High-resolution distance mapping in rhodopsin reveals the pattern of helix movement due to activation

Site-directed spin labeling has qualitatively shown that a key event during activation of rhodopsin is a rigid-body movement of transmembrane helix 6 (TM6) at the cytoplasmic surface of the molecule. To place this result on a quantitative footing, and to identify movements of other helices upon photoactivation, double electron-electron resonance (DEER) spectroscopy was used to determine distances and distance changes between pairs of nitroxide side chains introduced in helices at the cytoplasmic surface of rhodopsin. Sixteen pairs were selected from a set of nine individual sites, each located on the solvent exposed surface of the protein where structural perturbation due to the presence of the label is minimized. Importantly, the EPR spectra of the labeled proteins change little or not at all upon photoactivation, suggesting that rigid-body motions of helices rather than rearrangement of the nitroxide side chains are responsible for observed distance changes. For inactive rhodopsin, it was possible to find a globally minimized arrangement of nitroxide locations that simultaneously satisfied the crystal structure of rhodopsin (Protein Data Bank entry 1GZM), the experimentally measured distance data, and the known rotamers of the nitroxide side chain. A similar analysis of the data for activated rhodopsin yielded a new geometry consistent with a 5-A outward movement of TM6 and smaller movements involving TM1, TM7, and the C-terminal sequence following helix H8. The positions of nitroxides in other helices at the cytoplasmic surface remained largely unchanged.     

Adjuvant immunotoxin therapy with anti-B4-blocked ricin after autologous bone marrow transplantation for patients with B-cell non- Hodgkin's lymphoma

Anti-B-blocked ricin (anti-B4-bR) combines the specificity of the anti- B4 (CD19) monoclonal antibody with the protein toxin "blocked ricin." In blocked ricin, affinity ligands are attached to the ricin B-chain to attenuate its lectin binding capacity. In a phase I trial, Anti-B4-bR was administered by 7-day continuous infusion to 12 patients in complete remission after autologous bone marrow transplantation (ABMT) for relapsed B-cell non-Hodgkin's lymphoma (NHL). Patients were treated at 20, 40, and 50 micrograms/kg/d for 7 days. Potentially therapeutic serum levels could be sustained for 3 to 4 days. The maximum tolerated dose was 40 micrograms/kg/d for 7 days (total 280 micrograms/kg). The dose-limiting toxicities were reversible grade IV thrombocytopenia and elevation of hepatic transaminases. Mild capillary leak syndrome was manifested by hypoalbuminemia, peripheral edema (4 patients), and dyspnea (1 patient). Anti-immunotoxin antibodies developed in 7 patients. Eleven patients remain in complete remission between 13 and 26 months post-ABMT (median 17 months). These results show that Anti-B4- bR can be administered with tolerable, reversible toxicities to patients with B-cell NHL in complete remission following ABMT.     

Strong density- and diversity-related effects help to maintain tree species diversity in a neotropical forest

Intraspecific density-dependent effects in the Barro Colorado Island (Panama) study area are far stronger, and involve far more species, than previously had been suspected. Significant effects on recruitment, many extremely strong, are seen for 67 out of the 84 most common species in the plot, including the 10 most common. Significant effects on the intrinsic rate of increase are seen in 54 of the 84 species. These effects are far more common than interspecific effects, and are predominantly of the type that should maintain tree diversity. As a result, the more diverse an area in the forest is, the higher is the overall rate of increase of the trees in that area, although sheer crowding has by itself a negative effect. These findings are consistent with, but do not prove, an important role for host-pathogen interactions (defined broadly) in the maintenance of diversity. Ways are suggested by which to test host-pathogen models and competing models.     

Culture of autologous bone marrow in diffusion chambers: effect of host irradiation

Autologous bone marrow (BM) cells were cultured in diffusion chambers (DC) implanted into whole-body irradiated, non-irradiated, or sham- irradiated goats. Proliferation was apparent in DC implanted in both irradiated and nonirradiated goats. However, cells in DC cultured in irradiated hosts increased in number beginning earlier, proceeded at a faster rate, and reached higher numbers than in DC in nonirradiated hosts. Growth enhancement could not have occurred as a result of radiation-induced immunosuppression in autologous hosts. The nonirradiated "target cells" in the DC therefore constituted an indicator system for stimulatory or inhibitory substances in the host. The simultaneous increase in the number of granulocytes in peripheral blood and in DC of irradiated hosts was paralleled by an initial rise in serum colony-stimulating factor (CSF). A second, prolonged period of severe granulocytopenia following irradiation of the host correlated with high levels of serum CSF. Increased numbers of megakaryocytes were seen in DC as thrombocytopenia developed in the irradiated host. DC erythropoiesis disappeared rapidly in nonirradiated goats; however, in DC of irradiated goats, the number of erythrocytic precursors increased exponentially during ablation of host erythroid marrow. Anemia did not develop in the host during the culture period. Proliferation of mononuclear cells in DC was markedly stimulated by irradiation of the host. Proliferation of macrophages appeared independent of host treatment. These observations provide strong evidence for diffusion of specific and/or nonspecific humoral hematopoietic stimulators from the host into the DC. This stimulation appears to be elicited and/or intensified by irradiation of the host.     

