Lipid phosphate phosphohydrolase 3 (LPP3), also known as

phospholipid Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...

phosphatase In biochemistry, a phosphatase is an enzyme that uses water to cleave a phosphoric acid Ester, monoester into a phosphate ion and an Alcohol (chemistry), alcohol. Because a phosphatase enzyme catalysis, catalyzes the hydrolysis of its Substrate ...

3 (PLPP3) and phosphatidic acid phosphatase type 2B (PAP-2b or PPAP2B), is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

that in humans is encoded by the ''PPAP2B''

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

chromosome 1 Chromosome 1 is the designation for the largest human chromosome. Humans have two copies of chromosome 1, as they do with all of the autosomes, which are the non-sex chromosomes. Chromosome 1 spans about 249 million nucleotide base pairs, which ar ...

. It is ubiquitously expressed in many tissues and cell types. LPP3 is a

cell-surface The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...

that

hydrolyzes Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

extracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

lysophosphatidic acid Lysophosphatidic acid (LPA) is a phospholipid derivative that can act as a signaling molecule. Function LPA acts as a potent mitogen due to its activation of three high-affinity G-protein-coupled receptors called LPAR1, LPAR2, and LPAR3 (also kn ...

(LPA) and short-chain phosphatidic acid. Its function allows it to regulate

vascular The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...

and

embryonic development An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

by inhibiting LPA signaling, which is associated with a wide range of human diseases, including

cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...

and

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

, as well as developmental defects. The PPAP2B gene also contains one of 27 loci associated with increased risk of

coronary artery disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pla ...

Structure

Gene

The ''PPAP2B'' gene resides on chromosome 1 at the band 1p32.2 and includes 6

exon An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequen ...

Protein

LPP3 is a member of the PAP-related phosphoesterase family. It is a type 2 activity PAP, which localizes to the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

, and is one of four known LPP

isoforms A protein isoform, or "protein variant", is a member of a set of highly similar proteins that originate from a single gene or gene family and are the result of genetic differences. While many perform the same or similar biological roles, some isof ...

. As an

integral membrane protein An integral, or intrinsic, membrane protein (IMP) is a type of membrane protein that is permanently attached to the biological membrane. All ''transmembrane proteins'' are IMPs, but not all IMPs are transmembrane proteins. IMPs comprise a signi ...

, LPP3 contains six hydrophobic

transmembrane domain A transmembrane domain (TMD) is a membrane-spanning protein domain. TMDs generally adopt an alpha helix topological conformation, although some TMDs such as those in porins can adopt a different conformation. Because the interior of the lipid bil ...

s and a hydrophilic

catalytic site In biology and biochemistry, the active site is the region of an enzyme where Enzyme substrate, substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid, amino acid residues that form temporary bonds with t ...

composed of three conserved domains. One catalytic domain is proposed to bind the substrate while the other two contribute to

dephosphorylation In biochemistry, dephosphorylation is the removal of a phosphate (PO43−) group from an organic compound by hydrolysis. It is a reversible post-translational modification. Dephosphorylation and its counterpart, phosphorylation, activate and deac ...

of the substrate. The catalytic site typically faces the extracellular matrix when located on the cell membrane and faces the lumen when located in intracellular membranes. This protein can form homo- and hetero-

oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...

Function

This protein is a membrane glycoprotein localized at the cell

. It has been shown to actively hydrolyze extracellular lysophosphatidic acid (LPA) and short-chain

phosphatidic acid Phosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels. Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty ac ...

. As an LPA inhibitor, PPAP2B is known to suppress LPA receptor mediated cellular signaling, which is associated with activation of vascular and blood cells and

epithelial cell Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

migration and proliferation. In response to dynamic atherorelevant-flows, PPAP2B can promote anti-inflammatory phenotype via inhibition of LPA signaling and maintain vascular integrity of endothelial monolayer. This flow-sensitive PPAP2B expression is inhibited by microRNA-92a and activated by transcription factor

KLF2 Krüppel-like Factor 2 (KLF2), also known as lung Krüppel-like Factor (LKLF), is a protein that in humans is encoded by the ''KLF2'' gene on chromosome 19. It is in the Krüppel-like factor family of zinc finger transcription factors, and it has ...

