Development of resistance to tumour necrosis factor (TNF alpha) in KYM-1 cells involves both TNF receptors.

In this study, we investigated the type of TNF receptor expressed by the human rhabdomyosarcoma cell line KYM-1 and related TNF-sensitive sublines and showed that the majority (> 90%) of TNF receptors were type II (p75) receptors with only a relatively small number (< 10%) of type I (p55) receptors. Selection with TNF alpha led to the isolation of KYM-1 related TNF-resistant cell lines of which three cloned lines showed a near to total loss of type II TNF receptors. To investigate further the role of each type of TNF receptor in the regulation of TNF-mediated cytotoxicity and the development of TNF resistance, we used receptor-specific antibodies and antisera, able to compete with ligand binding to the respective receptor molecules, but representing efficient agonists via crosslinking of receptors. We found that in KYM-1 and related TNF-sensitive sublines both type I and type II TNF receptors can be functional on their own, as selective cross-linking of each receptor subset lead to cytolysis. However, investigation of three TNF-resistant KYM-1 related cell lines by selective receptor stimulation via cross-linking indicated different mechanisms underlied the development of TNF-resistant for each receptor type. Our data indicate that resistance to TNF-mediated cytotoxicity in KYM-1 related cell lines can be developed both by a selective loss of type II receptor expression and the selective loss of type I receptor function without reduction in type I receptor numbers.