Involvement of net and Hif1alpha in distinct yet intricately linked hypoxia-induced signaling pathways

ELK3 Targeting AEG1 Promotes Migration and Invasion of Ovarian Cancer Cells under Hypoxia

Ovarian cancer (OC) is one of the most common tumors in female reproductive organs with a five-year survival rate of less than 45%. Metastasis is a crucial contributor to OC development. ETS transcription factor (ELK3), as a transcriptional factor, have been involved in multiple tumor development. However, its role in OC remains elusive. In this study, we observed high expression of ELK3 and AEG1 in human OC tissues. OVCAR-3 and SKOV3 cells were treated with hypoxia to mimic tumor microenvironment in vivo. We found that the expression of ELK3 was significantly increased in cells under hypoxia compared with normoxia. ELK3 knockdown inhibited cell migration and invasion abilities under hypoxia. Moreover, ELK3 knockdown decreased β-catenin expression and inhibited the activation of Wnt/β-catenin pathway in SKOV3 cells under hypoxia. Astrocyte-elevated gene-1 (AEG1) has been reported to promote OC progression. Our results showed that the mRNA level of AEG1 was decreased when ELK3 knockdown under hypoxia. Dural luciferase assay confirmed that ELK3 bound to gene AEG1 promoter (-2005-+15) and enhanced its transcriptional activity under hypoxia. Overexpression of AEG1 increased the migration and invasion abilities of SKOV3 cell with ELK3 knockdown. In the absence of ELK3, the activation of β-catenin was recovered by AEG1 overexpression. To sum up, we conclude that ELK3 promotes AEG1 expression by binding to its promoter. ELK3 could promote migration and invasion of OC cells by targeting AEG1, which provides a potential basis for therapeutic approaches to OC.

LRG1 Promotes Keratinocyte Migration and Wound Repair through Regulation of HIF-1α Stability

Re-epithelialization is a complex process during skin wound healing, and cell migration is an integral part of this phenomenon. Here we identified a role for LRG1 as a key regulator of epidermal keratinocyte migration where LRG1 acts via enhancement of HIF-1α stability. We showed that LRG1 is upregulated at murine skin wound edges and that addition of recombinant human LRG1 accelerates keratinocyte migration and skin wound healing. Furthermore, we identified transcription factor ELK3 as a downstream effector of LRG1. We confirmed that elevated ELK3 levels manipulated by LRG1 can promote cell migration through upregulation of HIF-1α stability. Because hyperglycemia complicatedly affects HIF-1α stability and activation, our findings provide insights into the molecular controls of wound-associated cell migration and identify potential therapeutic targets for the treatment of chronic diabetic wounds. In conclusion, we demonstrated that LRG1 promotes wound repair through keratinocyte migration and is important for normalization of an abnormal process of diabetic wound healing where HIF-1α stability is insufficient.

XRP44X, an Inhibitor of Ras/Erk Activation of the Transcription Factor Elk3, Inhibits Tumour Growth and Metastasis in Mice

Transcription factors have an important role in cancer but are difficult targets for the development of tumour therapies. These factors include the Ets family, and in this study Elk3 that is activated by Ras oncogene /Erk signalling, and is involved in angiogenesis, malignant progression and epithelial-mesenchymal type processes. We previously described the identification and in-vitro characterisation of an inhibitor of Ras / Erk activation of Elk3 that also affects microtubules, XRP44X. We now report an initial characterisation of the effects of XRP44X in-vivo on tumour growth and metastasis in three preclinical models mouse models, subcutaneous xenografts, intra-cardiac injection-bone metastasis and the TRAMP transgenic mouse model of prostate cancer progression. XRP44X inhibits tumour growth and metastasis, with limited toxicity. Tumours from XRP44X-treated animals have decreased expression of genes containing Elk3-like binding motifs in their promoters, Elk3 protein and phosphorylated Elk3, suggesting that perhaps XRP44X acts in part by inhibiting the activity of Elk3. Further studies are now warranted to develop XRP44X for tumour therapy.