A retrospective analysis of the long-term effect of splenectomy on late infections, graft-versus-host disease, relapse, and survival after allogeneic marrow transplantation for chronic myelogenous leukemia

The present study was performed as a retrospective analysis of the role of pretransplant splenectomy to determine the incidence of late bacterial infections, acute and chronic graft-versus-host disease (GVHD), relapse, and survival among 358 patients receiving HLA- identical marrow grafts for chronic myelogenous leukemia. Sixty-eight (19%) of the 358 patients had undergone splenectomy before transplantation. There was a trend towards more grade II-IV acute GVHD among splenectomized patients, but this was not significant in the multivariate analysis. The incidence of chronic GVHD was similar for splenectomized and nonsplenectomized patients. Late infectious complications did not significantly differ between splenectomized and control patients (rates per patient year were 0.16 and 0.14, respectively). The overall risk of leukemic relapse was significantly increased for splenectomized patients (56% v 32% for controls, P = .001) and control patients with splenomegaly (P < .0001). Splenectomy and splenomegaly remained significant and independent hazards for relapse in the multivariate analysis (hazard ratio [HR], 1.82, P = .029; and HR, 1.49, P = .002; respectively). Relapse was also increased in patients with advanced disease (HR, 2.95; P = .0001), in patients with T-cell-depleted marrow (HR, 4.51; P = .0001), and in the female donor and male recipient combination (HR, 1.74; P = .044). Patients with splenectomy had an increased overall mortality (HR, 1.18), but this was not statistically significant in the multivariate analysis. In summary, our study showed no significant influence of splenectomy on late posttransplant infections, acute or chronic GVHD, or overall survival. There was no evidence that splenectomy decreased recurrence of chronic myelogenous leukemia.     

Biosynthetic defect in platelet glycoprotein IX mutants associated with Bernard-Soulier syndrome

To evaluate the biosynthetic basis for decreased glycoprotein (GP) Ib- IX expression resulting from GP IX mutations described in three siblings with Bernard-Soulier syndrome, we introduced each mutation into the cDNA for GP IX by site-directed mutagenesis (GP IX Asp21 --> Gly and GP IX Asn45 --> Ser) and examined the associations of the mutants with the two other subunits of the GP Ib-IX complex in transfected cells. Unlike wild-type GP IX, neither of the mutants was able to increase GP Ib expression on the cell surface, either when transfected into Chinese hamster ovary (CHO) alpha beta cells or when cotransfected with GP Ib alpha and GP Ib beta into wild-type CHO cells. We also evaluated whether cotransfecting wild-type or mutant GP IX with GP Ib beta would result in the appearance of GP IX on the surface of the transfected cells; the wild-type protein was detected on the surface of the cells, whereas neither mutant reached the cell surface in appreciable quantities. Immunofluorescence microscopy of permeabilized cells revealed that the failure to express mutant GP IX on the cell surface did not result from failure to synthesize the polypeptide. Both mutants were detected in intracellular compartments, albeit at lower levels than the wild-type polypeptide (the fluorescence of cells expressing the GP IX Asp21 --> Gly was consistently the lowest). Direct evidence that the mutants associate poorly with Gp Ib beta was obtained of 35S-labeled cells transiently expressing GP Ib beta and wild-type or mutant GP IX. The amount of GP IX coprecipitated with GP Ib beta was greatly diminished in cells expressing either mutant. These findings suggest an important role for the conserved leucine-rich motif of GP IX in the association of this polypeptide with GP Ib beta and provide further evidence for the importance of GP IX in the stability of the GP-Ib-IX complex.     

