|Aryl hydrocarbon receptor nuclear translocator-like|
|Symbols||; BMAL1; BMAL1c; JAP3; MOP3; PASD3; TIC; bHLHe5|
|RNA expression pattern|
ARNTL encodes for a transcription factor with a basic helix-loop-helix (bHLH) and a PAS domain. The human ARNTL gene has a predicted 24 exons and is located on the p15 band of the 11th chromosome. The BMAL1 protein is 626 amino acids long and plays a key role as one of the positive elements in the mammalian autoregulatory transcription translation negative feedback loop (TTFL), which is responsible for generating molecular circadian rhythms. BMAL1 has also been identified as a candidate gene for susceptibility to hypertension, diabetes, and obesity, and mutations in BMAL1 have been linked to infertility, gluconeogenesis and lipogenesis problems, and altered sleep patterns. BMAL1, according to genome-wide profiling, is estimated to target more than 150 sites in the human genome, including all of the clock genes and genes encoding for proteins that regulate metabolism.
The Arntl gene was originally discovered in 1997 by two groups of researchers, John B. Hogenesch et al. in March and Ikeda and Nomura in April  as part of a superfamily of PAS domain transcription factors. The ARNTL protein, also known as MOP3, was found to dimerize with MOP4, CLOCK, and hypoxia-inducible factors. The names BMAL1 and ARNTL were adopted in later papers. One of ARNTL protein's earliest discovered functions in circadian regulation was related to the CLOCK-BMAL1 (CLOCK-ARNTL) heterodimer, which would bind through an E-box enhancer to activate the transcription of the gene encoding vasopressin. However, the gene's importance in circadian rhythms was not fully realized until the knockout of the gene in mice showed complete loss of circadian rhythms in locomotion and other behaviors.
The BMAL1 protein contains fours domains according to its crystallographic structure: a bHLH domain, two PAS domains called PAS-A and PAS-B, and a trans-activating domain. The dimerization of CLOCK:BMAL1 proteins involves strong interactions between the bHLH, PAS A, and PAS B domains of both CLOCK and BMAL1 and forms an asymmetrical heterodimer with three distinct protein interfaces. The PAS-A interactions between CLOCK and BMAL1 involves an interaction, in which an α-helix of CLOCK PAS-A and the ß-sheet of BMAL1 PAS-A, and an α-helix motif of the BMAL1 PAS-A domain and the ß-sheet of CLOCK PAS-A. CLOCK and BMAL1 PAS-B domains stack in a parallel fashion, resulting in the concealment of different hydrophobic residues on the ß-sheet of BMAL1 PAS-B and the helical surface of CLOCK PAS-B, such as Tyr 310 and Phe 423. Key interactions with specific amino acid residues, specially CLOCK His 84 and BMAL1 Leu125, are important in the dimerization of these molecules.
The protein encoded by the Bmal1 gene in mammals binds with a second bHLH-PAS protein via the PAS domain, CLOCK (or its paralog, NPAS2) to form a heterodimer in the nucleus Via its BHLH domain, this heterodimer binds to E-box response elements in the promoter regions of Per (Per1 and Per2) and Cry genes (Cry1 and Cry2). This binding upregulates the transcription and translation of PER1, PER2, CRY1 and CRY2 proteins.
After the PER and CRY proteins have accumulated to sufficient levels, they interact by their PAS motifs to form a large repressor complex that travels into the nucleus to inhibit the transcriptional activity of the CLOCK:BMAL1 heterodimer  This inhibits the transcription of Per and Cry genes, and causes protein levels of PER and CRY drop. This transcription, translation negative feedback loop (TTFL) is modulated in the cytoplasm by phosphorylation of PER proteins by casein kinase 1ε or δ (CK1 ε or CK1 δ), signaling these proteins for degradation by the 26S proteasome. SIRT1 also regulates PER protein degradation by inhibiting transcriptional activity of the BMAL1:CLOCK heterodimer in a circadian manner through deacetylation. The degradation of PER proteins prevents the formation the large protein complex, and thus prevents the inhibition of transcriptional activity of the BMAL1:CLOCK heterodimer. The CRY protein is also signaled for degradation by poly-ubiquination from the FBXL3 protein, also preventing the inhibition of the CLOCK:BMAL1 heterodimer. This allows transcription of the Per and Cry genes to resume. It has also been observed in the TTFL loop of nocturnal mice that transcription levels of the Bmal1 gene peak at CT18, during the mid-subjective night, anti-phase to the transcription levels of Per, Cry, and other clock control genes, which peak at CT6, during the mid-subjective day. This process occurs with a period length of approximately 24 hours and supports the notion that this molecular mechanism is rhythmic.
