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GDF-5 is a member of the bone morphogenetic protein (BMP) family and the TGF-beta superfamily. This group of proteins is characterized by a polybasic proteolytic processing site which is cleaved to produce a mature protein containing seven conserved cysteine residues. The members of this family are regulators of cell growth and differentiation in both embryonic and adult tissues. Mutations in this gene are associated with acromesomelic dysplasia, Hunter-Thompson type; brachydactyly, type C; and chondrodysplasia, Grebe type. These associations confirm that the gene product plays a role in skeletal development.

Endothelial cells express three different vascular endothelial growth factor (VEGF) receptors, belonging to the family of receptor tyrosine kinases (RTKs). They are named VEGFR-1 (Flt-1), VEGFR-2 (KDR/Flk-1), VEGFR-3 (Flt-4). Their expression is almost exclusively restricted to endothelial cells, but VEGFR-1 can also be found on monocytes, dendritic cells and on trophoblast cells. The flt-1 gene was first described in 1990. The receptor contains seven immunoglobulin-like extracellular domains, a single transmembrane region and an intracellular splited tyrosine kinase domain. Compared to VEGFR-2 the Flt-1 receptor has a higher affinity for VEGF but a weaker signaling activity. VEGFR-1 thus leads not to proliferation of endothelial cells, but mediates signals for differentiation. Interestingly a naturally occuring soluble variant of VEGFR-1 (sVEGFR-1) was found in HUVE supernatants in 1996, which is generated by alternative splicing of the flt-1 mRNA. The biological functions of sVEGFR-1 still are not clear, but it seems to be an endogenous regulator of angiogenesis, binding VEGF with the same affinity as the full-length receptor.

TIE-1 (tyrosine kinase with Ig and EGF homology domains 1) and TIE-2/Tek comprise a receptor tyrosine kinase (RTK) subfamily with unique structural characteristics: two immunoglobulin-like domains flanking three epidermal growth factor (EGF)-like domains and followed by three fibronectin type III-like repeats in the extracellular region and a split tyrosine kinase domain in the cytoplasmic region. These receptors are expressed primarily on endothelial and hematopoietic progenitor cells and play critical roles in angiogenesis, vasculogenesis and hematopoiesis. Human TIE-1 cDNA encodes a 1122 amino acid (aa) residue precursor protein with an 18 residue putative signal peptide, a 726 residue extracellular domain and a 353 residue cytoplasmic domain. Two ligands, angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2), which bind TIE-2 with high-affinity have been identified. Ang2 has been reported to act as an antagonist for Ang1. Mice engineered to overexpress Ang2 or to lack Ang1 or Tie-1 display similar angiogenic defects.

Leukemia Inhibitory Factor also called LIF is a lymphoid factor that promotes long-term maintenance of embryonic stem cells by suppressing spontaneous differentiation. Leukemia Inhibitory Factor has several functions such as cholinergic neuron differentiation, control of stem cell pluripotency, bone & fat metabolism, mitogenesis of factor dependent cell lines & promotion of megakaryocyte production in vivo. Human and mouse LIF exhibit a 78% identity in its amino acid sequence.

CTBP1 participates in controlling the equilibrium between tubular and stacked structures in the Golgi complex. CTBP1 functions in brown adipose tissue differentiation. CTBP1 has dehydrogenase activity. CTBP1 binds to the C-terminus of adenovirus E1A proteins. CTBP1 phosphoprotein is a transcriptional repressor and that takes part during cellular proliferation. CTBP1 & CTBP2 can dimerize and interact with a polycomb group protein complex which is involved in regulation of gene expression during development.

Amino-terminal enhancer of split (AES) is a member of the groucho/TLE family of proteins. AES can function as a homooligomer or as a heteroologimer with other family members in order to forcefully repress the expression of other family member genes. Furthermore, AES can repress NFkB-regulated gene expression and is believed to have a significant role in initiating and maintaining cell differentiation events. AES is similar in sequence to the amino terminus of Drosophila enhancer of split groucho, a protein which is involved in neurogenesis during embryonic development. The AES protein is expressed predominately in the fetal brain, liver, lung, heart and kidney and also in the adult muscle.

