Primary prophylaxis for children with severe congenital factor VII deficiency - Clinical and laboratory assessment.

Severe congenital factor VII (FVII) deficiency is a rare bleeding disorder. Prophylaxis with replacement therapy has been suggested to patients, yet the most beneficial dosing regimens and therapy intervals are still to be defined. Due to the lack of evidence-based data, we hereby present our experience with long-term administration and monitoring primary prophylaxis in children with severe FVII deficiency and an extremely high bleeding risk. Four children with familial FVII deficiency, treated by prophylactic recombinant activated factor VII (rFVIIa), 15-30µg/kg/dose, given 2-3 times weekly since infancy, are discussed. Clinical follow up and monitoring laboratory assays, including thrombin generation, measured at various time points after prophylactic rFVIIa administration are presented. Among our treated patients neither FVII activity nor thrombin generation parameters (both already declined 24h post rFVIIa administration) were able to predict the impact of prophylaxis, and could not be used as surrogate markers in order to assess the most beneficial treatment frequency. However, the long clinical follow-up and comprehensive laboratory assessment performed, have shown that early primary prophylaxis as administered in our cohort was safe and effective.

Cloning and characterization of a lymphoid-specific, inducible human protein tyrosine phosphatase, Lyp.

Protein tyrosine phosphatases act in conjunction with protein kinases to regulate the tyrosine phosphorylation events that control cell activation and differentiation. We have isolated a previously undescribed human phosphatase, Lyp, that encodes an intracellular 105-kD protein containing a single tyrosine phosphatase catalytic domain. The noncatalytic domain contains four proline-rich potential SH3 domain binding sites and an NXXY motif that, if phosphorylated, may be recognized by phosphotyrosine binding (PTB) domains. Comparison of the Lyp amino acid sequence with other known proteins shows 70% identity with the murine phosphatase PEP. The human Lyp gene was localized to chromosome 1p13 by fluorescence in situ hybridization analysis. We also identified an alternative spliced form of Lyp RNA, Lyp2. This isoform encodes a smaller 85-kD protein with an alternative C-terminus. The lyp phosphatases are predominantly expressed in lymphoid tissues and cells, with Lyp1 being highly expressed in thymocytes and both mature B and T cells. Increased Lyp1 expression can be induced by activation of resting peripheral T lymphocytes with phytohemagglutinin or anti-CD3. Lyp1 was found to be constitutively associated with the proto-oncogene c-Cbl in thymocytes and T cells. Overexpression of lyp1 reduces Cbl tyrosine phosphorylation, suggesting that it may be a substrate of the phosphatase. Thus, Lyp may play a role in regulating the function of Cbl and its associated protein kinases.

Identification of glypican as a dual modulator of the biological activity of fibroblast growth factors.

Heparan sulfate moieties of cell-surface proteoglycans modulate the biological responses to fibroblast growth factors (FGFs). We have reported previously that cell-associated heparan sulfates inhibit the binding of the keratinocyte growth factor (KGF), but enhance the binding of acidic FGF to the KGF receptor, both in keratinocytes, which naturally express this receptor, and in rat myoblasts, which ectopically express it (Reich-Slotky, R., Bonneh-Barkay, D., Shaoul, E., Berman, B., Svahn, C. M., and Ron, D. (1994) J. Biol. Chem. 269, 32279-32285). The proteoglycan bearing these modulatory heparan sulfates was purified to homogeneity from salt extracts of rat myoblasts by anion-exchange and FGF affinity chromatography and was identified as rat glypican. Affinity-purified glypican augmented the binding of acidic FGF and basic FGF to human FGF receptor-1 in a cell-free system. This effect was abolished following digestion of glypican by heparinase. Addition of purified soluble glypican effectively replaced heparin in supporting basic FGF-induced cellular proliferation of heparan sulfate-negative cells expressing recombinant FGF receptor-1. In keratinocytes, glypican strongly inhibited the mitogenic response to KGF while enhancing the response to acidic FGF. Taken together, these findings demonstrate that glypican plays an important role in regulating the biological activity of fibroblast growth factors and that, for different growth factors, glypican can either enhance or suppress cellular responsiveness.

Chimeric molecules between keratinocyte growth factor and basic fibroblast growth factor define domains that confer receptor binding specificities.

Basic fibroblast growth factor (FGF) and keratinocyte growth factor (KGF) are structurally related fibroblast growth factors, yet they exhibit distinct receptor binding specificity. Basic FGF binds with high affinity to FGFR1, FGFR2, and FGFR4, whereas KGF does not interact with these receptors and can only bind an isoform of FGFR2 known as the KGFR. Basic GFG binds KGFR but with lower affinity than KGF. In order to identify domains that confer this specificity, four reciprocal chimeras were generated between the two growth factors and were analyzed for receptor recognition and biological activity. The chimeras are designated BK1 (bFGF1-54:KGF91-194), BK2 (bFGF1-74:KGF111-194), KB1 (KGF31-90:bFGF55-155), and KB2 (KGF31-110:bFGF75-155). The two BK chimera similarly interacted with FGFR1 and FGFR4 but differed from each other with respect to KGFR recognition. BK1 displayed a slightly better affinity for KGFR than BK2 and induced a higher level of DNA synthesis in keratinocytes compared with bFGF and BK2. A neutralizing monoclonal antibody directed against bFGF specifically neutralized the biological activity of the BK chimeras. The reciprocal chimeras, KB1 and KB2, exhibited KGF-like receptor binding and activation properties. However, KB2 displayed higher affinity for KGFR and was significantly more potent mitogen that KB1. Altogether, our results suggest that the amino-terminal part of KGF and bFGF plays an important role in determining their receptor binding specificity. In addition, the results point to the contribution of a segment from the middle part of KGF (residues 91-110) for recognition and activation of the KGFR, as the two chimeras containing these residues (BK1 and KB2) displayed an enhanced interaction with the KGFR.

