Early growth response-1 is a regulator of DR5-induced apoptosis in colon cancer cells

Abstract

BACKGROUND: Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) induces tumour cell apoptosis by binding to death receptor 4 (DR4) and DR5. DR4 and DR5 activation however can also induce inflammatory and pro-survival signalling. It is not known how these different cellular responses are regulated and what the individual role of DR4 vs DR5 is in these processes. METHODS: DNA microarray study was carried out to identify genes differentially expressed after DR4 and DR5 activation. RT -PCR and western blotting was used to examine the expression of early growth response gene-1 (Egr-1) and the proteins of the TRAIL signalling pathway. The function of Egr-1 was studied by siRNA-mediated knockdown and overexpression of a dominant-negative version of Egr-1. RESULTS: We show that the immediate early gene, Egr-1, regulates TRAIL sensitivity. Egr-1 is constitutively expressed in colon cancer cells and further induced upon activation of DR4 or DR5. Our results also show that DR4 mediates a type II, mitochondriondependent apoptotic pathway, whereas DR5 induces a mitochondrion-independent, type I apoptosis in HCT15 colon carcinoma cells. Egr-1 drives c-FLIP expression and the short splice variant of c-FLIP (c-FLIP S ) specifically inhibits DR5 activation. CONCLUSION: Selective knockdown of c-FLIP S sensitises cells to DR5-induced but not DR4-induced apoptosis and Egr-1 exerts an effect as an inhibitor of the DR5-induced apoptotic pathway, possibly by regulating the expression of c-FLIP S .

Egr1 Expression Is Induced Following Glatiramer Acetate Immunotherapy in Rodent Models of Glaucoma and Alzheimer's Disease

“…This increase was still apparent 1 month after the last GA administration, occurring most notably in proliferating Ki67-positive and DCX-positive newly formed hippocampal neurons. Protein analysis by Western blot, showing products of various size as previously reported by others, [112][113][114][115] suggested that EGR1 may undergo posttranslational modifications to differentially regulate downstream genes. It is possible that EGR1 forms a multimeric complex with other transcription factors to finely modulate important cellular responses.…”

Suppression of dual-specificity phosphatase–2 by hypoxia increases chemoresistance and malignancy in human cancer cells

“…Aberrant expression of genes with functions in drug response, angiogenesis, apoptosis, and cell survival, to name a few, often contributes notably to the acquisition of drug resistance. EGR-1, an important transcription factor that increases cell survival, is overexpressed in a majority of human cancers and contributes to tumorigenesis (18,41,42). Overexpression of MDR-1 in cancer cells increases cellular drug efflux and causes resistance to multiple drugs (43).…”

Decoy receptors block TRAIL sensitivity at a supracellular level: the role of stromal cells in controlling tumour TRAIL sensitivity

“…20 MTT cell viability assay Cell viability was determined using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) viability assay as described before. 41 TRAIL receptor immunocytochemistry Expression level of DR4, DR5, DcR1 and DcR2 on the surface of hFB were determined using immunofluorescence coupled with flow cytometry as described before. 42 Cloning, expression and purification of TRAIL variants and receptor-binding studies with SPR Cloning, expression and purification of TRAIL variants, as well as the SPR measurements have been carried out as as described previously.…”