Functional Characterization of the H3K4me2/3-Demethylase KDM5C in Hematopoiesis and Acute Myeloid Leukemia

Epigenetic regulation is not only crucial for regulation and maintenance of proper hematopoiesis but is also frequently abrupted in acute myeloid leukemia (AML). However, mutations in epigenetic regulators alone cannot alone account for the extensive epigenetic dysregulation observed in AML and only little is known about epigenetic drivers in this context. AML is an aggressive blood cancer characterized by uncontrolled expansion of immature myeloid cells which leads to rapid accumulation of immature myeloid blasts in the BM, blood and peripheral organs at the expense of normal hematopoiesis. Although most patients respond to initial treatment, the prognosis is generally poor due to high relapse rates. Thus, there is an unmet need for specialized treatment of this disease. Investigating potential epigenetic factors involved in the development and progression of AML would provide crucial knowledge to improve treatment options for patients. Therefore, we performed an in vivo shRNA-screen in a mouse model of CEBPA mutant AML. We identified KDM5C, a H3K4me2/3-demethylase, as a putative tumor suppressor in AML. KDM5C is believed to function as a transcriptional repressor due to its ability to regulate modifications found at active promoters. Here we demonstrate, that low expression of Kdm5c is associated with accelerated disease in mice as well as murine and human AML cell lines. Furthermore, low KDM5C expression was associated with decreased disease-free-survival in female patients. Mechanistically, we show that KDM5C is involved in repression of early differentiation genes. Kdm5c-knockdown led to spurious transcription from low-activity and bivalent/repressed KDM5C-targeted promoters and was associated with a higher frequency of immature blasts. By modulating the expression of late myeloid transcription factors c-Fos and c-Jun, we could mimic and partially rescue the Kdm5c-KD phenotype. Thus, supporting that differential expression of differentiation-associated genes drive the tumor suppressive
phenotype. Furthermore, members of KDM5 protein family have been implicated in both hematopoietic and leukemic maintenance. Based on our findings in leukemia, we hypothesized that KDM5C would likely have a role in normal hematopoiesis as well. Thus, we generated conditional Kdm5c
knockout mouse model. We show that knockout of Kdm5c perturbs normal hematopoiesis by impairing hematopoietic stem cell (HSC) maintenance suggesting KDM5C as a positive regulator of hematopoietic stem cell potential.
In conclusion, KDM5C is essential for HSC maintenance and additionally functions as a tumor suppressor in AML by aiding gene repression and thus maintaining cell identity. Thus, we here add further evidence to the significance of epigenetic regulation of HSC potential and leukemogenesis.