title: Transcriptional regulation of juvenile hormone-mediated induction of Krüppel homolog 1, a repressor of insect metamorphosis.
abstract: The Krüppel homolog 1 gene (Kr-h1) has been proposed to play a key role in the repression of insect metamorphosis. Kr-h1 is assumed to be induced by juvenile hormone (JH) via a JH receptor, methoprene-tolerant (Met), but the mechanism of induction is unclear. To elucidate the molecular mechanism of Kr-h1 induction, we first cloned cDNAs encoding Kr-h1 (BmKr-h1) and Met (BmMet1 and BmMet2) homologs from Bombyx mori. In a B. mori cell line, BmKr-h1 was rapidly induced by subnanomolar levels of natural JHs. Reporter assays identified a JH response element (kJHRE), comprising 141 nucleotides, located ∼2 kb upstream from the BmKr-h1 transcription start site. The core region of kJHRE (GGCCTCCACGTG) contains a canonical E-box sequence to which Met, a basic helix-loop-helix Per-ARNT-Sim (bHLH-PAS) transcription factor, is likely to bind. In mammalian HEK293 cells, which lack an intrinsic JH receptor, ectopic expression of BmMet2 fused with Gal4DBD induced JH-dependent activity of an upstream activation sequence reporter. Meanwhile, the kJHRE reporter was activated JH-dependently in HEK293 cells only when cotransfected with BmMet2 and BmSRC, another bHLH-PAS family member, suggesting that BmMet2 and BmSRC jointly interact with kJHRE. We also found that the interaction between BmMet2 and BmSRC is dependent on JH. Therefore, we propose the following hypothesis for the mechanism of JH-mediated induction of BmKr-h1: BmMet2 accepts JH as a ligand, JH-liganded BmMet2 interacts with BmSRC, and the JH/BmMet2/BmSRC complex activates BmKr-h1 by interacting with kJHRE.
authors: Division of Insect Sciences, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634,  Japan.
authors: Takumi
authors: T
authors: Kayukawa
authors: Chieka
authors: C
authors: Minakuchi
authors: Toshiki
authors: T
authors: Namiki
authors: Toru
authors: T
authors: Togawa
authors: Michiyo
authors: M
authors: Yoshiyama
authors: Manabu
authors: M
authors: Kamimura
authors: Kazuei
authors: K
authors: Mita
authors: Shigeo
authors: S
authors: Imanishi
authors: Makoto
authors: M
authors: Kiuchi
authors: Yukio
authors: Y
authors: Ishikawa
authors: Tetsuro
authors: T
authors: Shinoda
mesh_terms: D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D012831:Bombyx / Q000235:genetics*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D005786:Gene Expression Regulation / Q000235:genetics / Q000502:physiology*; D057809:HEK293 Cells; D006801:Humans; D007605:Juvenile Hormones / Q000378:metabolism*; D051741:Kruppel-Like Transcription Factors / Q000378:metabolism*; D008675:Metamorphosis, Biological / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D060888:Real-Time Polymerase Chain Reaction; D017422:Sequence Analysis, DNA
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D018076:DNA, Complementary; D007605:Juvenile Hormones; D051741:Kruppel-Like Transcription Factors