title: Calcium-dependent binding of Myc to calmodulin.
abstract: The bHLH-LZ (basic region/helix-loop-helix/leucine zipper) oncoprotein Myc and the bHLH-LZ protein Max form a binary transcription factor complex controlling fundamental cellular processes. Deregulated Myc expression leads to neoplastic transformation and is a hallmark of most human cancers. The dynamics of Myc transcription factor activity are post-translationally coordinated by defined protein-protein interactions. Here, we present evidence for a second messenger controlled physical interaction between the Ca2+ sensor calmodulin (CaM) and all Myc variants (v-Myc, c-Myc, N-Myc, and L-Myc). The predominantly cytoplasmic Myc:CaM interaction is Ca2+-dependent, and the binding site maps to the conserved bHLH domain of Myc. Ca2+-loaded CaM binds the monomeric and intrinsically disordered Myc protein with high affinity, whereas Myc:Max heterodimers show less, and Max homodimers no affinity for CaM. NMR spectroscopic analyses using alternating mixtures of 15N-labeled and unlabeled preparations of CaM and a monomeric Myc fragment containing the bHLH-LZ domain corroborate the biochemical results on the Myc:CaM interaction and confirm the interaction site mapping. In electrophoretic mobility shift assays, addition of CaM does not affect high-affinity DNA-binding of Myc:Max heterodimers. However, cell-based reporter analyses and cell transformation assays suggest that increasing CaM levels enhance Myc transcriptional and oncogenic activities. Our results point to a possible involvement of Ca2+ sensing CaM in the fine-tuning of Myc function.
authors.affiliation: Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria.|Present address: Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: Philipp
authors.initials: P
authors.lastname: Raffeiner
authors.affiliation: Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria.
authors.forename: Andrea
authors.initials: A
authors.lastname: Schraffl
authors.affiliation: Max F. Perutz Laboratories, Department of Structural and Computational Biology, University of Vienna, A-1030 Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schwarz
authors.affiliation: Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria.
authors.forename: Ruth
authors.initials: R
authors.lastname: Röck
authors.affiliation: Max F. Perutz Laboratories, Department of Structural and Computational Biology, University of Vienna, A-1030 Vienna, Austria.
authors.forename: Karin
authors.initials: K
authors.lastname: Ledolter
authors.affiliation: Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria.
authors.forename: Markus
authors.initials: M
authors.lastname: Hartl
authors.affiliation: Max F. Perutz Laboratories, Department of Structural and Computational Biology, University of Vienna, A-1030 Vienna, Austria.
authors.forename: Robert
authors.initials: R
authors.lastname: Konrat
authors.affiliation: Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria.
authors.forename: Eduard
authors.initials: E
authors.lastname: Stefan
authors.affiliation: Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria.
authors.forename: Klaus
authors.initials: K
authors.lastname: Bister
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D021381:Protein Transport; D016271:Proto-Oncogene Proteins c-myc / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015533:Transcriptional Activation
chemical_list: D002147:Calmodulin; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; D002118:Calcium
keywords: oncogene; protein-protein interaction; second messenger signaling; signal transduction; transcription factor