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Activins are homodimers or heterodimers of the different β subunit isoforms, part of the TGFβ family. Mature Activin A has two 116 amino acids residues βA subunits (βA-βA). Activin displays an extensive variety of biological activities, including mesoderm induction, neural cell differentiation, bone remodelling, haematopoiesis, and reproductive physiology. Activins takes part in the production and regulation of hormones such as FSH, LH, GnRH and ACTH. Cells that are identified to express Activin A include fibroblasts, endothelial cells, hepatocytes, vascular smooth muscle cells, macrophages, keratinocytes, osteoclasts, bone marrow monocytes, prostatic epithelium, neurons, chondrocytes, osteoblasts, Leydig cells, Sertoli cells, and ovarian granulosa cells.

Human Cystatin A (CSTA or Stefin A) belongs to family 1 of the cystatin superfamily, which is characterized by the lack of disulphide bonds and carbohydrates. CSTA is an intracellular inhibitor regulating the activities of cysteine proteases of the papain family such as Cathepsins B, H and L. Cystatin A has also been implicated in several disease states. Because of altered proteolytic state in cancer progression, CSTA may have a role in the proteolitic pathways.

Resistin, a product of the RSTN gene, is a peptide hormone belonging to the class of cysteine-rich secreted proteins which is termed the RELM family, and is also described as ADSF (Adipose Tissue- Specific Secretory Factor) and FIZZ3 (Found in Inflammatory Zone). Human resistin contains 108 amino acids as a prepeptide, and its hydrofobic signal peptide is cleaved before its secretion. Resistin circulates in human blood as a dimeric protein consisting of two 92 amino acid polypeptides, which are disulfide-linked via Cys26.
Resistin may be an important link between obesity and insulin resistance. Mouse resistin, specifically produced and secreted by adipocyte, acts on skeletal muscle myocytes, hepatocytes and adipocytes themselves so that it reduces their sensitivity to insulin. Steppan et al. have suggested that resistin suppresses the ability of insulin to stimulate glucose uptake. They have also suggested that resistin is present at elevated levels in blood of obese mice, and is down regulated by fasting and antidiabetic drugs. Way et al., on the other hand, have found that resistin expression is severly suppressed in obesity and is stimulated by several antidiabetic drugs.
Other studies have shown that mouse resistin increases during the differentiation of adipocytes, but it also seems to inhibit adipogenesis. In contrast, the human adipogenic differentiation is likely to be associated with a down regulation of resistin gene expression.

MAX protein is part of the basic helix-loop-helix leucine zipper (bHLHZ) family of transcription factors. MAX forms homodimers and heterodimers with Mad, Mxi1 and Myc. Myc is an oncoprotein implicated in cell proliferation, differentiation and apoptosis. The homodimers and heterodimers compete for a common DNA target site (the E box) and rearrangement among these dimer forms offers a complex system of transcriptional regulation. In contrast to Myc, which is exceedingly regulated throughout progression during the cell cycle, Max is very stable and is much more abundant than Myc.

STC2 is a homodimeric glycoprotein that is expressed in a wide variety of tissues and may have autocrine or paracrine functions. The encoded protein has 10 of its 15 cysteine residues conserved among stanniocalcin family members and is phosphorylated by casein kinase 2 exclusively on its serine residues. Its C-terminus contains a cluster of histidine residues which may interact with metal ions. The protein may play a role in the regulation of renal and intestinal calcium and phosphate transport, cell metabolism, or cellular calcium/phosphate homeostasis. Constitutive over expression of human stanniocalcin 2 in mice resulted in pre- and postnatal growth restriction, reduced bone and skeletal muscle growth, and organomegaly. Expression of this gene is induced by estrogen and altered in some breast cancers.

Cystatins are a superfamily of cysteine proteinase inhibitors found in both plants and animals. They comprise a group of proteinase inhibitors, widely distributed in tissues and body fluids, and form tight complexes with cysteine proteases such as cathepsin B, H, L and S. Cystatin C, a secreted molecule of this family, is of interest from biochemical, medicine and evolutionary points of view. Cystatin C, with molecular weight of 13260 Da, is composed of 120 amino acids, lacks carbohydrate and has two disulfide bridges located near the carboxyl terminus. Cystatin C is increased in patients with malignant diseases, and is related to the insufficiency of renal function and appears to be a better marker than creatinine. On the other hand, low levels of cystatin C involve cause the breakdown of the elastic laminae and, subsequently, the atherosclerosis and abdominal aortic aneurysm.

