HO-1 promotes resistance to an EZH2 inhibitor through the pRB-E2F pathway: correlation with the progression of myelodysplastic syndrome into acute myeloid leukemia

Abstract

BackgroundMyelodysplastic syndrome (MDS) can progress to acute myeloid leukemia (AML), and conventional chemotherapy (decitabine) does not effectively inhibit tumor cells. Enhancer of zeste homologue 2 (EZH2) and Heme oxygenase-1 (HO-1) are two key factors in patients resistance and deterioration.MethodsIn total, 58 MDS patients were divided into four groups. We analyzed the difference in HO-1 and EZH2 expression among the groups by real-time PCR. After treatment with Hemin or Znpp IX, flow cytometry was used to detect apoptosis and assess the cell cycle distribution of tumor cells. Following injection of mice with very high-risk MDS cells, spleen and bone marrow samples were studied by immunohistochemistry (IHC) and hematoxylin and eosin (H&E) staining. MDS cells overexpressing EZH2 and HO-1 were analyzed by high-throughput sequencing. The effect of HO-1 on the pRB-E2F pathway was analyzed by Western blotting. The effects of decitabine on P15INK4B and TP53 in MDS cells after inhibiting HO-1 were detected by Western blotting.ResultsReal-time PCR results showed that EZH2 and HO-1 expression levels were higher in MDS patients than in normal donors. The levels of HO-1 and EZH2 were simultaneously increased in the high-risk and very high-risk groups. Linear correlation analysis and laser scanning confocal microscopy results indicated that EZH2 was related to HO-1. MDS cells that highly expressed EZH2 and HO-1 infiltrated the tissues of experimental mice. IHC results indicated that these phenomena were related to the pRB-E2F pathway. High-throughput sequencing indicated that the progression of MDS to AML was related to EZH2. Using the E2F inhibitor HLM006474 and the EZH2 inhibitor JQEZ5, we showed that HO-1 could regulate EZH2 expression. HO-1 could stimulate the transcription and activation of EZH2 through the pRB-E2F pathway in MDS patients during chemotherapy, which reduced TP53 and P15INK4B expression.ConclusionsEZH2 was associated with HO-1 in high-risk and very high-risk MDS patients. HO-1 could influence MDS resistance and progression to AML.

E2F1 as a potential prognostic and therapeutic biomarker by affecting tumor development and immune microenvironment in hepatocellular carcinoma

“…Moreover, HLM006474 could induce cell cycle arrest in the G2/M phase, apoptosis via caspase-3 and p53, and senescence. Meanwhile, it proved that HLM006474 could reduce the viability of lung cancer cell lines (84) and potentially alter the progression of myelodysplastic syndrome into acute myeloid leukemia (85). Meanwhile, Sheldon (86) indicated that in breast cancer, arsenic trioxid could inhibit the dissociation of E2F1 from the tumor suppressor, retinoblastoma protein (pRB) due to changes in pRB phosphorylation which leads to decreased E2F1 transcriptional activity.…”

EZH2/EHMT2 Histone Methyltransferases Inhibit the Transcription of DLX5 and Promote the Transformation of Myelodysplastic Syndrome to Acute Myeloid Leukemia

“…NHD13 mice with high expression of EZH2 or EHMT2 rapidly transformed from MDS to AML in a short time, and the survival rate was also notably reduced. He et al (2019) have also clarified that EZH2 is associated with drug resistance and deterioration of MDS, as well as the progression from MDS to AML. Lehnertz et al (2014) have shown that EHMT2 inhibitor can significantly delay the progression of disease and reduce the frequency of leukemia stem cells in a mouse model of AML.…”

Clinical Significance of Heme Oxygenase 1 in Tumor Progression

“…Thus, cholangiocarcinoma [ 166 ], acute myeloid leukemia (AML) [ 167 ], and neuroblastoma [ 168 ] show a correlation between high HO-1 expression and poor disease outcomes. Furthermore, HO-1 positivity in chronic myeloid leukemia [ 169 ], acute myeloid leukemia [ 170 ], and myelodysplastic syndrome [ 171 ] correlate with disease progression, resistance to therapy, and relapse.…”

“…It is worth noting, in melanoma [ 176 ], thyroid cancer [ 172 ], and acute myeloid leukemia [ 167 ], HO-1 positivity correlates with the gain of function mutations of specific oncogenes B-Raf and RET. Moreover, in high-risk and very high-risk myelodysplastic syndrome, HO-1 expression correlates with overexpression of the enhancer of the zeste homologue 2 (EZH2) gene [ 171 ].…”