This study was aimed to detect the expression of leukemia stem/progenitor cell (LSPC) related genes (ABCB1, BMI-1, HOXB4) in the patients with acute leukemia, and to explore its clinical significance in acute leukemia. Bone marrow samples were collected from de novo acute leukemia patients (41 cases), patients with complete remission (CR, 16 cases) and the patients with non-malignant hematologic diseases (10 cases) respectively. And the expressions of ABCB1, BMI-1, HOXB4 genes were detected by comparative real-time quantitative PCR (RQ-PCR) with SYBR Green assay. The results showed that the expressions of ABCB1, BMI-1, HOXB4 were not detected in the patients with non-malignant hematologic diseases, but were higher (relative expressive level: 4.26 ± 2.26, 3.72 ± 1.91, 3.74 ± 2.38) in de novo acute leukemia patients and lower (relative expressive level: 2.14 ± 1.47, 2.07 ± 0.99, 1.47 ± 0.89) in the acute leukemia patients with CR (p < 0.05). The expressions of LSPC related genes were lower (relative expressive level: 1.77 ± 1.29, 2.09 ± 1.26, 1.78 ± 1.49) in the patients acquired CR/partial remission (PR) than those in the patients not acquired CR/PR (relative expressive level: 7.23 ± 1.78, 3.96 ± 0.92, 4.48 ± 2.57) (p < 0.01). Univariate analysis revealed that there were more cases with the expression of LSPC immunophenotype (CD34(+)CD38(-)CD96(+) and CD34(+)CD38(-)CD123(+)) and more hyperleukocytosis cases in patients with any higher expression of LSPC related gene (p < 0.05). Analysis of multiple parameters discovered larger significance (p < 0.01). It is concluded that there is a good relationship between LSPC related genes (ABCB1, BMI-1, HOXB4) and LSPC immunophenotype. The expression of LSPC-related genes is higher in de novo acute leukemia patients, and lower in patients acquired CR/PR. The patients with higher expressed LSPC-related genes display worse response to chemotherapy, lower CR/PR rate and higher leukocytosis, the analysis of multiple parameters may be a good method for assessing the therapeutic efficacy/prognosis of acute leukemia.
ATP Binding Cassette Transporter, Sub-Family B ; ATP-Binding Cassette, Sub-Family B, Member 1 ; genetics ; metabolism ; Adolescent ; Adult ; Aged ; Female ; Gene Expression ; Homeodomain Proteins ; genetics ; metabolism ; Humans ; Immunophenotyping ; Leukemia, Myeloid, Acute ; genetics ; metabolism ; Male ; Middle Aged ; Neoplastic Stem Cells ; metabolism ; Polycomb Repressive Complex 1 ; genetics ; metabolism ; Transcription Factors ; genetics ; metabolism ; Young Adult

Protein phosphatase 2A (PP2A) accounts for the majority of total Ser/Thr phosphatase activities in most cell types and regulates many biological processes. PP2A holoenzymes contain a scaffold A subunit, a catalytic C subunit, and one of the regulatory/targeting B subunits. How the B subunit controls PP2A localization and substrate specificity, which is a crucial aspect of PP2A regulation, remains poorly understood. The kinetochore is a critical site for PP2A functioning, where PP2A orchestrates chromosome segregation through its interactions with BubR1. The PP2A-BubR1 interaction plays important roles in both spindle checkpoint silencing and stable microtubule-kinetochore attachment. Here we present the crystal structure of a PP2A B56-BubR1 complex, which demonstrates that a conserved BubR1 LxxIxE motif binds to the concave side of the B56 pseudo-HEAT repeats. The BubR1 motif binds to a groove formed between B56 HEAT repeats 3 and 4, which is quite distant from the B56 binding surface for PP2A catalytic C subunit and thus is unlikely to affect PP2A activity. In addition, the BubR1 binding site on B56 is far from the B56 binding site of shugoshin, another kinetochore PP2A-binding protein, and thus BubR1 and shugoshin can potentially interact with PP2A-B56 simultaneously. Our structural and biochemical analysis indicates that other proteins with the LxxIxE motif may also bind to the same PP2A B56 surface. Thus, our structure of the PP2A B56-BubR1 complex provides important insights into how the B56 subunit directs the recruitment of PP2A to specific targets.
Amino Acid Motifs ; Binding Sites ; Cell Cycle Proteins ; chemistry ; Crystallography, X-Ray ; Humans ; Multienzyme Complexes ; chemistry ; Protein Phosphatase 2 ; chemistry ; Protein Structure, Quaternary ; Protein-Serine-Threonine Kinases ; chemistry