claim: Natasha Lyonne is an American citizen.
evidence: In the biological context of organisms ' production of gene products , downregulation is the process by which a cell decreases the quantity of a cellular component , such as RNA or protein , in response to an external stimulus .. biological. biology. organisms. organism. production. regulation of gene expression. gene products. gene products. cell. cell ( biology ). RNA. RNA. protein. protein. The complementary process that involves increases of such components is called upregulation .. An example of downregulation is the cellular decrease in the number of receptors to a molecule , such as a hormone or neurotransmitter , which reduces the cell 's sensitivity to the molecule .. cell. cell ( biology ). receptors. Receptor ( biochemistry ). hormone. hormone. neurotransmitter. neurotransmitter. This is an example of a locally acting negative feedback mechanism .. negative feedback. negative feedback. An example of upregulation is the response of liver cells exposed to such xenobiotic molecules as dioxin .. liver. liver. xenobiotic. xenobiotic. dioxin. Polychlorinated dibenzodioxins. In this situation , the cells increase their production of cytochrome P450 enzymes , which in turn increases their degradation of these molecules .. production. regulation of gene expression. cytochrome P450 enzymes. cytochrome P450