Potential Role of Notch Signalling in CD34+ Chronic Myeloid Leukaemia Cells: Cross-Talk between Notch and BCR-ABL

• Published in: PloS one Vol. 10; no. 4; p. e0123016
• Main Authors: Aljedai, Abdullah, Buckle, Anne-Marie, Hiwarkar, Prashant, Syed, Farhatullah
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 07.04.2015; Public Library of Science (PLoS)
• Subjects: Abl gene; Abl protein; Antagonism; Antigens, CD34 - metabolism; Apoptosis - drug effects; Basic Helix-Loop-Helix Transcription Factors - genetics; Basic Helix-Loop-Helix Transcription Factors - metabolism; BCR gene; BCR protein; BCR-ABL protein; BCR-ABL1 gene; Blotting, Western; Bone marrow; CD34 antigen; Cell Cycle - drug effects; Cell lines; Cell Proliferation - drug effects; Cell self-renewal; Cell survival; Cells (biology); Chronic myeloid leukemia; Drosophila; Enzyme inhibitors; Fusion protein; Fusion Proteins, bcr-abl - genetics; Fusion Proteins, bcr-abl - metabolism; Gene expression; Histone deacetylase; Homeodomain Proteins - genetics; Homeodomain Proteins - metabolism; Humans; Imatinib; Imatinib Mesylate - therapeutic use; Inhibition; Inhibitors; Leukemia; Leukemia, Myelogenous, Chronic, BCR-ABL Positive - drug therapy; Leukemia, Myelogenous, Chronic, BCR-ABL Positive - genetics; Leukemia, Myelogenous, Chronic, BCR-ABL Positive - metabolism; Neoplastic Stem Cells - metabolism; Notch protein; Notch1 protein; Notch2 protein; Patients; Protein Kinase Inhibitors - therapeutic use; Protein-tyrosine kinase; Real-Time Polymerase Chain Reaction; Receptor, Notch1 - genetics; Receptor, Notch1 - metabolism; Receptor, Notch2 - genetics; Receptor, Notch2 - metabolism; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; Signal transduction; Signaling; Stem cells; Transcription Factor HES-1; Tumor Cells, Cultured; Tyrosine; Valproic acid
• DOI: 10.1371/journal.pone.0123016
• ISSN: 1932-6203

Notch signalling is critical for haemopoietic stem cell (HSC) self-renewal and survival. The role of Notch signalling has been reported recently in chronic myeloid leukaemia (CML) - a stem cell disease characterized by BCR-ABL tyrosine kinase activation. Therefore, we studied the relationship between BCR-ABL and Notch signalling and assessed the expression patterns of Notch and its downstream target Hes1 in CD34+ stem and progenitor cells from chronic-phase CML patients and bone marrow (BM) from normal subjects (NBM). We found significant upregulation (p<0.05) of Notch1, Notch2 and Hes1 on the most primitive CD34+Thy+ subset of CML CD34+ cells suggesting that active Notch signalling in CML primitive progenitors. In addition, Notch1 was also expressed in distinct lymphoid and myeloid progenitors within the CD34+ population of primary CML cells. To further delineate the possible role and interactions of Notch with BCR-ABL in CD34+ primary cells from chronic-phase CML, we used P-crkl detection as a surrogate assay of BCR-ABL tyrosine kinase activity. Our data revealed that Imatinib (IM) induced BCR-ABL inhibition results in significant (p<0.05) upregulation of Notch activity, assessed by Hes1 expression. Similarly, inhibition of Notch leads to hyperactivation of BCR-ABL. This antagonistic relationship between Notch and BCR-ABL signalling was confirmed in K562 and ALL-SIL cell lines. In K562, we further validated this antagonistic relationship by inhibiting histone deacetylase (HDAC) - an effector pathway of Hes1, using valproic acid (VPA) - a HDAC inhibitor. Finally, we also confirmed the potential antagonism between Notch and BCR/ABL in In Vivo, using publically available GSE-database, by analysing gene expression profile of paired samples from chronic-phase CML patients pre- and post-Imatinib therapy. Thus, we have demonstrated an antagonistic relationship between Notch and BCR-ABL in CML. A combined inhibition of Notch and BCR-ABL may therefore provide superior clinical response over tyrosine-kinase inhibitor monotherapy by targeting both quiescent leukaemic stem cells and differentiated leukaemic cells and hence must be explored.