RESUMO
The boronic acid dipeptide bortezomib inhibits the chymotrypsin-like activity of the 26S proteasome and shows significant therapeutic efficacy in multiple myeloma. However, recent studies suggest that bortezomib may have more complex mechanisms of action in treating cancer. We report here that the endocytosis and lysosomal degradation of the receptor tyrosine kinase C-KIT are required for bortezomib- but not tyrosine kinase inhibitor imatinib-caused apoptosis of t(8;21) leukemia and gastrointestinal stromal tumor cells, suggesting that C-KIT may recruit an apoptosis initiator. We show that C-KIT binds and phosphorylates heat shock protein 90ß (Hsp90ß), which sequestrates apoptotic protease activating factor 1 (Apaf-1). Bortezomib dephosphorylates pHsp90ß and releases Apaf-1. Although the activated caspase-3 is not sufficient to cause marked apoptosis, it cleaves the t(8;21) generated acute myeloid leukemia 1-eight twenty one (AML1-ETO) and AML1-ETO9a fusion proteins, with production of cleavage fragments that perturb the functions of the parental oncoproteins and further contribute to apoptosis. Notably, bortezomib exerts potent therapeutic efficacy in mice bearing AML1-ETO9a-driven leukemia. These data show that C-KIT-pHsp90ß-Apaf-1 cascade is critical for some malignant cells to evade apoptosis, and the clinical therapeutic potentials of bortezomib in C-KIT-driven neoplasms should be further explored.
Assuntos
Ácidos Borônicos/farmacologia , Cromossomos Humanos Par 21 , Cromossomos Humanos Par 8 , Leucemia/patologia , Proteínas Proto-Oncogênicas c-kit/metabolismo , Pirazinas/farmacologia , Translocação Genética , Apoptose , Bortezomib , Humanos , Leucemia/genética , Fosforilação , Ligação ProteicaRESUMO
Triptolide is a compound isolated from the traditional Chinese medicinal herb Tripterygium wilfordii that shows potent anti-tumor activities, but its effects on acute myeloid leukemia with t(8;21) remain unclear. Here we report that triptolide inhibits cell proliferation and induces apoptosis in a dose- and time-dependent manner of t(8;21)-bearing Kasumi-1, SKNO-1 and CD34+ cells harvested from bone marrow samples of patients with t(8;21) leukemia. We show that triptolide triggers cleavage of the resultant AML1-ETO fusion protein of t(8;21), and causes downregulation of C-KIT followed by inhibition of JAK-STAT signaling. Triptolide downregulates p65 and inhibits the DNA-binding activity of NF-κB. Our data indicate that triptolide might be an effective agent for t(8;21) leukemia.
Assuntos
Antineoplásicos Alquilantes/farmacologia , Apoptose/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , Cromossomos Humanos Par 21/genética , Cromossomos Humanos Par 8/genética , Diterpenos/farmacologia , Leucemia Mieloide Aguda/genética , Fenantrenos/farmacologia , Transdução de Sinais/efeitos dos fármacos , Western Blotting , Células Cultivadas , Subunidade alfa 2 de Fator de Ligação ao Core/efeitos dos fármacos , Compostos de Epóxi/farmacologia , Humanos , Janus Quinases/efeitos dos fármacos , Janus Quinases/metabolismo , Leucemia Mieloide Aguda/metabolismo , Proteínas de Fusão Oncogênica/efeitos dos fármacos , Proteínas Proto-Oncogênicas c-kit/biossíntese , Proteínas Proto-Oncogênicas c-kit/efeitos dos fármacos , Proteína 1 Parceira de Translocação de RUNX1 , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fatores de Transcrição STAT/efeitos dos fármacos , Fatores de Transcrição STAT/metabolismoRESUMO
BACKGROUND: Resistance developed by leukemic cells, unsatisfactory efficacy on patients with chronic myeloid leukemia (CML) at accelerated and blastic phases, and potential cardiotoxity, have been limitations for imatinib mesylate (IM) in treating CML. Whether low dose IM in combination with agents of distinct but related mechanisms could be one of the strategies to overcome these concerns warrants careful investigation. METHODS AND FINDINGS: We tested the therapeutic efficacies as well as adverse effects of low dose IM in combination with proteasome inhibitor, Bortezomib (BOR) or proteasome inhibitor I (PSI), in two CML murine models, and investigated possible mechanisms of action on CML cells. Our results demonstrated that low dose IM in combination with BOR exerted satisfactory efficacy in prolongation of life span and inhibition of tumor growth in mice, and did not cause cardiotoxicity or body weight loss. Consistently, BOR and PSI enhanced IM-induced inhibition of long-term clonogenic activity and short-term cell growth of CML stem/progenitor cells, and potentiated IM-caused inhibition of proliferation and induction of apoptosis of BCR-ABL+ cells. IM/BOR and IM/PSI inhibited Bcl-2, increased cytoplasmic cytochrome C, and activated caspases. While exerting suppressive effects on BCR-ABL, E2F1, and beta-catenin, IM/BOR and IM/PSI inhibited proteasomal degradation of protein phosphatase 2A (PP2A), leading to a re-activation of this important negative regulator of BCR-ABL. In addition, both combination therapties inhibited Bruton's tyrosine kinase via suppression of NFkappaB. CONCLUSION: These data suggest that combined use of tyrosine kinase inhibitor and proteasome inhibitor might be helpful for optimizing CML treatment.
