Recombinant platelet factor 4, an angiogenic marker for human breast carcinoma.

The present study was designed to test the hypothesis that rhPF4 binds with high specificity to the neovasculature of breast cancer carcinoma. To achieve this goal, we used intravital microscopy to study the binding characteristics of systemically injected fluorescently labeled rhPF4 (FITC-rhPF4) to the microvasculature of dorsal skinfold chambers in nude mice implanted with tumor spheroids prepared from the human breast cancer cell line MCF-7. Our results show that intravenously as well as intra-arterially injected FITC-rhPF4 exclusively labeled, with high intensity and specificity, the endothelium of the breast cancer induced neovasculature.

Heparin binding to platelet factor-4. An NMR and site-directed mutagenesis study: arginine residues are crucial for binding.

Native platelet factor-4 (PF4) is an asymmetrically associated, homo-tetrameric protein (70 residues/subunit) known for binding polysulphated glycosaminoglycans like heparin. PF4 N-terminal chimeric mutant M2 (PF4-M2), on the other hand, forms symmetric tetramers [Mayo, Roongta, Ilyina, Milius, Barker, Quinlan, La Rosa and Daly (1995) Biochemistry 34, 11399-11409] making NMR studies with this 32 kDa protein tractable. PF4-M2, moreover, binds heparin with a similar affinity to that of native PF4.

High activity suppression of myeloid progenitor proliferation by chimeric mutants of interleukin 8 and platelet factor 4.

The proliferation of human myeloid progenitor cells is negatively regulated in the presence of certain members of the chemokine family of molecules. This includes interleukin 8 (IL-8) and platelet factor 4 (PF4), which in combination are able to synergize, resulting in cell suppression at very low concentrations of these molecules. A series of PF4 and IL-8 mutant proteins were analyzed in an in vitro colony formation assay for myeloid progenitor cells to assess domains of these proteins that are required for activity.

Selective binding of platelet factor 4 to regions of active angiogenesis in vivo.

In a previous study we suggested that recombinant human platelet factor 4 (rhPF4) preferentially binds in vivo to regions of active angiogenesis/endothelial cell migration. To test this hypothesis, binding of fluorescently labeled rhPF4 to newly formed vessels was compared with that of the normal skin vasculature, using syngeneic Langerhans islets as inducers of angiogenesis. Islets were implanted in the dorsal skinfold chamber of the hamster, and the binding of rhPF4 was studied using intravital fluorescence microscopy.

Differences in binding of platelet factor 4 to vascular endothelium in vivo and endothelial cells in vitro.

The binding of fluorescein-labelled recombinant human platelet factor 4 (rhPF4) to the vasculature of the hamster cheek pouch in vivo was compared with that to cultured endothelial cells (EC) from human umbilical veins (HUVEC) and arteries (HUAEC) and from human aorta (HAEC). In vivo data: systemically injected rhPF4 rapidly disappeared from plasma in a biphasic pattern (t1/2 = 2 and 41 min). High intensity non-uniform binding of rhPF4 occurred at short specific sites along both arterioles and venules.