Stimulation of the human promonocytic cell line, THP-1, with endotoxin results in a rapid and transient increase in interleukin 1β expression. Endotoxin pretreatment of THP-1 cells results in tolerance, characterized by decreased levels of endotoxin-induced interleukin 1β expression due to decreased transcription of the interleukin 1β gene. We hypothesized that tolerant cells could not activate transcription factors necessary to express the interleukin 1β gene. This hypothesis was tested in tolerant THP-1 cells by using stable and transiently transfected reporter genes containing the interleukin 1β promoter. We found decreased endotoxin-induced transcription of all reporter genes tested; however, individual transcription factors, such as NFκB, retain normal, CD14-dependent, nuclear translocation and DNA binding. Tolerance is specific for endotoxin, because phorbol ester is still able to activate transcription of the endogenous interleukin 1β gene and transfected reporter genes. A constitutively active reporter gene that is not inducible by endotoxin is unaffected. We further show that nuclear extracts of tolerant cells show transcription inhibitor activity that is specific for promoter sequences of the interleukin 1β gene. These results support a mechanism of endotoxin tolerance that is independent of transcription factor DNA binding and appears to be associated with the inability of DNA-bound transcription factors to activate transcription, perhaps through the activity of a repressor.
Received 30 Jul 1999; first review completed 27 Aug 1999; accepted in final form 14 Oct 1999
Address reprint requests to Barbara K. Yoza, PhD, Department of Medicine, Section on Infectious Diseases, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157.
Supported in part by Public Health Service grants HL-29293 and AI-09169 and by General Clinical Research Center Grant RR07122 from the National Institutes of Health.
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