Interleukin 11 is a protein that in humans is encoded by the IL11gene. IL-11 is a cytokine and first isolated in 1990 from bone marrow-derived fibrocyte-like stromal cells. It was initially thought to be important for hematopoiesis, notably for megakaryocyte maturation, but subsequently shown to be redundant for platelets, and for other blood cell types, in both mice and humans. It is also known under the names adipogenesis inhibitory factor and was developed as a recombinant protein as the drug substance oprelvekin. The human IL-11 gene, consisting of 5 exons and 4 introns, is located on chromosome 19, and encodes a 23 kDa protein. IL-11 is a member of the IL-6-type cytokine family, distinguished based on their use of the common co-receptor gp130. Signal specificity is provided by the IL-11Rα subunit which is expressed at high levels in fibroblasts and other stromal cells but not immune cells, unlike IL6 receptors that are expressed at highest levels in immune cells and lowly expressed in stromal cells.
Downstream signalling
Signal transduction is initiated upon binding of IL-11 to IL-11Ralpha and gp130, facilitating the formation of higher order structures involving dimers of gp130:Il-11:Il11RA complexes. In some instances, in epithelial-derived cells and cancer cell lines, this permits gp130-associated Janus kinases activation and downstream STAT-mediated transcriptional activities. In other instances, in stromal cells, IL-11 activates non-canonical MAPK/ERK-dependent signalling to initiate the post-transcriptional upregulation of specific subsets of transcripts in the absence of an effect on transcription. In fibroblasts, IL-11 drives an ERK-dependent autocrine loop of fibrogenic protein synthesis that is at a nexus of fibrotic signalling and required for the pro-fibrotic activity of TGFB1, PDGF, endothelin1, angiotensin and many other pro-fibrotic factors.
Function
IL-11 through its binding to its transmembrane IL-11Rα receptor and resultant activation of downstream signaling pathways has been thought to regulate adipogenesis, osteoclastogenesis, neurogenesis and platelet maturation. More recently it has been discovered that over expression of IL-11 is associated with a variety of cancers and may provide a link between inflammation and cancer. IL-11 has been demonstrated to improve platelet recovery after chemotherapy-induced thrombocytopenia, induce acute phase proteins, modulate antigen-antibody responses, participate in the regulation of bone cellproliferation and differentiation IL-11 causes bone-resorption. It stimulates the growth of certain lymphocytes and, in the murine model, stimulates an increase in the cortical thickness and strength of long bones. In addition to having lymphopoietic/hematopoietic and osteotrophic properties, it has functions in many other tissues, including the brain, gut, testis and bone. As a signaling molecule, interleukin 11 has a variety of functions associated with its receptor interleukin 11 receptor alpha; such functions include placentation and to some extent of decidualization. IL11 has been expressed to have a role during implantation of the blastocyst in the endometrium of the uterus; as the blastocyst is imbedded within the endometrium, the extravillous trophoblasts will invade the maternal spiral arteries for stability and the transfer of essential life-sustaining elements via the maternal and fetal circulatory systems. This process is highly regulated due to detrimental consequences that can arise from aberrations of the placentation process: poor infiltration of the trophoblasts may result in preeclampsia while severely invasive trophoblasts may resolve in placenta accreta, increta or percreta; all defects which most likely would result in the early demise of the embryo and/or negative effects upon the mother. IL11 has been shown to be present in the decidua and chorionic villi to regulate the extent in which the placenta implants itself; regulations to ensure the well-being of the mother but also the normal growth and survival of the fetus. A murine knockout model has been produced for this particular gene, with initial studies involving IL11 role in bone pathologies but have since progressed to fertility research; further research utilizes endometrial and gestational tissue from humans.
Medical use
Interleukin 11 is manufactured using recombinant DNA technology and is marketed as a protein therapeutic called oprelvekin, for the prevention of severe thrombocytopenia in cancer patients.
As a therapeutic target
As IL-11 over expression is associated with a number of cancers, inhibition of its signaling pathway may have utility in treating cancer. Transforming growth factor β1 through up-regulation of IL-11, stimulates collagen production and is important in wound healing. However dysregulation of TGFβ1 and downstream IL-11 is associated with fibrotic diseases hence inhibition of IL-11 may have utility in treating fibrosis. Furthermore, this cytokine has been found to promote recruitment of immune suppressivecancer-associated fibroblasts to tumors and facilitates chemoresistance.
