Neural Cell Adhesion Molecule Contributes to Hemopoiesis‐Supporting Capacity of Stromal Cell Lines

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Abstract
To clarify mechanisms underlying cell‐to‐cell interactions between hemopoietic stem cells (HSCs) and stromal cells, we established a stromal cell line (FMS/PA6‐P) from day‐16 fetal bone marrow (BM) adherent cells using an anti‐PA6 monoclonal antibody (mAb) specific for BM stromal cells. Importantly, this FMS/PA6‐P cell line, showing homogenous fibroblastic morphology, is absent from hematolymphoid and endothelial lineage markers and maintains a high level of expression of PA6 molecule, recognized by the anti‐PA6 mAb, for approximately 20 passages. Further, the cell line expressing a high level of PA6 molecule has a better hemopoiesis‐supporting capacity in vitro than other stromal cell lines such as PA6 and MS‐5. In fact, the PA6 molecule is closely related to the hemopoiesis‐supporting capacity of the stromal cells because the proliferation of HSCs was suppressed to a great extent by the anti‐PA6 mAb. Affinity chromatography and mass peptide fingerprinting revealed that the protein reacting with the anti‐PA6 mAb is neural cell adhesion molecule (NCAM). The frequencies of long‐term cobblestone area–forming cells and long‐term culture‐initiating cells were significantly suppressed by repression of NCAM in the FMS/PA6‐P cells using NCAM small interfering RNA. Our findings clearly indicate that NCAM functions on the maintenance of HSCs.