# Transactivation

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In the context of gene regulation: '''transactivation''' is the increased rate of [gene expression](/source/gene_expression) triggered either by biological processes or by artificial means, through the expression of an intermediate transactivator protein.

In the context of receptor signaling, '''transactivation''' occurs when one or more receptors activate yet another;<ref name="Receptor transactivation">{{cite web|title=receptor transactivation|url=http://www.ebi.ac.uk/QuickGO/GTerm?id=GO:0035624|website=EMBL|publisher= GO Consortium|access-date=6 April 2015}}</ref><ref name="DA receptor 2015">{{cite journal | vauthors = Beaulieu JM, Espinoza S, Gainetdinov RR | title = Dopamine receptors - IUPHAR Review 13 | journal = Br. J. Pharmacol. | volume = 172 | issue = 1 | pages = 1–23 | date = January 2015 | pmid = 25671228 | pmc = 4280963 | doi = 10.1111/bph.12906 | quote = For instance, there are indications that both D1 and D2 receptors can trans-activate the brain-derived neurotrophic factor (BDNF) receptor in neurons (Swift et al., 2011). These two dopamine receptors can also regulate calcium channels through a direct protein–protein interaction in vivo (Kisilevsky and Zamponi, 2008; Kisilevsky et al., 2008). Direct interaction of D1 and D2 receptors and Na+-K+-ATPase has also been demonstrated (Hazelwood et al., 2008; Blom et al., 2012).}}</ref> receptor transactivation may result from the [crosstalk](/source/Crosstalk_(biology)) of [signaling cascade](/source/signaling_cascade)s or the activation of [G protein–coupled receptor hetero-oligomer](/source/GPCR_oligomer) subunits, among other mechanisms.<ref name="Receptor transactivation" />

== Natural transactivation ==
Transactivation can be triggered either by endogenous cellular or viral proteins, also called '''transactivators'''.  These protein factors [act in trans](/source/Trans_acting) (''i.e.'', [intermolecular](/source/intermolecular)ly). [HIV](/source/HIV) and [HTLV](/source/HTLV) are just two of the many viruses that encode transactivators to enhance viral gene expression. These transactivators can also be linked to cancer if they start interacting with, and increasing expression of, a cellular [proto-oncogene](/source/proto-oncogene). HTLV, for instance, has been associated with causing [leukemia](/source/leukemia) primarily through this process. Its transactivator, [''Tax''](/source/Tax_gene_product)'','' can interact with [p40](/source/p40_gene), inducing overexpression of [interleukin 2](/source/interleukin_2), [interleukin receptor](/source/interleukin_receptor)s, [GM-CSF](/source/GM-CSF) and the [transcription factor](/source/transcription_factor) [c-Fos](/source/c-Fos). HTLV infects [T-cell](/source/T-cell)s and via the increased expression of these stimulatory [cytokines](/source/cytokines) and [transcription factors](/source/transcription_factors), leads to uncontrolled proliferation of T-cells and hence [lymphoma](/source/lymphoma).

== Artificial transactivation ==
Artificial transactivation of a gene is achieved by inserting it into the genome at the appropriate area as transactivator gene adjoined to special promoter regions of [DNA](/source/DNA). The transactivator gene [expresses](/source/Gene_expression) a transcription factor that binds to specific promoter region of DNA. By binding to the [promoter region](/source/promoter_region) of a gene, the transcription factor causes that gene to be expressed. The expression of one transactivator gene can activate multiple genes, as long as they have the same, specific promoter region attached. Because the expression of the transactivator gene can be controlled, transactivation can be used to turn genes on and off. If this specific promoter region is also attached to a [reporter gene](/source/reporter_gene), we can measure when the transactivator is being expressed.

==See also==
* [Transrepression](/source/Transrepression)
* [Selective glucocorticoid receptor agonist](/source/Selective_glucocorticoid_receptor_agonist)

==References==
{{Reflist}}

==External links==
* {{MeshName|Transactivators}}

Category:Molecular biology

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Adapted from the Wikipedia article [Transactivation](https://en.wikipedia.org/wiki/Transactivation) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Transactivation?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.