Phosphatase and tensin homolog (PTEN) is a phosphatase in humans and is encoded by the PTEN gene. [6] Mutations of this gene are a step in the development of many cancers, specifically glioblastoma, lung cancer, breast cancer, and prostate cancer. Genes corresponding to PTEN (orthologs) [7] have been identified in most mammals for which complete genome data are available.
PTEN acts as a tumor suppressor gene through the action of its phosphatase protein product. This phosphatase is involved in the regulation of the cell cycle, preventing cells from growing and dividing too rapidly. [8] It is a target of many anticancer drugs.
The protein encoded by this gene is a phosphatidylinositol-3,4,5-trisphosphate 3-phosphatase. It contains a tensin-like domain as well as a catalytic domain similar to that of the dual specificity protein tyrosine phosphatases. Unlike most of the protein tyrosine phosphatases, this protein preferentially dephosphorylates phosphoinositide substrates. It negatively regulates intracellular levels of phosphatidylinositol-3,4,5-trisphosphate in cells and functions as a tumor suppressor by negatively regulating the Akt/PKB signaling pathway. [9]
PTEN protein acts as a phosphatase to dephosphorylate phosphatidylinositol (3,4,5)-trisphosphate (PtdIns (3,4,5)P3 or PIP3). PTEN specifically catalyses the dephosphorylation of the 3` phosphate of the inositol ring in PIP3, resulting in the biphosphate product PIP2 (PtdIns(4,5)P2). This dephosphorylation is important because it results in inhibition of the Akt signaling pathway, which plays an important role in regulating cellular behaviors such as cell growth, survival, and migration.
PTEN also has weak protein phosphatase activity, but this activity is also crucial for its role as a tumor suppressor. PTEN's protein phosphatase activity may be involved in the regulation of the cell cycle, preventing cells from growing and dividing too rapidly. [8] There have been numerous reported protein substrates for PTEN, including IRS1 [10] and Dishevelled. [11]
PTEN appears to play a critical role in the DNA damage response and the repair of DNA damage, particularly in double-strand break repair and nucleotide excision repair. [12]
The structure of the core of PTEN (solved by X-ray crystallography, see figure to the upper right [5] ) reveals that it consists primarily of a phosphatase domain, and a C2 domain: the phosphatase domain contains the active site, which carries out the enzymatic function of the protein, while the C2 domain binds the phospholipid membrane. Thus PTEN binds the membrane through both its phosphatase and C2 domains, bringing the active site to the membrane-bound PIP3 to dephosphorylate it.
The two domains of PTEN, a protein tyrosine phosphatase domain and a C2 domain, are inherited together as a single unit and thus constitute a superdomain, not only in PTEN but also in various other proteins in fungi, plants and animals, for example, tensin proteins and auxilin. [13]
The active site of PTEN consists of three loops, the TI Loop, the P Loop, and the WPD Loop, all named following the PTPB1 nomenclature. [5] Together they form an unusually deep and wide pocket which allows PTEN to accommodate the bulky phosphatidylinositol 3,4,5-trisphosphate substrate. The dephosphorylation reaction mechanism of PTEN is thought to proceed through a phosphoenzyme intermediate, with the formation of a phosphodiester bond on the active site cysteine, C124.
Not present in the crystal structure of PTEN is a short 10-amino-acid unstructured region N-terminal of the phosphatase domain (from residues 6 to 15), known variously as the PIP2 Binding Domain (PBD) or PIP2 Binding Motif (PBM) [14] [15] [16] This region increases PTEN's affinity for the plasma membrane by binding to Phosphatidylinositol 4,5-bisphosphate, or possibly any anionic lipid.
