Phosphorylation of PBX2, a novel downstream target of mTORC1, is determined by GSK3 and PP1

Area of Science:

• Cellular signaling
• Molecular biology
• Biochemistry

Background:

• Mechanistic target of rapamycin complex 1 (mTORC1) is a key kinase regulating cellular processes like protein synthesis and metabolism.
• mTORC1 activity is influenced by extracellular signals, including nutrients and growth factors.
• The precise phosphorylation targets of mTORC1 are not fully elucidated, necessitating further investigation.

Purpose of the Study:

• To identify novel target molecules regulated by mTORC1.
• To investigate the role of pre-B cell leukemia transcription factor 2 (PBX2) as a potential mTORC1 target.
• To elucidate the mechanisms controlling PBX2 phosphorylation status.

Main Methods:

• Reanalysis of large-scale phosphoproteomics data to identify mTORC1 targets.
• Confirmation of PBX2 dephosphorylation downstream of mTORC1 using biochemical assays.
• Pharmacological inhibition and gene knockdown experiments to identify kinases and phosphatases involved in PBX2 regulation.

Main Results:

• Pre-B cell leukemia transcription factor 2 (PBX2) was identified as a novel direct target of mTORC1, undergoing dephosphorylation.
• PBX2 dephosphorylation was confirmed to be dependent on mTORC1 activity.
• Glycogen synthase kinase 3 (GSK3) was identified as the kinase responsible for PBX2 phosphorylation, while protein phosphatase 1 (PP1) mediates its dephosphorylation.

Conclusions:

• The phosphorylation status of PBX2 is determined by the opposing activities of GSK3 and PP1.
• mTORC1 signaling regulates PBX2 phosphorylation through the modulation of GSK3 and PP1.
• These findings reveal a novel regulatory pathway for PBX2 within the mTORC1 signaling network.