ARNT Activity Unaltered by Phosphorylation

Gary Perdew
Pennsylvania State University
R01ES0927, R01ES04869 and T32ES05863

Background: Members of an emerging family of proteins known as the PAS proteins control a number of processes. ARNT (aryl hydrocarbon nuclear translocator protein) is one of the PAS proteins. Although phosphorylation of ARNT is poorly understood, previous research has suggested that serine residues, specifically serine at the 348th amino acid position (S348), are phosphorylated. Protein phosphorylations change enzyme activities and protein conformations. The eventual outcome is an alteration in cellular activity and changes in the program of genes expressed within the responding cells. ARNT interacts with the Ah receptor-ligand complex to form a heterodimer, which moves into the nucleus of the cell where it stimulates expression of numerous genes inlcuding those that are involved in the production of enzymes that metabolize aromatic environmental pollutants.

Advance: This laboratory has shown that phosphorylation of S348 is not necessary to set in motion the cascade of events leading to production of a battery of proteins involved in responding to environmental changes. A technique known as site-directed mutagenesis was used to create two altered forms of ARNT with alanine or glutamic acid substitutions in place of the S348 which prevented phosphorylation from occurring. Subsequent tests demonstrated that the substituted ARNT-Ah receptor-ligand performed normally.

Implication: PAS heterodimers are environmental sensors that turn on the transcriptional machinery to aid the cell in responding to environmental chemicals, oxygen deprivation and the biological clock. ARNT specifically partners with the Ah receptor thereby aiding the cellular response to environmental stressors. Understanding how it specifically interacts with its partners at the molecular level (ie. through phosphorylation) and the transcriptional machinery is critical to understanding how cells sense changes in the environment.

Citation: Levine SL, Perdew GH. Aryl hydrocarbon receptor (AhR)/AhR nuclear translocator (ARNT) activity is unaltered by phosphorylation of a periodicity/ARNT/single-minded (PAS)-region serine residue. Mol Pharmacol. 2001 Mar;59(3):557-66.