ALBERT

Description: The cytokine stem cell factor (SCF) synergizes with interleukin-7 (IL- 7) to enhance the proliferation of pre-B cells. To examine the role of SCF and its receptor, c-kit, in the pathogenesis of pediatric Burkitt's lymphomas (BL), we investigated the expression of SCF and c-kit in BL cells and the mitogenic activity of SCF on BL cells. A panel of 13 BL cell lines and 7 fresh biopsy tumors was investigated. BL cells were stimulated either by Epstein-Barr virus (EBV) infection or by different reagents and cytokines, and expression of SCF and c-kit was studied on the mRNA level by Northern blot analysis and reverse-transcriptase polymerase chain reaction (RT-PCR), followed by Southern blotting. c- kit expression was also studied by fluorescence-activated cell sorting and by crosslinking of digoxigenin-labeled recombinant human SCF to the cell surface. Proliferation of BL cell lines was measured by 3H- thymidine incorporation. Low-level expression of c-kit mRNA was detected in 2 of 13 unstimulated BL cell lines and in 1 fresh BL tumor. One cell line showed upregulation of c-kit mRNA with A23187 and downregulation with phorbol myristate acetate. Neither c-kit nor SCF could be detected in any other cell line under any condition of stimulation as analyzed by Northern blot analysis, RT-PCR followed by Southern blot analysis, crosslinking, and immunofluorescence. No response to SCF was seen in 3H-thymidine incorporation assays. We conclude that most BL cells express neither SCF nor c-kit and that the low-level expression of c-kit in some BL cells most likely has no biologic significance.

Description: Production of hematopoietic growth factors by endothelial cells plays a pivotal role during inflammatory processes. Stem cell factor (SCF) is known to be expressed constitutively in endothelial cells. To investigate the regulation of this cytokine expression by inflammatory stimuli, we cocultured human umbilical vein endothelial cells (HUVEC) with various gram-negative bacterial strains (Escherichia coli, Yersinia enterocolitica, Chlamydia trachomatis, and Neisseria meningitidis, respectively). Experiments were performed with bacterial concentrations ranging from 10(2) to 10(7) bacteria/mL for 3 hours. SCF- specific mRNA expression was studied using Northern blot analysis. Stimulation with the enteropathogenic bacterial strains Y enterocolitica and E coli resulted in a significant concentration- dependent increase of SCF mRNA expression. Similar results were obtained in coculture experiments with N meningitidis. As shown in experiments with E coli, the accumulation of SCF transcripts was also time-dependent. In contrast, coculture of HUVEC with the intracellular gram-negative strain C trachomatis had no effect on SCF mRNA expression. To elucidate the role of the gram-negative bacterial cell wall components, we stimulated HUVEC with bacterial lipopolysaccharide (LPS). LPS induced a maximal SCF mRNA accumulation within 2 hours followed by decrease of SCF-specific transcripts to the basal level after 24 hours. In addition, we exposed HUVEC to the classical inflammatory cytokine interleukin-1 alpha (IL-1 alpha). Kinetic experiments showed a similar pattern of regulation with an increase of SCF mRNA within 2 hours, persisting up to 12 hours, and a decrease to basal transcription after 24 hours. From these data, we conclude that SCF expression is regulated by inflammatory stimuli, such as IL-1 alpha and bacterial pathogens, suggesting an important role of SCF during inflammation.