Complementation between two cell lines lacking kappa enhancer activity: implications for the developmental control of immunoglobulin transcription.

Plasmacytoma S107 and the pre-B cell line 3-1 both lack immunoglobulin kappa (Ig kappa) enhancer activity due to the absence of the active form of a trans-acting nuclear factor, NF-kappa B, which binds to and activates the kappa enhancer. Pre-B cells possess the factor in a masked form and can activate it by a post-translational mechanism after treatment with specific inducing agents. In the experiments presented here somatic cell hybrids were used to determine whether S107 cells also possess NF-kappa B in a masked form, or alternatively, whether they possess the activation system but lack the factor. We observed that hybrids between S107 and pre-B cells produce the active form of NF-kappa B and exhibit transcriptional activation of previously silent kappa loci. These results demonstrate that S107 cells totally lack factor NF-kappa B but not the ability to activate it. Treatment of the hybrid cells with bacterial lipopolysaccharide (LPS), increases the NF-kappa B titer 4- to 5-fold and causes a concomitant 4- to 5-fold increase in kappa enhancer activity within these cells. However, the expression of the activated kappa loci remains unchanged after LPS-treatment, indicating that they are no longer under the control of the kappa enhancer. Therefore, a two-step transcriptional process occurs in these cells. First, the silent kappa loci are activated by the production of factor NF-kappa B. Subsequently, a second transcriptional mechanism overrides the dependence on the kappa enhancer and maintains kappa transcription at a constant level regardless of the level of kappa enhancer activity within the cell.(ABSTRACT TRUNCATED AT 250 WORDS)