Transactivation

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In the context of gene regulation: transactivation is the increased rate of gene expression triggered either by biological processes or by artificial means, through the expression of an intermediate transactivator protein.

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In the context of receptor signaling, transactivation occurs when one or more receptors activate yet another; [1] [2] receptor transactivation may result from the crosstalk of signaling cascades or the activation of G protein–coupled receptor hetero-oligomer subunits, among other mechanisms. [1]

Natural transactivation

Transactivation can be triggered either by endogenous cellular or viral proteins, also called transactivators. These protein factors act in trans (i.e., intermolecularly). HIV and 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. HTLV, for instance, has been associated with causing leukemia primarily through this process. Its transactivator, Tax , can interact with p40, inducing overexpression of interleukin 2, interleukin receptors, GM-CSF and the transcription factor c-Fos. HTLV infects T-cells and via the increased expression of these stimulatory cytokines and transcription factors, leads to uncontrolled proliferation of T-cells and hence 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. The transactivator gene expresses a transcription factor that binds to specific promoter region of DNA. By binding to the 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, we can measure when the transactivator is being expressed.

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Regulation of gene expression

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STAT protein

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c-Fos

In the fields of molecular biology and genetics, c-Fos is a proto-oncogene that is the human homolog of the retroviral oncogene v-fos. It was first discovered in rat fibroblasts as the transforming gene of the FBJ MSV. It is a part of a bigger Fos family of transcription factors which includes c-Fos, FosB, Fra-1 and Fra-2. It has been mapped to chromosome region 14q21→q31. c-Fos encodes a 62 kDa protein, which forms heterodimer with c-jun, resulting in the formation of AP-1 complex which binds DNA at AP-1 specific sites at the promoter and enhancer regions of target genes and converts extracellular signals into changes of gene expression. It plays an important role in many cellular functions and has been found to be overexpressed in a variety of cancers.

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AP-1 transcription factor

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CIITA

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ETS1

Protein C-ets-1 is a protein that in humans is encoded by the ETS1 gene. The protein encoded by this gene belongs to the ETS family of transcription factors.

CEBPB

CCAAT/enhancer-binding protein beta is a protein that in humans is encoded by the CEBPB gene.

ATF1

Cyclic AMP-dependent transcription factor ATF-1 is a protein that in humans is encoded by the ATF1 gene.

RFX1

MHC class II regulatory factor RFX1 is a protein that, in humans, is encoded by the RFX1 gene located on the short arm of chromosome 19.

NFATC4

Nuclear factor of activated T-cells, cytoplasmic 4 is a protein that in humans is encoded by the NFATC4 gene.

CREB3

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RFX2

DNA-binding protein RFX2 is a protein that in humans is encoded by the RFX2 gene.

FOXK2

Forkhead box protein K2 is a protein that in humans is encoded by the FOXK2 gene.

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References

  1. 1 2 "receptor transactivation". EMBL. GO Consortium. Retrieved 6 April 2015.
  2. Beaulieu JM, Espinoza S, Gainetdinov RR (January 2015). "Dopamine receptors - IUPHAR Review 13". Br. J. Pharmacol. 172 (1): 1–23. doi:10.1111/bph.12906. PMC   4280963 . PMID   25671228. 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).