Dephosphorylation of CCAAT/enhancer-binding protein ß by protein phosphatase 2A containing B56δ is required at the early time of adipogenesis.

ABSTRACT

It is known that protein phosphatase 2A (PP2A) expression is increased in high-fat diet (HFD)-induced obese mice, but the role of PP2A in adipogenesis as well as obesity remains to be addressed. In this study, the role of PP2A in adipogenesis was explored. Preadipocytes were treated with okadaic acid (OA) during adipogenesis and the degree of adipogenesis was determined. The OA treatment blocked adipogenesis at the early time of adipogenesis, but not at the late time. In the early time of adipogenesis, CCAAT/enhancer-binding protein ß (C/EBPß) activation is preceded by the expression of key adipogenic transcription factors including PPARγ and C/EBPα, which function at the late time of adipogenesis, and then C/EBPß is degraded. However, the inhibition of PP2A by OA treatment sustained phosphorylation of C/EBPß and delayed its degradation. In turn, PPARγ and C/EBPα activation was altered. Among the various regulatory B56 subunits consisting of PP2A holoenzyme, B56δ was directly bound to C/EBPß and was responsible for the dephosphorylation of C/EBPß by PP2A. Taken together, these findings suggest that the phosphorylation of C/EBPß after hormonal induction has to be inactivated by PP2A containing B56δ at the early time of adipogenesis to allow the completion of adipogenesis.