Over-expression of Trib1 overcomes self-degradation to induce myeloid leukemia

Cop1 encodes a ubiquitin E3 ligase that is well preserved during evolution both in plants and metazoan. In metazoan, C/EBP family transcription factors are Cop1 targets for degradation, and the process is regulated by Tribbles family pseudokinases. Over-expression of Tribbles homolog 1 (Trib1) induces acute myeloid leukemia (AML) via Cop1-dependent degradation of the C/EBP p42 isoform. Here we induce rapid growth arrest and granulocytic differentiation of Trib1-expressing AML by Cop1 conditional knockout (KO) that is associated with transient increase of the C/EBP p42 isoform. The growth suppressive effect by Cop1 KO was canceled by silencing of Cebpa and was reinforced by exogenous expression of p42 isoform. We further identify remarkable increase of the Trib1 protein by Cop1 KO, indicating that the Trib1 protein is self-degraded by the Cop1 degradosome. Cop1 KO modulates gene expression profiles of Trib1-expressing AML depicting hematopoietic cell proliferation and maturation pathways. COP1 downregulation also inhibited proliferation of human AML cells in a TRIB1-dependent manner. Taken together, our results provide new insights into the role of Trib1/Cop1 machinery in the C/EBPa p42-dependent leukemogenic activity, and a novel idea to develop new therapeutics.