HERG K⁺ Channel Is Essential for Leukemic Cell Migration Induced by SDF-1.

Background: Recent studies suggest that HERG K⁺ channel is an important regulator of non excitable cell proliferation and migration, and has been found in tumor cells including acute myeloid leukemia(AML), where HERG K⁺ channel is generally considered to be absent from their healthy counterparts. Bone marrow stromal cells constitutively secrete the stromal cell-derived factor-1 (SDF-1) which is a homeostatic chemokine that signals through CXCR4, SDF-1/CXCR4 axis and plays an important role in hematopoiesis development and leukemic cells migration. In this study, we investigated whether SDF-1-induced leukemic cell migration associated with HERG K⁺ channel.

Methods: primary CD34⁺/CD38⁻ leukemic stem cells (LSCs) were isolated by cell sorting using a FACS Vantage. Transwell was used to assess the effect of E-4031, a specific HERG K⁺ channel inhibitor, on leukemic cell migration, the lower chamber was filled with serum-free RPMI-1640 with 100ng/ml SDF-1. Flow cytometry was used to analyze the CXCR4 expression as well as phenotypical analysis of leukemia samples. HERG K⁺ channels were expressed in Xenopus oocyte by microinjection and the resulting currents were measured using the standard two microelectrode voltage clamp techniques.

Results: numbers of HL-60 cells with and without E-4031 treatment migrated towards SDF-1 in the lower chamber were 1.58±0.98 ×10⁴ and 3.47±0.81 ×10⁴ respectively, indicating E-4031 significantly blocked the cell migration induced by SDF-1. The similar results were also observed in primary leukemic cells (n=7) and leukemic stem cells(n=3). From a holding potential of −80 mV varying potentials from −70 mV to +50 mV in 10 mV increments (2s) were applied to elicit activating currents. Each pulse was followed by a constant return pulse to −50 mV (2s) to evoke outward tail currents. 100 ng/ml SDF-1 increased HERG K⁺ current expressed in oocytes, for example, at +50 mV, HERG current increased about 30% (n=5). The HERG K⁺ current increase by SDF-1 might contribute to the mechanism of SDF-1 induced leukemic cell migration. There were no significant changes of CXCR4 expression on both HL-60 cells and primary leukemic cells regardless of untreated and treated with E-4031 for 24 hours (p>0.05), suggesting that the leukemic cell migration induced by SDF-1 were specifically associated with HERG K⁺ channel, not by regulating CXCR4 expression.

Conclusion: the data showed that HERG K⁺ channel was essential for leukemic cell migration induced by SDF-1. SDF-1 enhanced herg current suggested that SDF-1 promotes leukemic cell migration. Blocking HERG K⁺ channel with specific inhibitor could decrease leukemic cell and leukemic stem cell migration caused by SDF-1. Prospectively, HERG K⁺ channel may be a potential therapeutic target with specific inhibitors in leukemia treatment.