CST6 belongs to the type 2 cystatin family. Unlike other family members that act as active cysteine protease inhibitors, CST6 restrain the inhibition of cathepsin B but is not active against cathepsin C. CST6 are secretable proteins that influence osteogenesis and bone resorption, regulation of the hepatocyte growth factor receptors, and the response to systemic inflammation.

Pleckstrin homology-like domain family A member 2 (PHLDA2) is a cytoplasmic protein, which is involved in fetal and placental growth. PHLDA2 is an apoptosis-related protein, which acts as a negative growth regulator and is expressed during normal human development. PHLDA2 is imprinted on placenta, liver and fetal tissues during embryogenesis and is removed once development is complete. The PHLDA2 gene is one of a number of genes in the imprinted gene domain of 11p15.5 which is considered to be an important tumor suppressor gene region. Changes in this region may be linked to the Beckwith-Wiedemann syndrome, Wilms tumor, rhabdomyosarcoma, adrenocortical carcinoma, and lung, ovarian, and breast cancer. PHLDA2 is expressed in placenta (present in all cells of the villous cytotrophoblast) and adult prostate gland. Furthermore, PHLDA2 is expressed in adult brain and neuroblastoma, medullablastoma and glioblastoma cell lines and at low levels in adult liver and lung, and fetal liver.

SERPINA1 is secreted and is a serine protease inhibitor which its targets include elastase, plasmin, collagenase, leucocytic proteases, trypsin, chymotrypsin, and plasminogen activator. Defects in SERPINA1 gene can cause emphysema or liver disease. SERPINA1 is an endogenous inhibitor of serine proteases and inhibits the catalytic domain of human recombinant matriptase in vitro. Rise in SERPINA1 occurs as an acute phase response to tissue necrosis and inflammation. mutations in SERPINA1 and SLC11A1 genes change the balance between elastase produced by leukocytes during phagocytosis.

Clusterin also named Apolipoprotein J (APO-J) is a 75-80 kD disulfide-linked heterodimeric protein containing about 30% of N-linked carbohydrate rich in sialic acid but truncated forms targeted to the nucleus have also been identified.
The precursor polypeptide chain is cleaved proteolytically to remove the 22-mer secretory signal peptide and subsequently between residues 227/228 to generate the a and b chains. These are assembled in anti-parallel to give a heterodimeric molecule in which the cysteine-rich centers are linked by five disulfide bridges and are flanked by two predicted coiled-coil a-helices and three predicted amphipathic a-helices.
Across a broad range of species clusterin shows a high degree of sequence homology ranging from 70% to 80%. It is nearly ubiquitously expressed in most mammalian tissues and can be found in plasma, milk, urine, cerebrospinal fluid and semen.
It is able to bind and form complexes with numerous partners such as immunoglobulins, lipids, heparin, bacteria, complement components, paraoxonase, beta amyloid, leptin and others. Clusterin has been ascribed a plethora of functions such as phagocyte recruitment, aggregation induction, complement attack prevention, apoptosis inhibition, membrane remodeling, lipid transport, hormone transport and/or scavenging, matrix metalloproteinase inhibition.
A genuine function of clusterin has not been defined. One tempting hypothesis says that clusterin is an extracellular chaperone protecting cells from stress induced insults caused by degraded and misfolded protein precipitates.
Clusterin is up- or down regulated on the mRNA or protein level in many pathological and clinically relevant situations including cancer, organ regeneration, infection, Alzheimer disease, retinitis pigmentosa, myocardial infarction, renal tubular damage, autoimmunity and others.

Cathepsin D is synthesized as a 54kDa precursor, which is proteolytically processed to an intermediate 48kDa single chain, which matures into more stable 34kDa and 14kDa two chain form. It is an estrogen-regulated lysosomal protease that has been suggested to facilitate cancer cell migration and invasion by digesting the basement membrane, extracellular matrix, and xonnective tissue. Because of its mitogenic and proteolytic activities, it has been implicated as a prognostic marker in many tumor types. Cathepsin D is expressed in epithelial cells as well as in macrophages.

