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Granulocyte Colony-Stimulating Factor (G-CSF) is a glycoprotein, growth factor or cytokine produced by a number of different tissues to stimulate the bone marrow to produce granulocytes. It also stimulates the survival, proliferation, differentiation, and function of neutrophil granulocyte progenitor cells and mature neutrophils.
G-CSF is also known as Colony-Stimulating Factor 3 (CSF 3).
G-CSF should not be confused with granulocyte macrophage colony-stimulating factor (GM-CSF), which is a different haemopoietic growth factor.
G-CSF is produced by endothelium, macrophages, and a number of other immune cells. The natural human glycoprotein exists in two forms of a 174- and 180-amino-acid-long protein of molecular weight 19,600 grams per mole. The more-abundant and more-active 174-amino acid form has been used in the development of pharmaceutical products by recombinant DNA (rDNA) technology.
Mouse granulocyte colony-stimulating factor (G-CSF) was first recognised and purified in Australia in 1983, and the human form was cloned by groups from Japan and the United States in 1986.
The G-CSF-receptor is present on precursor cells in the bone marrow, and, in response to stimulation by G-CSF, initiates proliferation and differentiation into mature granulocytes.
[edit]Genetics

The gene for G-CSF is located on chromosome 17, locus q11.2-q12. Nagata et al. (1986) found that the GCSF gene has 4 introns, and that 2 different polypeptides are synthesized from the same gene by differential splicing of mRNA. The 2 polypeptides differ by the presence or absence of 3 amino acids. Expression studies indicate that both have authentic GCSF activity.
[edit]Therapeutic use

G-CSF stimulates the production of white blood cells. In oncology and hematology, a recombinant form of G-CSF is used with certain cancer patients- especially in treatment-resistant and/or metastatic breast cancer- to prolong survival by accelerating recovery from neutropenia, allowing high-intensity chemotherapy regimens to be more sustained. Chemotherapy can cause myelosuppression and unacceptably-low levels of white blood cells, making patients prone to infections and sepsis. However, in a Washington University School of Medicine oncology study using mice, G-CSF is shown to lessen the density of bone tissue even while it increases the WBC count; if this is found to occur in human cases it would necessitate increased consumption of calcium and vitamins A and D, and maybe drug therapy.
The recombinant human G-CSF synthesised in an E. coli expression system is called filgrastim. The structure of filgrastim differs slightly from the structure of the natural glycoprotein. Most published studies have used filgrastim. Filgrastim (Neupogen®) and PEG-filgrastim (Neulasta®) are two commercially-available forms of rhG-CSF (recombinant human G-CSF). The PEG (polyethylene glycol) form has a much longer half-life, reducing the necessity of daily injections.
Another form of recombinant human G-CSF called lenograstim is synthesised in Chinese Hamster Ovary cells (CHO cells). As this is a mammalian cell expression system, lenograstim is indistinguishable from the 174-amino acid natural human G-CSF. No clinical or therapeutic consequences of the differences between filgrastim and lenograstim have yet been identified, but there are no formal comparative studies.