ABSTRACT
Drug resistance to tyrosine kinase inhibitors (TKIs) is currently a clinical problem in patients with chronic myelogenous leukemia (CML). Homoharringtonine (HHT) is an approved treatment for adult patients with chronic or acceleratedphase CML who are resistant to TKIs and other therapies; however, the underlying mechanisms remain unclear. In the present study, HHT treatment demonstrated induction of apoptosis in imatinibresistant K562G cells by using MTS assay and western blotting, and BCRABL protein was reduced. CHX chase assay revealed that HHT induced degradation of the BCRABL protein, which could be reversed by autophagy lysosome inhibitors BafA1 and CQ. Next, HHT treatment confirmed the induction of autophagy in K562G cells, and silencing the key autophagic proteins ATG5 and Beclin1 inhibited the degradation of the BCRABL protein and cytotoxicity. In addition, autophagic receptor p62/SQSTM1(p62) participated during the autophagic degradation of BCRABL induced by HHT, and this was confirmed by coimmunoprecipitation, in which HHT enhanced the ubiquitination of the BCRABL protein and promoted its binding to p62. In conclusion, HHT induced p62mediated autophagy in imatinibresistant CML K562G cells, thus promoting autophagic degradation of the BCRABL protein and providing a novel strategy for the treatment of TKIresistant CML.
Subject(s)
Antineoplastic Agents, Phytogenic/pharmacology , Fusion Proteins, bcr-abl/chemistry , Homoharringtonine/pharmacology , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/metabolism , RNA-Binding Proteins/metabolism , Autophagy , Cell Line, Tumor , Cell Proliferation/drug effects , Drug Resistance, Neoplasm/drug effects , Gene Expression Regulation, Neoplastic/drug effects , Humans , Imatinib Mesylate , K562 Cells , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/drug therapy , Proteolysis/drug effects , Signal Transduction/drug effectsABSTRACT
BACKGROUND: B7-H4 is among the B7 family members which may serve as a new targetable immune checkpoint molecule. It was reported that high level of serum B7-H4 level may be correlated with lymphoma. Nevertheless, the role of B7-H4 in Epstein-Barr Virus-Positive diffuse large B cell lymphoma (EBV+DLBCL) has not been addressed although it has been suggested that B7-H4 could promote tumor growth and metastatic progression in certain cancers. METHODS: Between January 2005 and November 2017 at the department of Hematology, Shanghai Jiao Tong University School of Medicine affiliated Shanghai General Hospital 260 DLBCL samples were analyzed for EBV-encoded small RNA (EBV-EBER) by in situ hybridization. The expression level of B7-H4 in DLBCL tumor tissue was evaluated by immunohistochemistry. Furthermore, the role of B7-H4 in DLBCL was further investigated in DLBCL cell line. RESULTS: EBV+DLBCL patients suffered from markedly lower overall survival (OS) and progression-free survival (PFS) rates in our study. We showed that B7-H4 was significantly overexpressed in 16 EBV+-subgroup cases out of 260 DLBCL patients. We further found that EBV infection in lymphoblast cells led to enhanced expression of B7-H4 followed by increased cell viability and reduced apoptosis. In contrast, inhibition of B7-H4 simultaneously impaired cell viability and induced apoptosis. Mechanistically, inhibiting B7-H4 resulted in decreased phosphorylation Erk 1/2 and Akt. CONCLUSION: Our study reveals a critical role of B7-H4 in EBV+DLBCL development by regulating cell survival and apoptosis through the Erk and Akt signalling pathways. Targetting B7-H4 may be promising in the therapy of EBV+DLBCL.
