Proteomic Identification of the C/EBPalpha Multiprotein Complex Reveals That JNK1, an Activator of C/EBPalpha, Is Inactive in Acute Myeloid Leukemia.

CCAAT Enhancer Binding Protein Alpha (C/EBPalpha) is one of the key myeloid transcription factors whose function is impaired in Acute Myeloid Leukemia (AML). This is either due to mutation or inhibition by other proteins via protein-protein interaction. Here, we hypothesised that protein-protein interaction of C/EBPalpha with other proteins might be important for its activation. Based on our hypothesis, we analysed the multiprotein complex of C/EBPalpha. After GST-pull down from U937 nuclear extract and using a proteomic approach we were able to identify JNK1, PAK6, MADP, ZNF45 and others as interacting proteins of C/EBPalpha. Following confirmation of physical interaction of JNK1 with C/EBPalpha, we were able to show that JNK1 phosphorylates C/EBPalpha, increases its protein half-life and thereby enhances its transactivation and DNA binding capacity. However, in various AML subtypes, JNK1 mRNA and Phospho-JNK1 protein expression is downregulated as compared with normal bone marrow which is one of the possible reasons why C/EBPalpha is inactive in AML. Thus, here we report that C/EBPalpha is impaired in AML due to inactivation of JNK1.