An emerin "proteome": purification of distinct emerin-containing complexes from HeLa cells suggests molecular basis for diverse roles including gene regulation, mRNA splicing, signaling, mechanosensing, and nuclear architecture.

Using recombinant bead-conjugated emerin, we affinity-purified seven proteins from HeLa cell nuclear lysates that bind emerin either directly or indirectly. These proteins were identified by mass spectrometry as nuclear alphaII-spectrin, nonmuscle myosin heavy chain alpha, Lmo7 (a predicted transcription regulator; reported separately), nuclear myosin I, beta-actin (reported separately), calponin 3, ...
and SIKE. We now report that emerin binds nuclear myosin I (NMI, a molecular motor) directly in vitro. Furthermore, bead-conjugated emerin bound nuclear alphaII-spectrin and NMI equally well with or without ATP (which stimulates motor activity), whereas ATP decreased actin binding by 65%. Thus alphaII-spectrin and NMI interact stably with emerin. To investigate the physiological relevance of these interactions, we used antibodies against emerin to affinity-purify emerin-associated protein complexes from HeLa cells and then further purified by ion-exchange chromatography to resolve by net charge and by size exclusion chromatography yielding six distinct emerin-containing fractions (0.5-1.6 MDa). Western blotting suggested that each complex had distinct components involved in nuclear architecture (e.g., NMI, alphaII-spectrin, lamins) or gene or chromatin regulation (BAF, transcription regulators, HDACs). Additional constituents were identified by mass spectrometry. One putative gene-regulatory complex (complex 32) included core components of the nuclear corepressor (NCoR) complex, which mediates gene regulation by thyroid hormone and other nuclear receptors. When expressed in HeLa cells, FLAG-tagged NCoR subunits Gps2, HDAC3, TBLR1, and NCoR each co-immunoprecipitated emerin, validating one putative complex. These findings support the hypothesis that emerin scaffolds a variety of functionally distinct multiprotein complexes at the nuclear envelope in vivo. Notably included are nuclear myosin I-containing complexes that might sense and regulate mechanical tension at the nuclear envelope.
Mesh Terms:
Adaptor Proteins, Signal Transducing, Binding Sites, Cell Line, Tumor, Chromatin, Chromatography, Affinity, Chromatography, Gel, Chromatography, Ion Exchange, Hela Cells, Humans, Immunoprecipitation, Intracellular Signaling Peptides and Proteins, Membrane Proteins, Multiprotein Complexes, Nuclear Matrix-Associated Proteins, Nuclear Proteins, Protein Binding, Protein Biosynthesis, Proteome, Recombinant Fusion Proteins, Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization, Transcription Factors
Biochemistry
Date: Jul. 31, 2007
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