The oncogenic MicroRNA Hsa-miR-155-5p targets the transcription factor ELK3 and links it to the hypoxia response

The molecular response to hypoxia is a critical cellular process implicated in cancer, and a target for drug development. The activity of the major player, HIF1α, is regulated at different levels by various factors, including the transcription factor ELK3. The molecular mechanisms of this intimate connection remain largely unknown. Whilst investigating global ELK3-chromatin interactions, we uncovered an unexpected connection that involves the microRNA hsa-miR-155-5p, a hypoxia-inducible oncomir that targets HIF1α. One of the ELK3 chromatin binding sites, detected by Chromatin Immuno-Precipitation Sequencing (ChIP-seq) of normal Human Umbilical Vein Endothelial Cells (HUVEC), is located at the transcription start site of the MIR155HG genes that expresses hsa-miR-155-5p. We confirmed that ELK3 binds to this promoter by ChIP and quantitative polymerase chain reaction (QPCR). We showed that ELK3 and hsa-miR-155-5p form a double-negative regulatory loop, in that ELK3 depletion induced hsa-miR-155-5p expression and hsa-miR-155-5p expression decreased ELK3 expression at the RNA level through a conserved target sequence in its 3'-UTR. We further showed that the activities of hsa-miR-155-5p and ELK3 are functionally linked. Pathway analysis indicates that both factors are implicated in related processes, including cancer and angiogenesis. Hsa-miR-155-5p expression and ELK3 depletion have similar effects on expression of known ELK3 target genes, and on in-vitro angiogenesis and wound closure. Bioinformatic analysis of cancer RNA-seq data shows that hsa-miR-155-5p and ELK3 expression are significantly anti-correlated, as would be expected from hsa-miR-155-5p targeting ELK3 RNA. Finally, hypoxia (0% oxygen) down-regulates ELK3 mRNA in a microRNA and hsa-miR-155-5p dependent manner. These results tie ELK3 into the hypoxia response pathway through an oncogenic microRNA and into a circuit implicated in the dynamics of the hypoxic response. This crosstalk could be important for the development of new treatments for a range of pathologies.

Robust coordination of cardiac functions from gene co-expression reveals a versatile combinatorial transcriptional control

The necessary overall coordination of cardiac cellular functions is little known at the mRNA level. Focusing on energy production and cardiac contraction, we analyzed microarray data from heart tissue obtained in groups of mice and rats in normal conditions and with a left ventricular dysfunction. In each group and for each function, we identified genes positively or negatively correlated with numerous genes of the function, which were called coordinated or inversely coordinated with the function. The genes coordinated with energy production or cardiac contraction showed the coupling of these functions in all groups. Among coordinated or inversely coordinated genes common to the two functions, we proposed a fair number of transcriptional regulators as potential determinants of the energy production and cardiac contraction coupling. Although this coupling was constant across the groups and unveiled a stable gene core, the combinations of transcriptional regulators were very different between the groups, including one half that has never been linked to heart function. These results highlighted the stable coordination of energy production or cardiac contraction at the mRNA level, and the combinatorial and versatile nature of potential transcriptional regulation. In addition, this work unveiled new transcriptional regulators potentially involved in normal or altered cardiac functional coupling.

Crosstalk between Mdm2, p53 and HIF1-α: distinct responses to oxygen stress and implications for tumour hypoxia

The E3 ubiquitin ligase Mdm2 regulates two transcription factors, p53 and HIF1α, which appear to be tailored towards different and specific roles within the cell, the DNA damage and hypoxia responses, respectively. However, evidence increasingly points towards the interplay between these factors being crucial for the regulation of cellular metabolism and survival in times of oxygen stress, which has particular relevance for tumour formation. Mdm2, p53 and HIF1α all respond to hypoxia, and intriguingly, have distinct roles depending on the level of hypoxia. The data from numerous studies across different conditions hint at the interplay between these key factors in cellular homeostasis. Here we try to weave these strands together, to create a picture of the complex tapestry of interactions that demonstrates the importance of the crosstalk between these key regulatory proteins during hypoxia.