title: Partition of Myc into immobile vs. mobile complexes within nuclei.
abstract: Myc levels are highly regulated and usually low in vivo. Dimerized with Max, it regulates most expressed genes and so directly and indirectly controls most cellular processes. Intranuclear diffusion of a functional c-Myc-eGFP, expressed from its native locus in murine fibroblasts and 3T3 cells or by transient transfection, was monitored using Two Photon Fluorescence Correlation Spectroscopy, revealing concentration and size (mobility) of complexes. With increased c-Myc-eGFP, a very immobile pool saturates as a 'mobile' pool increases. Both pools diffuse too slowly to be free Myc-Max dimers. Following serum stimulation, eGFP-c-Myc accumulated in the presence of the proteasome inhbitor MG132. Stimulating without MG132, Myc peaked at 2.5 hrs, and at steady was ~8 ± 1.3 nM. Inhbiting Myc-Max dimerization by Max-knockdown or drug treatment increased the 'mobile' c-Myc pool size. These results indicate that Myc populates macromolecular complexes of widely heterogenous size and mobility in vivo.
authors.affiliation: Laboratory of Molecular Biophysics, Optical Spectroscopy Section, NHLBI, NIH, MD, USA.
authors.forename: Tilman
authors.initials: T
authors.lastname: Rosales
authors.forename: Zuqin
authors.initials: Z
authors.lastname: Nie
authors.forename: Varun
authors.initials: V
authors.lastname: Kapoor
authors.forename: Rafael
authors.initials: R
authors.lastname: Casellas
authors.forename: Jay R
authors.initials: JR
authors.lastname: Knutson
authors.forename: David
authors.initials: D
authors.lastname: Levens
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics* / Q000378:metabolism*; D015870:Gene Expression; D005786:Gene Expression Regulation / Q000187:drug effects; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D041681:NIH 3T3 Cells; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics* / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000970:Antineoplastic Agents; D050976:Basic-Leucine Zipper Transcription Factors; D007976:Leupeptins; C067850:Myc associated factor X; D016271:Proto-Oncogene Proteins c-myc; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde