Conserved Mitotic Phosphorylation of a Proteasome Subunit Regulates Cell Proliferation.

Reversible phosphorylation has emerged as an important mechanism for regulating proteasome function in various physiological processes. Essentially all proteasome phosphorylations characterized thus far occur on proteasome holoenzyme or subcomplexes to regulate substrate degradation. Here, we report a highly conserved phosphorylation that only exists on the unassembled ?5 subunit of the ...
proteasome. The modified residue, ?5-Ser16, is within a SP motif typically recognized by cyclin-dependent kinases (CDKs). Using a phospho-specific antibody generated against this site, we found that ?5-S16 phosphorylation is mitosis-specific in both yeast and mammalian cells. Blocking this site with a S16A mutation caused growth defect and G2/M arrest of the cell cycle. ?5-S16 phosphorylation depends on CDK1 activity and is highly abundant in some but not all mitotic cells. Immunoprecipitation and mass spectrometry (IP-MS) studies identified numerous proteins that could interact with phosphorylated ?5, including PLK1, a key regulator of mitosis. ?5-PLK1 interaction increased upon mitosis and could be facilitated by S16 phosphorylation. CDK1 activation downstream of PLK1 activity was delayed in S16A mutant cells, suggesting an important role of ?5-S16 phosphorylation in regulating PLK1 and mitosis. These data have revealed an unappreciated function of "exo-proteasome" phosphorylation of a proteasome subunit and may bring new insights to our understanding of cell cycle control.
Mesh Terms:
Amino Acid Sequence, Cell Cycle Proteins, Cell Line, Tumor, Cell Proliferation, Conserved Sequence, Humans, Mitosis, Mutation, Phosphorylation, Phosphoserine, Proteasome Endopeptidase Complex, Protein Interaction Maps, Protein Serine-Threonine Kinases, Protein Subunits, Proto-Oncogene Proteins
Cells
Date: Dec. 08, 2020
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