c-Rel Deficiency Increases Caspase-4 Expression and Leads to ER Stress and Necrosis in EBV-Transformed Cells

Abstract

LMP1-mediated activation of nuclear factor of kappaB (NF-κB) is critical for the ligand independent proliferation and cell survival of in vitro EBV-transformed lymphoblastoid cell lines (LCLs). Previous experiments revealed that a majority of LMP1-dependent responses are regulated by NF-κB. However, the extent that individual NF-κB family members are required for these responses, in particular, c-Rel, whose expression is restricted to mature hematopoietic cells, remains unclear. Here we report that low c-Rel expression in LCLs derived from a patient with hyper-IgM syndrome (Pt1), resulted in defects in proliferation and cell survival. In contrast to studies that associated loss of NF-κB with increased apoptosis, Pt1 LCLs failed to initiate apoptosis and alternatively underwent autophagy and necrotic cell death. Whereas the proliferation defect appeared linked to a c-Rel-associated decrease in c-myc expression, identified pro-survival and pro-apoptotic targets were expressed at or near control levels consistent with the absence of apoptosis. Ultrastructural examination of Pt1 LCLs revealed a high level of cellular and ER stress that was further supported by gene expression profiling showing the upregulation of several genes involved in stress and inflammation. Apoptosis-independent cell death was accompanied by increased expression of the inflammatory marker, caspase-4. Using gene overexpression and siRNA knockdown we demonstrated that levels of c-Rel directly modulated expression of caspase-4 as well as other ER stress genes. Overall, these findings reveal the importance of c-Rel in maintaining LCL viability and that decreased expression results in ER stress and a default response leading to necrotic cell death.

A transcriptional signature associated with non-Hodgkin lymphoma in the blood of patients with Q fever

“…During EBV infection, REL and STAT3 have a potent effect on cell growth and in lymphomagenesis [26]. On the contrary, REL deficiency leads to decreased proliferation, decreased survival of EBV transformed cells and could even lead to their necrotic death [27]. In HTLV infection, REL proteins are involved in the canonical NF-κB pathway, which induces the transcription of anti-apoptotic BCL2A1 and BCL2L1 [28].…”

NF-κB Regulates Caspase-4 Expression and Sensitizes Neuroblastoma Cells to Fas-Induced Apoptosis

“…In our study, we also found that caspase-4 expression is NF-κB p65-dependent, as evidenced by increased caspase-4 expression in p65-overexpressing cells. Not uniquely, another NF-κB isoform, c-Rel, was also found to be associated with caspase-4 expression in EBV-transformed cells [ 40 ]. However, the authors demonstrated that c-Rel negatively modulates the expression of caspase-4.…”

HTLV-1 Tax deregulates autophagy by recruiting autophagic molecules into lipid raft microdomains

“…Similarly, the viral LMP1 protein from EBV associates with the lipid raft microdomains to activate NF-κB, and it also induces autophagy 33,60 . However it is currently not clear if the lipid raft microdomain is involved in the LMP1-mediated autophagic process.…”

“…Our study demonstrated that Tax-deregulated autophagy was involved in the lipid raft recruitment of the autophagic molecular complex containing Beclin1 and Bif-1 and that this action was also dependent on the activity of IκB kinases. Similarly, the viral LMP1 protein from EBV associates with the lipid raft microdomains to activate NF-κB, and it also induces autophagy 33 , 60 . However it is currently not clear if the lipid raft microdomain is involved in the LMP1-mediated autophagic process.…”