Quantification and characterization of high-affinity membrane receptors for tumor necrosis factor on human leukemic cell lines.
The expression of specific membrane receptors for TNF-alpha was determined on various human leukemic cell lines differing in their sensitivity to the growth-inhibitory activity of TNF-alpha. Binding studies with 125I-labelled TNF-alpha indicated specific binding in 8/10 cell lines with approximately 10-fold differences in the quantity of TNF-alpha bound by these distinct cell lines. Scatchard analyses of TNF-binding revealed the existence of high-affinity membrane receptors (Kd 1.5 X 10(-10) M) and approximately 3,000 binding sites/cell on both U937 and K562, representing 2 cell lines with high and low TNF sensitivity, respectively. Disuccinimidyl-suberate cross-linking of receptor-bound 125I-TNF-alpha and SDS-PAGE of membrane preparations of either U937 or K562 cells suggest a single receptor protein with an apparent molecular weight of 76 kDa. Comparison of the TNF-alpha binding capacity versus in vitro growth inhibition provides evidence that sensitivity to TNF-alpha is determined both at the level of receptor expression and at a post-receptor level. IFN-gamma strongly enhanced the TNF-alpha-mediated growth inhibition of 3 sensitive cell lines, but had no effect on 7 other leukemic cell lines with little or no TNF sensitivity. No correlation was found between this enhancement of TNF sensitivity and the IFN-gamma- mediated increase in TNF-cell membrane receptors, suggesting that IFN-gamma predominantly exerts its synergistic effect distal to TNF-binding.[1]References
- Quantification and characterization of high-affinity membrane receptors for tumor necrosis factor on human leukemic cell lines. Scheurich, P., Ucer, U., Krönke, M., Pfizenmaier, K. Int. J. Cancer (1986) [Pubmed]
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