Proteasomes degrade proteins in focal subdomains of the human cell nucleus.
The ubiquitin proteasome system plays a fundamental role in the regulation of cellular processes by degradation of endogenous proteins. Proteasomes are localized in both, the cytoplasm and the cell nucleus, however, little is known about nuclear proteolysis. Here, fluorogenic precursor substrates enabled detection of proteasomal activity in nucleoplasmic cell fractions (turnover 0.0541 microM/minute) and nuclei of living cells (turnover 0.0472 microM/minute). By contrast, cell fractions of nucleoli or nuclear envelopes did not contain proteasomal activity. Microinjection of ectopic fluorogenic protein DQ-ovalbumin revealed that proteasomal protein degradation occurs in distinct nucleoplasmic foci, which partially overlap with signature proteins of subnuclear domains, such as splicing speckles or promyelocytic leukemia bodies, ubiquitin, nucleoplasmic proteasomes and RNA polymerase II. Our results establish proteasomal proteolysis as an intrinsic function of the cell nucleus.
Rockel
Thomas Dino
TD
Institut für Umweltmedizinische Forschung at Heinrich-Heine-University, Auf'm Hennekamp 50, 40225 Düsseldorf, Germany.
Stuhlmann
Dominik
D
von Mikecz
Anna
A
D000818:Animals; D022003:Cell Nucleus Structures / Q000201:enzymology / Q000378:metabolism*; D002470:Cell Survival; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology; D005347:Fibroblasts / Q000166:cytology; D006801:Humans; D015603:Keratinocytes / Q000166:cytology; D034904:Lamin Type A / Q000378:metabolism; D034921:Lamin Type B / Q000378:metabolism; D051379:Mice; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000378:metabolism*; D014404:Tubulin / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
D002868:Chromosomal Proteins, Non-Histone; D034904:Lamin Type A; D034921:Lamin Type B; D061988:Proteasome Inhibitors; D011506:Proteins; D014404:Tubulin; D025801:Ubiquitin; C047458:fibrillarin; D046988:Proteasome Endopeptidase Complex