BMI-1 Overexpression in 32Dcl3 Cells Suppresses Granulocytic Differentiation and Ameliorates Their Growth under IL-3 Diminished Conditions.

The BMI-1 gene is one of the polycomb group (PcG) genes that have been shown to play essential roles in the self-renewal of both normal and leukemic stem cells. BMI-1 is reported to be highly expressed in primitive cells and its expression level decreases as bone marrow cells differentiate. We hypothesized that overexpression of BMI-1 might modulate the growth, differentiation and survival of 32D cells, and examined this hypothesis by generating BMI-1 overexpressing 32D cells. 32D cells were infected with MIG-BMI-1-IRES-EGFP vector or MIG vector, and the GFP positive rates of BMI-1 overexpressing 32D cells gradually increased under IL-3 diminished conditions, and the consecutive MTT assays using cells sorted by GFP positivity confirmed this finding, suggesting that BMI-1 could confer growth advantages on 32D cells under IL-3 diminished conditions.

Exposure of the GFP sorted 32D cells to G-CSF revealed that BMI-1 overexpression suppressed the granulocytic differentiation of 32D cells by G-CSF. The expressions of CD11b and Gr-1 were both suppressed by the overexpression of BMI-1, and real-time PCR analyses indicated that the expression levels of MPO was remarkably suppressed, while those of C/EBPα were not significantly changed.

Our experiments revealed that BMI-1 delayed granulocytic differentiation and ameliorated the growth of 32D cells under IL-3 diminished conditions.