Also not present in the crystal structure is the intrinsically disordered C-terminal region (CTR) (spanning residues 353–403). The CTR is constitutively phosphorylated at various positions that effect various aspects of PTEN, including its ability to bind to lipid membranes, and also act as either a protein or lipid phosphatase. [17] [18]
Additionally, PTEN can also be expressed as PTEN-L [19] (known as PTEN-Long, or PTEN-α [20] ), a leucine initiator alternative start site variant, which adds an additional 173 amino acids to the N-terminus of PTEN. The exact role of this 173-amino acid extension is not yet known, either causing PTEN to be secreted from the cell, or to interact with the mitochondria. The N-terminal extension has been predicted to be largely disordered, [21] although there is evidence that there is some structure in the last twenty amino acids of the extension (most proximal to the start methionine of PTEN). [18]
PTEN is one of the most commonly lost tumor suppressors in human cancer; in fact, up to 70% of men with prostate cancer are estimated to have lost a copy of the PTEN gene at the time of diagnosis. [22] A number of studies have found increased frequency of PTEN loss in tumours which are more highly visible on diagnostic scans such as mpMRI, potentially reflecting increased proliferation and cell density in these tumours. [23]
During tumor development, mutations and deletions of PTEN occur that inactivate its enzymatic activity leading to increased cell proliferation and reduced cell death. Frequent genetic inactivation of PTEN occurs in glioblastoma, endometrial cancer, and prostate cancer; and reduced expression is found in many other tumor types such as lung and breast cancer. Furthermore, PTEN mutation also causes a variety of inherited predispositions to cancer.
Researchers have identified more than 70 mutations in the PTEN gene in people with Cowden syndrome.[ citation needed ] These mutations can be changes in a small number of base pairs or, in some cases, deletions of a large number of base pairs.[ citation needed ] Most of these mutations cause the PTEN gene to make a protein that does not function properly or does not work at all. The defective protein is unable to stop cell division or signal abnormal cells to die, which can lead to tumor growth, particularly in the breast, thyroid, or uterus. [24]
Mutations in the PTEN gene cause several other disorders that, like Cowden syndrome, are characterized by the development of non-cancerous tumors called hamartomas. These disorders include Bannayan–Riley–Ruvalcaba syndrome and Proteus-like syndrome. Together, the disorders caused by PTEN mutations are called PTEN hamartoma tumor syndromes, or PHTS. Mutations responsible for these syndromes cause the resulting protein to be non-functional or absent. The defective protein allows the cell to divide in an uncontrolled way and prevents damaged cells from dying, which can lead to the growth of tumors. [24]
Defects of the PTEN gene have been cited to be a potential cause of autism spectrum disorders. [25]
When defective, PTEN protein interacts with the protein of a second gene known as Tp53 to dampen energy production in neurons. This severe stress leads to a spike in harmful mitochondrial DNA changes and abnormal levels of energy production in the cerebellum and hippocampus, brain regions critical for social behavior and cognition. When PTEN protein is insufficient, its interaction with p53 triggers deficiencies and defects in other proteins that also have been found in patients with learning disabilities including autism. [25] People with autism and PTEN mutations may have macrocephaly (unusually large heads). [26]
Patients with defective PTEN can develop cerebellar mass lesions called dysplastic gangliocytomas or Lhermitte–Duclos disease. [24]
PTEN's strong link to cell growth inhibition is being studied as a possible therapeutic target in tissues that do not traditionally regenerate in mature animals, such as central neurons. PTEN deletion mutants have recently [27] been shown to allow nerve regeneration in mice. [28] [29]
Bisperoxovanadium compounds may have a neuroprotective effect after CNS injury. [30] PTEN is inhibited by sarcopoterium. [31]
Cell lines with known PTEN mutations include:
PTEN has been shown to interact with:
A benign tumor is a mass of cells (tumor) that does not invade neighboring tissue or metastasize. Compared to malignant (cancerous) tumors, benign tumors generally have a slower growth rate. Benign tumors have relatively well differentiated cells. They are often surrounded by an outer surface or stay contained within the epithelium. Common examples of benign tumors include moles and uterine fibroids.
Protein kinase B (PKB), also known as Akt, is the collective name of a set of three serine/threonine-specific protein kinases that play key roles in multiple cellular processes such as glucose metabolism, apoptosis, cell proliferation, transcription, and cell migration.
Cowden syndrome is an autosomal dominant inherited condition characterized by benign overgrowths called hamartomas as well as an increased lifetime risk of breast, thyroid, uterine, and other cancers. It is often underdiagnosed due to variability in disease presentation, but 99% of patients report mucocutaneous symptoms by age 20–29. Despite some considering it a primarily dermatologic condition, Cowden's syndrome is a multi-system disorder that also includes neurodevelopmental disorders such as macrocephaly.
Phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3), abbreviated PIP3, is the product of the class I phosphoinositide 3-kinases' (PI 3-kinases) phosphorylation of phosphatidylinositol (4,5)-bisphosphate (PIP2). It is a phospholipid that resides on the plasma membrane.
Phosphoinositide 3-kinases (PI3Ks), also called phosphatidylinositol 3-kinases, are a family of enzymes involved in cellular functions such as cell growth, proliferation, differentiation, motility, survival and intracellular trafficking, which in turn are involved in cancer.
Phosphatidylinositol (3,4)-bisphosphate is a minor phospholipid component of cell membranes, yet an important second messenger. The generation of PtdIns(3,4)P2 at the plasma membrane activates a number of important cell signaling pathways.
Proto-oncogene c-KIT is the gene encoding the receptor tyrosine kinase protein known as tyrosine-protein kinase KIT, CD117 or mast/stem cell growth factor receptor (SCFR). Multiple transcript variants encoding different isoforms have been found for this gene. KIT was first described by the German biochemist Axel Ullrich in 1987 as the cellular homolog of the feline sarcoma viral oncogene v-kit.
CHEK2 is a tumor suppressor gene that encodes the protein CHK2, a serine-threonine kinase. CHK2 is involved in DNA repair, cell cycle arrest or apoptosis in response to DNA damage. Mutations to the CHEK2 gene have been linked to a wide range of cancers.
The enzyme phosphatidylinositol-3,4,5-trisphosphate 3-phosphatase (EC 3.1.3.67) catalyzes the chemical reaction
5′-nucleotidase (5′-NT), also known as ecto-5′-nucleotidase or CD73, is an enzyme that in humans is encoded by the NT5E gene. CD73 commonly serves to convert AMP to adenosine.
Deleted in Liver Cancer 1 also known as DLC1 and StAR-related lipid transfer protein 12 (STARD12) is a protein which in humans is encoded by the DLC1 gene.
Receptor-type tyrosine-protein phosphatase kappa is an enzyme that in humans is encoded by the PTPRK gene. PTPRK is also known as PTPkappa and PTPκ.
Receptor-type tyrosine-protein phosphatase T is an enzyme that in humans is encoded by the PTPRT gene.
Phosphatase and tensin homolog, pseudogene 1, also known as PTENP1, is a human pseudogene. which has a partial reactivated function as a competing endogenous RNA regulating the tumor suppressor gene PTEN.
Putative tyrosine-protein phosphatase TPTE is an enzyme that in humans is encoded by the TPTE gene.
The Akt signaling pathway or PI3K-Akt signaling pathway is a signal transduction pathway that promotes survival and growth in response to extracellular signals. Key proteins involved are PI3K and Akt.
In the field of biochemistry, PDPK1 refers to the protein 3-phosphoinositide-dependent protein kinase-1, an enzyme which is encoded by the PDPK1 gene in humans. It is implicated in the development and progression of melanomas.
The PI3K/AKT/mTOR pathway is an intracellular signaling pathway important in regulating the cell cycle. Therefore, it is directly related to cellular quiescence, proliferation, cancer, and longevity. PI3K activation phosphorylates and activates AKT, localizing it in the plasma membrane. AKT can have a number of downstream effects such as activating CREB, inhibiting p27, localizing FOXO in the cytoplasm, activating PtdIns-3ps, and activating mTOR which can affect transcription of p70 or 4EBP1. There are many known factors that enhance the PI3K/AKT pathway including EGF, shh, IGF-1, insulin, and calmodulin. Both leptin and insulin recruit PI3K signalling for metabolic regulation. The pathway is antagonized by various factors including PTEN, GSK3B, and HB9.
Tensin was first identified as a 220 kDa multi-domain protein localized to the specialized regions of plasma membrane called integrin-mediated focal adhesions. Genome sequencing and comparison have revealed the existence of four tensin genes in humans. These genes appear to be related by ancient instances of gene duplication.
Voltage sensitive phosphatases or voltage sensor-containing phosphatases, commonly abbreviated VSPs, are a protein family found in many species, including humans, mice, zebrafish, frogs, and sea squirt.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.