Brain And Acute Leukemia, Cytoplasmic Research Articles

Baalc, a marker of mesoderm and muscle

Transcripts of the Brain and Acute Leukemia, Cytoplasmic ( BAALC) gene are expressed in human neuroectodermal tissues and in CD34-positive bone marrow cells. High transcript levels occur in leukemic blasts from some patients with acute myeloid leukemia (AML), where high expression is an independent marker of poor prognosis. To gain insight into the hitherto unknown function of BAALC/Baalc, we studied its protein expression in embryonic and adult mouse tissue by immunohistochemical analysis. Baalc protein was mainly expressed in developing and mature muscle cells (cardiac, skeletal, and smooth) beginning on day E9 (heart). Signal was seen in the pre-muscle mesodermal cells of the dermatomyotome regions, and the derivatives of the lateral plate and intermediate mesoderm such as smooth muscle wall of the esophagus, stomach, the gut tube, bronchi, small blood vessels, and urinary bladder. This pattern continued through the late embryonic stages into adulthood. Baalc appeared to localize in the cytoplasm, adjacent to the cell membrane. This is distinctly observed in adult skeletal muscle cells. Baalc co-localized with known muscle-associated proteins but not with neural crest or neuronal markers. Scattered expression in adult bone marrow hematopoietic cells and weak expression in the brain neuropil also occurred. In conclusion, BAALC/Baalc is a marker of the mesodermal lineage, especially muscle.

Significant Down-Regulation of BAALC during Lineage Specific Hematopoietic Differentiation.

The human gene BAALC (Brain And Acute Leukemia, Cytoplasmic) implicated in normal hematopoiesis and leukemia is a marker of immature hematopoietic progenitor cells (PNAS 2001; 98:13901). To explore its role in hematopoiesis we investigated the regulation of BAALC during lineage specific differentiation. Semi-quantitative RT-PCR was performed on subsets of in vitro differentiated bone marrow CD34+ cells from healthy individuals using the cytokines G-CSF, M-CSF or EPO. Cultures were harvested on day 4, 8, 12, and 16. In addition, oligonucleotide microarray analyses (HG-U133A, Affymetrix) of in vitro stimulated CD34+ cells were independently carried out using EPO, TPO, G/GM-CSF to induce lineage-specific differentiation. For each of the lineages, cells were harvested at days 4, 7 and 11 for expression profiling. All experiments were done in triplicates for each time point and condition. RT-PCR revealed down-regulation of BAALC and CD34 as early as day 4 in cultures with G-CSF, M-CSF or EPO. In concordance, gene expression profiling showed significant down-regulation of BAALC and CD34 on day 4 of culture (BAALC: EPO p=0.04, G/GM-CSF p=0.17, TPO p=0.03; CD34: EPO p=0.01, G/GM-CSF p=0.003, TPO p=0.01). 275 genes showing a significant correlation (correlation coefficient r>0.95) to BAALC expression levels (at the 4 time points and using 3 different cytokines) were identified. Of these CD34 ranked second (r=0.99), and genes related to leukemia and neuronal cells included: Hepatic leukemia factor (HLF; r=0.99) and Paired box gene 5 (PAX5; r=0.99). It has been speculated that BAALC might be involved in cell movement or cell-cell interaction; we therefore investigated the association to genes implicated in cytoskeletal function. Expression of Myosin 5C (MYO5C; r=0.99) and Synaptic nulcei expressed gene 2 (SYNE2; r=0.95) were highly correlated with BAALC expression across all conditions (EPO, TPO, G/GM-CSF). In conclusion, using two independent approaches we show the significant down-regulation of BAALC during hematopoietic differentiation. This underscores the potential role of BAALC in early hematopoiesis and the possible contribution of aberrant BAALC expression in leukemogenesis. We postulate that similar to CD34, PAX, and HLF implicated in hematopoiesis and leukemia, down-regulation of BAALC and structural genes including Myosin 5C are critical steps during hematopoietic differentiation.

