Bcl-2 protects tumor cells from the apoptotic effects of various anti-neoplastic agents. Increased expression of Bcl-2 has been associated with a poor response to chemotherapy in various malignancies, including leukemia. Hence, bypassing the resistance conferred by anti-apoptotic factors such as Bcl-2 represents an attractive therapeutic strategy against cancer cells, including leukemic cells. This study was undertaken to examine whether the anticancer drug, cisplatin and the synthetic chenodeoxycholic acid (CDCA) derivative, HS-1200 show anti-tumor activity in U937 and U937/Bcl-2 cells. Viability assays revealed that HS-1200 overcomes the resistance conferred by Bcl-2 in human leukemic U937 cells. Various apoptosis assessment assays further demonstrated that HS-1200 overcomes the resistance conferred by Bcl-2 in human leukemic U937 cells by inducing apoptosis. In addition HS-1200, but not cisplatin, overcomes the anti-apoptotic effects of Bcl-2 in Bcl-2 over-expressing human leukemic cells (U937/Bcl-2 cells). Notably, we observed that the HS-1200-induced formation of mature promyelocytic leukemia (PML) nuclear bodies (NBs) correlates with a suppression of the anti-apoptotic effects of Bcl-2 in human leukemic cells over-expressing this protein (U937/Bcl-2 cells). Furthermore, HS-1200 was found to induce the association between PML and SUMO-1, Daxx, Sp100, p53 or CBP in the aggregated PML-NBs of U937/Bcl-2 cells. Thus, PML protein and the formation of mature PML-NBs could be considered as therapeutic targets that may help to bypass the resistance to apoptosis conferred by Bcl-2. Elucidating the exact mechanism by which PML regulates Bcl-2 will require further work.

[Background] Cordyceps militaris is a traditional popular mushroom, produces an important bioactive compound Cordycepin (3’-deoxyadenosine) used for the tonic and medicinal purpose in eastern Asia. Cordycepin is reported to possess many pharmacological activities including immunologically stimulating, anti-tumor, anti-virus, and anti-infection effects. [Methods] Growth inhibition of human leukemia cells was assessed by MTT assays. The determination of apoptotic cell death was performed by flow cytometry analysis, agarose gel electrophoresis and DAPI fluorescent staining methods. The apoptotic-regulated gene markers in both death receptor- and mitochondria-mediated apoptotic pathways were detected by RT-PCR and Western blot analysis etc. [Results] It was found that inhibition of cell proliferation was observed for human leukemia U937 and THP-1 cells treated with cordycepin in a dose-dependent manner. Cordycepin induced morphological change and apoptotic cell death such as formation of apoptotic bodies, DNA fragmentation and increased populations of apoptotic-sub G1 phase. Apoptosis of U937 and THP-1 cells by cordycepin was associated with a down-regulation of anti-apoptotic Bcl-2 and inhibitor of apoptosis proteins (IAPs) expression. Cordycepin treatment induced the proteolytic activation of caspase-3, caspase-8 and caspase-9, and a concomitant inhibition of poly(ADP-ribose) polymerase (PARP), β-catenin and phospholipase (PLC)-γ1 protein. Conclusions: Our results indicated that the apoptotic processes caused by cordycepin are mediated by the regulation of the Bcl-2 and caspase family in human leukemia U937 and THP-1 cells. Our data also suggested that cordycepin may be a potential chemotherapeutic agent for the treatment of leukemia cancer patients.

Agaricus blazeiMurill is an edible mushroom distributed in Brazil and presently cultivated in other areas, including Korea, Japan, and China. Its chemical components, including steroids and lectin and various polysaccharides have been widely studied. For this, we used U937/vector and U937/Bcl-2 cells, which were generated by transfection of the cDNA of the Bcl-2 gene. As compared with U937/vector, U937/Bcl-2 cells exhibited a 4-fold greater expression of Bcl-2. Treatment with 0.5 or 4 mg/ml A. blazei Murill for 24 h produced morphological features of apoptosis in U937/vector cells, respectively. This was associated with caspase-3 activation and PARP degradation. In contrast, A. blazei Murill-induced caspase-3 activation and PARP degradation and apoptosis were significantly inhibited by z-DEVD-fmk in U937 cells. Bcl-2 overexpressing cells exhibited sustained caspase-3 activation and expression levels of the Bcl-2 proteins during A. blazei Murill-induced apoptosis. In addition, these findings indicate that Bcl-2 inhibits A. blazei Murill-induced apoptosis by a mechanism that interferes with Bcl-2 degradation and activity of caspase-3 that is involved in the execution of apoptosi.

