The fusion oncoprotein RUNX1/ETO which results from the chromosomal translocation t (8;21) in acute myeloid leukemia (AML) is an essential driver of leukemic maintenance. We have previously shown that RUNX1/ETO knockdown impairs expression of the protein component of telomerase, TERT. However, the underlying molecular mechanism of how RUNX1/ETO controls TERT expression has not been fully elucidated. Here we show that RUNX1/ETO binds to an intergenic region 18 kb upstream of the TERT transcriptional start site and to a site located in intron 6 of TERT. Loss of RUNX1/ETO binding precedes inhibition of TERT expression. Repression of TERT expression is also dependent on the destabilization of the E3 ubiquitin ligase SKP2 and the resultant accumulation of the cell cycle inhibitor CDKN1B, that are both associated with RUNX1/ETO knockdown. Increased CDKN1B protein levels ultimately diminished TERT transcription with E2F1/Rb involvement. Collectively, our results show that RUNX1/ETO controls TERT expression directly by binding to its locus and indirectly via a SKP2-CDKN1B-E2F1/Rb axis.
The t(8;21) translocation is one of the most frequent chromosome abnormalities associated with acute myeloid leukaemia (AML). This abberation deregulates numerous molecular pathways including the ERK signalling pathway among others. Therefore, the aim of the present study was to investigate the gene expression patterns following siRNA‑mediated suppression of RUNX1‑RUNX1T1 and MAPK1 in Kasumi‑1 and SKNO‑1 cells and to determine the differentially expressed genes in enriched biological pathways. BeadChip microarray and gene ontology analysis revealed that RUNX1‑RUNX1T1 and MAPK1 suppression reduced the proliferation rate of the t(8;21) cells with deregulated expression of several classical positive regulator genes that are otherwise known to enhance cell proliferation. RUNX1‑RUNX1T1 suppression exerted an anti‑apoptotic effect through the overexpression of BCL2, BIRC3 and CFLAR genes, while MAPK1 suppression induced apopotosis in t(8;21) cells by the apoptotic mitochondrial changes stimulated by the activity of upregulated TP53 and TNFSF10, and downregulated JUN gene. RUNX1‑RUNX1T1 suppression supported myeloid differentiation by the differential expression of CEBPA, CEBPE, ID2, JMJD6, IKZF1, CBFB, KIT and CDK6, while MAPK1 depletion inhibited the differentiation of t(8;21) cells by elevated expression of ADA and downregulation of JUN. RUNX1‑RUNX1T1 and MAPK1 depletion induced cell cycle arrest at the G0/G1 phase. Accumulation of cells in the G1 phase was largely the result of downregulated expression of TBRG4, CCNE2, FOXO4, CDK6, ING4, IL8, MAD2L1 and CCNG2 in the case of RUNX1‑RUNX1T1 depletion and increased expression of RASSF1, FBXO6, DADD45A and P53 in the case of MAPK1 depletion. Taken together, the current results demonstrate that MAPK1 promotes myeloid cell proliferation and differentiation simultaneously by cell cycle progression while suppresing apoptosis.