ZBTB2 links p53 deficiency to HIF-1-mediated hypoxia signaling to promote cancer aggressiveness

DDX5 enhances HIF-1 activity by promoting the interaction of HIF-1α with HIF-1β and recruiting the resulting heterodimer to its target gene loci

BACKGROUND INFORMATION

Cancer cells acquire malignant characteristics and therapy resistance by employing the hypoxia-inducible factor 1 (HIF-1)-dependent adaptive response to hypoxic microenvironment in solid tumors. Since the underlying molecular mechanisms remain unclear, difficulties are associated with establishing effective therapeutic strategies.

RESULTS

We herein identified DEAD-box helicase 5 (DDX5) as a novel activator of HIF-1 and found that it enhanced the heterodimer formation of HIF-1α and HIF-1β and facilitated the recruitment of the resulting HIF-1 to its recognition sequence, hypoxia-response element (HRE), leading to the expression of a subset of cancer-related genes under hypoxia.

CONCLUSIONS

This study reveals that the regulation of HIF-1 recruitment to HRE is an important regulatory step in the control of HIF-1 activity.

SIGNIFICANCE

The present study provides novel insights for the development of strategies to inhibit the HIF-1-dependent expression of cancer-related genes.

Cellular signaling in the hypoxic cancer microenvironment: Implications for drug resistance and therapeutic targeting

The rewiring of cellular metabolism is a defining characteristic of cancer, as tumor cells adapt to acquire essential nutrients from a nutrient-poor environment to sustain their viability and biomass. While hypoxia has been identified as a major factor depriving cancer cells of nutrients, recent studies have revealed that cancer cells distant from supporting blood vessels also face nutrient limitations. To overcome this challenge, hypoxic cancer cells, which heavily rely on glucose as an energy source, employ alternative pathways such as glycogen metabolism and reductive carboxylation of glutamine to meet their energy requirements for survival. Our preliminary studies, alongside others in the field, have shown that under glucose-deficient conditions, hypoxic cells can utilize mannose and maltose as alternative energy sources. This review aims to comprehensively examine the hypoxic cancer microenvironment, its association with drug resistance, and potential therapeutic strategies for targeting this unique niche. Furthermore, we will critically evaluate the current literature on hypoxic cancer microenvironments and explore state-of-the-art techniques used to analyze alternate carbohydrates, specifically mannose and maltose, in complex biological fluids. We will also propose the most effective analytical methods for quantifying mannose and maltose in such biological samples. By gaining a deeper understanding of the hypoxic cancer cell microenvironment and its role in drug resistance, novel therapeutic approaches can be developed to exploit this knowledge.

ZBTB2 is recruited to a specific subset of HIF-1 target loci to facilitate full gene expression under hypoxia

The cellular response to hypoxia is mainly governed by a transcription factor, hypoxia-inducible factor 1 (HIF-1). Although upregulation of HIF-1 target genes has been hypothesized to require interaction of HIF-1 with other coactivators, much remains to be elucidated regarding the underlying mechanisms. Here, we demonstrate that zinc finger and BTB domain-containing protein 2 (ZBTB2) enhances the expression of certain HIF-1 target genes under hypoxia. ChIP-Seq analysis showed that there is a subset of HIF-1 target genes with overlapping HIF-1 and ZBTB2 peaks. Examination of a representative gene, EGFR antisense RNA 1 (EGFR-AS1), showed that HIF-1 binding to the consensus hypoxia-responsive element (HRE) sequence resulted in the recruitment of ZBTB2 to the gene locus and increased p300-mediated histone acetylation, leading to enhanced gene expression under hypoxia. In contrast, expression of HIF-1 target genes lacking ZBTB2 peaks, such as carbonic anhydrase 9 (CA9), was not upregulated by ZBTB2. These findings demonstrate that ZBTB2 is a novel factor that can be recruited to the vicinity of HREs on a subset of HIF-1 target gene loci, and is required for their full expression under hypoxia.