Editing Downregulation and upregulation (section)

{{Short description|Biological processes}}

In [[biochemistry]], in the [[biology|biological]] context of [[organism]]s' [[regulation of gene expression]] and production of [[gene products]], '''downregulation''' is the process by which a [[cell (biology)|cell]] decreases the production and quantities of its [[cellular component]]s, such as [[RNA]] and [[protein]]s, in response to an external stimulus. The complementary process that involves increase in quantities of cellular components is called '''upregulation.'''<ref>{{Cite journal |last1=Atkinson |first1=Taylor J |last2=Halfon |first2=Marc S |title=Regulation of Gene Expression in the Genomic Context |date=2014-01-01 |journal=Computational and Structural Biotechnology Journal |language=en |volume=9 |issue=13 |pages=e201401001 |doi=10.5936/csbj.201401001 |pmid=24688749 |pmc=3962188 |issn=2001-0370 |doi-access=free}}</ref>

An example of downregulation is the cellular decrease in the expression of a specific [[Receptor (biochemistry)|receptor]] in response to its increased activation by a molecule, such as a [[hormone]] or [[neurotransmitter]], which reduces the cell's sensitivity to the molecule. This is an example of a locally acting ([[negative feedback]]) mechanism.

An example of upregulation is the response of [[liver]] cells exposed to such [[xenobiotic]] molecules as [[Polychlorinated dibenzodioxins|dioxin]]. In this situation, the cells increase their production of [[cytochrome P450|cytochrome P450 enzymes]], which in turn increases degradation of these dioxin molecules.

Downregulation or upregulation of an RNA or protein may also arise by an [[epigenetics|epigenetic]] alteration. Such an epigenetic alteration can cause expression of the RNA or protein to no longer respond to an external stimulus. This occurs, for instance, during [[Behavioral epigenetics#Drug addiction|drug addiction]] or [[Cancer epigenetics|progression to cancer]].