|Aryl hydrocarbon receptor nuclear translocator-like|
|RNA expression pattern|
Aryl hydrocarbon receptor nuclear translocator-like, also known as Arntl, Bmal1, or Mop3, is a gene that encodes for a basic helix-loop-helix-PAS domain (bHLH-PAS domain) transcription factor. In the human, it is 110,615 bases long and located on the p15 band of the 11th chromosome. This protein 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. Arntl has also been identified as a candidate gene for susceptibility to hypertension and Type II diabetes.
Function and regulation
The Arntl gene was originally discovered in 1997 by two groups of researches, Hogenesch and Bradfield in March  and Ikeda and Nomura in April  as part of a superfamily of bHLH-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 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 knock-out of the gene in mice showed complete loss of circadian rhythms in locomotion and other behaviors. Thus, Artnl is the only clock gene that by itself is necessary for circadian rhythm generation.
The protein encoded by the Arntl gene forms a heterodimer with a second bHLH-PAS protein, CLOCK, or a paralog, NPAS2. This complex binds to E-box response elements in promoter regions of many genes including those encoding the Period (PER1, PER2, PER3) and Cryptochrome (CRY1 and CRY2) proteins. CLOCK/BMAL1 heterodimers also activate transcription of the orphan nuclear receptor gene Rev-Erb, where the REV-ERB protein it encodes for represses Bmal1 transcription by binding to Rev-Erb/ROR response elements in the Bmal1 promoter.
As PER and CRY proteins are translated, these repressor proteins bind in a repressor complex with casein kinase 1ε (CSNK1E) and 1δ (CSNK1D). This process can be modulated in the cytoplasm by the degradation of PER protein through its phosphorylation by casein kinase 1ε (CSNK1E) and 1δ (CSNK1D). Next, the repressor complex translocates to the nucleus, where it interacts with the CLOCK/BMAL1 heterodimer to inhibit its transactivation. This hypothesis is supported by the observation that point mutations in the Arntl and Clock genes render them resistant to interaction and repression by Cryptochromes. Transcription of Per and Cry genes, therefore, is inhibited and the protein levels of PER and CRY drop. The repressor complex also inhibits Rev-Erb transcription resulting in an activation of Bmal1 transcription. When such repression is eventually relieved by a drop in the protein levels of PER and CRY, a high level of BMAL1 allows transcription of the Per and Cry genes to begin again.
Several posttranslational modifications of BMAL1 have been shown to be important for the proper timing and activation of the CLOCK/BMAL1 complex. Acetylation of BMAL1 facilitates the recruitment of CRY1 to the CLOCK/BMAL1 complex and represses the complex's transactivation . The sumoylation of BMAL1 by small ubiquitin-related modifier 3 signals its ubiquitination in the nucleus which leads to the transactivation of the CLOCK/BMAL1 heterodimer and its protein turnover. In addition, phosphorylation of BMAL1 by multiple kinases has been reported through the functional interactions between phosphorylation and other posttranslational regulators. Phosphorylation by casein kinase 1ε activates CLOCK/BMAL1 transactivation, while phosphorylation by MAPK inhibits it. Phosphorylation by CK2α regulates BMAL1 intracellular localization  and phosphorylation by GSK3B controls BMAL1 stability and primes it for ubiquitination.
It has also been observed in the negative feedback 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.
In addition to the circadian regulatory transcriptional translational negative feedback loop (TTFL) described above, Arntl gene transcription is reciprocally regulated by the orphan nuclear receptors NR1D1 (Rev-erb-α) and NR1F1 (ROR-α), which establish a second interlocking loop in the mammalian circadian clock. This loop is induced when CLOCK-BMAL1 heterodimers activate the transcription of Rev-ErbA and Rora, two retinoic acid-related orphan nuclear receptors. REV-ERBa and RORa subsequently compete to bind retinoic acid-related orphan receptor response elements (ROREs) present in the Arntl promoter. Through the subsequent binding of ROREs, members of ROR and REV-ERB are able to regulate Arntl. While RORs activate the transcription of Arntl, REV-ERBs repress this transcription. Hence, the circadian oscillation of Arntl is both positively and negatively regulated by RORs and REV-ERBs. 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 the Arntl gene.
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.
The Arntl gene is an essential and nonredundant component within the mammalian clock gene regulatory network, since it is the only gene within the mammalian circadian clock whose sole deletion in a mouse model generates arrhythmicity at both the molecular and behavioral levels. However, recent research suggests that there might be some redundancy in the circadian function of Arntl with its paralog Bmal2. 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.
In addition to mammals like mice and humans, homologs of the Arntl gene are 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. In humans, three transcript variants encoding two different isoforms have been found for this gene. The importance of these transcript variants is unknown.
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 Gene". Gene Cards: The Human Genome Compendium. Lifemap Sciences, Inc. Retrieved 8 April 2013.
- Hogenesch JB, Chan WK, Jackiw VH, et al. (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. Bibcode:1998PNAS...95.5474H. doi:10.1073/pnas.95.10.5474. JSTOR 45109. PMC 20401. 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.
- Bunger MK, Wilsbacher LD, Moran SM, et al. (December 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.
- Gekakis N, Staknis D, Nguyen HB, Davis FC, Wilsbacher LD, King DP, Takahashi JS, Weitz CJ (1998). "Role of the CLOCK protein in the mammalian circadian mechanism". Science 280 (5369): 1564–9. Bibcode:1998Sci...280.1564G. doi:10.1126/science.280.5369.1564. PMID 9616112.
- Kume K, Zylka MJ, Sriram S, Shearman LP, Weaver DR, Jin X, Maywood ES, Hastings MH, Reppert SM (1999). "mCRY1 and mCRY2 are essential components of the negative limb of the circadian clock feedback loop". Cell 98 (2): 193–205. doi:10.1016/S0092-8674(00)81014-4. PMID 10428031.
