Depletion of γ-catenin by Histone Deacetylase Inhibition Confers Elimination of CML Stem Cells in Combination with Imatinib

Abstract

Quiescent leukemia stem cells (LSCs) that are insensitive to BCR-ABL tyrosine kinase inhibitors confer resistance to imatinib in chronic myelogenous leukemia (CML). Identifying proteins to regulate survival and stemness of LSCs is urgently needed. Although histone deacetylase inhibitors (HDACis) can eliminate quiescent LSCs in CML, little is known about the underlying mechanism that HDACis kill LSCs. By fishing with a biotin-labeled probe, we identified that HDACi JSL-1 bound to the protein γ-catenin. γ-Catenin expression was higher in LSCs from CML patients than normal hematopoietic stem cells. Silencing γ-catenin in human CML CD34+ bone-marrow (BM) cells sufficiently eliminated LSCs, which suggests that γ-catenin is required for survival of CML LSCs. Pharmacological inhibition of γ-catenin thwarted survival and self-renewal of human CML CD34+ cells in vitro, and of murine LSCs in BCR-ABL-driven CML mice. γ-Catenin inhibition reduced long-term engraftment of human CML CD34+ cells in NOD.Cg-Prkdcscid II2rgtm1Sug/JicCrl (NOG) mice. Silencing γ-catenin by shRNA in human primary CD34+ cells did not alter β-catenin, implying a β-catenin-independent role of γ-catenin in survival and self-renewal of CML LSCs. Taken together, our findings validate that γ-catenin may be a novel therapeutic target of LSCs, and suppression of γ-catenin by HDACi may explain elimination of CML LSCs.

Role of HDACs in normal and malignant hematopoiesis

“…To date, the different mechanisms of HDACis combined with chemotherapeutic agents such as topoisomerase inhibitors, platinumbased chemotherapeutics, proteasome inhibitors, tyrosine kinase pathway inhibitors and epigenetic modifiers for advanced or drug-resistant hematological malignancies include (1) acetylating histones and inducing p21-CDK-mediated cell cycle arrest; (2) inducing apoptosis by regulating the expression of pro-and antiapoptotic genes through the intrinsic or extrinsic pathway; (3) inducing DNA damage and oxidative stress; (4) activating BTK (in CLL) or inhibiting ERK (in MM) and AKT (in CML) signaling pathways; and (5) regulating the expression of drug resistance-related molecules, such as downregulating BCR-ABL and upregulating Bim in hematological malignancies and downregulating CD44 in multiple myeloma (MM), NF-κB in ALL, γ-catenin in CML, and BRCA1, CHK1 and RAD51 in AML [126][127][128][129][130][131][132][133][134][135][136][137][138][139][140][141][142][143][144][145]. Specific combination strategies and their corresponding mechanisms are summarized in Table 3 [146][147][148][149][150][151][152][153][154][155]. Moreover, two-phase I clinical trials were carried out to assess the DNA methyltransferase (5-azacitidine) and HDACi (phenylbutyrate) for the treatment of hematological malignancies.…”

HDAC6 – An Emerging Target against Chronic Myeloid Leukemia?

“…Inhibitors of the HDAC family have promising results in combination with TKIs [186], some of which also inhibit HDAC6 [187][188][189]. The combination of HDAC class I inhibitors [190] or HDAC inhibitors including HDAC6 [191] and TKIs induces elimination of the quiescent LSCs that are not eradicated during treatment with imatinib alone. Although a decrease in HDAC6 expression, an increase in HSP90α acetylation, and a decrease in BCR-ABL expression were observed in imatinib-resistant K562 cells, these cells still showed sensitivity to SAHA, an inhibitor of HDACs including HDAC6 [180].…”

Dual cyclin‐dependent kinase 4/6 inhibition by PD‐0332991 induces apoptosis and senescence in oesophageal squamous cell carcinoma cells

“…Abbreviations CDK4, cyclin-dependent kinase 4; CDK6, cyclin-dependent kinase 6; ESCC, oesophageal squamous cell carcinoma; FOXM1, forkhead box M1; MMPs, matrix metalloproteinases; PI, propidium iodide; SA-β-gal, senescence-associated β-galactosidase; XIAP, X-linked inhibitor of apoptosis Apoptosis was measured using an annexin V-FITC Apoptosis Detection Kit (Sigma-Aldrich, Shanghai, China) by flow cytometry as previously described (Jin et al, 2016a). After PD-0332991 treatment, cells were collected and stained with annexin V-FITC at room temperature for 15 min in the dark.…”

“…Apoptosis was measured using an annexin V‐FITC Apoptosis Detection Kit (Sigma‐Aldrich, Shanghai, China) by flow cytometry as previously described (Jin et al, ). After PD‐0332991 treatment, cells were collected and stained with annexin V‐FITC at room temperature for 15 min in the dark.…”