Epidermal growth factor regulates Mcl-1 expression through the MAPK-Elk-1 signalling pathway contributing to cell survival in breast cancer

Abstract

Myeloid cell leukaemia-1 (Mcl-1) is an anti-apoptotic member of the Bcl-2 family that is elevated in a variety of tumour types including breast cancer. In breast tumours, increased Mcl-1 expression correlates with high tumour grade and poor patient survival. We have previously demonstrated that Her-2 levels correspond to increased Mcl-1 expression in breast tumours. Epidermal growth factor (EGF) receptor signalling is frequently deregulated in breast cancer and leads to increased proliferation and survival. Herein, we determined the critical downstream signals responsible for the EGF mediated increase of Mcl-1 and their role in cell survival. We found that both Mcl-1 mRNA and protein levels are rapidly induced upon stimulation with EGF. Promoter analysis revealed that an Elk-1 transcription factor-binding site is critical for EGF activation of the Mcl-1 promoter. Furthermore, we found that knockdown of Elk-1or inhibition of the Erk signalling pathway was sufficient to block EGF upregulation of Mcl-1 and EGF mediated cell survival. Using chromatin immunoprecipitation and biotin labelled probes of the Mcl-1 promoter, we found that Elk-1 and serum response factor are bound to the promoter after EGF stimulation. To determine whether Mcl-1 confers a survival advantage, we found that knockdown of Mcl-1 expression increased apoptosis whereas overexpression of Mcl-1 inhibited drug induced cell death. In human breast tumours, we found a correlation between phosphorylated Elk-1 and Mcl-1 protein levels. These results indicate that the EGF induced activation of Elk-1 is an important mediator of Mcl-1 expression and cell survival and therefore a potential therapeutic target in breast cancer.

Bcl-2 family member Mcl-1 expression is reduced under hypoxia by the E3 ligase FBW7 contributing to BNIP3 induced cell death in glioma cells

“…EGF has been shown to increase Mcl-1 and block hypoxia induced cell death. 6 We showed that EGF treatment of cells transfected with BNIP3 expression vector (BNIP3) reduced the ability of BNIP3 in induce cell death (Fig. 8B).…”

“…4 At the transcriptional level, Mcl-1 is regulated by several transcription factors, including members of the STAT family and Elk-1. 4,6 Mcl-1 is also regulated at the translational level by several mechanisms controlling both caspase and proteasomal degradation. 4 Posttranslational modifications, such as phosphorylation and ubiquitination also allow for tight regulation of Mcl-1 stability and degradation.…”

“…6,8,17 We first treated HEK 293 cells with epidermal growth factor (EGF) for 24 hours under hypoxia. The amount of cell death was significantly reduced when EGF was present reducing cell death from 23% to 6% (Fig.…”

“…5 Mcl-1 is a downstream target of epidermal growth factor receptor (EGFR) activation in many different types of cancer, including GBM, through the activation of transcription factors including NFkB, Elk1 and Stat3. 6,7 In addition, Mcl-1 expression is regulated by hypoxia inducible factor 1 (HIF1) under hypoxia and over-expression of Mcl-1 has been shown to protect against hypoxia induced apoptosis. Unlike other Bcl-2 family members, Mcl-1 expression is tightly regulated by ubiquitination mediated degradation.…”

The anti-apoptotic protein MCL1, a novel target of lung cancer therapy

“…In lung cancer, activation of STAT3 and NF-κB are frequently observed and their roles have been analyzed experimentally [12][13][14][15][16] . Moreover, STAT3 and ELK-1 are activated by EGFR (epidermal growth factor receptor) 13,14 .…”