Adapter protein involved in protein degradation by interacting with COP1 ubiquitin ligase (PubMed:27041596). The COP1- binding motif is masked by autoinhibitory interactions with the protein kinase domain (PubMed:26455797). Serves to alter COP1 substrate specificity by directing the activity of COP1 toward CEBPA (PubMed:27041596). Binds selectively the recognition sequence of CEBPA (PubMed:26455797). Regulates myeloid cell differentiation by altering the expression of CEBPA in a COP1-dependent manner (By similarity). Controls macrophage, eosinophil and neutrophil differentiation via the COP1-binding domain (By similarity). Interacts with MAPK kinases and regulates activation of MAP kinases, but has no kinase activity (PubMed:15299019, PubMed:26455797). {ECO:0000250|UniProtKB:Q8K4K4, ECO:0000269|PubMed:15299019, ECO:0000269|PubMed:26455797, ECO:0000305|PubMed:27041596}. This is the function of TRIB1 (tribbles pseudokinase 1, Ensembl gene identifier ENSG00000173334).