von Willebrand disease in the RIIIS/J mouse is caused by a defect outside of the von Willebrand factor gene.

An animal model for human type I von Willebrand disease (vWD) has been previously described in the inbred mouse strain RIIIS/J. Murine vWD is characterized by a prolonged bleeding time, normal von Willebrand factor (vWF) multimer distribution, autosomal dominant inheritance, and proportionately decreased plasma vWF antigen, ristocetin cofactor, and factor VIII (FVIII) activities. To study the molecular genetics of murine vWD, a portion of the vWF gene surrounding exon 28 was cloned, sequenced, and used to develop two informative DNA sequence polymorphisms for rapid genotyping by DNA polymerase chain reaction. RIIIS/J mice were crossed with PWK/Ph mice, an inbred line of Mus musculus musculus, and the F1 progeny backcrossed to the parental PWK/Ph strain. vWF antigen levels in F1 mice were not significantly different from the parental RIIIS/J strain but were markedly decreased compared with the parental PWK/Ph mice. Genetic linkage analysis of 104 backcross progeny showed no correlation between vWF antigen level and vWF genotype. These data indicate that murine vWD is caused by a defect at a novel genetic locus, distinct from the murine vWF gene. The distribution of vWF antigen levels among backcross progeny suggests the presence of one major dominant vWD gene in the RIIIS/J mouse with possible modifying contributions from one or more additional minor loci. These observations may provide new insights into the molecular basis and variable expressivity of human vWD.

Impaired intracellular transport produced by a subset of type IIA von Willebrand disease mutations.

Type IIA von Willebrand disease (vWD) results from abnormalities in von Willebrand factor (vWF) characterized by absence of plasma high molecular weight (HMW) vWF multimers. In this report, 5 distinct point mutations were identified in 6 Type IIA vWD families. A total of 7 mutations, all clustered within a 124-amino acid segment of the vWF A2 domain, now account for 9 of a panel of 11 Type IIA families. In COS-7 cells, 3 single amino acid substitutions, Val844----Asp, Ser743----Leu, and Gly742----Arg, impaired the transport of vWF multimers between the endoplasmic reticulum and the Golgi complex, with more profound effects on the secretion of HMW multimers than lower molecular weight forms. In contrast, 2 substitutions, Arg834----Trp and Gly742----Glu, resulted in secretion of HMW multimers similar to wild-type vWF. The vWF structure observed within patient platelets correlated closely with the synthesis pattern seen for the corresponding mutants in COS-7 cells. These findings demonstrate that structural alterations within the A2 domain of vWF can produce the characteristic phenotype of Type IIA vWD via two distinct molecular mechanisms.

The molecular defect in type IIB von Willebrand disease. Identification of four potential missense mutations within the putative GpIb binding domain.

Type IIB von Willebrand Disease (vWD) is characterized by the selective loss of large von Willebrand Factor (vWF) multimers from plasma, presumably due to their increased reactivity with platelets and subsequent clearance from the circulation. Using the PCR, one of a panel of four potential missense mutations was identified in each of the 14 patients studied from 11 unrelated families. None of these substitutions was encountered in a large panel of normal DNAs. These changes all represent C----T transitions at CpG dinucleotides, proposed "hot spots" for mutation in the human genome. The four resulting amino acid substitutions, Arg543----Trp, Arg545----Cys, Val553----Met, and Arg578----Gln, are all clustered within the GpIb binding domain of vWF. Disruption of this latter functional domain may explain the pathogenesis of Type IIB vWD. By sequence polymorphism analysis, the Arg543----Trp substitution was shown to have occurred as at least two independent mutational events. This latter observation, along with the identification of mutations in all 14 patients studied and their localization to the GpIb binding domain, all strongly suggest that these substitutions represent the authentic defects responsible for Type IIB vWD. This panel of mutations may provide a useful diagnostic tool for the majority of patients with Type IIB vWD.

Analysis of the relationship of von Willebrand disease (vWD) and hereditary hemorrhagic telangiectasia and identification of a potential type IIA vWD mutation (IIe865 to Thr).

Reports of families with members affected with both von Willebrand disease (vWD) and hereditary hemorrhagic telangiectasia (HHT) suggest a possible relationship between these two disorders. vWD, the most common inherited bleeding disorder in humans, is due to either a quantitative or qualitative defect in von Willebrand factor (vWF). The gene for vWF has been cloned and mapped to chromosome 12 (12p12----12pter). HHT, an uncommon inherited bleeding disorder, is characterized by malformed, dilated, fragile blood vessels. The chromosomal location of the gene for HHT is unknown. We studied two families by RFLP analysis to determine whether there is a molecular basis for the association of vWD and HHT. Family A is affected with both type IIA vWD and HHT; family B is affected with HHT alone. Linkage of HHT to the vWF gene was not detected, and vWF was ruled out as a candidate gene for HHT. The vWF gene was found to be tightly linked to type IIA vWD in family A (lod score 3.61 at recombination fraction .00). By PCR and DNA sequence analysis of vWF exon 28, a single T----C transition resulting in the substitution of Thr for Ile865 was identified. This substitution is located immediately adjacent to two previously identified type IIA vWD mutations.

Purification of Thermus aquaticus DNA polymerase expressed in Escherichia coli.

DNA polymerase from Thermus aquaticus has become a common reagent in molecular biology because of its utility in DNA amplification and DNA sequencing protocols. A simplified method is described here for isolating the recombinant Taq enzyme after overproduction in Escherichia coli. Purification requires 8 to 10 h and entails heat treating and clearing the E. coli lysate, followed by precipitation of the enzyme with polyethyleneimine and elution from Bio Rex 70 ion exchange resin in a single salt step. The resulting enzyme preparation contains a single, nearly homogeneous protein consistent with the previously established size of the Taq DNA polymerase in a yield of 40-50 mg of protein per liter of cell culture.

Chemoattractants stimulate phosphatidylinositol-4-phosphate kinase in human polymorphonuclear leukocytes.

Chemoattractant receptor-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) by phospholipase C is instrumental for leukocyte activation. Previous studies have demonstrated that chemoattractant treatment of intact polymorphonuclear leukocytes (PMN) causes a transient decrease in PIP2 due to phospholipase C activation, followed by an increase in cellular PIP2 levels. The present study determined whether chemoattractants altered the activities of the two enzymes responsible for the synthesis of PIP2, phosphatidylinositol kinase, and phosphatidylinositol-4-phosphate (PIP) kinase. Incubation of intact PMN with the N-formylated peptide chemoattractant formyl-methionyl-leucyl-phenylalanine at 37 degrees C caused a rapid (3 min), 2-fold stimulation of PIP kinase activity isolated from a particulate membrane fraction. The increase in PIP kinase was dose-dependent for a variety of N-formylated chemoattractants as well as leukotriene B4. Lineweaver-Burk analysis showed that the Vmax of PIP kinase was increased 2-fold by formyl-methionyl-leucyl-phenylalanine, without a significant change in the apparent Km of the enzyme for ATP. Phosphatidylinositol kinase was, however, not altered by any chemoattractants tested. Nonchemotactic activators of the oxidative burst in leukocytes such as phorbol myristate acetate and ionophore A23187 did not significantly alter PIP kinase, suggesting a specificity for chemotactic agents. These findings demonstrate direct, chemoattractant-induced stimulation of PMN PIP kinase which may serve to replenish the important phospholipid, PIP2, in the membrane following its hydrolysis by phospholipase C.