Heme Oxygenase-1(HO-1): A Promising Novel Target Molecule for Overcoming Imatinib Resistance in Chronic Myeloid Leukemia

Objective : HO-1 is a microsomal enzyme catalyzing the first, rate-limiting step in degradation of heme, HO-1 is a inducible isoform of HO, it can be strongly induced in response to cellular stress and diverse oxidative stimuli, including its substrate heme, Many studies have convincingly shown that HO-1 is a cytoprotective and antiapoptotic enzyme. the objective of this study was to investigate the influence on the K562 cell growth and apoptosis after hemin-induced HO-1 expression, and to investigate the influence on K562 cells and imatinib-resistant CML cells after ZnPPIX-induced HO-1 inhibition.

Methods: different concentrations hemin (0umol/l A20umol/l 30umol/l)was used respectively to induce HO-1 expression of cultured chronic myeloid leukemia cell line K562, then detected HO-1 mRNA expression under different time by RT-PCR, and MTT was used to detected the viability of K562 cells. In addition, we used STI571(2 μmol/L) deal with the hemin-induced cells, then confirm HO-1 protective effect against STI571 use MTT. Then ZnPPIX was used to inhibition HO-1 expression of K562 and imatinib-resistant cells, similarly, RT-PCR and MTT was used for analyzed.

Results:

1. The HO-1 mRNA was not tested when absence of hemin, 8h after treated with hemin of 20 μmol/L, we can test the HO-1 mRNA expression, and at 16h the expression is reach to the peak, 16h after treated hemin under different concentrations (10umol/l, 20umol/l, 30umol/l), we found the expression is in a dose-dependent manner.

2. In the group of 10 umol/l and 20 umol/l, the survival of cells is significantly increased in comparison to the control and also have significantly difference in the two groups(p<0.05), in the group of 20 μmol/L, 16h to 48h after hemin-induced, the survival of cells presents a time-dependent manner.

3. In the group of 10μmol/L and 20 μmol/L, exposure of K562 cells to STI571 resulted in a substantial decrease of cell viability in comparison to the STI571 single treatment group(p<0.05).

4. ZnPPIX-induced HO-1 inhibition leads to induction of apoptosis in K562 cells, having significant difference with the control group(p<0.05).

5. ZnPPIX-induced HO-1 inhibition can suppress the survival of imatinib-resistant cells(p<0.05).

Conclusion: our studies have shown that hemin-induced HO-1 gene expression may promote the proliferation of K562 cells, and can against the cell apoptosis. And we found hemin-induced HO-1 gene expression can protect K562 cells against STI571-induced apoptosis, ZnPPIX-induced HO-1 inhibition leads to decreased viability of imatinb-resistant CML cells. these all indicates HO-1 may represent a novel targeting in CML.