Abnormal κB-binding protein in the cytoplasm of a plasmacytoma cell line that lacks nuclear expression of NF-κB

The transcription factor NF-κB appears to play an important role in immunoglobulin gene expression and lymphokine production, and may play a role in primary B cell activation. Constitutive nuclear expression of NF-κB has been found in all mature B cell lines with the notable exception of the murine plasmacytoma, S107. We report herein that S107 cells express cytoplasmic κB-binding material detected by electrophoretic mobility shift assay that by several criteria represents authentic NF-κB. Despite the presence of cytoplasmic NF-κB, several stimuli known to induce nuclear translocation of NF-κB failed to do so in S107 cells, including: the PKC agonist, PMA; the protein synthesis inhibitor, cycloheximide; and LPS. Transfection of S107 cells with a κB-CAT reporter gene construct confirmed the absence of functional activity. Importantly, a global failure of nuclear transcription factor expression was ruled out by the ability of PMA to induce nuclear expression of another trans -acting factor, AP-1. Thus, rather than lacking NF-κB altogether, S107 cells manifest disordered regulation of NF-κB in which cytoplasmic material is incapable of translocation to the nucleus. While Northern analysis failed to reveal a gross defect in the mRNA coding for the DNA binding subunit of NF-κB, UV-photo-cross-linking followed by denaturing gel electrophoresis demonstrated the presence of a cytoplasmic κB-binding protein of abnormally elevated molecular size. This finding suggests that the abnormal regulation of NF-κ B in S107 cells is associated with the appearance of an unusual κB-binding molecule.