Defining how Pak1 regulates cell polarity and cell division in fission yeast

ABSTRACT: For polarized growth of cells, protein kinases regulate the assembly of cytoskeletal structures at the correct time and place. Large cytoskeletal structures must also be assembled in a regulated manner during cytokinesis and cell separation. We performed a visual screen to identify cell polarity protein kinases that might also function in cytokinesis and cell separation. We found that the Cdc42-activated protein kinase Pak1 (also called Orb2 and Shk1) colocalizes with the assembling cytokinetic ring and remains in the cell middle during septation. Mutations in pak1 led to defects in cytokinetic ring assembly and cell separation, as well as previously known cell polarity defects. We performed a phosphoproteomic screen and identified novel Pak1 targets that were verified as direct substrates in vitro. Top targets included proteins that function in polarized growth, cytokinesis, and septation. For cytokinesis, we found that Pak1 regulates the localization of its substrates Mid1 and Cdc15 to the cell cortex and the cytokinetic ring. For cell separation, Pak1 phosphorylates the RNA-binding protein Sts5 to prevent its assembly into P-body granules. The cell separation defect of pak1 mutants was suppressed by a non-phosphorylatable sts5 mutant. These results show that Pak1 acts directly on components of the cytokinetic ring, but unexpectedly promotes the later stages of cell division by inhibiting the assembly of ribonucleoprotein granules. More broadly, our work reveals that cell polarity signaling proteins coordinate diverse events to promote cell division at the end of the cell cycle.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Schizosaccharomyces Pombe (ncbitaxon:4896)

SUBMITTER: Arminja Kettenbach  

PROVIDER: MSV000084047 | MassIVE | Tue Jul 02 09:50:00 BST 2019

SECONDARY ACCESSION(S): PXD014463

REPOSITORIES: MassIVE