Alpha-Catenin, ARHGAP21 and β-Catenin Are Abnormally Expressed in Bone Marrow Cells From Patients with Myelodysplatic Syndromes and Are a Possible Target for Decitabine Treatment.

Myelodysplastic syndrome (MDS) encloses a group of clonal hematopoietic disorders clinically and morphologically characterized by ineffective hematopoiesis. The gene encoding alpha-catenin (CTNNA1) is expressed at a much lower level in leukemia-initiating stem cells from individuals with MDS del(5q). Thus, loss of alpha-catenin tumor suppressor expression in hematopoietic cells may provide a growth advantage that collaborates MDS pathogenesis. ARHGAP21, a negative regulator of RhoGTPase signaling pathways, is a partner of alpha-catenin that controls its recruitment to the adherens junctions. ARHGAP21 is upregulated during myeloid differentiation, and could be involved in the malignant process of hematopoietic cells. In addition, alpha-catenin is a target for decitabine (DAC) treatment, a demethylating agent with potent antitumorigenic properties against MDS. The aim of this work was to evaluate the expression of alpha-catenin, ARHGAP21 and beta-catenin (gene CTNNB1) in bone marrow cells from MDS patients with or without del(5q) and to analyze CTNNA1, ARHGAP21 and CTNNB1 expression after DAC treatment.

cells were isolated from bone marrow of 6 MDS patients, including 5 refractory anemia (RA), being two with del(5q), and 1 refractory anemia with excess blasts (RAEB), based on the French-American-British classification, and 4 control subjects (normal hematopoietic tissues were obtained from healthy donors). The study was approved by the National Ethical Committee Board and bone marrow samples were collected at the Hematology and Hemotherapy Center, University of Campinas, after all participants provided informed written consent. Alpha-catenin, ARHGAP21 and beta-catenin localization in CD34+ cells was obtained using confocal microscopic analysis. ARHGAP21 localization was also analyzed in HS-5 stromal cells that were submitted to a CTNNA1 RNA interference (RNAi) approach. Leukemia cells lines (HL-60 and P-39) and bone marrow mononuclear cells obtained from 7 MDS patients, 5 RA and 2 refractory anemia with ringed sideroblasts (RARS), were treated with DAC for 72 hours; then mRNA expression of CTNNA1, ARHGAP21 and CTNNB1 was analyzed by Real-time PCR (normalized by GAPDH and beta-actin).

alpha-catenin, ARHGAP21 and beta-catenin are preferentially localized in the nucleus of CD34+ cells from MDS patients in contrast to the preferential cytoplasm and membrane localization in healthy donors and in MDS patients with del(5q). In del(5q) patients and healthy donors, ARHGAP21 and alpha-catenin co-localizated in the cell membrane. ARHGAP21 was abnormally expressed in cells with decreased CTNNA1 expression: in HS-5 stromal cells, ARHGAP21 was localized at the cytoplasm (mainly in the perinuclear region) and at the nucleus, in contrast, ARHGAP21 was poorly detectable in the nucleus of CTNNA1-RNAi treated cells. DAC treatment of MDS cells and leukemia cell lines induced CTNNA1, ARHGAP21, and CTNNB1 expression in a dose-dependent way. In HL60 and P39 cells, ARHGAP21 relocate to the cell membrane after DAC treatment.

The abnormal localization of alpha-catenin, ARHGAP21 and beta-catenin in MDS may compromise the reorganization of actin dynamics at sites of cell–cell contact that stabilizes cadherin-mediated cell–cell adhesion; moreover, these results also suggest a deficient recruitment of alpha-catenin to the cell membrane and an aberrant signaling in the Wnt pathway. In addition, ARHGAP21, alpha-catenin and beta-catenin are a target for DAC treatment in MDS. Supported by: FAPESP.

Keywords: alpha-catenin, ARHGAP21, beta-catenin, myelodysplastic syndrome, Rho-GAP, decitabine

No relevant conflicts of interest to declare.