Cardiotrophin-like cytokine (CLC), also referred to as novel neurotrophin-1 (NNT-1) or B cell-stimulating factor-3 (BSF-3), is a new member of the IL-6 family of structurally related cytokines that includes IL-6, CNTF, LIF, CT-1, IL-11 and OSM. All family members share the receptor subunit gp130 that belong to the type I cytokine receptor superfamily. Ligand binding leads to gp130 homodimerization or heterodimerization (with LIF receptor or OSM receptor beta ), and induces cell signaling and functional activity. For several family members, including CNTF, IL-6, and IL-11, binding of the ligand to a specific receptor alpha subunit (CNTF R alpha, IL-6 R alpha, or IL-11 R alpha ) is required prior to gp130 homo- or hetero-dimerization.
CLC cDNA encodes a 225 amino acid (aa) residue precursor protein with a putative 27 aa residue signal peptide that is cleaved to yield the mature protein. Among the IL-6 family, CLC is the most homologous to cardiotrophin, having 29% aa sequence homology. CLC has been shown to bind with the soluble orphan receptor cytokine-like factor-1 (CLF) to form a heterodimeric composite cytokine that subsequently interacts with the membrane‑associated CNTF R alpha to initiate gp130-LIF R dimerization and cell signaling. Alternatively, when co-expressed within the cell, CLC can complex with soluble CNTF R alpha to form an alternate composite cytokine that is secreted. This composite cytokine is also capable of initiating gp130-LIF R dimerization. The E. coli-expressed CLC can initiate cell signaling via the tripartite membrane‑associated CNTF R alpha and gp130-LIF R. E. coli-expressed CLC does not bind efficiently with soluble CNTF R alpha in solution to initiate cell signaling on cells expressing gp130 and LIF R.
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