Serum Starvation Promotes the Proteolysis of OGT by Activating AMPK and the CUL1/SKP1/SKP2 E3 Ubiquitin Ligase in 3T3-L1 Cells

초록

Post-translational modifications (PTMs) play a crucial role in the regulation of protein function. Protein O-linked N-acetylglucosamine (O-GlcNAc) is a type of nutrient-sensitive PTM that occurs on serine or threonine residues of substrates, catalysed by single pair of enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). In the present study, we have observed that serum deprivation decreased OGT levels without affecting its transcription. Instead, we found that serum deprivation activated AMPactivated protein kinase (AMPK) and induced the phosphorylation of OGT at threonine 444, resulting in the proteolysis of OGT by the CUL1/SKP1/SKP2 E3 ubiquitin ligase. Knocking down OGT significantly impaired 3T3-L1 cell differentiation in the presence of serum. Likewise, treatment with AICAR, an AMPK activator, or OSMI-1, an OGT small molecule inhibitor, attenuated seruminduced 3T3-L1 differentiation. Together, our results demonstrate that OGT is essential for 3T3 cell differentiation in which serum starvation activates AMPK to phosphorylate OGT at Thr444, triggering the proteolysis of OGT by the CUL1/SKP1/SKP2 E3 ligase.

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