RECEPTOR TYROSINE KINASE EXPRESSION IN HUMAN BONE-MARROW STROMAL CELLS

Bone marrow stromal cells (BMSCs) are a heterogeneous population of ce lls derived from colony-forming units-fibroblastic (CFU-Fs. These cell s reside in the bone marrow cavity and are capable of differentiating into several cell phenotypes including osteoblasts, chondroblasts, hem atopoiesis-supporting stromal cells, and adipocytes. However, the fact ors that regulate the proliferation and differentiation of the BMSC po pulation are for the most part unknown. Since many members of the rece ptor tyrosine kinase (RTK) family have been shown to participate in gr owth control of various mesenchymal cell populations, in this study we examined the expression and function of RTKs in the BMSC population. Degenerate oligonucleotides corresponding to two conserved catalytic d omains of the RTK family and RT-PCR were used initially to determine w hich RTKs are expressed in the human BMSC (hBMSC) system. After subclo ning the amplification product generated from mRNA of a multicolony-de rived hBMSC strain, PDGF receptor (beta), EGF receptor, FGF receptor 1 ,and Axl were identified by DNA sequencing of 26 bacterial colonies. F urthermore, PDGF and EGF were found to enhance BMSC growth in a dose-d ependent manner and to induce tyrosine phosphorylation of intracellula r molecules, including the PDGF and EGF receptors themselves, demonstr ating the functionality of these receptors. On the other hand, bFGF wa s found to have little effect on proliferation or tyrosine phosphoryla tion. Since single colony-derived hBMSC strains are known to vary from one colon), to another in colony habit (growth rate and colony struct ure) and the ability to form bone in vivo, the expression levels of th ese RTKs were determined in 18 hBMSC clonal strains by semiquantitativ e RT-PCR and were found to vary from one clonal strain to another. Whi le not absolutely predictive of the osteogenic capacity of individual clonal strains, on average, relatively high levels of PDGF-receptor we re found in bone-forming strains, while on average, nonbone-forming st rains had relatively high levels of EGF-receptor. Taken together, thes e results indicate that RTKs play a role in the control of hBMSC proli feration, and that the differential pattern of RTK expression may be u seful in correlating the biochemical properties of individual clonal s trains with their ability to produce bone in vivo. (C) 1998 Wiley-Liss , Inc.dagger.