Cdk2-Instigates C/Ebp Alpha Degradation Through Skp2 In Acute Myeloid Leukemia

Transcription factor CCAAT/enhancer-binding protein-alpha (C/EBP alpha) regulates myelopoiesis by coupling growth arrest with differentiation of myeloid progenitors. Mutations in one or both alleles are observed in 10-14% AML cases that render C/EBP alpha functionally inactive. Besides, antagonistic protein-protein interactions also impair C/EBP alpha expression and function. In recent independent studies, we showed that CDK2 and SKP2 downregulated C/EBP alpha expression in an ubiquitin-dependent proteasome degradation manner leading to differentiation block in AML. Here, we demonstrate that CDK2-instigated C/EBP alpha downregulation is actually mediated by SKP2. Mechanistically, we show that CDK2 stabilizes SKP2 by phosphorylating it at Ser64 and thereby potentiates C/EBP alpha ubiquitination and subsequent degradation in AML cells. Immunoblot experiments showed that CDK2 inhibition downregulated SKP2 levels and concomitantly enhanced C/EBP alpha levels in myeloid cells. We further show that while CDK2 promoted C/EBP alpha ubiquitination and inhibited its protein levels, negatively affected its transactivation potential and DNA binding ability, simultaneous SKP2 depletion abrogated CDK2-promoted ubiquitination and restored C/EBP alpha expression and function. Taken together, these findings consolidate that CDK2 potentiates SKP2-mediated C/EBP alpha degradation in AML and targeting CDK2-SKP2 axis can be harnessed for therapeutic benefit in AML.