Support of human hematopoiesis in long-term bone marrow cultures by murine stromal cells selectively expressing the membrane-bound and secreted forms of the human homolog of the steel gene product, stem cell factor.

Abstract

The maintenance and differentiation of hematopoietic stem cells is influenced by cells making up the hematopoietic microenvironment (HM), including bone marrow-derived stromal cells. We and several other investigators have recently demonstrated the molecular basis of abnormal HM observed in the steel mutant mouse and cloned the normal cDNA products of this gene (termed SCF, KL, or MCF). In this report, we focus on the human counterpart of the mouse Steel (Sl) gene. Alternative splicing of the human SCF pre-mRNA transcript results in secreted and membrane-bound forms of the protein. To investigate the role of these two forms of human SCF, we targeted an immortalized stromal cell line derived from fetal murine homozygous (Sl/Sl) SCF-deficient embryos for gene transfer of various human cDNAs encoding SCF. We report that stable stromal cell transfectants can differentially process the two forms of human SCF protein product. We also demonstrate that both soluble SCF and membrane-bound SCF are active in increasing the number of human progenitor cells in the context of stromal cell cultures, although in a qualitatively different manner. Hence, the membrane-bound form of SCF may play an important role in the cell-cell interactions observed between stromal and hematopoietic cells both in vitro and in vivo.

Establishment and properties of fetal dermis-derived mesenchymal stem cell lines: plasticity in vitro and hematopoietic protection in vivo

“…28 It is thought that these progenitors give rise to mesenchymal cells in the marrow that fabricate the connective tissue scaffolding, and produce cytokines, chemokines, and extracellular matrix proteins that regulate hematopoietic homing and proliferation. 7,29,30 A number of preclinical animal models of stromal cell transplantation have been established to support hematopoietic engraftment, including using human fetal lung-derived MSCs. [31][32][33] Both autologous and allogeneic human marrow stromal cells were shown to improve the quantity and duration of human hematopoietic engraftment in a preimmune sheep model.…”

Retroviral transduction of quiescent haematopoietic cells using a packaging cell line expressing the membrane-bound form of stem cell factor

“…Also, mice carrying the steel mutation have defects in the gene encoding SCF and suffer from a variety of severe haematopoietic defects, are sterile, lack pigment (except in retina) and have reduced numbers of mast cells in their skin. 14,[32][33][34] Significantly, mice that harbour the 'dickie' allele of steel produce a, biologically active, soluble form of SCF but not the membrane-bound form, 32,34 yet they display a phenotype very similar to those that make no SCF at all. Thus, the membrane-bound isoform of SCF may have greater physiological significance for early haematopoiesis than the soluble form.…”

Regulation of stem cell factor expression in inflammation and asthma

“…mSCF also stimulates the development of hematopoietic cells still more than sSCF (Toksoz et al 1992). A possible explanation is that the mSCF stimulation of the Kit receptor delays internalization of the SCF-Kit complex and accordingly delays the end of the stimulation (Miyazawa et al 1991, Toksoz et al 1992. Moreover, mSCF acts as an adhesion molecule for mast cells (Kinashi et al 1994, Adachi et al 1995.…”

“…Membrane-bound SCF, for example, may play a more important role than sSCF in the in vivo development of mast cells, as suggested by work in mutant mice homozygous for the Steel Dickie (Sld) allele: they produce biologically active sSCF but not mSCF and suffer from a profound mast cell deficiency (Brannan et al 1991). mSCF also stimulates the development of hematopoietic cells still more than sSCF (Toksoz et al 1992). A possible explanation is that the mSCF stimulation of the Kit receptor delays internalization of the SCF-Kit complex and accordingly delays the end of the stimulation (Miyazawa et al 1991, Toksoz et al 1992.…”