High BAALC Expression as an Independent Adverse Risk Factor in 309 Patients with Acute Myeloid Leukemia (AML) and Normal Cytogenetics: Results of the SHG'96 Study.

High mRNA expression levels of the human gene BAALC (Brain And Acute Leukemia, Cytoplasmic) have been shown to be an adverse risk factor in newly diagnosed AML patients (pts; Blood 2003; 102:1613). The first study included 86 de novo AML pts under the age of 60 with normal cytogenetics and a more favorable FLT3 mutation status, which were uniformly treated on the Cancer And Leukemia Group B protocol 9621. An independent confirmation of these data is necessary, to confirm the impact of BAALC expression in intermediate risk AML pts. Here we present the results of a Süddeutschen Hämoblastosegruppe (SHG) study including 309 adult pts diagnosed with de novo (n=280) and secondary AML (n=29), normal cytogenetics, age <60 years that were uniformly treated on the SHG'96 protocol. Treatment consisted of 2 cycles of induction therapy followed by intensive consolidation including autologous as well as allogeneic stem cell transplantation. Median follow-up for patients alive was 28.7 months (range: 0–86 months). BAALC expression was measured in pretreatment peripheral blood blasts by comparative real-time RT-PCR. Pts having BAALC expression values within the lower 50% were classified as low BAALC and pts having BAALC expression values within the upper 50% were classified as high BAALC. Whereas no correlation was seen between BAALC expression and the prevalence of FLT3 internal tandem duplications (ITD; P=0.16), high BAALC patients had a significantly higher FLT3 mutant/wild-type (wt) ratio as determined by Genescan analysis (mean mutant/wt ratio: 0.59 vs. 0.17; P=0.012). There was no significant difference in the prevalence of MLL partial tandem duplications between the high and the low BAALC group. High BAALC expression was significantly more frequent in FAB groups M0/M1 as compared to the other subtypes (P=0.002). Pts with high BAALC expression levels had a significantly lower CR rate (62.3% vs. 73.5%; P=0.039) and a higher relapse rate (43.8% vs. 28.9%; P=0.030). The overall survival (OS) was significantly shorter for pts with high BAALC expression (OS at 4 years: 29.8% vs. 53.3%; P=0.0018), event-free survival (EFS, at 4 years: 21.6% vs. 45.8%; P=0.0001), and disease-free survival (DFS, at 4 years: 30.4% vs. 57.6%; P=0.0018). Pts with a high FLT3 mutant/wt ratio (greater than 0.8) had a significantly shorter OS and DFS. For patients with a low FLT3 mutant/wt ratio, high BAALC expression allowed identification of pts with a high risk of treatment failure. A multivariate analysis confirmed high BAALC expression and a high mutant/wt FLT3 ratio as the only independent adverse risk factors. For pts with high BAALC expression the hazard ratio of death was 1.7 (95% CI 1.18–2.48; P=0.005), and the hazard ratios for EFS and DFS were 1.8 (95% CI 1.3–2.6; P=0.0003) and 2.0 (95% CI 1.2–3.3; P=0.004), respectively. In conclusion, this independent and larger study strengthens high BAALC expression as one of the most relevant adverse prognostic risk factors in intermediate risk AML pts with normal cytogenetics. Thus, determination of BAALC expression should be considered for risk adaptive treatment strategies.

