A pathway linking translation stress to checkpoint kinase 2 signaling in Neurospora crassa

Area of Science:

• Cellular signaling pathways
• Molecular biology
• Mycology

Background:

• Checkpoint kinase 2 (CHK-2) is crucial for the DNA damage response (DDR), activated by kinases like ATM and ATR.
• Known CHK-2 activation pathways are primarily DNA damage-dependent.
• Additional regulatory mechanisms for CHK-2 and its orthologs remain largely unexplored.

Purpose of the Study:

• To investigate novel activation pathways for CHK-2 orthologs.
• To identify the signaling mechanisms linking translation stress to PRD-4 activation in *Neurospora crassa*.
• To elucidate the role of mechanistic target of rapamycin (mTOR) in this process.

Main Methods:

• Utilized *Neurospora crassa* as a model organism.
• Investigated the phosphorylation of PERIOD-4 (PRD-4) under conditions of translation stress.
• Employed biochemical assays to identify the kinases involved in PRD-4 activation.
• Analyzed the role of protein phosphatases in regulating PRD-4 activity.

Main Results:

• Discovered that PRD-4 is activated by translation stress, independent of DNA damage.
• Identified a novel PI3-kinase-like kinase (PI3KK) that phosphorylates PRD-4 during translation stress.
• Provided evidence that mechanistic target of rapamycin (mTOR), specifically mTOR complex 1 (TORC1), is the activating PI3KK.
• Demonstrated that translation stress is sensed through the imbalance of an unstable protein phosphatase that regulates PRD-4 phosphorylation by TORC1.

Conclusions:

• *Neurospora crassa* PRD-4 is activated by translation stress via a novel pathway involving mTOR/TORC1.
• This pathway represents a distinct mechanism for CHK-2 ortholog activation.
• The findings suggest a coordination between metabolic state (translation) and cell cycle progression mediated by *Neurospora* mTOR and PRD-4.