Constitutive Expression Of NF-kappaB Research Articles

Expression of NF-kappaB in hRPE cells stimulated by PDTC and IL-1beta.

The constitutive expression of nuclear-factor-kappaB (NF-kappaB) in human pigment epithelial (hRPE) cells cultivated in vitro and the possible changes when incubated with PDTC and IL-1beta were investigated. The synchronized hRPE cells in vitro were divided into two groups. In non-PDTC group, hRPE cells were exposed respectively to IL-1beta and NS (for detecting the constitutive expressions of NF-kappaB in hRPE cells); In PDTC group, PDTC-pretreated hRPE cells were exposed respectively to IL-1beta and NS (for detecting the constitutive expression of NF-kappaB in PDTC-pretreated hRPE cells). The expression of NF-kappaB in hRPE cells in two groups was detected by immunofluorescence stain and flow cytometry. The results showed that the constitutive expression of NF-kappaB in hRPE cells in vitro was 8.05%, and increased to 30.26% by IL-1beta. After PDTC pretreatment, the constitutive expression of NF-kappaB in hRPE cells was decreased to 3.74%, and 3.66% by IL-1beta respectively. It was concluded that the expressions of NF-kappaB in hRPE cells could be increased significantly by IL-1beta and depressed effectively by PDTC. Also, PDTC could significantly inhibit the activation of NF-kappaB induced by IL-1beta.

Chemopreventive Agents Induce Suppression of Nuclear Factor‐κB Leading to Chemosensitization

Nuclear factor-kappaB (NF-kappaB), a transcription factor, is present normally in the cytoplasm as an inactive heterotrimer consisting of p50, p65, and IkappaBalpha subunits. When activated, NF-kappaB translocates to the nucleus as a p50-p65 heterodimer. This factor regulates the expression of various genes that control apoptosis, viral replication, tumorigenesis, various autoimmune diseases, and inflammation. NF-kappaB has been linked to the development of carcinogenesis for several reasons. First, various carcinogens and tumor promoters have been shown to activate NF-kappaB. Second, activation of NF-kappaB has been shown to block apoptosis and promote proliferation. Third, the tumor microenvironment can induce NF-kappaB activation. Fourth, constitutive expression of NF-kappaB is frequently found in tumor cells. Fifth, NF-kappaB activation induces resistance to chemotherapeutic agents. Sixth, several genes involved in tumor initiation, promotion, and metastasis are regulated by NF-kappaB. Seventh, various chemopreventive agents have been found to down-regulate the NF-kappaB activation. All these observation suggest that NF-kappaB could mediate tumorigenesis and thus can be used as a target for chemoprevention and for the treatment of cancer. Agents that suppress NF-kappaB activation can suppress the expression of genes involved in carcinogenesis and tumorigenesis in vivo.

Defective IkappaBalpha in Hodgkin cell lines with constitutively active NF-kappaB.

The molecular mechanisms underlying Hodgkin's disease remain obscure, but it has been recognized that the neoplastic cells display high levels of constitutively active nuclear NF-kappaB. Here we demonstrate that although nuclear NF-kappaB is transcriptionally active, the Hodgkin cells fail to activate NF-kappaB dependent transcription in response to CD40 ligand. In three Hodgkin cell lines examined each had abnormalities in expression of IkappaBalpha which could account for the deregulated NF-kappaB. Although all three cell lines had greater than normal levels of IkappaBalpha mRNA no IkappaBalpha protein could be detected in the KM-H2 cells, while the L428 cell line contains a C-terminally truncated IkappaBalpha species that fails to associate with NF-kappaB. The HDLM-2 cell line contains a more slowly migrating form of IkappaBalpha that can associate with NF-kappaB, but increasing the level of this protein within the cell fails to inhibit nuclear NF-kappaB. Addition of recombinant IkappaBalpha to nuclear extracts from all three cell lines resulted in complete inhibition of NF-kappaB DNA binding activity and introduction of a plasmid expressing IkappaBalpha into the cells inhibited the transcriptional activity of an NF-kappaB dependent reporter plasmid. Thus the constitutive expression of NF-kappaB in Hodgkin cells is a direct consequence of the abnormal expression of IkappaBalpha rather than changes in NF-kappaB that render it refractory to inhibition by IkappaB proteins. These changes could, at least in part, account for the characteristic activated phenotype of Hodgkin cells and their pattern of cytokine secretion, which determine the pathological appearance and clinical manifestations of Hodgkin's disease.

Constitutive expression of p50 homodimer in freshly isolated human monocytes decreases with in vitro and in vivo differentiation: a possible mechanism influencing human immunodeficiency virus replication in monocytes and mature macrophages.

Human immunodeficiency virus type 1 (HIV-1) replicates more efficiently in vitro in differentiated macrophages than in freshly isolated monocytes. We investigated whether this may be partly explained by changes in expression of NF-kappaB with monocyte differentiation. We demonstrated that constitutive expression of NF-kappaB in primary human monocytes changed significantly with differentiation in vitro to monocyte-derived macrophages (MDMs) and differentiation in vivo to alveolar macrophages (AMs). Freshly isolated monocytes constitutively expressed high levels of transcriptionally inactive p50 homodimer which decreased with time in culture in favor of the transcriptionally active p50/p65 and p50/RelB heterodimers. As in MDMs, AMs constitutively expressed p50/p65 and p50/RelB although at lower levels. HIV infection of fresh monocytes failed to induce p50/p65 as seen in MDMs. The replacement of p50 homodimers with transcriptionally active heterodimers following time in culture may partially explain the progressive increase in susceptibility of monocytes to HIV infection during in vitro culture. The change in NF-kappaB components with monocyte differentiation in vivo may also explain the different transcriptional activities of these cell populations in HIV-infected individuals.