The loss of circadian PAR bZip transcription factors results in epilepsy

Abstract

DBP (albumin D-site-binding protein), HLF (hepatic leukemia factor), and TEF (thyrotroph embryonic factor) are the three members of the PAR bZip (proline and acidic amino acid-rich basic leucine zipper) transcription factor family. All three of these transcriptional regulatory proteins accumulate with robust circadian rhythms in tissues with high amplitudes of clock gene expression, such as the suprachiasmatic nucleus (SCN) and the liver. However, they are expressed at nearly invariable levels in most brain regions, in which clock gene expression only cycles with low amplitude. Here we show that mice deficient for all three PAR bZip proteins are highly susceptible to generalized spontaneous and audiogenic epilepsies that frequently are lethal. Transcriptome profiling revealed pyridoxal kinase (Pdxk) as a target gene of PAR bZip proteins in both liver and brain. Pyridoxal kinase converts vitamin B6 derivatives into pyridoxal phosphate (PLP), the coenzyme of many enzymes involved in amino acid and neurotransmitter metabolism. PAR bZip-deficient mice show decreased brain levels of PLP, serotonin, and dopamine, and such changes have previously been reported to cause epilepsies in other systems. Hence, the expression of some clock-controlled genes, such as Pdxk, may have to remain within narrow limits in the brain. This could explain why the circadian oscillator has evolved to generate only low-amplitude cycles in most brain regions.[Keywords: PAR bZip proteins; circadian transcription factors; epilepsy; pyridoxal kinase] Supplemental material is available at http://www.genesdev.org.

PAR bZIP-bik is a novel transcriptional pathway that mediates oxidative stress-induced apoptosis in fibroblasts

“…To verify the transcriptional regulation of bik by PAR bZIP proteins, we searched for consensus sequences in the human bik gene promoter and found a putative PAR bZIP-binding site of 413 bases upstream from the transcription start site (Figure 3a), which closely matched the consensus sequence of these transcription factors. 4 Then, a 877-bp fragment from the promoter region of bik, encompassing the transcription start site, was cloned into a promoterless luciferase reporter vector (bik-Luc). We found that the levels of luciferase activity in HEK293T cells co-transfected with the reporter Figure 1 Expression of BH3-only genes in wild-type and PAR bZIP knockout fibroblasts.…”

“…4 In addition, gene expression analyses in different organs indicated that these transcription factors control the expres- Cross-linked chromatin was incubated with an antibody against Flag, and immunoprecipitates from each sample were analyzed by PCR using primers flanking the PAR bZIP site of the bik promoter. As a positive control, a sample representing 0.1% of the total input chromatin was included.…”

“…Fibroblasts were obtained from wild-type and PAR bZIP knockout mice, 4 as described. 33 In brief, mouse tails were minced and digested with 1 mg/ml type 1 collagenase in Dulbecco's modified Eagle's medium (DMEM) (Invitrogen, Carlsbad, CA, USA) containing 100 units/ml penicillin and 100 mg/ml streptomycin for 1 h at 37 1C.…”

“…Mice deficient for all three PAR bZIP proteins are highly susceptible to generalized spontaneous and audiogenic epilepsies that frequently are lethal. 4 These proteins have recently been shown to control the expression of many enzymes and regulators involved in detoxification and drug metabolism, such as cytochrome P450 enzymes, carboxylesterases, and constitutive androstane receptor. 5 In addition, we showed for the first time that PAR bZIP proteins regulate the expression of a gene, bcl-gS, involved in the execution of apoptosis.…”

Impact of behavior on central and peripheral circadian clocks in the common vole Microtus arvalis , a mammal with ultradian rhythms

“…TaqMan real-time RT-PCR experiments with mouse liver RNAs were performed as described in ref. 28. We thank Gottlieb Zumbrunn, Yves-Alain Poget, and Marc Schneider (Mechanical Workshop, Department of Molecular Biology, University of Geneva) for designing and constructing the computer-driven feeding machine used for mice; Ger Veltman (Mechanical Workshop, Department of Biology, University of Groningen) for building the cages used to measure vole behavior; and Nicolas Roggli for expert preparation of the artwork.…”