REGULATION OF P100 (NFKB2) EXPRESSION IN HUMAN MONOCYTES IN RESPONSE TO INFLAMMATORY MEDIATORS AND LYMPHOKINES

The transcription factor NF-KB plays an important role in the regulate d expression of cytokines in human monocytes. A p100 subunit of NF-kap pa B has I kappa B-like properties by sequestering the p65 transactiva ting subunit in the cytosol of cells. In transient transfection assays we demonstrated that p100 has an inhibitory effect on the NF-kappa B- dependent IL-6 promoter activity. In view of this finding, we studied the regulation of the p100 subunit in human monocytes in response to L PS, the inflammatory cytokines IL-I beta and TNF-alpha and lymphokines . The results demonstrate that LPS, IL-1 beta, and TNF-alpha induce p1 00 expression at mRNA and protein level while lFN-gamma, IL-3 and IL-4 /IL-10 have no effect. The induction of p100 expression was shown to b e mediated by a two-fold increase in the p100 transcription rate and a two-fold increase in p100 mRNA stability. Furthermore the p100 mediat ed upregulation was dependent on a tyrosine kinase dependent pathway r ather than the protein kinase C pathway. NF-kappa B is a complex of ei ther p50 homodimers or a p50/p65 heterodimer. The latter is known to s trongly autoregulate p100 transcription. We therefore examined the com position of NF-kappa B induced by LPS vs the different lymphokines. LP S-induced NF-kappa B showed a distinct p65 supershift whereas the comp osition of NF-kappa B induced by different lymphokines did not show a change in p65. We conclude that the p100 subunit of the transcription factor NF-kappa B is induced by different inflammatory mediators while lymphokines fail to induce p100 expression which may be caused by the induction of NF-kappa B predominantly consisting of p50 homodimers.