Epigenetic regulator genes direct lineage switching in MLL/AF4 leukemia

The fusion gene MLL/AF4 defines a high-risk subtype of pro-B acute lymphoblastic leukemia. Relapse can be associated with a lineage switch from acute lymphoblastic to acute myeloid leukemia, resulting in poor clinical outcomes caused by resistance to chemotherapies and immunotherapies. In this study, the myeloid relapses shared oncogene fusion breakpoints with their matched lymphoid presentations and originated from various differentiation stages from immature progenitors through to committed B-cell precursors. Lineage switching is linked to substantial changes in chromatin accessibility and rewiring of transcriptional programs, including alternative splicing. These findings indicate that the execution and maintenance of lymphoid lineage differentiation is impaired. The relapsed myeloid phenotype is recurrently associated with the altered expression, splicing, or mutation of chromatin modifiers, including CHD4 coding for the ATPase/helicase of the nucleosome remodelling and deacetylation complex. Perturbation of CHD4 alone or in combination with other mutated epigenetic modifiers induces myeloid gene expression in MLL/AF4+ cell models, indicating that lineage switching in MLL/AF4 leukemia is driven and maintained by disrupted epigenetic regulation.

hiPSC-derived bone marrow milieu identifies a clinically actionable driver of niche-mediated treatment resistance in leukemia

Leukemia cells re-program their microenvironment to augment blast proliferation and enhance treatment resistance. Means of clinically targeting such niche-driven treatment resistance remain ambiguous. We develop human induced pluripotent stem cell (hiPSC)-engineered niches to reveal druggable cancer-niche dependencies. We reveal that mesenchymal (iMSC) and vascular niche-like (iANG) hiPSC-derived cells support ex vivo proliferation of patient-derived leukemia cells, affect dormancy, and mediate treatment resistance. iMSCs protect dormant and cycling blasts against dexamethasone, while iANGs protect only dormant blasts. Leukemia proliferation and protection from dexamethasone-induced apoptosis is dependent on cancer-niche interactions mediated by CDH2. Consequently, we test CDH2 antagonist ADH-1 (previously in Phase I/II trials for solid tumors) in a very aggressive patient-derived xenograft leukemia mouse model. ADH-1 shows high in vivo efficacy; ADH-1/dexamethasone combination is superior to dexamethasone alone, with no ADH-1-conferred additional toxicity. These findings provide a proof-of-concept starting point to develop improved, potentially safer therapeutics targeting niche-mediated cancer dependencies in blood cancers.

The One Minute Preceptor: A Vital Tool During COVID-19

The One Minute Preceptor (OMP) model of teaching has an important role to play during the COVID-19 pandemic. It's quick and easy to learn and can be applied to any clinical setting. By responding directly to a student's needs, and building on the knowledge they already hold, the OMP is able to offer relevant and opportunistic teaching that the learner can immediately apply. Finally, the OMP can be taught in under two hours meaning medical staff not used to regularly teaching can develop the confidence to offer high quality educational interventions.

RUNX1/RUNX1T1 mediates alternative splicing and reorganises the transcriptional landscape in leukemia

The fusion oncogene RUNX1/RUNX1T1 encodes an aberrant transcription factor, which plays a key role in the initiation and maintenance of acute myeloid leukemia. Here we show that the RUNX1/RUNX1T1 oncogene is a regulator of alternative RNA splicing in leukemic cells. The comprehensive analysis of RUNX1/RUNX1T1-associated splicing events identifies two principal mechanisms that underlie the differential production of RNA isoforms: (i) RUNX1/RUNX1T1-mediated regulation of alternative transcription start site selection, and (ii) direct or indirect control of the expression of genes encoding splicing factors. The first mechanism leads to the expression of RNA isoforms with alternative structure of the 5'-UTR regions. The second mechanism generates alternative transcripts with new junctions between internal cassettes and constitutive exons. We also show that RUNX1/RUNX1T1-mediated differential splicing affects several functional groups of genes and produces proteins with unique conserved domain structures. In summary, this study reveals alternative splicing as an important component of transcriptome re-organization in leukemia by an aberrant transcriptional regulator.