Fibroblast growth factor receptors display both common and distinct signaling pathways.

We compared the mitogenic and signaling pathways of three Fibroblast Growth Factor Receptors (FGFRs), FGFR1, KGFR and FGFR4 in the same cell line. Each receptor was expressed in L6E9 rat myoblasts that do not normally express detectable levels of FGFRs and clones that express comparable levels of each receptor were selected. Our results show that FGFs induce an effective survival and growth of FGFR1 and KGFR expressing cells. In addition, these cells exhibit a morphology that is reminiscent of that of malignantly transformed cells and display anchorage independent growth in a ligand dependent manner. Unlike KGFR and FGFR1, FGFR4 mediates a less effective growth, and cells overexpressing this receptor do not undergo any morphological changes nor do they display an anchorage independent growth in response to FGFs. All three receptors exhibit both quantitative and qualitative differences in their ability to induce tyrosine phosphorylation of cellular substrates. Both FGFR1 and KGFR induce strong phosphorylation of phospholipase C-gamma and a 90 kDa protein, while FGFR4 induces a relatively weak phosphorylation of phospholipase C-gamma and completely fails to induce phosphorylation of the 90 kDa. The three receptors also induce phosphorylation of the mitogen activated protein kinases (MAPK) but the effect of FGFR1 is far stronger than that of the other two receptors. Since FGFR4 is expressed in myoblasts in vivo, we examined whether this receptor can function in the differentiation pathway of myoblasts. Contrary to its weak mitogenic activity, FGFR4 effectively mediates the inhibition of myogenic differentiation in L6E9 cells and also suppresses the expression of the myogenic regulatory protein myogenin. Taken together, our results suggest that the signaling mechanism of FGFR4 differs from that of FGFR1 and KGFR, and that the primary role of FGFR4 in myoblasts may be the maintenance of their non differentiated state.

Differential effect of cell-associated heparan sulfates on the binding of keratinocyte growth factor (KGF) and acidic fibroblast growth factor to the KGF receptor.

The fibroblast growth factors (FGFs) act through high affinity tyrosine kinase receptors and, in addition, interact with lower affinity receptors that represent cell- or matrix-associated heparan sulfate proteoglycans. These lower affinity receptors modulate the biological activities of FGFs, but the mechanism by which they exert these effects is rather controversial. We have previously shown (Ron, D., Bottaro, D. P., Finch, P. W., Morris, D., Rubin, J. S., and Aaronson, S. A. (1993) J. Biol. Chem. 268, 2984-2988) that heparin potentiates the mitogenic activity of acidic FGF (aFGF) but inhibits that of the keratinocyte growth factor (KGF) in cells that express the KGF receptor (KGFR). Both growth factors bind the KGFR with high affinity. To gain an insight into the mechanism by which heparin modulates the biological activity of aFGF and KGF, we studied the effect of heparin and cell-associated heparan sulfates on the binding of these two growth factors to the KGFR. To work in a well defined system, we expressed functional KGFR in L6E9 myoblasts that lack detectable high affinity binding sites for FGFs. Low concentrations of heparin inhibited the binding of KGF to the KGFR. By contrast, similar concentrations of heparin enhanced the binding of aFGF to this receptor. The effect of heparin was not unique to L6E9 cells expressing the KGFR; it was also observed in Balb/MK cells that naturally express KGFR. Treatment of cells with sodium chlorate, which blocks sulfation of proteoglycans, reduced the binding of aFGF to its low and high affinity binding sites by 95 and 80%, respectively. In contrast, the binding of KGF to its high affinity binding sites was enhanced about 2-fold. Similar results were obtained after degradation of cell-associated heparan sulfates by heparinase and heparitinase. Heparin restored the high affinity binding of aFGF to chlorate-treated cells and completely abolished the high affinity binding of KGF. Binding competition experiments suggest that aFGF and KGF bind to the same population of cell-associated heparan sulfates. In addition, KGF is apparently interacting with an as yet unidentified type of low affinity binding site that is not affected by chlorate or heparan sulfate-degrading enzymes. An important property of the FGF high affinity receptors is their ability to bind more than one ligand with high affinity. Based on the differential effect of cell-associated heparan sulfates on the binding of KGF and aFGF to the KGFR, we propose a regulatory role for cell-associated heparan sulfates as coordinators of the interaction of aFGF and KGF with the KGFR.(ABSTRACT TRUNCATED AT 400 WORDS)