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Tetraspanin family member, CD82, regulates expression of EZH2 via inactivation of p38 MAPK signaling in leukemia cells. The novel function of CD82 and its impact on BCL2L12 via AKT/STAT5 signal pathway in acute myelogenous leukemia cells.

ABSTRACT: We recently found that the tetraspanin family member, CD82, which is aberrantly expressed in chemotherapy-resistant CD34+/CD38− acute myelogenous leukemia (AML) cells, negatively regulates matrix metalloproteinase 9, and plays an important role in enabling CD34+/CD38− AML cells to adhere to the bone marrow microenvironment. This study explored novel functions of CD82 that contribute to AML progression. We employed microarray analysis comparing the gene expression profiles between CD34+/CD38− AML cells transduced with CD82 shRNA and CD34+/CD38− AML cells transduced with control shRNA. Real-time RT-PCR and western blot analysis were performed to examine the effect of CD82 knockdown on the expression of the polycomb group member, enhancer of zeste homolog 2 (EZH2), in leukemia cells. A chromatin immunoprecipitation assay was performed to examine the effect of CD82 expression on the amount of EZH2 bound to the promoter regions of tumor suppressor genes in leukemia cells. We also utilized methylation-specific PCR to examine whether CD82 expression influences the methylation status of the tumor suppressor gene promoter regions in leukemia cells. Microarray analysis revealed that levels of EZH2 decreased after shRNA-mediated depletion of CD82 in CD34+/CD38− AML cells. Moreover, the antibody-mediated blockade of CD82 in leukemia cells lowered EZH2 expression via activation of p38 MAPK signaling, decreased the amount of EZH2 bound to the promoter regions of the tumor suppressor genes, and inhibited histone H3 lysine 27 trimethylation in these promoter regions, resulting in upregulation of the tumor suppressors at both the mRNA and protein levels. The aim of this study was to explore the biological functions of a tetraspanin family protein––CD82–– expressed aberrantly in chemotherapy-resistant CD34+/CD38- acute myelogenous leukemia (AML) cells. Microarray analysis of patient-isolated CD34+/CD38- AML cells revealed that the levels of anti-apoptotic protein BCL2L12 were downregulated after CD82 depletion by specific shRNA. Western blot analysis indicated that BCL2L12 was aberrantly expressed in patient-isolated AML cells and AML cell lines. Furthermore, CD82 blockade by a specific antibody downregulated BCL2L12 in parallel with de-phosphorylation of STAT5 and AKT, while pharmacological inhibition of STAT5 and AKT activation decreased BCL2L12 expression in leukemia cells. In addition, shRNA-mediated downregulation of BCL2L12 increased the levels of cleaved caspase 3and suppressed proliferation of leukemia cells, impairing their engraftment in immunodeficient mice. Taken together, our results indicate that CD82 regulated BCL2L12 expression via STAT5A and AKT signaling and stimulated proliferation and engrafting of leukemia cells, suggesting that CD82 and BCL2L12 may be promising therapeutic targets in AML.

ORGANISM(S): Homo sapiens

PROVIDER: GSE64527 | GEO | 2014/12/30

SECONDARY ACCESSION(S): PRJNA271257

REPOSITORIES: GEO

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Project description:Differences in chemo-sensitivity of subpopulations of AML stem cells could have important clinical implications. Using in vitro cytotoxicity, xenograft models and colony forming assays, we compared chemotherapy sensitivity between Lineage (Lin-)CD34-CD38-, Lin-CD34-CD38+, Lin-CD34+CD38- and Lin-CD34+CD38+ populations from 26 primary AMLs (19 paediatric and 7 adult). We identified a common recurring pattern of chemo-response associated with a poor clinical outcome: In each of 16/26 (62%) AMLs, Lin-CD34-CD38- cells were the most chemoresistant of the four subpopulations to daunorubicin in vitro. Cytarabine-resistant colonies formed only from Lin-CD34-CD38- populations following tertiary passages through both NOG mice and methylcellulose in these AMLs The presence of chemo-resistant Lin-CD34-CD38- populations was signficantly associated with reduced relapse-free survival in childhood AML. Consistently, CD34 negativity was significantly associated with an increased risk of relapse in a larger retropsective cohort (n=89). Samples enriched for chemo-resistant Lin-CD34-CD38- LSCs with a stem cell profile and an undifferentiated genotype revealed pathways likely to confer chemo-resistance, These strongly indicated dependence of chemo-resistant Lin-CD34-CD38- LSCs on their niche environment as well as deregulated DNA damage responses, lipid and Notch1 signalling, Our findings have major implications for the risk stratification of childhood AML and could lead to the development of novel therapeutic approaches. 3 subpopulations of leukemia stem cells from 9 patients with primary childhood AML were analysed. We compared gene expression profiles of Lin-CD34+CD38- (Q1), Lin-CD34+CD38+ (Q2) and Lin-CD34-CD38- (Q3) cells between 3 AMLs in which the CD34+ cells were most chemo-resistant (AML-1P, AML-6P and AML-10P) and the same cells from the remaining AMLs in which the Lin-CD34-CD38- cells were the most chemo-resistant population. We also compared the gene expression profiles of Lin-CD34-CD38- (Q3) cells in the 3 samples with the highest LC50 values (AML-15P, AML-17P and AML-19P) with that of the 3 AMLs exhibiting the lowest LC50 values (AML-2P, AML-5P and AML-11P).

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Tetraspanin family member, CD82, regulates expression of EZH2 via inactivation of p38 MAPK signaling in leukemia cells. The novel function of CD82 and its impact on BCL2L12 via AKT/STAT5 signal pathway in acute myelogenous leukemia cells.

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