Intracellular manipulation and measurement with multipole magnetic tweezers

The capability to directly interrogate intracellular structures inside a single cell for measurement and manipulation is important for understanding subcellular and suborganelle activities, diagnosing diseases, and developing new therapeutic approaches. Compared with measurements of single cells, physical measurement and manipulation of subcellular structures and organelles remain underexplored. To improve intracellular physical measurement and manipulation, we have developed a multipole magnetic tweezers system for micromanipulation involving submicrometer position control and piconewton force control of a submicrometer magnetic bead inside a single cell for measurement in different locations (spatial) and different time points (temporal). The bead was three-dimensionally positioned in the cell using a generalized predictive controller that addresses the control challenge caused by the low bandwidth of visual feedback from high-resolution confocal imaging. The average positioning error was quantified to be 0.4 μm, slightly larger than the Brownian motion–imposed constraint (0.31 μm). The system is also capable of applying a force up to 60 pN with a resolution of 4 pN for a period of time longer than 30 min. The measurement results revealed that significantly higher stiffness exists in the nucleus’ major axis than in the minor axis. This stiffness polarity is likely attributed to the aligned actin filament. We also showed that the nucleus stiffens upon the application of an intracellularly applied force, which can be attributed to the response of structural protein lamin A/C and the intracellular stress fiber actin filaments.

Molecular parameters of siRNA--cell penetrating peptide nanocomplexes for efficient cellular delivery

Cell-penetrating peptides (CPPs) are versatile tools for the intracellular delivery of various biomolecules, including siRNA. Recently, CPPs were introduced that showed greatly enhanced delivery efficiency. However, the molecular basis of this increased activity is poorly understood. Here, we performed a detailed analysis of the molecular and physicochemical properties of seven different siRNA-CPP nanoparticles. In addition, we determined which complexes are internalized most efficiently into the leukemia cell-line SKNO-1, and subsequently inhibited the expression of a luciferase reporter gene. We demonstrated effective complexation of siRNA for all tested CPPs, and optimal encapsulation of the siRNA was achieved at very similar molar ratios independent of peptide charge. However, CPPs with an extreme high or low overall charge proved to be exceptions, suggesting an optimal range of charge for CPP-siRNA nanoparticle formation based on opposite charge. The most active CPP (PepFect6) displayed high serum resistance but also high sensitivity to decomplexation by polyanionic macromolecules, indicating the necessity for partial decomplexation for efficient uptake. Surprisingly, CPP-siRNA complexes acquired a negative ζ-potential in the presence of serum. These novel insights shed light on the observation that cell association is necessary but not sufficient for activity and motivate new research into the nature of the nanoparticle-cell interaction. Overall, our results provide a comprehensive molecular basis for the further development of peptide-based oligonucleotide transfection agents.

Depletion of RUNX1/ETO in t(8;21) AML cells leads to genome-wide changes in chromatin structure and transcription factor binding

The t(8;21) translocation fuses the DNA-binding domain of the hematopoietic master regulator RUNX1 to the ETO protein. The resultant RUNX1/ETO fusion protein is a leukemia-initiating transcription factor that interferes with RUNX1 function. The result of this interference is a block in differentiation and, finally, the development of acute myeloid leukemia (AML). To obtain insights into RUNX1/ETO-dependant alterations of the epigenetic landscape, we measured genome-wide RUNX1- and RUNX1/ETO-bound regions in t(8;21) cells and assessed to what extent the effects of RUNX1/ETO on the epigenome depend on its continued expression in established leukemic cells. To this end, we determined dynamic alterations of histone acetylation, RNA Polymerase II binding and RUNX1 occupancy in the presence or absence of RUNX1/ETO using a knockdown approach. Combined global assessments of chromatin accessibility and kinetic gene expression data show that RUNX1/ETO controls the expression of important regulators of hematopoietic differentiation and self-renewal. We show that selective removal of RUNX1/ETO leads to a widespread reversal of epigenetic reprogramming and a genome-wide redistribution of RUNX1 binding, resulting in the inhibition of leukemic proliferation and self-renewal, and the induction of differentiation. This demonstrates that RUNX1/ETO represents a pivotal therapeutic target in AML.

Cystic kidney diseases and planar cell polarity signaling

Renal cystic diseases are a major clinical concern as they are the most common genetic cause of end-stage renal disease. While many of the genes causing cystic disease have been identified in recent years, knowing the molecular nature of the mutations has not clarified the mechanisms underlying cyst formation. Recent research in model organisms has suggested that cyst formation may be because of defective planar cell polarity (PCP) and/or ciliary defects. In this review, we first outline the clinical features of renal cystic diseases and then discuss current research linking our understanding of cystic kidney disease to PCP and cilia.

