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. 2007 Mar 15;109(6):2373-9.
doi: 10.1182/blood-2006-05-026039. Epub 2006 Nov 9.

Cytokine and integrin stimulation synergize to promote higher levels of GATA-2, c-myb, and CD34 protein in primary human hematopoietic progenitors from bone marrow

Mo A Dao  1 , Jan A Nolta
Affiliations

Cytokine and integrin stimulation synergize to promote higher levels of GATA-2, c-myb, and CD34 protein in primary human hematopoietic progenitors from bone marrow

Mo A Dao et al. Blood. .

Abstract

We have previously shown that engagement of the integrins VLA-4 and VLA-5 to the fibronectin fragment CH-296 in combination with cytokines sustained the capacity of cultured human CD34(+) cells to undergo hematopoiesis in immunodeficient mice for 7 to 12 months, whereas this capacity was rapidly lost in cells cultured in suspension with the same cytokines. In the current study, we assessed the molecular pathways that might explain the loss of long-term engraftment capacity in cells cultured in suspension. Although the cell cycle profile was similar between cells cultured in suspension versus on fibronectin, levels of cell death were higher in the suspended cultures. While the CDK inhibitors p27Kip1 and p57Kip2 were present at equal levels in cells from both cultures, low levels of p21Cip1 were detectable only in the cytoplasmic compartment of cells cultured in suspension. Cytoplasmic location of p21Cip1 has been linked to monocytic differentiation. The levels of c-myb and GATA-2, transcription factors associated with stem cell maintenance, were higher in cells cultured on fibronectin as compared with suspension. In contrast, the levels of PU.1, which is induced during myeloid differentiation, were higher in cells cultured in suspension. There were no significant differences in surface expression of CD34 on the cells after culture, but total CD34 protein, assessed by immunoblotting, was significantly higher in cells cultured on fibronectin. Our data suggest that, in the presence of cytokines, the engagement of VLA-4 and VLA-5 integrins to the fibronectin fragment CH-296 preserves the expression of specific transcription factors associated with primitive stem cell maintenance. In contrast, a lack of integrin engagement leads to the induction of cellular markers associated with myeloid differentiation.

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Figures

Figure 1
Figure 1
Comparison of cell cycle kinetics and regulators between CD34+ progenitors cultured on FN- versus BSA-coated plates. Human bone marrow CD34+ progenitors were cultured in the presence of IL-3, IL-6, and SCF for 48 hours on either FN- or BSA-coated plates prior to analysis. (A) Ki67/7-AAD staining was performed to identify the percentage of G0, G1, and S/G2M cells after 48 hours on FN- (□) and BSA- (■) coated plates. (B) Subcellular fractionations were performed on 106 cells recovered from FN- and BSA-coated plates and immunoblotted with an antibody against p21Cip1 and p27Kip1. Freshly isolated CD34+ progenitors and mononuclear cells were subfractionated and immunoblotted with an antibody against p21Cip1 (left) and compared with cells harvested after 48-hour culture on FN- versus BSA-coated plates (right). Total protein lysates were immunoblotted to assess for p57Kip2 (lower left). MNC indicates mononuclear cells. Error bars indicate standard deviation.
Figure 2
Figure 2
Assessment of the levels of cyclin E, A, and B and their CDK-associated kinase activity in CD34+ cells cultured on FN- versus BSA-coated plates. After 48 hours of culture in cytokines on FN- versus BSA-coated plates, cell numbers were equalized and half of the cells were used for subcellular fractionation, immunoblotting for cyclin D3 and CDK6 (A, left), cyclin A and CDK2 (A, right), cyclin E (B, left), cyclin A (B, left), and cyclin B (B, left). The other half of the cells were used for immunoprecipitation with antibodies against specific cyclins (as indicated) followed by in vitro histone H1 kinase assay to assess activity of CDKs associated with cyclin E (A, right), cyclin A (B, right), and cyclin B (B, right).
Figure 3
Figure 3
Comparison of CD34 surface expression versus total CD34 protein expression in CD34+ progenitors after culturing on FN- versus BSA-coated plates. After a 48-hour culture, 200 000 cells were stained with anti-CD34–FITC and anti-CD38–PE and analyzed by flow cytometry to assess CD34 cell-surface expression (A). An additional 2 × 106 cells from the same cultures (n = 4) were lysed in protein lysis buffer for CD34 total protein expression by immunoblotting (B). The top half of the blot was immunoblotted for CD34, and the bottom half was immunoblotted for actin as a loading control.
Figure 4
Figure 4
Detection of c-Myb, GATA-2, and PU.1 protein after ex vivo culture on FN- versus BSA-coated plates. To determine whether integrin engagement preserves the primitiveness of CD34+ cells, the cells were cultured on FN- versus BSA-coated plates in the presence of IL-3, IL-6, and SCF for 96 hours. A total of 2 × 106 cells were normalized at the end of each culture and subjected to subcellular fractionation and protein analysis for c-Myb and GATA-2, 2 transcription factors reported to be abundant in primitive cells versus PU.1, a transcription factor highly expressed in committed monocytes (A). A quantitative representation of 1 of the 4 bone marrow experiments assessing c-Myb and GATA-2 is shown by normalizing the densitometry value of the transcription factor with that of the corresponding actin densitometry value (B). NA indicates nonadherent; AD, adherent.
Figure 5
Figure 5
Assessment of cell death in cultures of CD34+ progenitors maintained on FN- versus BSA-coated plates. (A) A total of 500 000 cells from each of the culture conditions were subjected to annexin V (FITC) and 7-AAD staining. FACS acquisition and analysis were done on FACSCalibur. (B) Percentage of live cells from 3 independent experiments using marrow samples from 3 donors.
Figure 6
Figure 6
Hypothesis model. We hypothesize that maintenance of CD34+ progenitors in suspension culture with cytokines induces differentiation and sensitivity to cell death. In contrast, CD34+ progenitors maintained in culture on CH-296–coated plates generate 2 pools of cells: the less primitive nonadherent cell pool and the more primitive adherent cell pool.
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