NPAS2: A Gas-Responsive Transcription Factor

Abstract

Neuronal PAS domain protein 2 (NPAS2) is a mammalian transcription factor that binds DNA as an obligate dimeric partner of BMAL1 and is implicated in the regulation of circadian rhythm. Here we show that both PAS domains of NPAS2 bind heme as a prosthetic group and that the heme status controls DNA binding in vitro. NPAS2-BMAL1 heterodimers, existing in either the apo (heme-free) or holo (heme-loaded) state, bound DNA avidly under favorably reducing ratios of the reduced and oxidized forms of nicotinamide adenine dinucleotide phosphate. Low micromolar concentrations of carbon monoxide inhibited the DNA binding activity of holo-NPAS2 but not that of apo-NPAS2. Upon exposure to carbon monoxide, inactive BMAL1 homodimers were formed at the expense of NPAS2-BMAL1 heterodimers. These results indicate that the heterodimerization of NPAS2, and presumably the expression of its target genes, are regulated by a gas through the heme-based sensor described here.

A novel diffuse large B-cell lymphoma-associated cancer testis antigen encoding a PAS domain protein

“…They are most closely related to the PAS family members CLOCK and NPAS2 that play an important role in regulating eukaryotic circadian rhythms (Dunlap et al, 1999;Dioum et al, 2002). Overlapping the PAS domains was a partial aryl-hydrocarbon receptor nuclear translocator domain (ARNT), aa 3 -187.…”

A Time to Fast, a Time to Feast: The Crosstalk between Metabolism and the Circadian Clock

“…Carbon monoxide (CO) inhibits the DNA binding of NPAS2 by favouring inactive BMAL1 homodimerization instead of active NPAS2/BMAL1 heterodimerization (Dioum et al, 2002). Along this line, NPAS2 and REV-ERBα have both been shown to act as heme sensors, where heme binding controls the DNA binding activity of these two core clock components (Kaasik and Lee, 2004;Yin et al, 2007).…”

Reciprocal regulation of carbon monoxide metabolism and the circadian clock

“…Mechanistically, we favor the hypothesis that, in mammals, heme oxygenase-derived CO attenuates CLOCK(NPAS2)-BMAL1 DNA binding, probably via coordination by a heme molecule bound to NPAS2 (ref. 6) and probably also to CLOCK 31 , and thereby modulates expression of CLOCK(NPAS2)-BMAL1-target genes. Although this scenario is not the only possible interpretation of our results (as described below), our preferred model is consistent with both past and present observations.…”

“…(i) In vitro, micromolar concentrations of CO have been shown to impair DNA binding and BMAL-heterodimer formation of heme-bound NPAS2 but not apo-NPAS2 (ref. 6), and in the brain, these concentrations of CO are generated by heme oxygenases 32 (detailed discussion of CO concentration in Supplementary Note 1). (ii) Mutation of heme-coordinating residues within NPAS2 also impairs heterodimer formation with BMAL1, thus decreasing both specific DNA binding to canonical E boxes and NPAS2-BMAL1 transactivation activity, probably via conformational changes within the PAS-A domain of NPAS2 (ref.…”

“…In vitro, CO inhibits binding of NPAS2-BMAL1 to DNA 6 . If such an inhibitory effect also occurs in vivo, transcription of NPAS2-BMAL1-target genes should increase when endogenous CO levels are decreased.…”