Constitutive expression of steel factor gene by human stromal cells

Abstract

Steel factor (SF), the ligand for c-kit, is an essential regulator of normal hematopoiesis, melanogenesis, gametogenesis, and mast-cell growth and development. Hematopoietic stromal cells are important sources of SF, because inactivation of SF in mice results in defects in the support function of hematopoietic stromal cells. To identify specific cells that produce, and factors that govern the expression of the different isoforms of SF in human hematopoiesis, we quantified levels of SF mRNA and membrane-bound protein in human stromal cells before and after exposure to recombinant human interleukin (IL)-1 alpha, a cytokine known to induce the expression of a variety of hematopoietic growth factors. In addition, because stromal cells in longterm bone marrow cultures (LTBMC) are supportive of hematopoietic progenitor cell survival in vitro, while umbilical vein endothelial cells (EC) and diploid fibroblasts (DF) are not, we also sought to test the hypothesis that SF gene expression would differ in cells from LTBMC when compared with EC or DF. Using reverse-transcription polymerase chain reaction amplification (RT-PCR), ribonuclease protection assays (RPA), and Northern blot analysis, SF was found to be constitutively transcribed in EC, DF, and LTBMC. IL-1 alpha neither induced accumulation of SF mRNA nor altered the ratio of exon 6+ to exon 6- transcripts in these stromal cells. By Northern blot analysis, the predominant SF mRNA species was shown to be 5.6 kb; a minor population of 3.6 kb was also found. Low levels of membrane-bound SF protein were found to be constitutively expressed by all three types of stromal cells, and were not regulated by IL-1 alpha. We conclude that the unique capacity of LTBMC to support in vitro hematopoiesis, when compared with EC or DF, cannot be explained on the basis of qualitative or quantitative differences in SF gene expression in these cells.

Plasma levels and production of soluble stem cell factor by marrow stromal cells in patients with aplastic anaemia

“…In contrast to the other haemopoietic growth factors, SCF is produced mainly by the BM stroma (Heinrich et al, 1993). By itself, it does not have a strong stimulatory effect on haemopoietic cells, but it acts synergistically with a number of other haemopoietic growth factors and has the capacity to stimulate the earliest haemopoietic stem cells (Tsuji et al, 1991;McNiece et al, 1991).…”

Mast cells as sources of cytokines, chemokines, and growth factors

“…[268][269][270][271] Non-hematopoietic cells such as endothelial cells or fibroblasts are considered to be more important sources of SCF than are hematopoietic cells. [272][273][274] However, human MCs have been reported to exhibit SCF immunoreactivity in their granules. [275][276][277][278][279] SCF mRNA and/or protein has been reported in human skin and lung mast cells and human PBMCs and CBMCs.…”

Oestrogen‐deficiency inducing haematopoiesis dysfunction via reduction in haematopoietic stem cells and haematopoietic growth factors in rats

“…In addition they give rise to daughter progeny for self-renewal throughout life (Lemischka et al 1986). Haematopoietic growth factors, a group of haematopoietic regulatory proteins, which are produced by mesenchymal cells, together with HSCs constitute the HSC niches in bone marrow (Heinrich et al 1993). HSC make the process of selfreplication and are regulated in a complicated fashion by HGFs and other cytokines in the HSC niches and then release the daughter cells outside for further proliferation and differentiation (Zhang et al 2003).…”