Regulation of Bmal1 activity
In addition to the circadian regulatory TTFL loop described above, Bmal1 transcription is regulated by competitive binding to the retinoic acid-related orphan receptor response element-binding site (RORE) within the promoter of Bmal1. The CLOCK/BMAL1 heterodimer also binds to E-box elements in promotor regions of Rev-Erbα and RORα/ß genes, upregulating transcription and translation of REV-ERB and ROR proteins. REV-ERBα and ROR proteins regulate BMAL1 expression through a secondary feedback loop and compete to bind to Rev-Erb/ROR response elements in the Bmal1 promoter, resulting in BMAL1 expression repressed by REV-ERBα and activated by ROR proteins. Other nuclear receptors of the same families (NR1D2 (Rev-erb-β); NR1F2 (ROR-β); and NR1F3 (ROR-γ)) have also been shown to act on Bmal1 transcriptional activity in a similar manner.
Several posttranslational modifications of BMAL1 dictate the timing of the CLOCK/BMAL1 feedback loops. Phosphorylation of BMAL1 targets it for ubiquitination and degradation, as well as deubiquitination and stabilization. Acetylation of BMAL1 recruits CRY1 to suppress the transactivation of CLOCK/BMAL1. The sumoylation of BMAL1 by small ubiquitin-related modifier 3 signals its ubiquitination in the nucleus, leading to transactivation of the CLOCK/BMAL1 heterodimer. CLOCK/BMAL1 transactivation, is activated by phosphorylation by casein kinase 1ε and inhibited by phosphorylation by MAPK. Phosphorylation by CK2α regulates BMAL1 intracellular localization  and phosphorylation by GSK3B controls BMAL1 stability and primes it for ubiquitination.
The Arntl gene is located within the hypertension susceptibility loci of chromosome 1 in rats. A study of single nucleotide polymorphisms (SNPs) within this loci found two polymorphisms that occurred in the sequence encoding for Arntl and were associated with type II diabetes and hypertension. When translated from a rat model to a human model, this research suggests a causative role of Arntl gene variation in the pathology of type II diabetes. Recent phenotype data also suggest this gene and its partner Clock play a role in the regulation of glucose homeostasis and metabolism, which can lead to hypoinsulinaemia, or diabetes, when disrupted. In regards to other functions, another study shows that the CLOCK/BMAL1 complex upregulates human LDLR promoter activity, suggesting the Arntl gene also plays a role in cholesterol homeostasis. In addition, Arntl gene expression, along with that of other core clock genes, were discovered to be lower in patients with bipolar disorder, suggesting a problem with circadian function in these patients. Arntl, Npas2, and Per2 have also been associated with seasonal affective disorder in humans. Lastly, Arntl has been identified through functional genetic screening as a putative regulator of the p53 tumor suppressor pathway suggesting potential involvement in the circadian rhythms exhibited by cancer cells.
Along with mammals such as humans and mice, orthologs of the Arntl gene are also found in fish (AF144690.1), birds (Arntl), reptiles, amphibians (XI.2098), and Drosophila (Cycle, which encodes a protein lacking the homologous C-terminal domain, but still dimerizes with the CLOCK protein). Unlike the mammalian Artnl, however, the drosophila Cycle (gene) is constitutively expressed instead of circadian regulated, meaning that it is present in relatively constant amounts. In humans, three transcript variants encoding two different isoforms have been found for this gene. The importance of these transcript variants is unknown.
The Arntl gene is an essential component within the mammalian clock gene regulatory network. It is a point of sensitivity within the network, as it is the only gene whose single knockout in a mouse model generates arrhythmicity at both the molecular and behavioral levels. In addition to defects in the clock, these Arntl null-mice also have reproductive problems, are small in stature, age quickly, and have progressive arthropathy that results in having less overall locomotor activity than wild type mice. However, recent research suggests that there might be some redundancy in the circadian function of Arntl with its paralog Bmal2.