Distribution of extracellular signal-regulated protein kinases 1 and 2 in the rat adrenal and their activation by angiotensin II

The adrenal gland of the rat is continuously regenerated through proliferation of a stem cell population in the outer part of the gland. To clarify the location of proliferative events within the adrenal gland, and the factors that stimulate them, rat adrenal capsule preparations, consisting of capsule, zona glomerulosa (ZG) and the outer zona fasciculata (ZF) were maintained in vitro under different conditions of stimulation, for varying periods. Sites of proliferation were identified by 5-bromo-2'-deoxy-uridine (BrdU) staining, and the distribution of classical MAP kinase (MAPK) family members, extracellular signal-regulated kinase (ERK) 1 and 2, immunoreactivity was determined using immunocytochemistry. BrdU staining was limited to the outer glomerulosa and the capsule, where it was enhanced by angiotensin II, but not by a high potassium ion concentration nor by ACTH. In contrast, ERK1/2 immunoreactivity was distributed throughout the ZG and in the medulla, with none detectable in the ZF and reticularis. Furthermore, angiotensin II, potassium ions and ACTH were all shown to induce ERK1 and ERK2 phosphorylation in the ZG. Treatment of adrenal capsule tissue with the specific MAPK kinase inhibitor PD98059 revealed inhibition of ERK1/2 phosphorylation, but no effect on angiotensin II-induced aldosterone secretion. Although the distribution and activation of the MAPK pathway suggest a link with proliferation, the findings clearly designated only the outer part of the glomerulosa and capsule as a potential stem cell population. Further functions should be sought for the apparently silent major part of the glomerulosa.

Sticking together and sorting things out: adhesion as a force in development

During development it is not sufficient for cells to differentiate properly--they must also become physically grouped into appropriate structures, to form skin on the outside, and blood and muscle on the inside. How does this three-dimensional patterning occur? One classic explanation for this resolution of cells and tissues into distinct three-dimensional structures has been that as cells differentiate, they develop differential adhesive properties, and that these affinity differences allow cells to sort out from one another. This classic hypothesis is being investigated with increasing intensity, as recent work on the Drosophila wing and the vertebrate brain has shown that signalling between tissues is essential for the establishment of differential affinities.

Regulation of MAPK activity in response to dietary sodium in the rat adrenal gland

Stimulation of aldosterone biosynthesis by angiotensin II (AII) is thought to be mediated via the PLC, IP3 and intracellular calcium signalling pathway. MAPK (p42/p44) is involved in cell proliferation, and is also activated by AII, but its role in the adrenal response to dietary sodium is unclear. To study the relationship between AII receptor (ATR), MAPK and PKC isoforms, PKCalpha and PKCepsilon, mature Wistar rats were maintained on low or high sodium diets for 1 week. In adrenals from animals on a sodium deplete diet, total ligand binding to both ATR subtypes decreased in the zona glomerulosa (ZG). Under these conditions, active MAPK in the ZG decreased paralleling a decrease in active PKCalpha. In the inner zones (IZ), largely reflecting medullary events, low sodium did not affect MAPK activity. However active PKCalpha decreased. In adrenals from sodium-loaded animals, type 2 ATR (AT2R) binding was reduced in the ZG, while type 1 ATR (AT1R) increased in the IZ. Active MAPK increased in ZG, as did active PKCalpha and PKCepsilon. In IZ, ERK, PKCalpha and PKCepsilon were unchanged. These results suggest that in the ZG and IZ, two different modes of MAPK regulation may exist, utilising different PKC isoforms.

The homeobox gene mirror links EGF signalling to embryonic dorso-ventral axis formation through notch activation

Recent studies in vertebrates and Drosophila melanogaster have revealed that Fringe-mediated activation of the Notch pathway has a role in patterning cell layers during organogenesis. In these processes, a homeobox-containing transcription factor is responsible for spatially regulating fringe (fng) expression and thus directing activation of the Notch pathway along the fng expression border. Here we show that this may be a general mechanism for patterning epithelial cell layers. At three stages in Drosophila oogenesis, mirror (mirr) and fng have complementary expression patterns in the follicle-cell epithelial layer, and at all three stages loss of mirr enlarges, and ectopic expression of mirr restricts, fng expression, with consequences for follicle-cell patterning. These morphological changes are similar to those caused by Notch mutations. Ectopic expression of mirr in the posterior follicle cells induces a stripe of rhomboid (rho) expression and represses pipe (pip), a gene with a role in the establishment of the dorsal-ventral axis, at a distance. Ectopic Notch activation has a similar long-range effect on pip. Our results suggest that Mirror and Notch induce secretion of diffusible morphogens and we have identified TGF-beta (encoded by dpp) as such a molecule in germarium. We also found that mirr expression in dorsal follicle cells is induced by the EGF-receptor (EGFR) pathway and that mirr then represses pip expression in all but the ventral follicle cells, connecting EGFR activation in the dorsal follicle cells to repression of pip in the dorsal and lateral follicle cells. Our results suggest that the differentiation of ventral follicle cells is not a direct consequence of germline signalling, but depends on long-range signals from dorsal follicle cells, and provide a link between early and late events in Drosophila embryonic dorsal-ventral axis formation.

