Activation of mitogen-activated protein kinase through alpha5/beta1 integrin is required for cell cycle progression of B progenitor cell line, Reh, on human marrow stromal cells.
OBJECTIVE
Attachment to bone marrow (BM) stromal cells is crucial for the normal growth and development of B-cell progenitors (pro-B). However, the molecular mechanisms by which contact facilitates the proliferation of pro-B cells are not completely understood. This study was performed to investigate this interaction.


METHODS
A model pro-B cell line (Reh) and a human BM stromal cell line (KM102) were used. Flow cytomery was used for cell cycle analysis. Western Blotting and immunoprecipitation were utilized to examine the levels of cyclin-dependent kinase (cdk) and p27(Kip1).


RESULTS
Attachment to both KM102 and normal BM stromal cells significantly promoted the growth of Reh cells. Pretreatment of Reh cells with anti-integrin beta1 or alpha5 monoclonal antibody (mAb), but not alpha4 or ICAM-1 mAb, abrogated this enhancement of proliferation. Furthermore, stroma attachment resulted in shortening of the G(1) phase of cell cycle, significant increases cdk2 activity, degradation of cdk inhibitor p27-GST protein, and decrease in levels of p27(Kip1) protein. In addition, solid-phase cross-linking of alpha5 via immobilized antibody also resulted in extracellular signal-regulated (ERK)-2 kinase phosphorylation, increase in cdk2 activity, decrease in levels of p27(Kip1) protein, and enhanced proliferation that was inhibited by treatment with PD98059, a specific ERK inhibitor.


CONCLUSIONS
Integrin alpha5beta1-mediated stroma contact promotes the proliferation of B-cell progenitors through the activation of ERK-2, which in turn modulates cell cycle regulation machinery including induction of cdk2 activity and degradation of p27(Kip1) and contributing to acceleration of the G(1) phase of cell cycle progression.
Qiang
Y W
YW
Division of Molecular and Tumor Pathology, Department of Pathology, Chiba University School of Medicine, Chiba, Japan.
Kitagawa
M
M
Higashi
M
M
Ishii
G
G
Morimoto
C
C
Harigaya
K
K
D001402:B-Lymphocytes / Q000166:cytology*; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000166:cytology; D002450:Cell Communication; D002453:Cell Cycle; D002455:Cell Division; D002460:Cell Line; D004789:Enzyme Activation; D005434:Flow Cytometry; D016193:G1 Phase; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017469:Receptors, Fibronectin / Q000502:physiology*; D017154:Stromal Cells / Q000166:cytology / Q000502:physiology*
D017469:Receptors, Fibronectin; D019950:Mitogen-Activated Protein Kinase 1; D020928:Mitogen-Activated Protein Kinases