FKBP1A is a 12kDa protein initialy discovered onin immune cells on the basis of its capability to bind and mediate the intracellular effect of the immunosuppressant FK506. FKBP1A is also known to mediate the action of Rapamycin-immunosuppressive agent. FKBP1A is part of the family of immunophilins, which have in common high affinity for immunosuppressant drugs and a peptidyl-prolyl cis-trans isomerase (PPIase). Activity which participates in folding of proline-containing protein. In the absence of immunosuppressive ligands, FKBP1A is involved in intracellular calcium regulation by associating with 3 types of Ca2+ release channel complexes: skeletal ryanodine receptors, cardiac ryanodine receptors and the inositol 1,4,5-triphosphate receptor. FKBP1A also interact with TGF-b type I receptor exerting an inhibitory effect on the TGF-b signaling pathway. FKBP12 plays a role in modulation of ryanodine receptor isoform-1 (ryr-1), a component of the calcium release channel of skeletal muscle sarcoplasmic reticulum. FKBP1A increase the folding of proteins and catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides.

Penta-EF-hand domain containing 1 (PEF1) is a member of the penta-EF-hand protein family, which shares similarities to the apoptosis linked gene ALG-2. PEF1 forms heterodimers with PDCD6/ALG2 and dissociates from PDCD6/ALG2 in the presence of Ca (2+). Furthermore, PEF1 proteins bind calcium and participate in a various calcium-dependent processes in vertebrates.

Sex-hormone-binding globulin (SHBG) is a beta-globulin which specifically binds steroid hormones; it is involved in the transport of sex steroids in plasma. The main site of SHBG synthesis is assumed to be the hepatocytes. The production of SHBG is regulated by androgen/estrogen balance, thyroid hormones, and dietary factors, among others. The concentration of SHBG is a key factor regulating their distribution between protein-bound and free states. SHBG concentration determination is primarily significant in the evaluation of mild disorders of androgen metabolism and it allows detection of women with hirsutism who are likely to react to estrogen therapy. Testosterone/SHBG-ratios correlate well with both measured and calculated values for free testosterone thus aid to distinguish between subjects with excessive androgen activity and normal individuals. SHBG gene polymorphisms are linked with polycystic ovary syndrome and type 2 diabetes mellitus.

BMP2 belongs to the transforming growth factor-beta (TGFB) superfamily. Bone morphogenic protein induces bone formation. BMP2 is a candidate gene for the autosomal dominant disease of fibrodysplasia (myositis) ossificans progressiva.

Growth arrest and DNA Damage-Inducible Protein (GADD45A) binds both Cdks and PCNA. GADD45A is involved in DNA replication and repair. GADD45A stimulates DNA excision repair in vitro and inhibits entry of cells into S phase. GADD45A may serve as a link between p53-dependent cell cycle checkpoint and DNA repair. The GADD45A gene belongs to a group of genes whose transcript levels are increased following stressful growth arrest conditions and treatment with DNA-damaging agents. GADD45A responds to environmental stresses by mediating activation of the p38/JNK pathway via MTK1/MEKK4 kinase. GADD45A binds to proliferating cell nuclear antigen.

Collagen triple helix repeat-containing protein 1 or CTHRC1 acts as a negative regulator of collagen matrix deposition. The protein is secreted from a 28kDa protein which is glycosylated and very conserved from lower chordates to mammals. CTHRC1 is found qualitatively in plasma of healthy human subjects. CTHRC1 plasma levels are also significantly elevated during pregnancy, in diabetes, in inflammatory and infectious conditions, in subjects with acute myeloid leukemia but not in subjects with solid cancers.CTHRC1 is highly connected with calcified tissues and cartilaginous matrix, but not with endothelial cells.

FABP12 is a member of the calycin superfamily and fatty-acid binding protein (FABP) family. The FABPs are a family of carrier proteins for fatty acids and other lipophilic substances for example eicosanoids and retinoids. These proteins are believed to enable the transfer of fatty acids between extra- and intracellular membranes. FABP12 has a role in lipid transport. FABP12 is expressed in several retinoblastoma cell lines. FABP12 has not been detected in fetal tissues.

Ectodysplasin A Receptor, also known as EDAR belongs to the tumor necrosis factor receptor family. EDAR is a receptor for the soluble ligand ectodysplasin A, and is capable of activating the nuclear factor-kappaB, JNK, as well as caspase-independent cell death pathways. EDAR is necessary for the development of hair, teeth, and other ectodermal derivatives. Furthermore, mutations in EDAR resulted in autosomal dominant and recessive forms of hypohidrotic ectodermal dysplasia.

FKBP6 is part of the immunophilin protein family, and is involved in immunoregulation and basic cellular functions involving protein folding and trafficking. FKBP6 is widely expressed in all tissues, FKBP6 is present at utmost levels in testis, liver, kidney, skeletal muscle and heart. Deletion of FKBP6 contributes to hypercalcemia and growth delay in Williams-Beuren syndrome.