mirror controls planar polarity and equator formation through repression of fringe expression and through control of cell affinities

The Drosophila eye is divided into dorsal and ventral mirror image fields that are separated by a sharp boundary known as the equator. We have previously demonstrated that Mirror, a homeodomain-containing putative transcription factor with a dorsal-specific expression pattern in the eye, induces the formation of the equator at the boundary between mirror-expressing and non-expressing cells. Here, we provide evidence that suggests mirror regulates equator formation by two mechanisms. First, mirror defines the location of the equator by creating a boundary of fringe expression at the mid-point of the eye. We show that mirror creates this boundary by repressing fringe expression in the dorsal half of the eye. Significantly, a boundary of mirror expression cannot induce the formation of an equator unless a boundary of fringe expression is formed simultaneously. Second, mirror acts to sharpen the equator by reducing the mixing of dorsal and ventral cells at the equator. In support of this model, we show that clones of cells lacking mirror function tend not to mix with surrounding mirror-expressing cells. The tendency of mirror-expressing and non-expressing cells to avoid mixing with each other is not determined by their differences in fringe expression. Thus mirror acts to regulate equator formation by both physically separating the dorsal cells from ventral cells, and restricting the formation of a fng expression boundary to the border where the dorsal and ventral cells meet.

Apoptosis: Ras to the rescue in the fly eye

Programmed cell death has seemed to be regulated in quite different ways in mammals and Drosophila. Recent results on the way Ras and downstream pathways can influence cell-death induction suggest the regulatory pathways in these distinct organisms might be more similar than was at first sight apparent.

MAP Kinase in the rat adrenal gland

The role of MAP Kinase (MAPK/ERK) in adrenal growth and steroidogenesis is unclear, though in other tissues it is known to act as an integrator of mitogenic signals originating from receptor tyrosine kinases and G-protein coupled receptors. Angiotensin II (AngII) is a major regulator of tissue differentiation and function in the adrenal, acting mainly through the AT1 receptor. Immunocytochemical and enzyme assay methods were used to study the distribution of MAPK and the action of AngII and associated antagonists saralasin and losartan(DuP753) in the rat adrenal gland. MAPK is localised in the zona glomerulosa (ZG) and the medulla, but absent from the zonae fasiculata and reticularis (ZF/ZR). Stimulation with AngII led to decreases in cytosolic and increases in nuclear MAPK activity, and its redistribution from the cytoplasm in unstimulated cells to its localisation around the nucleus, which was confirmed by immunocytochemistry. This translocation was inhibited in the presence of the AngII antagonist saralasin. Therefore, MAPK is located in the glomerulosa, where the AT1 receptor is localised and concerned with aldosterone biosynthesis, and in the medulla where MAPK activation results from AT2R activation. The results indicate the importance of the glomerulosa as the main site of cell proliferation in the adrenal cortex, and that MAPK may represent new signalling pathways related to zone function in the adrenal gland.

mirror encodes a novel PBX-class homeoprotein that functions in the definition of the dorsal-ventral border in the Drosophila eye

The Drosophila eye is composed of dorsal and ventral mirror-image fields of opposite chiral forms of ommatidia. The boundary between these fields is known as the equator. We describe a novel gene, mirror (mrr), which is expressed in the dorsal half of the eye and plays a key role in forming the equator. Ectopic equators can be generated by juxtaposing mrr expressing and nonexpressing cells, and the path of the normal equator can be altered by changing the domain of mrr expression. These observations suggest that mrr is a key component in defining the dorsal-ventral boundary of tissue polarity in the eye. In addition, loss of mrr function leads to embryonic lethality and segmental defects, and its expression pattern suggests that it may also act to define segmental borders. Mirror is a member of the class of homeoproteins defined by the human proto-oncogene PBX1. mrr is similar to the Iroquois genes ara and caup and is located adjacent to them in this recently described homeotic cluster.

