Increased Expression of HERG1 K+ Channels Contribute to MDS Progression and Display Correlation with Prognosis Stratification

Background: Myelodysplastic syndromes (MDS) are defined as a heterogeneous group of clonal hematopoietic stem cell (HSC) malignant disorders which are characterized by bone marrow failure and dysplasia of blood cells. As continually terminated in AML, MDS are treated as the "pre-leukemia" condition. HERG K⁺ channels, being three subtypes: HERG1, HERG.2, HERG3, are expressed transiently at early stages of cells such as progenitor and stem cells, disappearing at later stages of cells like mature cells. Our previous work and others demonstrated that HERG1, as an oncoprotein, was over expressed in AML cells and played crucial roles in SDF-1induced leukemia cell migration. The expression and functional role of HERG1 K⁺ channels in MDS development is not reported. We investigated the HERG1 K⁺ channels expression and explored the functional link between HERG1 K+ channels and MDS progression

Methods: The expression of HERG1 K⁺ channels in untreated MDS, AML patients and normal control was detected by flow cytometry. The roles of HERG1K⁺ channels in regulation of SKM-1 cell proliferation, apoptosis and cell cycle by CCK-8 assay and flow cytometry, respectively.

Results: We observed that the expression of HERG1 K⁺ channels on bone marrow (BM) mononuclear cells (MNCs) in MDS patients was significantly higher than that in the controls (42 ± 7.62% vs 19.8 ± 2.79%, p < 0.01) , but was lower than that in AML (42 ± 7.62% vs 52.18 ± 9.72%, p < 0.01). MDS subtypes mainly contained refractory cytopenia unilineage dysplasia (RCUD), refractory cytopenia with multilineage dysplasia (RCMD), refractory anemia with excess blast I (RAEB-I), refractory anemia with excess blasts II (RAEB-II) and MDS-unclassified (MDS-U). We next analyzed percentage of HERG1 K⁺ channels in MDS subtypes and found that level of HERG1 K⁺ channels on the MNCs in each subtypes of MDS was significant higher than that in the control group (Control: 19.8 ± 2.79%, MDS-RCUD: 30.91 ± 1.48%, MDS-RCMD: 39.06 ± 2.47%, MDS-RAEB-I: 44.76 ± 5.54%, MDS-RAEB-II: 49.69 ± 3.28%, p < 0.01), suggesting that HERG1 K⁺ channels expression might be positively associated with malignancy degree of MDS.

HSCs played important roles in the pathophysiology of MDS. Our results also revealed that with the increase of malignancy degree, the percentage of HERG1K⁺ channels on CD34+CD38- derived cells from MDS subtypes tended to elevate in corresponding MDS subtypes (MDS-RCUD: 61.21 ± 9.46%, MDS-RCMD: 65.66 ± 4.57%, MDS-RAEB-I: 72.35 ± 9.38%, MDS-RAEB-II: 75.71 ± 4.24%, p < 0.05), which supported the notion in other way that MDS are HSC malignant disorders. The over-expression of HERG1 K⁺ channels on CD34+CD38- cells in MDS patients might be correlated with the oncogenesis of MDS.

In addition, the prognosis stratification of MDS patients was performed according to International Prognostic Scoring System (IPSS) scores and the untreated MDS cohort was categorized as four risk groups: Low-R, Int-1-R, Int-2-R and High-R. Our results showed that there was a positively correlation between HERG1 level and IPSS scores of patients (Low-R: 31.93 ± 3.47%, Int-1-R: 39.95 ± 5.76%, Int-2-R: 45.94 ± 6.34%, High-R: 49.05 ± 3.04%, p < 0.01). This showed that expression level of HERG1 K⁺ channels was helpful for predicting the prognosis of de novo MDS.

Furthermore, we analyzed HERG1 K+ channel role on MDS cell proliferation and apoptosis. Incubation with 0, 10, 20 uM E-4031 ( HERG K⁺ channels inhibitor) with SKM-1 cells (MDS cell line) for 48 h, the results showed that blockage of HERG1 decreased the proliferation of SKM-1 cells but had rarely effects on cell apoptosis and cell cycle distribution. In consistent with other studies, HERG1 K⁺ channels had already been shown to be necessary for growth of cancer cells through specific activities independent of cell cycle such as interacting with TNFR1 protein which could activate NF-κB to facilitate cell proliferation and favoring transduction of growth signals by MAP kinase/c-fos pathway. These findings showed that physiological activity of HERG1 K⁺ channels was crucial for MDS cell proliferation and HERG1 K⁺ channels may be a potential therapeutic target for MDS.

Conclusion: Briefly, our study firstly showed that HERG1 K⁺ channels were aberrantly over-expressed on MDS stem cells, mononuclear cells, and positively associated with malignancy degree of MDS. HERG1 K⁺ channels functionally contribute to MDS progression and may be a potential therapeutic target for MDS.