Casein Kinase I Protein Hrr25 Is Required for Pin4 Phosphorylation and Mediates Cell Wall Integrity Signaling in .

BACKGROUND

Casein kinase I protein Hrr25 plays important roles in many cellular processes, including autophagy, vesicular trafficking, ribosome biogenesis, mitochondrial biogenesis, and the DNA damage response in . Pin4 is a multi-phosphorylated protein that has been reported to be involved in the cell wall integrity (CWI) pathway and DNA damage response. Pin4 was reported to interact with Hrr25 in yeast two-hybrid and large-scale pulldown assays.

METHODS/OBJECTIVES: Co-immunoprecipitation and yeast two-hybrid assays were utilized to confirm whether Pin4 and Hrr25 interact and to determine how they interact. Genetic interaction analysis was conducted to examine whether mutations form synthetic growth defects with mutations in genes involved in CWI signaling. Immunoblotting was used to determine whether Hrr25 phosphorylates Pin4.

RESULTS

We show that Hrr25 interacts with Pin4 and is required for Pin4 phosphorylation. mutations result in synthetic slow-growth phenotypes with mutations in genes encoding Bck1 and Slt2, two of the protein kinases in the MAP kinase cascade that regulates CWI in the budding yeast. We show that mutations result in similar phenotypes to mutations. Hrr25 consists of an N-terminal kinase domain, a middle region, and a C-terminal proline/glutamine-rich domain. The function of the C-terminal P/Q-rich domain of Hrr25 has been elusive. We found that the C-terminal region of Hrr25 is required both for Pin4 interaction and CWI.

CONCLUSIONS

Our data suggest that Hrr25 is implicated in cell wall integrity signaling via its association with Pin4.