Arntl has been shown to interact with:
- Arntl2 - Arntl2 (Bmal2) is a paralog of Arntl (Bmal1) that encodes for a basic helix-loop-helix PAS domain transcription factor. It, too, has been shown to play a circadian role, with its protein BMAL2 forming a transcriptionally active heterodimer with the CLOCK protein. It may also play a role in hypoxia.
- Cycle - Cycle is the Drosophila melanogaster ortholog of Arntl.
- "ARNTL aryl hydrocarbon receptor nuclear translocator-like [ Homo sapiens (human) ]". National Center for Biotechnology Information.
- Pappa KI, Gazouli M, Anastasiou E, Iliodromiti Z, Antsaklis A, Anagnou NP (Feb 2013). "The major circadian pacemaker ARNT-like protein-1 (BMAL1) is associated with susceptibility to gestational diabetes mellitus". Diabetes Research and Clinical Practice 99 (2). doi:10.1016/j.diabres.2012.10.015. PMID 23206673.
- Richards J, Diaz AN, Gumz ML (Oct 2014). "Clock genes in hypertension: novel insights from rodent models". Blood Pressure Monitoring 19 (5). doi:10.1097/MBP.0000000000000060. PMID 25025868.
- "ARNTL Gene". Gene Cards: The Human Genome Compendium. Lifemap Sciences, Inc.
- Hatanaka F, Matsubara C, Myung J, Yoritaka T, Kamimura N, Tsutsumi S, Kanai A, Suzuki Y, Sassone-Corsi P, Aburatani H, Sugano S, Takumi T (Dec 2010). "Genome-wide profiling of the core clock protein BMAL1 targets reveals a strict relationship with metabolism". Molecular and Cellular Biology 30 (24): 5636–5648. doi:10.1128/MCB.00781-10. PMID 20937769.
- Hogenesch JB, Chan WK, Jackiw VH, Brown RC, Gu YZ, Pray-Grant M, Perdew GH, Bradfield CA (March 1997). "Characterization of a subset of the basic-helix-loop-helix-PAS superfamily that interacts with components of the dioxin signaling pathway". J. Biol. Chem. 272 (13): 8581–93. doi:10.1074/jbc.272.13.8581. PMID 9079689.
- Ikeda M, Nomura M (April 1997). "cDNA cloning and tissue-specific expression of a novel basic helix-loop-helix/PAS protein (BMAL1) and identification of alternatively spliced variants with alternative translation initiation site usage". Biochem. Biophys. Res. Commun. 233 (1): 258–64. doi:10.1006/bbrc.1997.6371. PMID 9144434.
- Hogenesch JB, Gu YZ, Jain S, Bradfield CA (May 1998). "The basic-helix-loop-helix-PAS orphan MOP3 forms transcriptionally active complexes with circadian and hypoxia factors". Proceedings of the National Academy of Sciences of the United States of America 95 (10): 5474–9. PMID 9576906.
- Jin X, Shearman LP, Weaver DR, Zylka MJ, de Vries GJ, Reppert SM (January 1999). "A molecular mechanism regulating rhythmic output from the suprachiasmatic circadian clock". Cell 96 (1): 57–68. doi:10.1016/S0092-8674(00)80959-9. PMID 9989497.
- Bunger MK, Wilsbacher LD, Moran SM, Clendenin C, Radcliffe LA, Hogenesch JB, Simon MC, Takahashi JS, Bradfield CA (2000). "Mop3 is an essential component of the master circadian pacemaker in mammals". Cell 103 (7): 1009–17. doi:10.1016/S0092-8674(00)00205-1. PMID 11163178.
- Huang N, Chelliah Y, Shan Y, Taylor CA, Yoo SH, Partch C, Green CB, Zhang H, Takahashi JS (Jul 2012). "Crystal structure of the heterodimeric CLOCK:BMAL1 transcriptional activator complex". Science 337 (6091): 189–94. doi:10.1126/science.1222804. PMID 22653727.
- Wang Z, Wu Y, Li L, Su XD (Feb 2013). "Intermolecular recognition revealed by the complex structure of human CLOCK-BMAL1 basic helix-loop-helix domains with E-box DNA". Cell Research 23 (2): 213–224. doi:10.1038/cr.2012.170. PMID 23229515.
