BMI-1 is essential for the self-renewal and proliferation of leukemic and hematopoietic stem and progenitor cells. Increased expression of BMI-1 is known to be an indicator for a poor prognosis in cancer patients. Analysis of the expression of BMI-1 and survivin in 6 patients with B-cell lymphoma (3 drug-resistant and 3 sensitive cases) showed that in the drug-resistant patients, high levels of BMI-1 and survivin were maintained even after drug administration in vitro. However, there observed was a down-regulation of both BMI-1 and survivin expression in the drug-sensitive patients. BMI-1 transduction induced the drug-resistance of two B-cell lymphoma cell lines, HT and RL, to the anti-cancer drugs etoposide and oxaliplatin, but not to irinotecan. The expression of survivin was clearly augmented in the cells transduced with BMI-1. Moreover, we detected sustained expression of survivin level in the presence of etoposide in the BMI-1-overexpressing cells. By contrast, the mock-transduced cells succumbed in the medium with anti-cancer drugs with an accompanying decrease in the expression of survivin as well as BMI-1. Survivin has been reportedly implicated in resistance to chemotherapeutic agents. Intriguingly, survivin mRNA levels in BMI-1-overexpressing cells were consistent with those in controls. Also, the level of survivin was enhanced by treatment with a proteasomal inhibitor, MG132, suggesting that overexpression of BMI-1 stabilized survivin expression post-translationally. We further showed that sh RNA-mediated knockdown of BMI-1 or survivin restored sensitivity to etoposide in the HT cells overexpressing BMI-1. Our findings suggest survivin as a potential target for BMI-1. Thus BMI-1, by acting as an upstream regulator, may control the expression of survivin, facilitating drug resistance in B-cell lymphoma. Next, we examined whether B-cell lymphoma cells overexpressing BMI-1 are abrogated by immunotherapy with T cells containing anti-CD38 chimeric receptor in vitro. Interestingly, these B-cell lymphoma cells were effectively eliminated by specific T cells against B-cell lymphoma cells bearing CD38. These results suggest that the immunotherapy is useful for treatment of patients with B-cell lymphoma cells overexpressing BMI-1, which are refractory to chemotherapeutic reagents. BMI-1 may be an important prognostic marker as well as a future therapeutic target in the treatment of drug-resistant lymphomas.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.