. In addition to LPA receptor-mediated signaling, PPAP2B is also associated with

Wnt signaling The Wnt signaling pathways are a group of signal transduction pathways which begin with proteins that pass signals into a cell through cell surface receptors. The name Wnt is a portmanteau created from the names Wingless and Int-1. Wnt signaling p ...

, functioning in embryonic development for proper formation of important tissues including bone, heart and muscle. The phenotype of axis duplication in mice globally lacking PPAP2B resembles that observed in animals with altered Wnt signaling. Furthermore, Wnt signaling mediated TCF/LEF-transcription via

β-catenin Catenin beta-1, also known as beta-catenin (β-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene. Beta-catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcriptio ...

is upregulated in PPAP2B null

embryonic stem cell Embryonic stem cells (ESCs) are pluripotent stem cells derived from the inner cell mass of a blastocyst, an early-stage pre- implantation embryo. Human embryos reach the blastocyst stage 4–5 days post fertilization, at which time they consi ...

s, implicating LPP3 as a negative regulator of the Wnt pathway.

Clinical Significance

Due to the regulatory role of LPP3 in vascular and

, inactivation of this protein can contribute to cardiovascular disease and developmental complications. For example, inducible inactivation of LPP3 in both endothelial and hematopoietic cells leads to atherosclerosis due to accumulation of LPA in human plaques. Likewise, plasma LPA levels are significantly elevated in patients with

acute coronary syndrome Acute coronary syndrome (ACS) is a syndrome (a set of signs and symptoms) due to decreased blood flow in the coronary arteries such that part of the heart muscle is unable to function properly or dies. The most common symptom is centrally loca ...

s. It was further observed that reduced levels of

endothelial The endothelium 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 rest of the vessel ...

LPP3 is associated with disturbed flow and mechano-regulation in blood vessels. During embryonic development in mice, inactivation of LPP3 results in early lethality in part due to failure of extra-embryonic vascular development. Abnormal activation of LPA signaling has also been implicated in cancer,

fibrotic Fibrosis, also known as fibrotic scarring, is a pathological wound healing in which connective tissue replaces normal parenchymal tissue to the extent that it goes unchecked, leading to considerable tissue remodelling and the formation of perman ...

disorders, and

metabolic syndrome Metabolic syndrome is a clustering of at least three of the following five medical conditions: abdominal obesity, high blood pressure, high blood sugar, high serum triglycerides, and low serum high-density lipoprotein (HDL). Metabolic syndrome ...

(involving

insulin resistance Insulin resistance (IR) is a pathological condition in which cell (biology), cells fail to respond normally to the hormone insulin. Insulin is a hormone that facilitates the transport of glucose from blood into cells, thereby reducing blood gluco ...

Clinical Marker

In humans, PPAP2B emerged as 1 of 13 new loci associated with coronary artery disease by

genome-wide association studies In genomics, a genome-wide association study (GWA study, or GWAS), also known as whole genome association study (WGA study, or WGAS), is an observational study of a genome-wide set of genetic variants in different individuals to see if any varia ...

(GWAS). This prediction appears to be independent of traditional risk factors for cardiovascular disease such as high cholesterol levels, high blood pressure, obesity, smoking, and

diabetes mellitus Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...

. Additionally, a multi-locus genetic risk score study, based on a combination of 27 loci including the PPAP2B gene, identified individuals at increased risk for both incident and recurrent coronary artery disease events, as well as an enhanced clinical benefit from

statin Statins, also known as HMG-CoA reductase inhibitors, are a class of lipid-lowering medications that reduce illness and mortality in those who are at high risk of cardiovascular disease. They are the most common cholesterol-lowering drugs. Low- ...

therapy. The study was based on a community cohort study (the Malmo Diet and Cancer study) and four additional randomized controlled trials of primary prevention cohorts (JUPITER and ASCOT) and secondary prevention cohorts (CARE and PROVE IT-TIMI 22). Taken together, these findings also suggest that PPAP2B and LPA may serve a role in predicting and screening coronary artery disease for early prevention.

Interactions

Interactive Pathway Map

LPP3 participates in interactions within th
triacylglyceride synthesis
an
sphingolipid metabolism pathways