Depletion of Ric-8B leads to reduced mTORC2 activity

Area of Science:

• Cellular Biology
• Developmental Biology
• Biochemistry

Background:

• The mechanistic target of rapamycin (mTOR) kinase exists in two complexes, mTORC1 and mTORC2, with mTORC2 regulation being less understood.
• Ric-8B is a conserved protein functioning as a non-canonical guanine nucleotide exchange factor (GEF).

Purpose of the Study:

• To investigate the role of Ric-8B in embryonic development and its potential involvement in mTORC2 regulation.
• To elucidate the mechanisms underlying mTORC2 signaling pathways.

Main Methods:

• Analysis of Ric-8B hypomorphic mutant mice and embryos.
• Comparative transcriptome analysis of mutant and wild-type embryos.
• Gene knockdown experiments in cultured cell lines.
• Assessment of Akt phosphorylation at Ser473 as an indicator of mTORC2 activity.

Main Results:

• Ric-8B hypomorphic mutation leads to embryonic lethality during mid-gestation, characterized by developmental defects like failed neural tube closure.
• Transcriptome analysis reveals dysregulation of G protein-coupled receptor (GPCR) and G protein signaling pathways.
• A significant decrease in Akt phosphorylation at Ser473 indicates impaired mTORC2 activity in Ric-8B mutant embryos and cell lines.
• Knockdown of Ric-8B in cell lines recapitulates the reduced Akt phosphorylation observed in mutant embryos.

Conclusions:

• Ric-8B plays a critical, previously unrecognized role in embryonic development.
• Ric-8B is essential for proper mTORC2 signaling, evidenced by reduced Akt phosphorylation.
• This study provides novel insights into the regulatory mechanisms of mTORC2 and its developmental importance.