Proteasome inhibition down-regulates endothelial nitric-oxide synthase phosphorylation and function

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Medicine

Background:

• Endothelial nitric-oxide synthase (eNOS) activity is crucial for vascular function.
• eNOS phosphorylation, particularly at serine 1179/1177 by Akt, is a key regulatory mechanism.
• The role of the proteasome in eNOS regulation is not fully understood.

Purpose of the Study:

• To investigate the novel role of the proteasome in modulating eNOS phosphorylation and function.
• To elucidate the specific mechanism by which proteasome activity affects eNOS serine 1179 phosphorylation.

Main Methods:

• Utilized proteasome inhibitors and protein phosphatase 2A (PP2A) modulators (okadaic acid, knockdown).
• Assessed eNOS phosphorylation at serine 1179/1177 and enzymatic activity.
• Investigated PP2A ubiquitination, cellular localization, and association with eNOS and Akt using biochemical analyses.

Main Results:

• Proteasome inhibition specifically dephosphorylated eNOS serine 1179, decreasing its activity.
• Blocking PP2A activity or expression restored eNOS phosphorylation and activity in proteasome-inhibited cells.
• Proteasome inhibition induced PP2A ubiquitination, promoting its translocation to the cell membrane and enhancing its association with eNOS, leading to dephosphorylation of eNOS and Akt.

Conclusions:

• The proteasome plays a novel role in regulating eNOS phosphorylation and function.
• Proteasomal activity controls eNOS phosphorylation by regulating PP2A localization and activity.
• This pathway highlights a new mechanism involving proteasome-mediated PP2A translocation in eNOS regulation.