Dissecting The Mechanisms Of MED20 In Promoting Adipogenesis

Adipogenesis is the differentiation process from preadipocytes to mature adipocytes orchestrated by a cascade of transcriptional events.It consists of early and late stages of adipogenesis.In the early stage of adipogenesis,C/EBPβ forms an early adipogenic complex with multiple early adipogenic factors to organize hotspots and superenhancers and promotes the transcription of late adipogenic factors including PPARy.The Mediator complex is an evolutionarily conserved complex,It plays a key role in transcription initiation at eukaryotic protein-coding genes by functioning as a physical and functional bridge between transcriptional activators and RNA polymeraseⅡ(Pol Ⅱ).Structurally,the complex can be divided into head,middle and tail modules.Although the head module is part of the essential core Mediator,MED20 in the module has been shown to be a non-essential subunit.However,the underlying mechanism and the physiological functions of MED20 remain largely unknown.WDTC1 is an adaptor protein between CUL4-DDB1 E3 ligase(CRL4)and the substrate.Overexpression of WDTC1 inhibits adipogenesis,but its substrate remains unclear.Here,we identify MED20 as a substrate of the anti-obesity CRL4-WDTC1 E3 ubiquitin ligase complex through affinity purification and candidate screening,Overexpression of WDTC1 leads to degradation of MED20,whereas depletion of Wdtc1 or Cul4a/b causes accumulation of MED20,and a non-degradable MED20 mutant restores adipogenesis in WDTC1-overexpressing cells.Furthermore,removing one allele of Med20 in preadipocytes protects mice from diet-induced obesity,and reverses weight gain in Cul4a-or Cul4b-depleted mice.Mechanistically,we show that MED20 is required for the transcriptional activity of C/EBPβ,ChIP-Seq analysis reveals that MED20 functions by bridging C/EBPβ and RNA polymerase Ⅱ to promote transcription of the central adipogenic factor,PPARγ.Our findings have uncovered that MED20 is the physiological substrate of the antiobesity CRL4-WDTC1 E3 ubiquitin ligase complex in cells and mice.Here we show that MED20,through direct interaction with C/EBPβ,is recruited to C/EBPβ binding sites to control the transcription of PPARγ.Given that WDTC1,CUL4 and MED20 are all evolutionarily conserved,targeting MED20 by the CRL4-WDTC1 E3 complex might play a general role in regulating adipogenesis in evolution.Furthermore,considering that loss of one allele of Med20 in preadipocytes protects mice from dietinduced obesity,In view of the current situation that obesity has become a global pandemic,MED20 might represent a potential target for obesity treatment in the future.