Nuclear-localized Calcineurin Homologous Protein CHP1 Interacts with Upstream Binding Factor and Inhibits Ribosomal RNA Synthesis

• Published in: The Journal of biological chemistry 2010-11, Vol.285 (47), p.36260-36266
• Main Authors: Jiménez-Vidal, Maite, Srivastava, Jyoti, Putney, Luanna K., Barber, Diane L.
• Format: Article
• Language: English
• Subjects: Animals; Binding Sites; Blotting, Western; Calcineurin; Calcineurin Homologous Protein; Calcium; Calcium-binding protein; Calcium-binding Proteins; Calcium-Binding Proteins - genetics; Calcium-Binding Proteins - metabolism; Calmodulin; Cell activation; Cell Biology; Cell Membrane - metabolism; Cell Nucleus - metabolism; Cells, Cultured; Chromatin Immunoprecipitation; Cricetinae; Cytoplasm - metabolism; Cytosol; Data processing; DNA-binding protein; DNA-directed RNA polymerase; EF-hand; Fibroblasts - metabolism; Golgi; Golgi apparatus; Golgi Apparatus - metabolism; Lung - cytology; Lung - metabolism; Lymphocytes T; Mutation; Nuclear Translocation; Nuclear transport; Nucleoli; Plasma membranes; Pol1 Transcription Initiation Complex Proteins - genetics; Pol1 Transcription Initiation Complex Proteins - metabolism; polymerase I; Protein Binding; Protein Transport; Reverse Transcriptase Polymerase Chain Reaction; Ribosomes - metabolism; RNA Synthesis; RNA, Messenger - genetics; RNA, Ribosomal - antagonists & inhibitors; RNA, Ribosomal - metabolism; rRNA; Secretory vesicles; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Subcellular Fractionation; Transcription; UBF
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.165555

Calcineurin homologous protein 1 (CHP1) is a widely expressed, 22-kDa myristoylated EF-hand Ca2+-binding protein that shares a high degree of similarity with the regulatory B subunit of calcineurin (65%) and with calmodulin (59%). CHP1 localizes to the plasma membrane, the Golgi apparatus, and the nucleus and functions to regulate trafficking of early secretory vesicles, activation of T cells, and expression and transport of the Na-H exchanger NHE1. Although CHP1 contains nuclear export signals, whether its nuclear and cytoplasmic localization is regulated and has distinct functions remain unknown. We show that CHP1 is predominantly in the nucleus in quiescent fibrobasts, is translocated to cytoplasmic compartments with growth medium, and that translocation is inhibited by mutations in the nuclear export motifs. In a screen for proteins co-precipitating with CHP1 in quiescent cells we identified the upstream binding factor UBF, a DNA-binding protein and component of the RNA polymerase I complex regulating RNA synthesis. The CHP1-UBF interaction is restricted to the nucleus and inhibited by Ca2+. Nuclear retention of CHP1 attenuates the abundance of UBF in the nucleolus and inhibits RNA synthesis when quiescent cells are transferred to growth medium. These data show UBF as a newly identified CHP1-binding protein and regulation of RNA synthesis as a newly identified function for nuclear-localized CHP1, which is distinct from CHP1 functions in the cytosol.