Complement C5 is cleaved into C5a and C5b and is activated by all 3 pathways of complement activation. Each pathway of complement activation generates proteolytic enzyme complexes which binds to the target surface. These enzymes cleave a peptide bond in the larger alpha chain of C5 releasing the highly potent anaphylatoxin C5a and activating C5b. C5a has an imperative role in chemotaxis and C5b forms the 1st part of the complement membrane attack complex. Complement C5 is the 5th component of complement, which plays a central role in inflammatory and cell killing processes.

IHH belongs to the hedgehog family of secreted signaling molecules. Hedgehog proteins are vital regulators of various developmental processes including growth, patterning and morphogenesis. The vertebrate homologues of Hh comprise several proteins including sonic hedgehog (Shh), Indian hedgehog (Ihh), and Desert hedgehog (Dhh). IHH has a specific role in bone growth and differentiation. In addition, IHH is involved in yolk sac vasculogenesis, having a central role in differentiation of epiblast cells into endothelial and red blood cells. IHH mRNA expression is detected in fetal lung, gut, stomach, liver, kidney, pancreas and strongly in cartilage in growth regions of the developing bone. IHH gene mutations cause the brachydactyly type A1 which is characterized by shortening or malformation of the phalanges and also the acrocapitofemoral dysplasia.

SPARC, an acronym for “secreted protein, acidic and rich in cysteine”, is also known as osteonectin or BM-40. It is the founding member of a family of secreted matricellular proteins with similar domain structure. The 303 amino acid, 43 kDa protein contains a 17 aa signal sequence, an N-terminal acidic region that binds calcium, a follistatin domain containing Kazal-like sequences, and a C-terminal extracellular calcium (EC) binding domain with two EF-hand motifs. SPARC is produced by fibroblasts, capillary endothelial cells, platelets and macrophages, especially in areas of tissue morphogenesis and remodeling. SPARC shows context-specific effects, but generally inhibits adhesion, spreading and proliferation, and promotes collagen matrix formation. For endothelial cells, SPARC disrupts focal adhesions and binds and sequesters PDGF and VEGF. SPARC is abundantly expressed in bone, where it promotes osteoblast differentiation and inhibits adipogenesis.

APOA1 (Apolipoprotein A-1) is a human protein with a specific role in lipid metabolism being the main protein component of HDL in the plasma. APOA1 promotes cholesterol efflux from tissues to the liver for excretion. Furthermore, APOA1 is a cofactor for LCAT, which is responsible for the formation of most plasma cholesteryl esters. In addition, APOA1 activates spermatozoa motility as part of the SPAP complex. The APOA1 gene is strongly linked with two other apolipoprotein genes on chromosome 11. Defects in the APOA1 gene are linked to HDL deficiency including Tangier disease, and with systemic non-neuropathic amyloidosis. High levels of APOA1 are linked to the manifestation of asthma and atopy.

Cystatin 7 (CST7) is a glycosylated cysteine protease inhibitor with a putative role in immune regulation through inhibition of a unique target in the hematopoietic system. Cystatin-7 is comprised of multiple cystatin-like sequences. The superfamily is comprised of 3 inhibitory families: the type 1 cystatins (stefins), type 2 cystatins and the kininogens. Some members are active cysteine protease inhibitors, while others have lost or possibly never had this inhibitory activity. Type 2 cystatin proteins are a class of cysteine proteinase inhibitors found in various human fluids and secretions. CST7 protein expression has been observed in numerous human cancer cell lines established from malignant tumors.

Coiled-Coil Domain Containing 25 (CCDC25) is a 208 amino acid protein belonging to the CCDC25 family.

Non-homologous end-joining factor 1 (NHEJ1) is a member of the XLF family. NHEJ1 is a DNA repair factor vital for the nonhomologous end-joining pathway, which preferentially mediates repair of double-stranded breaks. NHEJ1 gene mutations cause different kinds of severe combined immunodeficiency disorders. NHEJ1 was initially detected as the protein mutated in five patients with growth retardation, microcephaly, and immunodeficiency. In addition, patients with NHEJ1 mutations have immunodeficiency caused by a defect in V(D)J recombination, which employs NHEJ to promote immune system diversity.

ASB13 belongs to the ankyrin repeat and SOCS box-containing (ASB) family of proteins which contains ankyrin repeat sequence and a SOCS box domain. ASB13 is a protein coding gene that plays a role as a substrate-recognition part of a SCF-like ECS E3 ubiquitin-protein ligase complex which arbitrates the ubiquitination and subsequent proteasomal degradation of target proteins.