The SH2-containing tyrosine phosphatase corkscrew is required during signaling by sevenless, Ras1 and Raf

The sevenless gene encodes a receptor tyrosine kinase which is required for the development of the R7 photoreceptor cell in each ommatidium of the Drosophila eye. We have previously used a sensitized genetic screen to identify mutations, designated Enhancers of sevenless (E(sev)), which affect genes that encode components of the sevenless signaling pathway. Here, we report that one of these mutations, E(sev)1Ae0P is a dominantly inhibiting allele of corkscrew, which encodes an SH2 domain-containing protein tyrosine phosphatase (Perkins et al., 1992). We show that corkscrew function is essential for sevenless signaling and that expression of a membrane-targeted form of corkscrew can drive R7 photoreceptor development in the absence of sevenless function. Furthermore, we have used the dominantly inhibiting corkscrew allele to examine the role of corkscrew during signaling by activated forms of Ras1 and Raf. Our analysis indicates that corkscrew function is still required during signaling by activated forms Ras1 and Raf proteins. These results define a function for corkscrew that is either downstream of Ras1 activation or in a parallel pathway that acts with activated Ras1/Raf to specify R7 photoreceptor development.

Construction, expression, and immunogenicity of multiple tandem copies of the Schistosoma mansoni peptide 115-131 of the P28 glutathione S-transferase expressed as C-terminal fusions to tetanus toxin fragment C in a live aro-attenuated vaccine strain of Salmonella

Genetic fusions have been constructed between the highly immunogenic but atoxic fragment C of tetanus toxin and a guest peptide, aa115-131, from the protective 28-kDa glutathione S-transferase Ag of Schistosoma mansoni. Fusions have been assembled to express one, two, four, and eight tandem copies of the peptide. The recombinant vectors have been electroporated into the nonvirulent aroA strain of Salmonella typhimurium SL3261. The fusion proteins are soluble and stably expressed in Salmonella as evaluated by Western blotting with fragment C and glutathione S-transferase antisera. Mice have been immunized i.v. with a single dose of the live recombinant salmonellae. The strains are stable in mice and elicit Ab responses directed against fragment C, as determined by enzyme-linked immunosorbent assays. Ab responses were also detected against the guest peptide. The Ab responses improved dramatically toward the aa115-131 peptide with increasing copy number, with the octameric "repitope" fusion displaying the greatest potency. This approach may represent a general strategy for eliciting immune responses against peptides in live bacterial vaccines.

Construction, expression, and immunogenicity of multiple tandem copies of the Schistosoma mansoni peptide 115-131 of the P28 glutathione S-transferase expressed as C-terminal fusions to tetanus toxin fragment C in a live aro-attenuated vaccine strain of Salmonella

Genetic fusions have been constructed between the highly immunogenic but atoxic fragment C of tetanus toxin and a guest peptide, aa115-131, from the protective 28-kDa glutathione S-transferase Ag of Schistosoma mansoni. Fusions have been assembled to express one, two, four, and eight tandem copies of the peptide. The recombinant vectors have been electroporated into the nonvirulent aroA strain of Salmonella typhimurium SL3261. The fusion proteins are soluble and stably expressed in Salmonella as evaluated by Western blotting with fragment C and glutathione S-transferase antisera. Mice have been immunized i.v. with a single dose of the live recombinant salmonellae. The strains are stable in mice and elicit Ab responses directed against fragment C, as determined by enzyme-linked immunosorbent assays. Ab responses were also detected against the guest peptide. The Ab responses improved dramatically toward the aa115-131 peptide with increasing copy number, with the octameric "repitope" fusion displaying the greatest potency. This approach may represent a general strategy for eliciting immune responses against peptides in live bacterial vaccines.

Construction, expression, and immunogenicity of the Schistosoma mansoni P28 glutathione S-transferase as a genetic fusion to tetanus toxin fragment C in a live Aro attenuated vaccine strain of Salmonella

A vector has been constructed to allow genetic fusions of guest antigens via a hinge domain to the C terminus of the highly immunogenic C fragment of tetanus toxin. A fusion has been constructed with the gene encoding the protective 28-kDa glutathione S-transferase (EC 2.5.1.18) from Schistosoma mansoni. The recombinant vector has been electroporated into the nonvirulent Salmonella typhimurium aroA live vaccine strain SL3261. The corresponding chimeric protein is stably expressed in a soluble form in Salmonella as evaluated by Western blotting with fragment C and glutathione S-transferase antisera. Mice immunized intravenously with a single dose of the live recombinant bacteria elicit antibodies to both fragment C and glutathione S-transferase as detected by enzyme-linked immunosorbent assays. Furthermore, all of the mice were solidly protected when challenged with lethal doses of either tetanus toxin or the virulent Salmonella typhimurium strain C5. Mice have also elicited antibodies to fragment C and glutathione S-transferase after oral immunization. It may be that a live trivalent vaccine against typhoid, tetanus, and schistosomiasis is feasible.