- Griffin EA, Staknis D, Weitz CJ (1999). "Light-independent role of CRY1 and CRY2 in the mammalian circadian clock". Science 286 (5440): 768–71. doi:10.1126/science.286.5440.768. PMID 10531061.
- Steven M. Reppert & David R. Weaver (2002). "Coordination of circadian timing in mammals". Nature 418 (6901): 935–941. Bibcode:2002Natur.418..935R. doi:10.1038/nature00965. PMID 12198538.
- Lowrey PL, Shimomura K, Antoch MP, Yamazaki S, Zemenides PD, Ralph MR, Menaker M, Takahashi JS (2000). "Positional syntenic cloning and functional characterization of the mammalian circadian mutation tau". Science 288 (5465): 483–92. Bibcode:2000Sci...288..483L. doi:10.1126/science.288.5465.483. PMID 10775102.
- Lee C, Etchegaray JP, Cagampang FR, Loudon AS, Reppert SM (December 2001). "Posttranslational mechanisms regulate the mammalian circadian clock". Cell 107 (7): 855–67. doi:10.1016/S0092-8674(01)00610-9. PMID 11779462.
- Sato TK, Yamada RG, Ukai H, Baggs JE, Miraglia LJ, Kobayashi TJ, Welsh DK, Kay SA, Ueda HR, Hogenesch JB (2006). "Feedback repression is required for mammalian circadian clock function". Nat. Genet. 38 (3): 312–9. doi:10.1038/ng1745. PMC 1994933. PMID 16474406.
- Yu W, Nomura M, Ikeda M (2002). "Interactivating feedback loops within the mammalian clock: BMAL1 is negatively autoregulated and upregulated by CRY1, CRY2, and PER2.". Biochem Biophys Res Commun 290 (3): 933–41. doi:10.1006/bbrc.2001.6300. PMID 11798163.
- Hirayama J, Sahar S, Sassone-Corsi P, et al. (2007). "CLOCK-mediated acetylation of BMAL1 controls circadian function". Nature 450 (7172): 1086–1090. Bibcode:2007Natur.450.1086H. doi:10.1038/nature06394.
- Lee J, Lee Y, Kim K, et al. (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 E, Vielhaber E, Hinz W, Virshup D (2002). "The circadian regulatory proteins BMAL1 and cryptochromes are substrates of casein kinase Iepsilon". The Journal Of Biological Chemistry 277 (19): 17248–17254.
- 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.
- Tamaru T, Hirayama J, Sassone-Corsi P, et al (2009). "CK2alpha phosphorylates BMAL1 to regulate the mammalian clock.". Nature Structural & Molecular Biology 16 (4): 446–448.
- 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.
- 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). "A transcription factor response element for gene expression during circadian night". Nature 418 (5897): 534–9. Bibcode:2002Natur.418..534U.
- Preitner N, Damiola F, Lopez-Molina L, Zakany J, Duboule D, Albrecht U, Schibler U (2002). "The orphan nuclear receptor REV-ERBalpha controls circadian transcription within the positive limb of the mammalian circadian oscillator". Cell 110 (2): 251–60. doi:10.1016/S0092-8674(02)00825-5. PMID 12150932.
- 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 (October 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.
- Sato TK, Panda S, Miraglia LJ, Reyes TM, Rudic RD, McNamara P, Naik KA, FitzGerald GA, Kay SA, Hogenesch JB' (2004). "A functional genomics strategy reveals Rora as a component of the mammalian circadian clock". Neuron 43 (4): 527–37. doi:10.1016/j.neuron.2004.07.018. PMID 15312651.
- Shearman LP, Sriram S, Weaver DR, Maywood ES, Chaves I, Zheng B, Kume K, Lee CC, van der Horst GT, Hastings MH, Reppert SM (2000). "Interacting molecular loops in the mammalian circadian clock". Science 288 (5468): 1013–9. Bibcode:2000Sci...288.1013S. doi:10.1126/science.288.5468.1013. PMID 10807566.
- Ko CH, Takahashi JS (October 2006). "Molecular components of the mammalian circadian clock". Hum. Mol. Genet. 15 Spec No 2: R271–7. doi:10.1093/hmg/ddl207. PMID 16987893.
- 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). "Redundant Function of REV-ERBα and β and Non-Essential Role for Bmal1 Cycling in Transcriptional Regulation of Intracellular Circadian Rhythms". In Takahashi, Joseph S. PLoS genetics 4 (2): e1000023. doi:10.1371/journal.pgen.1000023. PMC 2265523. PMID 18454201.
- 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. PMID 15845877.
- Marcheva B, Ramsey KM, Buhr ED, et al. (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". Exp. Mol. Med. 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 AWM, 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.
- 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.
- 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.
- 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, et al. (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.
- Ikeda M, Nomura M (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, 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.
- Ooe, Norihisa; Saito Koichi, Mikami Nobuyoshi, Nakatuka Iwao, Kaneko Hideo (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. (United States) 24 (2): 608–16. doi:10.1128/MCB.24.2.608-616.2004. ISSN 0270-7306. 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.
- Lee J, Lee Y, Lee MJ, Park E, Kang SH, Chung CH, Lee KH, Kim K (October 2008). "Dual modification of BMAL1 by SUMO2/3 and ubiquitin promotes circadian activation of the CLOCK/BMAL1 complex". Mol. Cell. Biol. 28 (19): 6056–65. doi:10.1128/MCB.00583-08. PMC 2546997. PMID 18644859.
- Hogenesch JB, Gu YZ, Moran SM, et al. (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.