biology

Tissue factor

Tissue factor is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Tissue factor rather than just read about it. In short: Tissue factor, also called platelet tissue factor or Coagulation factor III, is a protein present in subendothelial tissue and leukocytes which plays a major role in coagulation and, in humans, is encoded by F3 gene. Its role in the blood clotting is the initiation of thrombin formation from the zymogen prothrombin.

Key takeaways

Tissue factor belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tissue factor to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tissue factor from memory before moving on to harder problems.

Reference excerpt

Tissue factor, also called platelet tissue factor or Coagulation factor III, is a protein present in subendothelial tissue and leukocytes which plays a major role in coagulation and, in humans, is encoded by F3 gene. Its role in the blood clotting is the initiation of thrombin formation from the zymogen prothrombin. Thromboplastin defines the cascade that leads to the activation of factor X—the tissue factor pathway. In doing so, it has replaced the previously named extrinsic pathway in order to eliminate ambiguity.

Function The F3 gene encodes tissue factor also known as coagulation factor III, which is a cell surface glycoprotein. This factor enables cells to initiate the blood coagulation cascades, and it functions as the high-affinity receptor for the coagulation factor VII. The resulting complex provides a catalytic event that is responsible for initiation of the coagulation protease cascades by specific limited proteolysis. Unlike the other cofactors of these protease cascades, which circulate as nonfunctional precursors, this factor is a potent initiator that is fully functional when expressed on cell surfaces. There are three distinct domains of this factor: extracellular, transmembrane, and cytoplasmic. This protein is the only one in the coagulation pathway for which a congenital deficiency has not been described. In addition to the membrane-bound tissue factor, soluble form of tissue factor was also found which results from alternatively spliced tissue factor mRNA transcripts, in which exon 5 is absent and exon 4 is spliced directly to exon 6.

Coagulation

Tissue factor (TF) is the cell surface receptor for the serine protease factor VIIa. The best known function of tissue factor is its role in blood coagulation. The complex of TF with factor VIIa catalyzes the conversion of the inactive protease factor X into the active protease factor Xa. Together with factor VIIa, tissue factor forms the extrinsic pathway of coagulation. This is opposed to the intrinsic (amplification) pathway, which involves both activated factor IX and factor VIII. Both pathways lead to the activation of factor X (the common pathway), which combines with activated factor V in the presence of calcium and phospholipid to produce thrombin (thromboplastin activity).

Cytokine signaling TF is related to a protein family known as the cytokine receptor class II family. The members of this receptor family are activated by cytokines. Cytokines are small proteins that can influence the behavior of white blood cells. Binding of VIIa to TF has also been found to start signaling processes inside the cell. The signaling function of TF/VIIa plays a role in angiogenesis and apoptosis. Pro-inflammatory and pro-angiogenic responses are activated by TF/VIIa-mediated cleavage by the protease-activated receptor 2 (PAR2). EphB2 and EphA2 of the Eph tyrosine kinase receptor (RTK) family can also be cleaved by TF/VIIa.

Structure Tissue factor belongs to the cytokine receptor protein superfamily and consists of three domains:

an extracellular domain, which consists of two fibronectin type III modules whose hydrophobic cores merge in the domain-domain interface. This serves as a (probably rigid) template for factor VIIa binding. a transmembrane domain. a cytosolic domain of 21 amino acids length inside the cell which is involved in the signaling function of TF. Note that one of factor VIIa's domains, GLA domain, binds in the presence of calcium to negatively charged phospholipids, and this binding greatly enhances factor VIIa binding to tissue factor.

Tissue distribution Some cells release TF in response to blood vessel damage (see next paragraph) and some do only in response to inflammatory mediators (endothelial cells/macrophages). TF is expressed by cells which are normally not exposed to flowing blood, such as sub-endothelial cells (e.g. smooth muscle cells) and cells surrounding blood vessels (e.g. fibroblasts). This can change when the blood vessel is damaged by, for example, physical injury or rupture of atherosclerotic plaques. Exposure of TF-expressing cells during injury allows the complex formation of TF with factor VII. Factor VII and TF form an equimolar complex in the presence of calcium ions, leading to the activation of factor VII on a membrane surface. The inner surface of the blood vessel consists of endothelial cells. Endothelial cells do not express TF except when they are exposed to inflammatory molecules such as tumor necrosis factor-alpha (TNF-alpha). Another cell type that expresses TF on the cell surface in inflammatory conditions is the monocyte (a white blood cell).

Thromboplastin Historically, thromboplastin was a lab reagent, usually derived from placental sources, used to assay prothrombin times (PT time). Thromboplastin, by itself, could activate the extrinsic coagulation pathway. When manipulated in the laboratory, a derivative could be created called partial thromboplastin, which was used to measure the intrinsic pathway. This test is called the aPTT, or activated partial thromboplastin time. It was not until much later that the subcomponents of thromboplastin and partial thromboplastin were identified. Thromboplastin contains phospholipids as well as tissue factor, both of which are needed in the activation of the extrinsic pathway, whereas partial thromboplastin does not contain tissue factor. Tissue factor is not needed to activate the intrinsic pathway.

Interactions Tissue factor has been shown to interact with Factor VII.

Additional images

Illustrations

Worked examples

Example 1 — a first encounter with Tissue factor

Start with the simplest possible case. Write down what Tissue factor claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tissue factor before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tissue factor ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tissue factor

In research: Tissue factor appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tissue factor in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tissue factor is common in secondary-school and first-year university syllabi. It links to neighbouring topics Clusters of differentiation, Coagulation system, Genes on human chromosome 1, so understanding it makes those chapters shorter.
In everyday life: Look for Tissue factor outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Tissue factor in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tissue factor means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Tissue factor out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tissue factor in simple terms?

Why does Tissue factor matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tissue factor?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tissue factor.