Platelet endothelial cell adhesion molecule (PECAM-1) also known as cluster of differentiation 31 (CD31) is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

that in humans is encoded by the ''PECAM1''

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

found on chromosome17q23.3. PECAM-1 plays a key role in removing aged neutrophils from the body.

Structure

PECAM-1 is a highly glycosylated

with a mass of approximately 130 kDa. The structure of this protein was determined by

molecular cloning Molecular cloning is a set of experimental methods in molecular biology that are used to assemble recombinant DNA molecules and to direct their DNA replication, replication within Host (biology), host organisms. The use of the word ''cloning'' re ...

in 1990, when it was found out that PECAM-1 has an N-terminal domain with 574 amino acids, a transmembrane domain with 19 amino acids and a C-terminal cytoplasmic domain with 118 amino acids. The N-terminal domain consists of six extracellular Ig-like domains.

Interactions

PECAM-1 is a cell-cell adhesion protein which interacts with other PECAM-1 molecules through homophilic interactions or with non-PECAM-1 molecules through heterophilic interactions''.'' Homophilic interactions between PECAM-1 molecules are mediated by antiparallel interactions between extracellular Ig-like domain 1 and Ig-like domain 2. These interactions are regulated by the level of PECAM-1 expression. Homophilic interactions occur, only when the surface expression of PECAM-1 is high. Otherwise, when expression is low, heterophilic interactions occur.

Tissue distribution

CD31 is normally found on endothelial cells, platelets, macrophages and Kupffer cells, granulocytes, lymphocytes (T cells, B cells, and NK cells), megakaryocytes, osteoclasts, and brown adipocytes.

Immunohistochemistry

immunohistochemistry Immunohistochemistry is a form of immunostaining. It involves the process of selectively identifying antigens in cells and tissue, by exploiting the principle of Antibody, antibodies binding specifically to antigens in biological tissues. Alber ...

, CD31 is used primarily to demonstrate the presence of

endothelial cells The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the res ...

in histological tissue sections. This can help to evaluate the degree of tumor

angiogenesis Angiogenesis is the physiological process through which new blood vessels form from pre-existing vessels, formed in the earlier stage of vasculogenesis. Angiogenesis continues the growth of the vasculature mainly by processes of sprouting and ...

, which can imply a rapidly growing tumor. Malignant endothelial cells also commonly retain the antigen, so that CD31 immunohistochemistry can also be used to demonstrate both angiomas and

angiosarcoma Angiosarcoma is a rare and aggressive cancer that starts in the endothelial cells that line the walls of blood vessels or lymphatic vessels. Since they are made from Endothelium, vascular lining, they can appear anywhere and at any age, but older ...

s. It can also be demonstrated in small lymphocytic and lymphoblastic lymphomas, although more specific markers are available for these conditions.

Function

PECAM-1 is found on the surface of

platelet Platelets or thrombocytes () are a part of blood whose function (along with the coagulation#Coagulation factors, coagulation factors) is to react to bleeding from blood vessel injury by clumping to form a thrombus, blood clot. Platelets have no ...

monocyte Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and monocyte-derived dendritic cells. As a part of the vertebrate innate immune system monocytes also ...

neutrophil Neutrophils are a type of phagocytic white blood cell and part of innate immunity. More specifically, they form the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. Their functions vary in differe ...

s, and some types of

T-cell T cells (also known as T lymphocytes) are an important part of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor (TCR) on their ce ...

s, and makes up a large portion of endothelial cell intercellular junctions. The encoded protein is a member of the

immunoglobulin An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as pathogenic bacteria, bacteria and viruses, includin ...

superfamily and is likely involved in

leukocyte White blood cells (scientific name leukocytes), also called immune cells or immunocytes, are cells of the immune system that are involved in protecting the body against both infectious disease and foreign entities. White blood cells are genera ...

transmigration,

, and

integrin Integrins are transmembrane receptors that help cell–cell and cell–extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, o ...

activation. CD31 on

endothelial cell The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and th ...

s binds to the

CD38 CD38 (cluster of differentiation 38), also known as cyclic ADP ribose hydrolase, is a glycoprotein found on the surface of many immune cells (white blood cells), including CD4+, CD8+, B lymphocytes and natural killer cells. CD38 also functions in ...

receptor on

natural killer cell Natural killer cells, also known as NK cells, are a type of cytotoxic lymphocyte critical to the innate immune system. They are a kind of large granular lymphocytes (LGL), and belong to the rapidly expanding family of known innate lymphoid cells ...

s for those cells to attach to the

endothelium The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the r ...

Role in signaling

PECAM-1 plays a role in

cell signaling In biology, cell signaling (cell signalling in British English) is the Biological process, process by which a Cell (biology), cell interacts with itself, other cells, and the environment. Cell signaling is a fundamental property of all Cell (biol ...

. In the cytoplasmic domain of PECAM-1 are serine and tyrosine residues which are suitable for

phosphorylation In biochemistry, phosphorylation is described as the "transfer of a phosphate group" from a donor to an acceptor. A common phosphorylating agent (phosphate donor) is ATP and a common family of acceptor are alcohols: : This equation can be writ ...