Neuronal rescue with transforming growth factor-beta 1 after hypoxic-ischaemic brain injury

Transforming growth factor-beta 1 (TGF-beta 1) mRNA is induced from 5 h to 3 days following hypoxic-ischaemic brain injury. Cell death also develops during this time suggesting that extracellular accumulation of this peptide may be involved in the processes that regulate cell loss. We examined the effect of rhTGF-beta 1 (0,2.5, 10,50 ng) injected into the cerebral lateral ventricle of rats 2 h after severe hypoxic-ischaemic brain injury. Histological outcome and B4-isolectin histochemistry were assessed 5 and 2 days, respectively following hypoxia. Treatment with 10 ng TGF-beta 1 reduced the microglia reaction (p < 0.05), the magnitude of neuronal loss (p < 0.01) and the area of cortical infarction (p < 0.05). Exogenous TGF-beta 1 given soon after hypoxic-ischaemic brain injury may have therapeutic potential and act by inhibiting the microglial reaction.

Spatial and temporal dissection of immediate and early events following cadherin-mediated epithelial cell adhesion

Cell-cell adhesion is at the top of a molecular cascade of protein interactions that leads to the remodeling of epithelial cell structure and function. The earliest events that initiate this cascade are poorly understood. Using high resolution differential interference contrast microscopy and retrospective immunohistochemistry, we observed that cell-cell contact in MDCK epithelial cells consists of distinct stages that correlate with specific changes in the interaction of E-cadherin with the cytoskeleton. We show that formation of a stable contact is preceded by numerous, transient contacts. During this time and immediately following formation of a stable contact, there are no detectable changes in the distribution, relative amount, or Triton X-100 insolubility of E-cadherin at the contact. After a lag period of approximately 10 min, there is a rapid acquisition of Triton X-100 insolubility of E-cadherin localized to the stable contact. Significantly, the total amount of E-cadherin at the contact remains unchanged during this time. The increase in the Triton X-100 insoluble pool of E-cadherin does not correlate with changes in the distribution of actin or fodrin, suggesting that the acquisition of the Triton X-100 insolubility is due to changes in E-cadherin itself, or closely associated proteins such as the catenins. The 10 minute lag period, and subsequent prompt and localized nature of E-cadherin reorganization indicate a form of signaling is occurring.

Initial experience of laparoscopic cholecystectomy in a district hospital

Fifty-five consecutive unselected patients were submitted for laparoscopic cholecystectomy, and the procedure completed laparoscopically in fifty cases. The outcome is presented with particular reference to the duration of surgery, postoperative pain and nausea, the length of hospital stay and the time taken to recover normal activities. This technique is shown to have major advantages over conventional gallbladder surgery for the majority of patients.

A high-affinity receptor for urokinase plasminogen activator on human keratinocytes: characterization and potential modulation during migration

Low passage cultures of normal human keratinocytes produce several components of the plasminogen activator/plasmin proteolytic cascade, including urokinase plasminogen activator (uPA), tissue plasminogen activator (tPA), and two specific inhibitors. Studies here presented demonstrate that these cells also contain a high-affinity (Kd = 3 x 10(-10) M) plasma membrane-binding site for uPA. High molecular weight uPA, either as the single-chain precursor or two-chain activated form, bound to the receptor; however, low molecular weight (33 kD) uPA, tPA, or epidermal growth factor did not compete for binding, demonstrating specificity. Acid treatment, which removed endogenous uPA from the receptor, was required to detect maximal binding (45,000 sites per cell). To investigate the possibility that the uPA receptor on keratinocytes may be involved in epithelial migration during wound repair, cultures were wounded and allowed to migrate into the wounded site. Binding sites for uPA were localized by autoradiographic analysis of 125I-uPA binding as well as by immunocytochemical studies using anti-uPA IgG. With both techniques uPA binding sites were detected selectively on the plasma membrane of cells at the leading edge of the migrating epithelial sheet. This localization pattern suggests that uPA receptor expression on keratinocytes may be coupled to cell migration during cutaneous wounding.

