Design, synthesis, and biological evaluation of simplified alpha-keto heterocycle, trifluoromethyl ketone, and formyl substituted folate analogues as potential inhibitors of GAR transformylase and AICAR transformylase

A series of simplified alpha-keto heterocycle, trifluoromethyl ketone, and formyl substituted folate analogues lacking the benzoylglutamate subunit were prepared and examined as potential inhibitors of glycinamide ribonucleotide transformylase (GAR Tfase) and aminoimidazole carboxamide transformylase (AICAR Tfase).     

Liver endothelium mediates the uptake of iron-transferrin complex by hepatocytes

We have previously shown that in the liver, transferrin (TF) receptors are limited to endothelial cells, and hepatocytes and Kupffer cells do not have TF receptors. To study the transport of iron into hepatocytes, we fractionated liver cell suspensions into endothelium and hepatocyte fractions. At 4 degrees C liver (but not umbilical cord) endothelium bound Fe-TF with a saturable kinetics. At 37 degrees C, the endothelial uptake was followed by its gradual release. Transendothelial transport of TF was visually demonstrated by perfusion of liver using colloidal gold-labeled TF. The released Fe-TF acquired the potential for binding to fresh target hepatocytes and binding was not inhibited by excess cold TF but was inhibitable by asialofetuin, suggesting galactosyl receptors and not TF receptors as a recognition mechanism. Isoelectrofocusing of the supernate after preincubation for 90 min at 37 degrees C with endothelial cells, demonstrated the presence of a newly generated band which co-migrated with asialotransferrin. We conclude that Fe-TF is initially removed by liver endothelium where it is modified probably by desialation to expose the galactosyl residues of the glycoproteins. The modified molecule is subsequently released and recognized by hepatocytes through a TF receptor-independent mechanism which may involve galactosyl receptors of hepatocytes. The findings indicate a key role for endothelium in the transport of Fe-TF into the liver and may suggest a physiological function for galactosyl receptors on hepatocyte surface.     

OTO method for preservation of actin filaments in electron microscopy

Osmium tetroxide, commonly used as a fixative in electron microscopy, can destroy actin filaments. Thiocarbohydrizide (TCH) is a bipolar substance that binds to the osmium. By sandwiching TCH between two phases of osmium treatment, tissue exposure to osmium could be minimized without destroying actin filaments. The contrast of osmophilic components of cells was also enhanced.     

Membrane-associated chondroitin sulfate proteoglycan and fibronectin mediate the binding of hemopoietic progenitor cells to stromal cells.

The initial step in hemopoiesis is the binding of progenitor cells to stroma. What mediates this binding at the molecular level is not entirely clear. We have previously reported that the cell line FDCP-1, a factor-dependent hemopoietic progenitor cell, actively synthesizes a membrane-associated chondroitin sulfate (CS) proteoglycan (MA-PG) which is unstable. After the binding of the progenitor cell to stromal, the stability of the MA-PG is enhanced, suggesting its involvement in the binding of progenitor cells to the stroma. Since stromal cells possess pericellular fibronectin (FN), we examined the possibility that binding to stromal cells may involve interactions between MA-PG of FDCP-1 on the one side and pericellular FN in stromal cells on the other side. To examine this hypothesis, we developed a cell adherence assay to measure the binding of FDCP-1 cells to a monolayer of stromal cells or to FN-coated dishes. Cell binding was inhibited by a monoclonal antibody against CS as well as by free CS and heparin, suggesting the involvement of MA-PG in the binding. Pretreatment of FDCP-1 cells with chondroitinase ABC, which selectively removes the CS portion of the MA-PG, also affects binding to the stromal cells. The binding was also inhibited by a pentapeptide (GRGDS) which competes with the cell-binding domain of FN as well as by a monoclonal antibody anti-FN. We conclude that interactions between MA-PG and a putative integrin-like molecule in FDCP-1 and the heparin and the cell binding domains in pericellular FN in the stromal cells contribute to the stabilization of progenitor-stromal cell binding which originally comes about by homing receptors of progenitor cells.     

Ceruloplasmin receptors in liver cell suspensions are limited to the endothelium

The interaction of ceruloplasmin (CP) with isolated liver cell suspensions was studied using 125I-labeled and latex minibead-derivatized CP. Fractionation of liver cell suspensions was done using metrizamide gradient centrifugation. In crude liver cell suspensions only endothelial cells, but not hepatocytes and Kupffer cells bound the minibead probe. The binding was specific and inhibited by excess native CP. These results were confirmed using 125I-CP combined with cell fractionation technique. Kinetic data, obtained from the latter system, indicated a dissociation constant (Kd) of 1 X 10(-7) M and the number of receptors to be 5.7 X 10(5) per endothelial cell. The exclusive binding of CP to liver endothelium suggests that this cell may mediate the hepatocytes uptake of CP and is, therefore, a crucial element of the tissue-blood barrier.     

Structural and functional conservation of the human homolog of the Schizosaccharomyces pombe rad2 gene, which is required for chromosome segregation and recovery from DNA damage.

The rad2 mutant of Schizosaccharomyces pombe is sensitive to UV irradiation and deficient in the repair of UV damage. In addition, it has a very high degree of chromosome loss and/or nondisjunction. We have cloned the rad2 gene and have shown it to be a member of the Saccharomyces cerevisiae RAD2/S. pombe rad13/human XPG family. Using degenerate PCR, we have cloned the human homolog of the rad2 gene. Human cDNA has 55% amino acid sequence identity to the rad2 gene and is able to complement the UV sensitivity of the rad2 null mutant. We have thus isolated a novel human gene which is likely to be involved both in controlling the fidelity of chromosome segregation and in the repair of UV-induced DNA damage. Its involvement in two fundamental processes for maintaining chromosomal integrity suggests that it is likely to be an important component of cancer avoidance mechanisms.     

A deletion/insertion leading to the generation of a direct repeat as a result of slipped mispairing and intragenic recombination in the factor VIII gene

A deletion/insertion in the human factor VIII gene was found in a patient with severe hemophilia A; 316 bp were removed, viz., those enclosing part of intron 15 and the first 7 bp of exon 16. In addition to the deletion, 6 bp were added to the deletion breakpoints; this resulted in the duplication of an existing 13-bp unit. Thus, an overlapping 13-bp direct repeat was generated at the deletion junction. Moreover, the deleted fragment itself was flanked by two homologous 6-bp sequences, one unit being lost by the deletion. A combination of slipped mispairing during replication and an intragenic recombination is discussed to describe this deletion/insertion process. Received: 4 January 1999 / Accepted: 22 March 1999