Expansion of the nonadherent myeloid cell population by monoclonal antibodies against tenascin-C in murine long-term bone marrow cultures.
Tenascin-C, a predominantly mesenchymal extracellular matrix protein, has a restricted distribution in adult tissues. It has previously been shown that this protein is expressed in the bone marrow. In this paper we show that murine myeloid and lymphoid long-term bone marrow cultures differ in their expression of tenascin-C splice variants. In the adherent stromal layer of myeloid cultures, the 260-kDa polypeptide encoded by the 8-kb mRNA was the major splice variant, whereas in the stromal layer of lymphoid cultures both the shorter 210-kDa polypeptide encoded by the 6-kb mRNA and the 260-kDa polypeptide were abundantly expressed. However, in both culture systems the larger 260-kDa tenascin-C polypeptide was the major isoform secreted in the culture supernatant. This finding is in agreement with previous reports indicating that the smaller 210-kDa isoform is preferentially deposited in the stroma, whereas the alternatively spliced segment in the 260-kDa tenascin-C may contain anti-adhesive domains. Glucocorticoids in myeloid long-term bone marrow cultures and in the MC3T3-G2/PA6 cell line downregulated the expression of tenascin-C. In the present study we observed that this was due primarily to downregulation of the 8-kb major splice variant of the tenascin-C mRNA. We also studied the possible role of tenascin-C in the bone marrow by using antibodies against tenascin-C in long-term bone marrow cultures. We found that three monoclonal antibodies against the carboxyterminal type III fibronectin repeats of tenascin-C (TNCfn 7-8) increased the number of the non-adherent myeloid cells in myeloid long-term bone marrow cultures. It has recently been suggested that the TNCfn 6-8 domain of tenascin-C binds to the alpha8beta1 integrin. Using Northern blotting, we found that the integrin alpha8 subunit was expressed in adherent cells in bone marrow cultures, raising the possibility that tenascin-C acts in bone marrow cultures by binding to the alpha8beta1 integrin.
Talts
J F
JF
Department of Animal Physiology, Uppsala University, Sweden.
Falk
M
M
Ekblom
M
M
D000818:Animals; D000911:Antibodies, Monoclonal; D001854:Bone Marrow Cells / Q000276:immunology*; D002448:Cell Adhesion / Q000276:immunology; D002452:Cell Count; D003470:Culture Media; D006801:Humans; D006825:Hybridomas; D039001:Integrin alpha Chains; D016023:Integrins / Q000032:analysis; D051379:Mice; D017154:Stromal Cells / Q000276:immunology; D019063:Tenascin / Q000276:immunology*
D000911:Antibodies, Monoclonal; D003470:Culture Media; D039001:Integrin alpha Chains; D016023:Integrins; D019063:Tenascin; C093856:integrin alpha8