Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Recombinant dna technique included in method of making a...
Reexamination Certificate
1992-07-09
2001-05-08
Kunz, Gary L. (Department: 1647)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Recombinant dna technique included in method of making a...
C435S173300, C435S320100, C536S023500
Reexamination Certificate
active
06228609
ABSTRACT:
TECHNICAL FIELD
The field of this invention is the identification and use of hematopoietic factor receptors.
BACKGROUND
The process for the development of hematopoietic cells from a self-regenerating stem cell to the mature multi-lineage cells has been the subject of intense investigation. How the host is able to direct a single cell into the multiplicity of pathways which provide such varied cells as lymphocytes, monocytes, macrophages, megakaryocytes and osteoclasts, which is not a complete list, still remains to be elucidated. However, substantial strides have been made in identifying various intermediate cells associated with the different lineages and identifying factors which appear to direct, either by themselves or in combination with other factors, the cells to mature to a particular cell type. For the most part, the factors have been associated with progenitors which are committed to a particular lineage, where the factors result in maturation of the progenitor. Less is known about the factors which direct a totipotent or multipotent cell to be directed to one among many possible lineages.
In order to understand the processes of differentiation and maturation, it will be necessary to know which surface membrane proteins act as receptors for transduction of signals, whether they have soluble forms, the role of soluble forms, and which ligands are associated with the surface membrane proteins. It is therefore of substantial interest to be able to identify ligands, receptors and their soluble forms associated with cell regeneration, proliferation, differentiation, and maturation.
Relevant Literature
Jordan et al. (1990) Cell 81, 953-963 and Matthews et al. (1991) Cell 65, 1143-1152 describe isolation of fetal liver stem cells and molecular cloning of FLK-2, a putative stem cell growth factor receptor. Jordan and Lemischka (1990)
Genes and Development
4, 220-232 describe a clonal and systemic analysis of long-term hematopoiesis in the mouse.
SUMMARY OF THE INVENTION
A soluble form of FLK-2 molecule (SEQ ID NO:3 and SEQ ID NO:4) is provided where the soluble form lacks the transmembrane sequence as well as portions of the extracellular and intra-cellular sequences. In addition, a partial nucleic acid sequence (SEQ ID NO:5) of the gene for human FLK-2 is provided.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
Methods and compositions are provided associated with the mammalian regulation of hematopoiesis. Particularly, a soluble form of the mammalian fetal liver kinase-2 (FLK-2) is provided, as well as the human FLK-2.
The soluble form of the FLK-2 is characterized by lacking the transmembrane sequence, by being encoded by about a 1.9 kb cDNA, capable of competing with the surface membrane FLK-2 for ligand and having at least 80% homology with the sequence (SEQ ID NO:3) set forth for Flk-2ws in the Experimental section. Substantial sequence conservation of the gene and protein is observed, so that the soluble form may be from primate, particularly human, murine, bovine, ovine, equine, lagomorpha, feline, canine, etc.
Nucleic acid encoding Flk-2ws may be obtained from host hematopoietic stem cells by using as a probe, at least twelve, usually at least eighteen, nucleotides of the subject sequence. The subject sequence, which is the mouse sequence, may be used to identify other mammalian analogs by hybridizing under less stringent conditions, e.g., (1) 6×SSC, 35° C., 1 hr.; (2) 0.5×SSC, 35° C., 0.5 hr.; (3) 0.5×SSC, 50° C., 1 hr., and using Northern blots, dot-blots, or the like. cDNA's may then be prepared from the mRNA in accordance with known procedures.
The cDNA may be used for expression of the Flk-2ws in any convenient expression host, both prokaryotic and eukaryotic hosts. By forming an expression cassette in the direction of transcription of a transcriptional initiation regulatory region, which may or may not include an enhancer, the cDNA or other sequence encoding the same or substantially the same protein, and a transcriptional termination regulatory region, desirably including a polyadenylation signal sequence, the cassette then may be used for introduction into the appropriate host, where the regulatory regions are functional in the host. A wide variety of both prokaryotic and eukaryotic hosts are available, such as
E. coli, B. subtilis,
yeast, such as
S. cerevisiae,
Kluyveromyces, fungi, such as proteus, etc., insect cells, mammalian cells, e.g., COS cells, CHO cells, etc., plant cells, and the like. The particular choice of the host is not critical to this invention, and any host may be employed which allows for the desired expression and, as appropriate, processing.
For scientific investigation, the subject composition may be labeled for detection. Various labels include radioisotopes, enzymes, fluorescers, and the like. Methods of labeling a protein are well established in the literature, and need not be exemplified here.
The strategy employed for identifying the Flk-2ws was to isolate hematopoietic stem cells by separation using long-term cultured w/w hematopoietic stem cells, where the w/w mice lack a functional c-kit gene, the receptor for the steel ligand. The cultured cells were then used for isolation of mRNA, followed by reverse transcription to provide cDNA. Amplification was then achieved using the polymerase chain reaction (PCR), with primers having homology to the 5′ terminal sequence and the sequence 3′ of about nucleotide 3400, from about 3400 to about 3430. After separation by 1% agarose gel electrophoresis, two major amplified fragments were cloned, namely a 3.4 and a 1.9 kb DNA fragment. The 3.4 kb DNA fragment represents the native Flk-2 molecule, while the 1.9 kb DNA fragment (SEQUENCE ID NO:3) represents a secreted form of Flk-2, designated Flk-2ws.
For isolation of the human, Flk-2, human fetal bone marrow cells were selected for carrying the markers CD 34
+
Thy-1
+
, separation being by any convenient means such as magnetic particles, fluorescence activated cell sorter, panning or the like. Isolated mRNA was used to prepare a cDNA library and mouse Flk-2ws (SEQUENCE ID NO:3), or a major portion thereof, may be used as a probe. Stringent conditions were used, employing elevated temperature in the range of about 50 to 65° C., employing a stringency of about 6×SSC. After cloning in &lgr; phage, positive plaques were selected and re-screened and phagemids rescued from the secondary positive &lgr; phage clones. The clones which were obtained lack the 5′ end which was obtained by using a portion of the mouse Flk-2 (SEQUENCE ID NO:6) as a probe. The positive clones were then used to provide the 5′ end sequence.
The human Flk-2 is (SEQUENCE ID NO:5) substantially homologous to the mouse Flk-2 (SEQUENCE ID NO:6) having the sequence as set forth in the experimental section. It is characterized by being 2.5 kbp. It defines domains analogous to the domains for the mouse membrane bound Flk-2 and soluble Flk-2.
The subject protein may be obtained in purified form, usually at least about 90% pure, preferably at least about 99% pure, as evidenced by a single band in gel electrophoresis.
The subject proteins find use in culture and in vivo in competing with Flk-2 receptor for Flk-2 ligand. Thus, the subject compositions may be used for modulating the growth of hematopoietic progenitor cells. In addition, the subject proteins or fragments thereof of at least about 12 amino acids, preferably at least about 18 amino acids, may be used for the production of antibodies, either polyclonal anti-serum or monoclonal antibodies. Particularly, the soluble Flk-2 may be used to produce antibodies which are specific for the juncture or sequences proximal to the juncture between about amino acids 680 and 700, particular at about 690, ±10 amino acids. The antibodies may be used for identifying cells carrying Flk-2, removing soluble Flk-2 from culture fluids or natural fluids, purifying Flk-2, and the like. The antibodies may also be used for assaying for the presence of Flk-2.
REFERENCES:
patent: 518
Karny Geoffrey M.
Kunz Gary L.
Landsman Robert S.
Systemix, Inc.
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