- Harfmann BD, Schroder EA, Esser KA (Apr 2015). "Circadian Rhythms, the Molecular Clock, and Skeletal Muscle". Journal of Biological Rhythms 30 (2): 84–94. doi:10.1177/0748730414561638. PMID 25512305.
- Buhr ED, Takahashi JS (2013). "Molecular components of the Mammalian circadian clock". Handbook of Experimental Pharmacology (217): 3–27. doi:10.1007/978-3-642-25950-0_1. PMID 23604473.
- Bollinger T, Schibler U (2014). "Circadian rhythms - from genes to physiology and disease". Swiss Medical Weekly 144: w13984. doi:10.4414/smw.2014.13984. PMID 25058693.
- Maywood ES, Chesham JE, Smyllie NJ, Hastings MH (Apr 2014). "The Tau mutation of casein kinase 1ε sets the period of the mammalian pacemaker via regulation of Period1 or Period2 clock proteins". Journal of Biological Rhythms 29 (2): 110–8. doi:10.1177/0748730414520663. PMID 24682205.
- Asher G, Gatfield D, Stratmann M, Reinke H, Dibner C, Kreppel F, Mostoslavsky R, Alt FW, Schibler U (Jul 2008). "SIRT1 regulates circadian clock gene expression through PER2 deacetylation". Cell 134 (2). doi:10.1016/j.cell.2008.06.050. PMID 18662546.
- Ueda HR, Chen W, Adachi A, Wakamatsu H, Hayashi S, Takasugi T, Nagano M, Nakahama K, Suzuki Y, Sugano S, Iino M, Shigeyoshi Y, Hashimoto S (1 August 2002). "A transcription factor response element for gene expression during circadian night". Nature 418 (5897): 534–9. Bibcode:2002Natur.418..534U. doi:10.1038/nature00906. PMID 12152080.
- Akashi M, Takumi T (May 2005). "The orphan nuclear receptor RORalpha regulates circadian transcription of the mammalian core-clock Bmal1". Nature Structural & Molecular Biology 12 (5): 441–8. doi:10.1038/nsmb925. PMID 15821743.
- Guillaumond F, Dardente H, Giguère V, Cermakian N (Oct 2005). "Differential control of Bmal1 circadian transcription by REV-ERB and ROR nuclear receptors". Journal of Biological Rhythms 20 (5): 391–403. doi:10.1177/0748730405277232. PMID 16267379.
- Ueda HR, Hayashi S, Chen W, Sano M, Machida M, Shigeyoshi Y, Iino M, Hashimoto S (February 2005). "System-level identification of transcriptional circuits underlying mammalian circadian clocks". Nature Genetics 37 (2): 187–92. doi:10.1038/ng1504. PMID 15665827.
- Liu AC, Tran HG, Zhang EE, Priest AA, Welsh DK, Kay SA (February 2008). Takahashi JS, ed. "Redundant Function of REV-ERBα and β and Non-Essential Role for Bmal1 Cycling in Transcriptional Regulation of Intracellular Circadian Rhythms". PLoS genetics 4 (2): e1000023. doi:10.1371/journal.pgen.1000023. PMC 2265523. PMID 18454201.
- Hirayama J, Sahar S, Grimaldi B, Tamaru T, Takamatsu K, Nakahata Y, Sassone-Corsi P (2007). "CLOCK-mediated acetylation of BMAL1 controls circadian function". Nature 450 (7172): 1086–1090. Bibcode:2007Natur.450.1086H. doi:10.1038/nature06394. PMID 18075593.
- Lee J, Lee Y, Lee MJ, Park E, Kang SH, Chung CH, Lee KH, Kim K (2008). "Dual Modification of BMAL1 by SUMO2/3 and Ubiquitin Promotes Circadian Activation of the CLOCK/BMAL1 Complex". Molecular and Cell Biology 28 (19): 6056–6065. doi:10.1128/MCB.00583-08. PMC 2546997. PMID 18644859.
- Eide EJ, Vielhaber EL, Hinz WA, Virshup DM (2002). "The circadian regulatory proteins BMAL1 and cryptochromes are substrates of casein kinase Iepsilon". The Journal Of Biological Chemistry 277 (19): 17248–17254. doi:10.1074/jbc.m111466200. PMID 11875063.
