Transactivator

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.

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

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.

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