FHIT enzyme cleaves adenosine 5'' PPP 5'' A to yield AMP and ADP. FHIT gene includees the regular fragile site FRA3B on chromosome 3. Alterations and deletions of the FHIT gene are highly linked to the genesis and establishment of human tumors of the lung, cervix, breast, colon, stomach and pancreas. In normal cells, FHIT functions as a tumor suppressor and physically relates with ubiquitin conjugating enzyme 9.

Ferritin is a fairly large, iron-storage heteropolymeric protein composed of 2 subunit types, light Ferritin & heavy Ferritin polypeptides, which is expressed in most kinds of cells and co-assemble in different proportion in a tissue-specific manner. Ferritin is composed of 24 self-assembled polypeptide subunits of the heavy and light ferritin chains and is characterized by the capacity to remove Fe (II) from solution in the presence of oxygen.
Ferritin light polypeptide protein is the main intracellular iron storage protein in prokaryotes and eukaryotes. Variation in ferritin subunit composition influence the rates of iron uptake and release in various tissues. A key function of ferritin is the storage of iron in a soluble and nontoxic state. Defects in this light chain ferritin gene are associated with several neurodegenerative diseases and hyper ferrit anemia-cataract syndrome.
Ferritin stores iron in a soluble, nontoxic, readily accessible form. Ferritin is needed for iron homeostasis. Iron is taken up in the ferrous form and deposited as ferric hydroxides after it has been oxidized.

SELPLG glycoprotein functions as a high affinity counter-receptor for the cell adhesion selectin molecules (P, E and L) located in stimulated T lymphocytes and myeloid cells. SELPLG binds leukocytes to activated platelets or endothelia expressing selectins, a vital role in leukocyte trafficking throughout inflammation. In order to have a high-affinity binding activity SELPLG needs two post-translational modifications, tyrosine sulfation and the addition of the sialyl Lewis x tetrasaccharide (sLex) to its O-linked glycans. Polymorphisms and abnormal expression of SELPLG are linked to defects in the innate and adaptive immune response. Alternate splicing results in multiple transcript variants.

Complement Factor D (Adipsin), which belongs to the trypsin family of peptidases, is involved in the alternative complement pathway of the complement system where it cleaves factor B. In the alternative complement pathway, Adipsin is best known for its role in humoral suppression of infectious agents. In addition, Adipsin is a serine protease which is secreted by adipocytes into the bloodstream. Ultimately, Adipsin has a high level of expression in fat, proposing a role for adipose tissue in immune system biology.

Fibronectin Leucine Rich Transmembrane Protein 3, also known as FLRT3 is a member of the fibronectin leucine rich transmembrane protein (FLRT) family. FLRT3 contains one fibronectin type-III domain as well as 10 LRR (leucine-rich) repeats and is expressed in the kidney, brain, pancreas, skeletal muscle, lung, liver, placenta, and heart. In addition, the members of the FLRT family play a role in cell adhesion as well as receptor signaling. FLRT3 has been implicated in neurite outgrowth after nerve damage, as a positive regulator of FGF signalling and in homotypic cell adhesion. Furthermore, FLRT3 has an essential function in regulating cellular adhesion among the epithelial apical ridge and the underlying mesenchyme and also in the establishment of the dorso-ventral position of the ridge.

SRGN is identified as a hematopoietic cell granule proteoglycan. Proteoglycans stored in the secretory granules of various hematopoietic cells also hold a protease-resistant peptide core, and is vital for neutralizing hydrolytic enzymes. SRGN is related to the macromolecular complex of granzymes and perforin that acts as a intermediary of granule-mediated apoptosis.

Filamin binding LIM protein 1 (FBLIM1) plays a role as an anchoring site for cell-ECM adhesion proteins and filamin-containing actin filaments. FBLIM1 is involved in cell shape spreading and motility. FBLIM1 participates in the regulation of filamin-mediated cross-linking and stabilization of actin filaments. FBLIM1 promotes stimulation of integrins and regulates integrin-mediated cell-cell adhesion.

A 16-kDa peptide hormone secreted from white adipocytes and implicated in the regulation of food intake and energy balance. Leptin provides the key afferent signal from fat cells in the feedback system that controls body fat stores.