TNF and Phorbol Esters Induce Lymphotoxin-β Expression through Distinct Pathways Involving Ets and NF-κB Family Members

Abstract

Lymphotoxin-β (LT-β) is a transmembrane protein expressed mainly on cells of the lymphoid lineage. It associates with LT-α on the cell surface to form the heterotrimeric LTα1,β2 complex, which binds the LT-β receptor. Membrane lymphotoxin is a crucial signal for the appropriate development of lymph nodes and Peyer’s patches, and in the formation of B and T cell compartments in the spleen. In this study we report the characterization of mechanisms governing both basal as well as PMA- and TNF-inducible regulation of the human LT-β promoter. Using a Jurkat T cell line, induction with either PMA or TNF resulted in an increase in mRNA levels compared with uninduced values. This induction corresponded to an increase in transcriptional activity of the human LT-β promoter. Mutational and deletion analysis demonstrated the importance of Ets and NF-κB motifs in the regulation of basal transcription. Furthermore, the ability of PMA to induce activity was lost in the Ets mutant constructs. Interestingly, the same mutation had little effect on the ability of TNF to induce transcription of the LT-β promoter. TNF inducibility was localized to the NF-κB site positioned at −83 of the promoter sequence. Thus, it appears that the Ets site, although playing a major role in PMA induction, did not mediate TNF inducibility. Therefore, our study suggests that alternative signaling pathways may be present to induce the expression of LT-β in response to different immunological or inflammatory stimuli.