Early Growth Response 3 regulates genes of inflammation and directly activates IL6 and IL8 expression in prostate cancer.

BACKGROUND: Transcription factor EGR3 (Early Growth Response 3) is a little-studied member of the EGR family that is highly expressed in human prostate tumours compared with normal tissue. Its function in prostate cancer, however, is unknown. METHODS: Stable shRNA silencing was achieved in naturally overexpressing prostate cancer cells, followed by Affymetrix expression analysis. Fold changes of ⩾2 and ⩽-2 were considered valid and t-tests P-values of ⩽0.01 were considered statistically significant. Potential EGR3 target genes were validated by real-time qPCR, chromatin immunoprecipitation, and gain-of-function experiments. Promoter analysis confirmed the presence of consensus binding sites in the promoters of target genes. RESULTS: Early Growth Response 3 regulates the expression of ∼330 genes, 35% of which are involved in immune responses and inflammatory processes, and 15% crosstalk with the NF-κB signalling pathway. In particular, EGR3 induces the expression of over 50 secreted cytokines, growth factors, and matrix remodelling factors. Two interleukins of great relevance to prostate cancer, IL6 and IL8, were further validated as EGR3 target genes: both promoters contain EGR consensus binding sites and are pulled down in intact cells by EGR3 chromatin immunoprecipitation. Silencing of EGR3 decreased IL6 and IL8 expression, whereas overexpression of EGR3 in nontransformed cells induced IL6 and IL8 expression. CONCLUSIONS: Chronic inflammation plays a critical role in prostate cancer and elevated production of pro-inflammatory cytokines IL8 and IL6, in particular, contributes to disease progression and to the onset of castration resistance. It is shown for the first time that EGR3 is involved in the upregulation of both IL6 and IL8. Together with our previous observation that EGR3 is highly expressed in prostate tumours compared with normal tissue and strongly correlates with IL6 and IL8 expression in clinical samples, the present study suggests that EGR3 promotes excessive production of IL6 and IL8 observed during the progression of prostate cancer.

Mutant p53 initiates a feedback loop that involves Egr-1/EGF receptor/ERK in prostate cancer cells.

Early growth response-1 (Egr-1) is overexpressed in human prostate tumors and contributes to cancer progression. On the other hand, mutation of p53 is associated with advanced prostate cancer, as well as with metastasis and hormone independence. This study shows that in prostate cell lines in culture, Egr-1 overexpression correlated with an alteration of p53 activity because of the expression of SV40 large T-antigen or because of a mutation in the TP53 gene. In cells containing altered p53 activity, Egr-1 expression was abolished by pharmacological inhibition or RNAi silencing of p53. Although forced expression of wild-type p53 was not sufficient to trigger Egr-1 transcription, four different mutants of p53 were shown to induce Egr-1. Direct binding of p53 to the EGR1 promoter could not be detected. Instead, Egr-1 transcription was driven by the ERK1/2 pathway, as it was abrogated by specific inhibitors of MEK. Egr-1 increased the transcription of HB-EGF (epidermal growth factor), amphiregulin and epiregulin, resulting in autocrine activation of the EGF receptor (EGFR) and downstream MEK/ERK cascade. Thus, mutant p53 initiates a feedback loop that involves ERK1/2-mediated transactivation of Egr-1, which in turn increases the secretion of EGFR ligands and stimulates the EGFR signaling pathway. Finally, p53 may further regulate this feedback loop by altering the level of EGFR expression.