Inhibition of Siah2 Ubiquitin Ligase By Vitamin K3 Attenuates Hypoxia and Blocks K562-R Cells Resistance

Background and objective: Hypoxia has been shown to favor the self-renewal of murine and human hematopoietic stem cells. Hypoxia as a key feature of the “stem cell niches” in vivo, and studies found that hypoxia modified proliferation and differentiation of chronic myeloid leukemia (CML) stem cells.The E3 ubiquitin ligase Siah2 is an important regulator of the hypoxic response,which has been implicated in the regulation of the hypoxia response, as well as in the control of Ras, JNK/p38/NF-κB, MAPK signaling pathways. In the present study, we identified that SIAH2 induced k562 cells resistance to imatinib by hypoxia-inducible factor (HIF)-1a activated vascular epithelial growth factor (VEGF) pathway in hypoxia micro environment. In this study we show that SIAH2/Hif-1α induced K562 cell remain in G0 stage and resistance to imatinib, and we verified that vitamin K3 (SIAH2 inhibitor) reversed K562-R drug resistance in hypoxia microenvironment.

Methods: We detected Siah2 expression levels in K562-wild type (K562-W) and K562-imatinib-resistance type (K562-R) cell lines by western blot analysis. Those two cell lines were further cultured for 24 h and 48 h under the condition of normal and hypoxia concentration of oxygen (1%, 5%), and treated K562-R with 0A5A15A30mM vitamin K3 for 72 hours in hypoxia concentration, explored cell cycle and apoptosis by flow cytometry (FCM) dyed by Annexin-V; analyzed the expression levels of Siah2, HIF-1α respectively by real-time PCR and western blot.

Results: The protein of Siah2 and HIF-1α was significantly higher in K562-R compared with K562-w cells (P<0.01). Cell cycle analysis showed a 3% increase in K562-W G0/G1 cells in 1% O2 compared with normal O2, and 7% in K562-R. Under hypoxia condition, the cellular apoptotic ratio of K562-R was 5.46%, much less than 11.08% in K562-W cells. G0 cell proportion increased significantly with the long time Hypoxia (P<0.01); After being cultured in 1% oxygen concentration for 24 hours, we confirmed Siah2,HIF-1α were all up regulated in both cell lines, moreover, it was more obvious in K562-R cells. Siah2 protein expression increased along treated with vitamin K3 concentration (0, 5, 15, 30 mM) (P<0.05), on the contrary ,HIF-1α protein expression decreased with vitamin K3 concentration (P<0.05). the proportion of G0 cell was decreased in K562-R cells treated with Vitamin K3 (15mM)for 48h Under the condition of 1% oxygen concentration compared with control group (P=0.02).

Conclusions: Hypoxia up-regulated of Siah2 and Hif-1α expression in K562-R, promoted cell apoptosis and arrested cells in G0 stage, and reduced cell sensitivity to Imatinib. Vitamin K3 could inhibit Siah2 and lowered Hif-1α in K562-R. These findings reveal an effective treatment for the identification of Siah2 inhibitors and would reverse TKI resistance for CML patients.