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Background
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Leukemia Inhibitory Factor (or LIF) is a variably glycosylated, 38 - 67 kDa polypeptide originally identified as a proliferation inhibitor and differentiation inducer of the mouse M1 myeloid leukemia cell line. The mature LIF molecule measures 180 amino acid (aa) residues in length, with multiple potential N-linked and O-linked glycosylation sites plus six conserved cysteines that form three intramolecular disulfide bridges. Mature mouse LIF is 78% identical to human LIF at the aa sequence level. Although such homology might suggest a high conservation of LIF biology, notable differences exist between the reported forms of mouse and human LIF proteins and their receptors. For example, alternative splice events are known to occur in mice, but not humans, creating two isoforms of secreted LIF. Also, three isoforms of the LIF receptor a-chain, two soluble forms and one transmembrane form, have been reported in mice, but not in humans. Based on its helical structure, LIF is considered to be a member of the Interleukin-6 family of cytokines. Cells known to express LIF include activated T-cells, monocytes, and astrocytes, osteoblasts , keratinocytes, regenerating skeletal muscle, mast cells , and fibroblasts.
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