- Sanada K, Okano T, Fukada Y (2002). "Mitogen-activated protein kinase phosphorylates and negatively regulates basic helix-loop-helix-PAS transcription factor BMAL1". The Journal Of Biological Chemistry 277 (1): 267–271. doi:10.1074/jbc.m107850200. PMID 11687575.
- Tamaru T, Hirayama J, Isojima Y, Nagai K, Norioka S, Takamatsu K, Sassone-Corsi P (2009). "CK2alpha phosphorylates BMAL1 to regulate the mammalian clock.". Nature Structural & Molecular Biology 16 (4): 446–448. doi:10.1038/nsmb.1578. PMID 19330005.
- Sahar S, Zocchi L, Kinoshita C, Borrelli E, Sassone-Corsi P (2010). "Regulation of BMAL1 Protein Stability and Circadian Function by GSK3β-Mediated Phosphorylation". PLOS ONE 5 (1): 1–9.
- Woon PY, Kaisaki PJ, Bragança J, Bihoreau MT, Levy JC, Farrall M, Gauguier D (September 2007). "Aryl hydrocarbon receptor nuclear translocator-like (BMAL1) is associated with susceptibility to hypertension and type 2 diabetes". Proceedings of the National Academy of Sciences of the United States of America 104 (36): 14412–7. Bibcode:2007PNAS..10414412W. doi:10.1073/pnas.0703247104. PMC 1958818. PMID 17728404.
- Rudic RD, McNamara P, Curtis AM, Boston RC, Panda S, Hogenesch JB, Fitzgerald GA (2004). "BMAL1 and CLOCK, Two Essential Components of the Circadian Clock, Are Involved in Glucose Homeostasis". PLOS Biology 2 (11): e377. doi:10.1371/journal.pbio.0020377. PMC 524471. PMID 15523558.
- Turek FW, Joshu C, Kohsaka A, Lin E, Ivanova G, McDearmon E, Laposky A, Losee-Olson S, Easton A, Jensen DR, Eckel RH, Takahashi JS, Bass J (2005). "Obesity and metabolic syndrome in circadian Clock mutant mice". Science 308 (5724): 1043–5. Bibcode:2005Sci...308.1043T. doi:10.1126/science.1108750. PMC 3764501. PMID 15845877.
- Marcheva B, Ramsey KM, Buhr ED, Kobayashi Y, Su H, Ko CH, Ivanova G, Omura C, Mo S, Vitaterna MH, Lopez JP, Philipson LH, Bradfield CA, Crosby SD, JeBailey L, Wang X, Takahashi JS, Bass J (July 2010). "Disruption of the clock components CLOCK and BMAL1 leads to hypoinsulinaemia and diabetes". Nature 466 (7306): 627–31. Bibcode:2010Natur.466..627M. doi:10.1038/nature09253. PMC 2920067. PMID 20562852.
- Lee YJ, Han DH, Pak YK, Cho SH (November 2012). "Circadian regulation of low density lipoprotein receptor promoter activity by CLOCK/BMAL1, Hes1 and Hes6". Experimental & Molecular Medicine 44 (11): 642–52. doi:10.3858/emm.2012.44.11.073. PMC 3509181. PMID 22913986.
- Yang S, Van Dongen HP, Wang K, Berrettini W, Bućan M (February 2009). "Assessment of circadian function in fibroblasts of patients with bipolar disorder". Mol. Psychiatry 14 (2): 143–55. doi:10.1038/mp.2008.10. PMID 18301395.
- Partonen T, Treutlein J, Alpman A, Frank J, Johansson C, Depner M, Aron L, Rietschel M, Wellek S, Soronen P, Paunio T, Koch A, Chen P, Lathrop M, Adolfsson R, Persson ML, Kasper S, Schalling M, Peltonen L, Schumann G (2007). "Three circadian clock genes Per2, Arntl, and Npas2 contribute to winter depression". Ann. Med. 39 (3): 229–38. doi:10.1080/07853890701278795. PMID 17457720.
- Mullenders J, Fabius AW, Madiredjo M, Bernards R, Beijersbergen RL (2009). "A Large Scale shRNA Barcode Screen Identifies the Circadian Clock Component ARNTL as Putative Regulator of the p53 Tumor Suppressor Pathway". PLOS ONE 4 (3): e4798. Bibcode:2009PLoSO...4.4798M. doi:10.1371/journal.pone.0004798. PMID 19277210.
