Differential baseline and response profile to IFN-gamma gene transduction of IL-6/IL-6 receptor-alpha secretion discriminate primary tumors versus bone marrow metastases of nasopharyngeal carcinomas in culture.
BACKGROUND: Understanding of immunobiology of bone marrow metastases (designated BM-NPC) versus primary tumors (P-NPC) of the nasopharynx is far from complete. The aim of this study was to determine if there would be differences between cultured P-NPCs and BM-NPCs with respect to (i) constitutive IL-6 and the IL-6 receptor gp80 subunit (IL-6Ralpha) levels in the spent media of nontransduced cells, and (ii) IL-6 and IL-6Ralpha levels in the spent media of cells transduced with a retroviral vector containing the IFN-gamma gene. METHODS: A panel of NPC cell lines were transduced with the IFN-gamma gene through a retroviral vector. Four clonal sublines were isolated via limiting dilution methods. Cytofluorometric analysis was performed for the detection of cell surface antigens of HLA class I, HLA class II and ICAM-1. ELISA was used to assay for IFN-gamma, IL-6 and IL-6Ralpha in the spent media of cultured cell lines. RESULTS: Our results showed that in day 3 culture supernatants, low levels of soluble IL-6 were detected in 5/5 cultured tumors derived from P-NPCs, while much higher constitutive levels of IL-6 were detected in 3/3 metastasis-derived NPC cell lines including one originated from ascites; the difference was significant (p = 0.025). An inverse relationship was found between IL-6Ralpha and IL-6 in their release levels in cultured P-NPCs and metastasis-derived NPCs. In IFN-gamma-transduced-P-NPCs, IL-6 production increased and yet IL-6Ralpha decreased substantially, as compared to nontransduced counterparts. At variance with P-NPC cells, the respective ongoing IL-6 and IL-6Ralpha release patterns of BM-NPC cells were not impeded as much following IFN-gamma transduction. These observations were confirmed by extended kinetic studies with representative NPC cell lines and clonal sublines. The latter observation with the clonal sublines also indicates that selection for high IL-6 or low IL-6Ralpha producing subpopulations did not occur as a result of IFN-gamma-transduction process. P-NPCs, which secreted constitutively only marginal levels of IFN-gamma (8.4 ~ 10.5 pg/ml), could be enhanced to produce higher levels of IFN-gamma (6.8- to 10.3-fold increase) after IFN-gamma transduction. Unlike P-NPCs, BM-NPCs spontaneously released IFN-gamma at moderate levels (83.8 ~ 100.7 pg/ml), which were enhanced by 1.3- to 2.2-fold in the spent media of their IFN-gamma-transduced counterparts. CONCLUSION: Our results showed that cultured P-NPCs and BM-NPCs could be distinguished from one another on the basis of their differential baseline secretion pattern of IFN-gamma, IL-6 and IL-6Ralpha, and their differential response profiles to IFN-gamma gene transfer of the production of these three soluble molecules. These results suggest that the IL-6 and IFN-gamma pathways in a background of genetic instability be involved in the acquisition of metastatic behaviour in BM-NPCs.