NF-κB regulator IκBNS in macrophages and diffuse large B cell lymphomas

Abstract

Innate immunity is one of our first lines of defense of the organism against invading pathogens. One cell type of the innate immune system consists of macrophages, which recognize a highly conserved set of structures on pathogens by specific receptors and initialize the unspecific and specific immune response by secreting signaling molecules with pro-inflammatory and chemotactic effects. A key signaling mediator of the primary immune response is the transcription factor NF-κB. NF-κB proteins are sequestered by classical IκB proteins in the cytoplasm of resting cells, but are released after cellular activation and degradation of the IκB. NF-κB is also regulated by atypical IκB proteins that can only be found in the nucleus of activated cells. One member of this atypical IκB protein family is IκBNS, which is the main focus here. This project aimed to elucidate the effect of IκBNS on the differentiation and activation of human macrophages, on macrophages infected with HIV and on DLBCL. Since two isoforms of IκBNS exist, the effect of overexpression of each isoform was analyzed to uncover specific functions of these isoforms. The analyses showed a conserved function of IκBNS in murine and human cells. Moreover, IκBNS isoform 1 and 2 showed marked different effects on macrophage activation. While IκBNS isoform 1 mainly showed a suppressing effect, isoform 2 showed suppressing as well as activating effects on the expression of pro-inflammatory factors. Overexpression of IκBNS isoforms 1 and 2 resulted in a shift from macrophage to dendritic cell phenotype. During HIV expression, overexpression of IκBNS isoform 1 resulted in reduced expression of antiviral factors, while overexpression of IκBNS isoform 2 showed no significant effects. In ABC DLBCL, no IκBNS-deficient cell line could be established, suggesting a crucial effect of IκBNS on DLBCL survival and growth. This was confirmed in on the transcriptional level for IκBNS isoform 1. In summary, IκBNS isoforms 1 showed no activating effect or even a suppressive effect on target gene expression, while IκBNS isoform 2 overexpression showed a strong activation of chemotactic chemokines and type I interferons in macrophages. In DLBCL, IκBNS isoform 1 overexpression resulted in a marked activation of chemotactic and angiogenetic chemokines and growth-promoting transcription factors, showing its importance in the development of negative prognostic factors.