. After the tyrosine is phosphorylated, PECAM-1 recruits Src homology 2 (SH2) domain–containing signaling proteins. These proteins can then initiate signaling pathways. Of all these proteins, the protein most widely reported as interacting with the PECAM-1 cytoplasmic domain is SH2 domain–containing protein-tyrosine phosphatase SHP-2. Signaling through PECAM-1 leads to the activation of

s and

Leukocyte transmigration

PECAM-1 is involved in migration of

monocytes Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and monocyte-derived dendritic cells. As a part of the vertebrate innate immune system monocytes also i ...

and neutrophils, natural killer cells, Vδ1+ γδ T lymphocytes and CD34+ hematopoietic progenitor cells through the endothelial cells. Moreover, PECAM-1 is involved in transendothelial migration of recent thymic emigrants to the secondary lymphoid organs. Mechanism of leukocyte transmigration can be explained by creating a homophilic interaction. In this interaction migrating leukocytes express PECAM-1 on the surface and then they react with PECAM-1 on the surface of endothelial cell.

Angiogenesis

PECAM-1 is also important for

because it enables the formation of new

blood vessels Blood vessels are the tubular structures of a circulatory system that transport blood throughout many animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the tissues of a body. They also take waste an ...

through the cell-cell adhesion.

Role of CD31 in diseases

Cancer

PECAM-1 is expressed by many solid tumor cell lines such as

hemangioma A hemangioma or haemangioma is a usually benign vascular tumor derived from blood vessel cell types. The most common form, seen in infants, is an infantile hemangioma, known colloquially as a "strawberry mark", most commonly presenting on the sk ...

, Kaposi’s sarcoma, breast carcinoma,

glioblastoma Glioblastoma, previously known as glioblastoma multiforme (GBM), is the most aggressive and most common type of cancer that originates in the brain, and has a very poor prognosis for survival. Initial signs and symptoms of glioblastoma are nons ...

, colon carcinoma, skin carcinoma and other tumor cell lines. On the surface of these tumor cells PECAM-1 mediates the adhesion to endothelial cells. PECAM-1 modulates tumor growth by the formation of new endothelial cell tubes. In mice, this process can be inhibited using an anti-PECAM-1

antibody An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as pathogenic bacteria, bacteria and viruses, includin ...

. Recently, it was found out that elderly patients with

gastric cancer Stomach cancer, also known as gastric cancer, is a malignant tumor of the stomach. It is a cancer that develops in the lining of the stomach. Most cases of stomach cancers are gastric carcinomas, which can be divided into a number of subtypes ...

have high concentration of PECAM-1 in the serum. That suggests that the use of a serum PECAM-1 level can be a good prognostic marker.

Atherosclerosis

Inhibition of PECAM-1 leads to a reduction of atherosclerotic lesions in mice. That means that PECAM-1 is involved in

atherosclerosis Atherosclerosis is a pattern of the disease arteriosclerosis, characterized by development of abnormalities called lesions in walls of arteries. This is a chronic inflammatory disease involving many different cell types and is driven by eleva ...

. The exact mechanism, how PECAM-1 contributes to

is not known, but there are some theories. PECAM-1 can act as a mechanoresponsive molecule. Or the pathogenesis can be caused by the infiltration of leukocytes mediated by PECAM-1. Finally, polymorphisms in the PECAM-1 gene can lead to the progression of atherosclerosis.

Disseminated intravascular coagulation

Extensive microvascular

thrombosis Thrombosis () is the formation of a Thrombus, blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (thrombocytes) and fib ...

and increased microvascular permeability are main characteristics of

disseminated intravascular coagulation Disseminated intravascular coagulation (DIC) is a condition in which blood clots form throughout the body, blocking Microvessel, small blood vessels. Symptoms may include chest pain, shortness of breath, leg pain, problems speaking, or problems ...

, a fatal complication of sepsis. Patients with this devastating condition have high levels of PECAM-1 in the serum indicating PECAM-1 as a good diagnostic marker. Moreover, PECAM-1 can protect from the development of

by inhibiting macrophage pyroptosis.

Neuroinflammation

PECAM-1 contributes to at least two of the nervous system diseases,

multiple sclerosis Multiple sclerosis (MS) is an autoimmune disease resulting in damage to myelinthe insulating covers of nerve cellsin the brain and spinal cord. As a demyelinating disease, MS disrupts the nervous system's ability to Action potential, transmit ...

and cerebral ischaemia. First signs of multiple sclerosis are defects in the blood brain barrier and leukocyte migration mediated by adhesion molecules such as PECAM-1. Moreover, monocytes in patients with multiple sclerosis express high level of PECAM-1. Cerebral ischaemia is caused by the accumulation of

leukocytes White blood cells (scientific name leukocytes), also called immune cells or immunocytes, are cells of the immune system that are involved in protecting the body against both infectious disease and foreign entities. White blood cells are genera ...

, which then infiltrate brain

parenchyma upright=1.6, Lung parenchyma showing damage due to large subpleural bullae. Parenchyma () is the bulk of functional substance in an animal organ such as the brain or lungs, or a structure such as a tumour. In zoology, it is the tissue that ...

and release toxic compounds such as oxygen radicals. Interactions between leukocyte and endothelium are mediated by PECAM-1. High levels of soluble PECAM-1 can be used to diagnose both diseases. Increased PECAM-1 levels indicate damage in the blood brain barrier in patients with multiple sclerosis and high PECAM-1 levels can be used as a short-term prediction of a stroke in patients with cerebral ischaemia.

References

External links

Human CD Antigen Chart (eBioscience)

* * {{Clusters of differentiation by lineage Clusters of differentiation