- Cermakian N, Whitmore D, Foulkes NS, Sassone-Corsi P (April 2000). "Asynchronous oscillations of two zebrafish CLOCK partners reveal differential clock control and function". Proceedings of the National Academy of Sciences of the United States of America 97 (8): 4339–44. Bibcode:2000PNAS...97.4339C. doi:10.1073/pnas.97.8.4339. PMC 18243. PMID 10760301.
- Okano T, Yamamoto K, Okano K, Hirota T, Kasahara T, Sasaki M, Takanaka Y, Fukada Y (September 2001). "Chicken pineal clock genes: implication of BMAL2 as a bidirectional regulator in circadian clock oscillation". Genes Cells 6 (9): 825–36. doi:10.1046/j.1365-2443.2001.00462.x. PMID 11554928.
- Rutila JE, Suri V, Le M, So WV, Rosbash M, Hall JC (May 1998). "CYCLE is a second bHLH-PAS clock protein essential for circadian rhythmicity and transcription of Drosophila period and timeless". Cell 93 (5): 805–14. doi:10.1016/S0092-8674(00)81441-5. PMID 9630224.
- Meireles-Filho AC, Amoretty PR, Souza NA, Kyriacou CP, Peixoto AA (2006). "Rhythmic expression of the cycle gene in a hematophagous insect vector". BMC Mol. Biol. 7: 38. doi:10.1186/1471-2199-7-38. PMC 1636064. PMID 17069657.
- Boden MJ, Kennaway DJ (2006). "Circadian rhythms and reproduction". Reproduction 132 (3): 379–92. doi:10.1530/rep.1.00614. PMID 16940279.
- Kondratov RV (2007). "A role of the circadian system and circadian proteins in aging". Ageing Res. Rev. 6 (1): 12–27. doi:10.1016/j.arr.2007.02.003. PMID 17369106.
- Bunger MK, Walisser JA, Sullivan R, Manley PA, Moran SM, Kalscheur VL, Colman RJ, Bradfield CA (2005). "Progressive arthropathy in mice with a targeted disruption of the Mop3/Bmal-1 locus". Genesis 41 (3): 122–32. doi:10.1002/gene.20102. PMID 15739187.
- Shi S, Hida A, McGuinness OP, Wasserman DH, Yamazaki S, Johnson CH (Feb 2010). "Circadian clock gene Bmal1 is not essential; functional replacement with its paralog, Bmal2.". Current Biology 20 (4): 316–21. doi:10.1016/j.cub.2009.12.034. PMID 20153195.
- Hogenesch JB, Gu YZ, Jain S, Bradfield CA (May 1998). "The basic-helix-loop-helix-PAS orphan MOP3 forms transcriptionally active complexes with circadian and hypoxia factors". Proceedings of the National Academy of Sciences of the United States of America 95 (10): 5474–9. Bibcode:1998PNAS...95.5474H. doi:10.1073/pnas.95.10.5474. PMC 20401. PMID 9576906.
- Ooe N, Saito K, Mikami N, Nakatuka I, Kaneko H (January 2004). "Identification of a Novel Basic Helix-Loop-Helix-PAS Factor, NXF, Reveals a Sim2 Competitive, Positive Regulatory Role in Dendritic-Cytoskeleton Modulator Drebrin Gene Expression". Mol. Cell. Biol. 24 (2): 608–16. doi:10.1128/MCB.24.2.608-616.2004. PMC 343817. PMID 14701734.
- McNamara P, Seo SB, Rudic RD, Sehgal A, Chakravarti D, FitzGerald GA (June 2001). "Regulation of CLOCK and MOP4 by nuclear hormone receptors in the vasculature: a humoral mechanism to reset a peripheral clock". Cell 105 (7): 877–89. doi:10.1016/S0092-8674(01)00401-9. PMID 11439184.
- Hogenesch JB, Gu YZ, Moran SM, Shimomura K, Radcliffe LA, Takahashi JS, Bradfield CA (July 2000). "The basic helix-loop-helix-PAS protein MOP9 is a brain-specific heterodimeric partner of circadian and hypoxia factors". J. Neurosci. 20 (13): RC83. PMID 10864977.