Novel function of the cell adhesion molecule uvomorulin as an inducer of cell surface polarity

Na+,K(+)-ATPase has distinctly different distributions in mesenchymal cells, where it has an unrestricted distribution over the entire cell surface, compared with polarized epithelial cells, where it is restricted to the basal-lateral membrane domain. The generation of this restricted distribution is important in mesenchyme to epithelia conversion in development and the function of transporting epithelia, but the mechanisms involved are unknown. Here we show that expression of the epithelial CAM uvomorulin in transfected fibroblasts is sufficient to induce a redistribution of Na+,K(+)-ATPase to sites of uvomorulin-mediated cell-cell contacts, similar to that in polarized epithelial cells. This restricted distribution of Na+,K(+)-ATPase occurs in the absence of tight junctions but coincides with the reorganization of the membrane cytoskeleton. The results indicate a direct role for CAMs as inducers of cell surface polarity of selective cytoplasmic and membrane proteins.

Chemoattractant-stimulated polymorphonuclear leukocytes contain two populations of actin filaments that differ in their spatial distributions and relative stabilities

Chemoattractants stimulate actin polymerization in lamellipodia of polymorphonuclear leukocytes. We find that removal of chemoattractant results in rapid (within 10 s at 37 degrees C) and selective depolymerization of the F-actin located in lamellipodia. Addition of 10 microM cytochalasin B, in the presence of chemoattractant, also resulted in rapid and selective depolymerization of lamellar F-actin. The elevated F-actin level induced by chemoattractant rapidly returns to the level present in unstimulated cells after (a) a 10-fold decrease in chemoattractant concentration; (b) the addition of 10 microM cytochalasin B; or (c) cooling to 4 degrees C. The F-actin levels of unstimulated cells are only slightly affected by these treatments. Based on the similar effects of cytochalasin addition and chemoattractant dilution, it is likely that both treatments result in actin depolymerization from the pointed ends of filaments. Based on our results we propose that chemoattractant-stimulated polymorphonuclear leukocytes contain two distinct populations of actin filaments. The actin filaments within the lamellipodia are highly labile and in the continued presence of chemoattractant these filaments are rapidly turning over, continually polymerizing at their plus (barbed) ends, and depolymerizing at their minus ends. In contrast, the cortical F-actin filaments of both stimulated and unstimulated cells are differentially stable.

Exaggerated renal thromboxane and prostaglandin release by angiotensin II in suprarenal aortic coarctation hypertension

The ability of angiotensin II and arachidonic acid to release immunoreactive prostaglandins into venous and ureteral effluents of rabbit isolated perfused kidneys was examined 7 days after suprarenal aortic coarctation (SRAC) or sham operation (SHAM). Renal vascular responses to angiotensin II were significantly enhanced in SRAC and accompanied by an enhanced venous efflux of bioassayable prostaglandins. Angiotension II-induced release of immunoreactive PGE2, PGF2 alpha, 6-keto PGF1 alpha and TxB2 into the venous effluent was exaggerated in SRAC. As angiotensin II did not stimulate TxB2 efflux in the SHAM group the induction of TxB2 release by SRAC is particularly noteworthy. These changes in eicosanoid release in response to angiotensin II were not mimicked by arachidonic acid administration. These results suggest that in renovascular hypertension angiotensin II-induced prostaglandin release is primarily augmented in the vascular compartment and is consistent with the sensitivity of renal function to cyclooxygenase inhibitors in renovascular hypertension.

SOD prevents damage and attenuates eicosanoid release in a rabbit model of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) was produced in anesthetized rabbits by transmural injection of intestinal loops with an acidified solution of casein and calcium gluconate, mimicking the luminal milieu of afflicted neonates. Intravenous infusion of superoxide dismutase (SOD) 15 min after NEC induction prevented intestinal damage. In ex vivo perfused intestinal loops, we determined the sites of eicosanoid release and their contribution to the vascular effects of N-formyl-methionyl-leucyl-phenylalanine (fMLP) and platelet-activating factor (PAF) in damaged and SOD-salvaged intestine. The vascular effluent was the primary site of stimulated eicosanoid release. The vascular responses to fMLP (vasoconstriction) and PAF (vasodilation) were not altered by SOD, although vascular resistance was higher in the SOD group. SOD treatment attenuated 1) transmural fluid shifts in ex vivo perfused intestinal preparations, an index of vascular permeability, 2) fMLP-induced prostaglandin E2, 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha), and leukotriene B4 (LTB4) release, and 3) PAF-induced release of 6-keto-PGF1 alpha and LTB4. Stimulated thromboxane B2 release was not altered by SOD. Thus NEC can be established by a luminal insult that causes local generation of free radicals and exaggerated release of prostaglandins and leukotrienes.