본 연구에서는 부처꽃 에탄올 추출물(ELM)에 대한 항암효능을 알아보기 위하여 인체백혈병 U937 세포의 증식에 미치는 영향과 이와 연관된 apoptosis 유발 여부와 함께 그에 따른 분자생물학적 기전에 대해서 조사하였다. 먼저 ELM 처리에 따른 증식 억제 정도를 조사한 결과, ELM 처리 농도 의존적으로 생존율 및 증식억제 현상이 나타났으며, 핵의 형태 변화, DNA 단편화 및 apoptosis 유발에 관하여 조사한 결과 역시 ELM 처리 농도 의존적으로 증가됨을 확인할 수 있었다. ELM 처리에 따른 U937 세포에서의 apoptosis 유발에 있어서 미토콘드리아 막의 기능 손상이 관여하는 지를 확인하기 위하여 MMP의 변화 정도를 확인 한 결과, ELM 처리 농도 증가에 따라 MMP의 소실이 증가하는 것을 관찰할 수 있었다. 이러한 MMP의 소실에 가 관여하는지를 확인하기 위하여 사멸수용체(DR4, 5, Fas) 및 사멸수용체에 결합하는 리간드(FasL, TRAIL)의 발현 변화를 확인한 결과, DR4 및 DR5의 발현이 증가하는 것으로 관찰되었다. 또한 내인적 경로에 관여하는 Bcl-2 family 유전자들의 발현변화를 확인 한 결과, Bcl-2 발현 감소 및 Bax의 발현 증가의 변화를 보였으며, Bid 단백질의 발현감소가 나타났으므로 상대적으로 tBid의 생성이 증가되었음을 추측할 수 있었다. 한편 apoptosis 유발에 직접적으로 관여하는 것으로 알려진 caspase-3, -8 및 -9의 발 현에 미치는 ELM의 영향에 대해서 조사하였다. 결과에서 알 수 있듯이 ELM은 death receptor에 의하여 활성화 되는 것으로 알려진 caspase-8 및 세포질로 방출된 cytochrome c에 의하여 활성화 되는 것으로 알려진 caspase-9의 활성화를 유발하였으며, caspase cascade에 의하여 apoptosis에 직접적으로 관여하는 caspase-3의 발현도 증가시키는 것으로 나타났다. 또한 활성화된 caspase-3에 의하여 분해가 일어나는 기질 단백질인 PARP의 경우 ELM 처리에 의하여 모두 단편화가 유발되는 것으로 나타났다. 이상의 결과를 종합해 보면 인체 백혈병 U937 세포에 ELM을 처리하였을 경우에 유발되는 apoptosis는 외인적 경로인 DR4 및 DR5의 발현 증가를 통한 caspase-8의 활성화와 이로 인한 Bid 단백질의 단편화와 함께 내인적 경로의 미토콘드리아 기능 손실에 의하여 caspase-9 및 -3의 활성화 유발과 기질단백질들의 분해가 중요한 역할을 하는 것으로 생각되며, IAP family의 발현 감소로 인하여 caspase의 활성이 억제되지 못하는 것도 apoptosis 유도에 어느 정도 관여했을 것으로 생각 된다. 따라서 ELM 처리에 의하여 유발되는 apoptosis는 외인적 경로 및 내인적 경로를 모두 경유하는 multiple apoptotic pathway에 의하여 조절되며, 이때 caspases가 중요한 역할을 한다는 것을 알 수 있었다.