BAALC, a novel marker of human hematopoietic progenitor cells

Objective The gene BAALC ( Brain And Acute Leukemia, Cytoplasmic), a novel molecular marker involved in leukemia, is highly expressed in a subset of patients with acute leukemia and predictive of clinical outcome in patients with acute myeloid leukemia and normal karyotype. The role of BAALC in hematopoiesis and leukemogenesis is unknown. Material and methods We used real-time RT-PCR to show that BAALC is strongly expressed in CD34 + cells from the bone marrow and blood and only weakly expressed in total normal bone marrow and blood cells. Results Expression analyses of FACSorted cells revealed high BAALC transcript levels in CD34 + bone marrow cells including CD34 +/CD38 −, CD34 +/CD33 +, as well as CD34 +/CD19 +/CD10 +, CD34 +/CD7 +, and CD34 +/CD71 +/CD45 − cell fractions. Expression was significantly lower in all CD34 − fractions. In vitro differentiation of CD34 + bone marrow cells showed downregulation of BAALC and CD34 transcripts as early as day 4 in suspension cultures supplemented with lineage-specific cytokines (G-CSF, M-CSF, or EPO). In cultures with only lineage-unspecific cytokines (IL-3, SCF, GM-CSF), BAALC transcripts persisted up to day 20, while CD34 transcripts disappeared earlier. These observations suggest that expression of BAALC is stage specific. Conclusions BAALC expression is restricted to progenitor cells, and downregulation of BAALC occurs with cell differentiation. We postulate that BAALC represents a novel marker of an early progenitor cell common to the myeloid, lymphoid, and erythroid pathways.

BAALC expression predicts clinical outcome of de novo acute myeloid leukemia patients with normal cytogenetics: a Cancer and Leukemia Group B Study

AbstractCytogenetic aberrations are important prognostic factors in acute myeloid leukemia (AML). Of adults with de novo AML, 45% lack cytogenetic abnormalities, and identification of predictive molecular markers might improve therapy. We studied the prognostic impact of BAALC (Brain And Acute Leukemia, Cytoplasmic), a novel gene involved in leukemia, in 86 de novo AML patients with normal cytogenetics who were uniformly treated on Cancer and Leukemia Group B 9621. BAALC expression was determined by comparative real-time reverse transcriptase–polymerase chain reaction in pretreatment blood samples, and patients were dichotomized at BAALC's median expression into low and high expressers. Low expressers had higher white counts (P = .03) and more frequent French-American-British M5 morphology (P = .007). Compared to low expressers, high BAALC expressers showed significantly inferior overall survival (OS; median, 1.7 vs 5.8 years, P = .02), event-free survival (EFS; median, 0.8 vs 4.9 years, P = .03), and disease-free survival (DFS; median, 1.4 vs 7.3 years, P = .03). Multivariable analysis confirmed high BAALC expression as an independent risk factor. For high BAALC expressers the hazard ratio of an event for OS, EFS, and DFS was respectively 2.7, 2.6, and 2.2. We conclude that high BAALC expression predicts an adverse prognosis and may define an important risk factor in AML with normal cytogenetics.

BAALC, the human member of a novel mammalian neuroectoderm gene lineage, is implicated in hematopoiesis and acute leukemia

The molecular basis of human leukemia is heterogeneous. Cytogenetic findings are increasingly associated with molecular abnormalities, some of which are being understood at the functional level. Specific therapies can be developed based on such knowledge. To search for new genes in the acute leukemias, we performed a representational difference analysis. We describe a human gene in chromosome 8q22.3, BAALC (brain and acute leukemia, cytoplasmic), that is highly conserved among mammals but evidently absent from lower organisms. We characterized BAALC on the genomic level and investigated its expression pattern in human and mouse, as well as its complex splicing behavior. In vitro studies of the protein showing its subcellular localization suggest a function in the cytoskeleton network. Two isoforms are specifically expressed in neuroectoderm-derived tissues, but not in tumors or cancer cell lines of nonneural tissue origin. We show that blasts from a subset of patients with acute leukemia greatly overexpress eight different BAALC transcripts, resulting in five protein isoforms. Among patients with acute myeloid leukemia, those overexpressing BAALC show distinctly poor prognosis, pointing to a key role of the BAALC products in leukemia. Our data suggest that BAALC is a gene implicated in both neuroectodermal and hematopoietic cell functions.