Actin-based modeling of a transcriptionally competent nuclear substructure induced by transcription inhibition.
During transcription inactivation, the nuclear bodies in the mammalian cells often undergo reorganization. In particular, the interchromatin granule clusters, or IGCs, become colocalized with RNA polymerase II (RNAP II) upon treatment with transcription inhibitors. This colocalization has also been observed in untreated but transcriptionally inactive cells. We report here that the reorganized IGC domains are unique substructure consisting of outer shells made of SC35, ERK2, SF2/ASF, and actin. The apparently hollow holes of these domains contain clusters of RNAP II, mostly phosphorylated, and the splicing regulator SMN. This class of complexes are also the sites where prominent transcription activities are detected once the inhibitors are removed. Furthermore, actin polymerization is required for reorganization of the IGCs. In connection with this, immunoprecipitation and immunostaining experiments showed that nuclear actin is associated with IGCs and the reorganized IGC domains. The study thus provides further evidence for the existence of an actin-based nuclear skeleton structure in association with the dynamic reorganization processes in the nucleus. Overall, our data suggest that mammalian cells have adapted to utilize the reorganized, uniquely shaped IGC domains as the temporary storage sites of RNAP II transcription machineries in response to certain transient states of transcription inactivation.
Wang
I-Fan
IF
Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, R.O.C.
Chang
Hsiang-Yu
HY
Shen
C-K James
CK
D000199:Actins / Q000378:metabolism*; D000546:Amanitins / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D022003:Cell Nucleus Structures / Q000187:drug effects / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D004004:Dichlororibofuranosylbenzimidazole / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D051379:Mice; D008954:Models, Biological; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D012319:RNA Polymerase II / Q000037:antagonists & inhibitors / Q000378:metabolism; D012326:RNA Splicing; D016601:RNA-Binding Proteins / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism; D055532:SMN Complex Proteins; D000068103:Serine-Arginine Splicing Factors; D014158:Transcription, Genetic / Q000187:drug effects
D000199:Actins; D000546:Amanitins; D017362:Cyclic AMP Response Element-Binding Protein; D004791:Enzyme Inhibitors; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D055532:SMN Complex Proteins; C499372:SRSF2 protein, mouse; C073288:SRSF2 protein, human; D000068103:Serine-Arginine Splicing Factors; D004004:Dichlororibofuranosylbenzimidazole; D012319:RNA Polymerase II