placed before correction of the deformity migrated proximally and had to be removed after completion of the correction. There were five fractures.

Regional differences in platelet-derived growth factor production by the canine aorta

Platelet-derived growth factor (PDGF) is a potent mitogen and chemotactic agent which may be involved in the formation of proliferative lesions of the arterial system, such as intimal hyperplasia and atherosclerosis. To examine the regional variation in vessel wall production of this mitogen, PDGF production and PDGF A chain mRNA expression by normal arterial wall was studied as a function of vessel location. PDGF production by canine aortic segments was measured after 72 h in organ culture, revealing significantly more PDGF produced by the distal compared to proximal aorta at 77 +/- 10 versus 14 +/- 6 pg/cm2/72 h (p<0.05). Endothelial cells (EC) and smooth muscle cells (SMC), isolated from analogous aortic sites, were grown in tissue culture and the conditioned medium was assayed for PDGF. EC in vitro demonstrated a similar geographic trend in PDGF production (distal=1,501 +/- 389 pg/microgram DNA/72 h, proximal=759 +/- 230 pg/microgram DNA/72 h; p=0.17). PDGF production by SMC in cell culture had a similar pattern with cells from the distal aorta producing 58 +/- 28 pg PDGF/microgram DNA/72 h, compared to cells from the proximal aorta producing 37 +/- 15 pg PDGF/microgram DNA/72 h (p=0.13). Freshly harvested EC and SMC, isolated from the same aortic sites, were subjected to quantitation of PDGF mRNA levels using a coupled reverse transcriptase and polymerase chain reaction amplification method, with glyceraldehyde-phosphate dehydrogenase (GAPDH) as a control. The ratio of PDGF A chain:GAPDH mRNA was significantly greater in distal aortic SMC, 2.30 +/- 0.99, compared to proximal aortic SMC, 1.27 +/- 0.46 (p=0.05), but was not significantly different between proximal and distal aortic EC (p=0.86). These findings demonstrate significant regional differences in PDGF production in the normal canine aorta. Additionally, SMC are implicated as a significant contributor to the regional variation in PDGF production.

A general strategy for producing conditional alleles of Src-like tyrosine kinases

The Src-like tyrosine kinases require membrane localization for transformation and probably for their normal role in signal transduction. We utilized this characteristic to prepare Src-like tyrosine kinases that can be readily activated with the rationally designed chemical inducer of dimerization FK1012. Dimerization of cytoplasmic Src-like tyrosine kinases was not sufficient for signaling, but their recruitment to the plasma membrane led to the rapid activation of transcription factors identical to those regulated by crosslinking the antigen receptor. Moreover, recruitment of activated Src-like kinases to the membrane replaced signaling by the T-lymphocyte antigen receptor complex, leading to the activation of both the Ras/protein kinase C and Ca2+/calcineurin pathways normally activated by antigen receptor signaling. Since these chemical inducers of dimerization are cell permeable, this approach permits the production of conditional alleles of any of the Src-like tyrosine kinases, thereby allowing a delineation of their developmental roles.

Signal transduction in T lymphocytes using a conditional allele of Sos

While Ras activation has been shown to play an important role in signal transduction by the T-lymphocyte antigen receptor, the mechanism of its activation in T cells is unclear. Membrane localization of the guanine nucleotide exchange factor Sos, but not Vav or Dbl, was sufficient for Ras-mediated signaling in T lymphocytes. Activation of Sos appears to involve membrane recruitment and not allosteric changes, because interaction of Sos with the linking molecule Grb-2 was not required for Ras activation. To extend this analysis, we constructed a modified Sos that could be localized to the membrane inducibly by using a rationally designed chemical inducer of dimerization, FK1012. The role of Grb-2 in signaling was mimicked with this technique, which induced the association of a modified Sos with the membrane, resulting in rapid activation of Ras-induced signaling. In contrast, inducible localization of Grb-2 to the membrane did not activate signaling and suggests that the interaction of Grb-2 with Sos in T cells is subject to regulation. This conditional allele of Sos demonstrates that membrane localization of Sos is sufficient for Ras activation in T cells and indicates that the role of Grb-2 is to realize the biologic advantages of linker-mediated dimerization: enhanced specificity and favorable kinetics for signaling. This method of generating conditional alleles may also be useful in dissecting other signal transduction pathways regulated by protein localization or protein-protein interactions.

New devices for scalp reduction. Intraoperative and prolonged scalp extension

BACKGROUND

Scalp reduction for male pattern and other extensive, permanent crown-vertex alopecias has been a beneficial, adjuvant procedure in hair replacement surgery and has been augmented by unsightly and sometimes painful intraoperative and chronic scalp expansion techniques.

METHODS

Ten patients underwent scalp reduction for male pattern baldness utilizing intraoperative Sure-Closure, a skin-stretching device. Ten patients had Frechet Extenders placed under the scalp during their scalp reductions with subsequent removal 28 days later followed immediately by second reduction procedures.

RESULTS

The skin-stretching device, Sure-Closure, allowed the excision of 20%-30% more alopecic scalp during scalp reduction than what would have been possible with scalp reduction alone. The Frechet Extender when combined with a lazy S excision pattern for scalp reduction procedures generated between 25% and 50% more excision of alopecic scalp than with scalp reduction alone.

CONCLUSION

Scalp reduction procedures can be more effectively performed with minimal complications and fewer reductions required per patient using either intraoperative scalp extension with the Sure-Closure device or chronic scalp extension with the Frechet Extender.

Hybrids obtained by protoplast fusion with a salt-tolerant yeast

An industrial strain of Saccharomyces cerevisiae was fused with an osmotolerant yeast, Debaryomyces hansenii, to obtain hybrids having increased tolerance to elevated salt concentrations. The hybrids were intermediate to parent species in production of ethanol and polyols.