THE MUTANT PLASMACYTOMA CELL-LINE S107 ALLOWS THE IDENTIFICATION OF DISTINCT PATHWAYS LEADING TO NF-KB ACTIVATION

Studies on the mechanisms of inducible and constitutive activity of NF -kappa B transcription factors have been hampered by the lack of appro priate mutant cell lines. We have analyzed the defect in the murine S1 07 plasmacytoma cell line, which was previously found to lack both con stitutive and inducible NF-kappa B activity. Our analysis shows that t hese cells bear a specific defect that interferes with NF-kappa B indu ction by many diverse stimuli, such as lipopolysaccharide, phorbol 12- myristate 13-acetate, UV light, x-rays, and H2O2. This does not howeve r represent a general signal transduction defect, because AP-1 transcr iption factors are readily induced by the same stimuli. Phosphatase in hibitors such as okadaic acid as well as calyculin A can efficiently i nduce NF-kappa B in S107 cells via a pathway apparently insensitive to the radical scavenger pyrrolidine dithiocarbamate. Furthermore, MEKK1 a protein kinase supposedly induced by some of the above stimuli, is also capable of activating NF-kappa B. Interestingly, both the potent physiological inducer of NF-kappa B TNF alpha as well as endoplasmic r eticulum overload can induce NF-kappa B via a PDTC sensitive pathway. In all cases, DNA-binding NF-kappa B complexes are comprised predomina ntly of p50-RelA heterodimers, and NF-kappa B activation results in th e induction of transiently transfected or resident reporter genes. In summary, these results suggest that the pathways for many NF-kappa B-i nducing stimuli converge at a specific junction, and this pivotal step is mutated in the S107 cell line. Yet there are alternative routes by passing this critical step that also lead to NF-kappa B induction. The se routes utilized by tumor necrosis factor alpha and endoplasmic reti culum overload are still intact in this cell line.