Repression of CDKN2C caused by PML/RARα binding promotes the proliferation and differentiation block in acute promyelocytic leukemia.

Inappropriate cell proliferation during oncogenesis is often accompanied by inactivation of components involved in the cell cycle machinery. Here, we report that cyclin-dependent kinase inhibitor 2C (CDKN2C) as a member of the cyclin-dependent kinase inhibitors is a target of the PML/RARα oncofusion protein in leukemogenesis of acute promyelocytic leukemia (APL).We found that CDKN2C was markedly downregulated in APL blasts compared with normal promyelocytes. Chromatin immunoprecipitation combined with quantitative polymerase chain reaction demonstrated that PML/RARα directly bound to the CDKN2C promoter in the APL patient-derived cell line NB4. Luciferase assays indicated that PML/RARα inhibited the CDKN2C promoter activity in a dose-dependent manner. Furthermore, all-trans retinoic acid treatment induced CDKN2C expression by releasing the PML/RARα binding on chromatin in NB4 cells. Functional studies showed that ectopic expression of CDKN2C induced a cell cycle arrest at the G0/G1 phase and a partial differentiation in NB4 cells. Finally, the transcriptional regulation of CDKN2C was validated in primary APL patient samples. Collectively, this study highlights the importance of CDKN2C inactivation in the abnormal cell cycle progression and differentiation block of APL cells and may provide new insights into the study of pathogenesis and targeted therapy of APL.