Impact of U.S. Citizenship status on cancer screening among immigrant women

OBJECTIVES: We evaluated the relationship between U.S. citizenship status and the receipt of Pap smears and mammograms among immigrant women in California. DESIGN: Cross-sectional study using data from the 2001 California Health Interview Survey. PATIENTS/PARTICIPANTS: Noninstitutionalized, civilian women, aged 18 years and older living in California. MEASUREMENTS AND MAIN RESULTS: We analyzed data from the 2001 California Health Interview Survey and used logistic regression models to adjust for sociodemographic factors and for access and utilization of health services. After adjusting we found that U.S. citizen immigrants were significantly more likely to report receiving a Pap smear ever (adjusted prevalence ratio [aPR], 1.05; 95% confidence interval [CI], 1.01 to 1.08), a recent Pap smear (aPR, 1.07; 95% CI, 1.03 to 1.11), a mammogram ever (aPR, 1.17; 95% CI, 1.12 to 1.21), and a recent mammogram (aPR, 1.38; 95% CI, 1.26 to 1.49) as compared to immigrants who are not U.S. citizens. Also associated with receiving cancer screening were income, having a usual source of care, and having health insurance. Hispanic women were more likely to receive Pap smears as compared to whites and Asians. CONCLUSIONS: Not being a U.S. citizen is a barrier to receiving cervical and breast cancer screening. Additional research is needed to explore causal factors for differences in cancer screening rates between citizens and noncitizens.     

Locations of Arg-82, Asp-85, and Asp-96 in helix C of bacteriorhodopsin relative to the aqueous boundaries.

The amino acids Asp-96, Asp-85, and Arg-82, which are important for proton transport by bacteriorhodopsin, are located in helix C. Site-directed spin labeling has been used to map their positions relative to the aqueous boundaries of the membrane. Selected amino acids in helix C, in the B-C loop on the extracellular side, and in the C-D loop on the intracellular side of the membrane were replaced by cysteine residues and derivatized with a sulfhydryl-specific spin label. The topographical locations of the nitroxide groups were determined by electron paramagnetic resonance spectroscopy in terms of both motional restriction and collision frequencies with dissolved molecular oxygen and membrane-impermeable chromium oxalate. The results show that in dark-adapted bacteriorhodopsin, Tyr-79 is at the aqueous-protein interface on the extracellular side of helix C whereas Val-101 is close to the aqueous boundary on the intracellular side of the protein. Further, Asp-96 is estimated to be within 7 A of the aqueous medium on the intracellular side of the membrane, whereas Arg-82 and Asp-85 are within 5 A and 9 A, respectively, of the aqueous boundary on the extracellular side of the membrane.     

Von Willebrand factor in the vessel wall mediates platelet adherence

A monoclonal antibody directed against the von Willebrand factor moiety (vWF) of factor VIII-von Willebrand factor (FVIII-vWF), which blocks ristocetin-induced platelet aggregation as well as the binding of FVIII- vWF to platelets in the presence of ristocetin, inhibited platelet adherence to human artery subendothelium when present in normal flowing blood. This monoclonal antibody, CLB-RAg 35, inhibited platelet adherence as a function of the shear rate. At wall shear rates below 500 s-1, platelet adherence was not affected, but at higher shear rates platelet adherence was gradually inhibited, reaching an average of 11% of the normal value at 2,500 s-1. Indirect immunofluorescence established the reactivity of CLB-RAg 35 with vWF present in artery subendothelium. Pretreatment of normal vessel walls with this antibody inhibited adherence of platelets in blood from a patient with severe homozygous von Willebrand's disease and in blood from normal individuals. The inhibition was shear-rate dependent and significant at high shear rates (2,500 s-1). By adding increasing amounts of purified FVIII-vWF to normal blood, the inhibition was gradually overcome. These data indicate that vWF present in the vessel wall contributes appreciably to platelet adherence. At high wall shear rates, platelet adherence is mediated virtually completely by both plasma FVIII-vWF and vWF in the vessel wall. At low wall shear rates (below 500 s-1), platelet adherence occurs independent of FVIII-vWF in plasma and vWF in the vessel wall.     

Sustained human hematopoiesis in immunodeficient mice by cotransplantation of marrow stroma expressing human interleukin-3: analysis of gene transduction of long-lived progenitors

We have developed a novel cotransplantation system in which gene- transduced human CD34+ progenitor cells are transplanted into immunodeficient (bnx) mice together with primary human bone marrow (BM) stromal cells engineered to produce human interleukin-3 (IL-3). The IL- 3-secreting stroma produced sustained circulating levels of human IL-3 for at least 4 months in the mice. The IL-3-secreting stroma, but not control stroma, supported human hematopoiesis from the cotransplanted human BM CD34+ progenitors for up to 9 months, such that an average of 6% of the hematopoietic cells removed from the mice were of human origin (human CD45+). Human multilineage progenitors were readily detected as colony-forming units from the mouse marrow over this time period. Retroviral-mediated transfer of the neomycin phosphotransferase gene or a human glucocerebrosidase cDNA into the human CD34+ progenitor cells was performed in vitro before cotransplantation. Human multilineage progenitors were recovered from the marrow of the mice 4 to 9 months later and were shown to contain the transduced genes. Mature human blood cells marked by vector DNA circulated in the murine peripheral blood throughout this time period. This xenograft system will be useful in the study of gene transduction of human hematopoietic stem cells, by tracing the development of individually marked BM stem cells into mature blood cells of different lineages.