Contribution of oxygen-derived free radicals to experimental necrotizing enterocolitis

Oxygen-derived free radicals, particularly superoxide anion, are considered important mediators of intestinal injury induced by ischemia/reperfusion based on the protective effects of superoxide dismutase and allopurinol. A role for free radicals was investigated in a model of necrotizing enterocolitis (NEC) which was initiated by a luminal, as opposed to a vascular, insult. Intestinal loops of weanling rabbits received either saline (control loops) or a solution of 10 mg/ml casein and 50 mg/ml calcium gluconate acidified to pH 4 with proprionic acid (treated loops). When the animals were sacrificed 3 hours later, severe damage was noted in the treated loops, which included blunting of villi and edema, with all animals surviving. At 16 hours only 5 of 8 rabbits survived, and 3 had hemorrhagic necrosis. Control loops were normal in each case. Intravenous infusion of superoxide dismutase (4 mg/kg/hr), commencing 15 minutes after NEC induction, totally prevented intestinal injury. On the other hand, pretreatment with allopurinol, an inhibitor of xanthine oxidase, for 2 days (30 and 60 mg/kg by mouth) was not protective against intestinal damage. A cellular infiltration in treated loops was not histologically evident in the majority of animals at 3 hours after treatment, a finding confirmed by the minimal accumulation of 111In-labeled leukocytes in damaged and intact intestinal tissue. These results suggest that superoxide generated locally from sources other than xanthine oxidase play a critical and early role in experimental NEC and that superoxide dismutase may prove to be an effective therapy in this devastating neonatal disease.

Renal prostaglandin efflux induced by vasopressin, dDAVP and arachidonic acid: contrasting profile and sites of release

Prostaglandin (PG) efflux into ureteral (UE) and venous effluents (VE) of rabbit isolated perfused kidneys was determined by superfusion bioassay and radioimmunoassay (RIA), in response to injections of arginine-vasopressin (AVP), the non-pressor vasopressin analogue 1-deamino-8-D-arginine vasopressin (dDAVP) and arachidonic acid (AA). dDAVP (10-1000 ng) failed to stimulate renal PG release, whereas AVP (10-100 ng) and AA (10-50 micrograms) caused a dose-dependent release of PG. AVP evoked PG release into both effluents with release into the VE greater than UE at high doses. In contrast, PG release by AA was almost exclusively into the VE. Indomethacin (2.8 X 10(-6) mol/l) abolished AVP- and AA-induced PG efflux in both effluents, and vasodepressor responses to AA. PGE2 was the predominant PG released in response to AVP in both effluents whereas AA released primarily 6-keto-PGF1 alpha. The contrasting sites and profile of released PG suggest that exogenous AA and AVP stimulate the release of PG from different regions/cell types within the kidney.

Compartmental prostaglandin release by angiotensin II and arginine-vasopressin in rabbit isolated perfused kidneys

The compartmental effects of angiotensin II (AII) and arginine-vasopressin (AVP) on renal prostaglandin (PG) formation were studied in the isolated perfused kidney of the rabbit by superfusion bioassay of venous and ureteral effluents (VE and UE) and radioimmunoassay (RIA). Comparable results were obtained with either bioassay or RIA when used to quantitate renal PG release. The effects on PG release into the VE were similar for AII and AVP, as were their pressor responses. However, their effects on PG release into the UE differed markedly. AII resulted in a 6-fold greater urinary efflux than venous of bioassayable PGs, whereas AVP-induced PG release into UE was slightly less than PG efflux into the VE at all doses of the peptide. The profile of released PGs varied according to the sampling source (VE or UE). Moreover, each peptide released a similar profile of PGs at all doses, i.e. UE PGE2 greater than PGF2 alpha greater than 6-keto PGF1 alpha; VE PGE2 greater than 6-keto PGF1 alpha greater than PGF2 alpha (TxB2 was not detected in either effluent). Thus, renal vascular PG release is similar for the vasoactive peptides, AII and AVP, whereas the urinary efflux of PGs is considerably greater in response to AII.