Tumor-Derived Factors and Reduced p53 Promote Endothelial Cell Centrosome Over-Duplication

Tumour hypoxia in driving genomic instability and tumour evolution

Intratumour hypoxia is a feature of all heterogenous solid tumours. Increased levels or subregions of tumour hypoxia are associated with an adverse clinical prognosis, particularly when this co-occurs with genomic instability. Experimental evidence points to the acquisition of DNA and chromosomal alterations in proliferating hypoxic cells secondary to inhibition of DNA repair pathways such as homologous recombination, base excision repair and mismatch repair. Cell adaptation and selection in repair-deficient cells give rise to a model whereby novel single-nucleotide mutations, structural variants and copy number alterations coexist with altered mitotic control to drive chromosomal instability and aneuploidy. Whole-genome sequencing studies support the concept that hypoxia is a critical microenvironmental cofactor alongside the driver mutations in MYC, BCL2, TP53 and PTEN in determining clonal and subclonal evolution in multiple tumour types. We propose that the hypoxic tumour microenvironment selects for unstable tumour clones which survive, propagate and metastasize under reduced immune surveillance. These aggressive features of hypoxic tumour cells underpin resistance to local and systemic therapies and unfavourable outcomes for patients with cancer. Possible ways to counter the effects of hypoxia to block tumour evolution and improve treatment outcomes are described.

The Endothelial Centrosome: Specific Features and Functional Significance for Endothelial Cell Activity and Barrier Maintenance

This review summarizes information about the specific features that are characteristic of the centrosome and its relationship with the cell function of highly specialized cells, such as endotheliocytes. It is based on data from other researchers and our own long-term experience. The participation of the centrosome in the functional activity of these cells, including its involvement in the performance of the main barrier function of the endothelium, is discussed. According to modern concepts, the centrosome is a multifunctional complex and an integral element of a living cell; the functions of which are not limited only to the ability to polymerize microtubules. The location of the centrosome near the center of the interphase cell, the concentration of various regulatory proteins in it, the organization of the centrosome radial system of microtubules through which intracellular transport is carried out by motor proteins and the involvement of the centrosome in the process of the perception of the external signals and their transmission make this cellular structure a universal regulatory and distribution center, controlling the entire dynamic morphology of an animal cell. Drawing from modern data on the tissue-specific features of the centrosome's structure, we discuss the direct involvement of the centrosome in the performance of functions by specialized cells.

Hypoxia Drives Centrosome Amplification in Cancer Cells via HIF1α-dependent Induction of Polo-Like Kinase 4

Centrosome amplification (CA) has been implicated in the progression of various cancer types. Although studies have shown that overexpression of PLK4 promotes CA, the effect of tumor microenvironment on polo-like kinase 4 (PLK4) regulation is understudied. The aim of this study was to examine the role of hypoxia in promoting CA via PLK4. We found that hypoxia induced CA via hypoxia-inducible factor-1α (HIF1α). We quantified the prevalence of CA in tumor cell lines and tissue sections from breast cancer, pancreatic ductal adenocarcinoma (PDAC), colorectal cancer, and prostate cancer and found that CA was prevalent in cells with increased HIF1α levels under normoxic conditions. HIF1α levels were correlated with the extent of CA and PLK4 expression in clinical samples. We analyzed the correlation between PLK4 and HIF1A mRNA levels in The Cancer Genome Atlas (TCGA) datasets to evaluate the role of PLK4 and HIF1α in breast cancer and PDAC prognosis. High HIF1A and PLK4 levels in patients with breast cancer and PDAC were associated with poor overall survival. We confirmed PLK4 as a transcriptional target of HIF1α and demonstrated that in PLK4 knockdown cells, hypoxia-mimicking agents did not affect CA and expression of CA-associated proteins, underscoring the necessity of PLK4 in HIF1α-related CA. To further dissect the HIF1α-PLK4 interplay, we used HIF1α-deficient cells overexpressing PLK4 and showed a significant increase in CA compared with HIF1α-deficient cells harboring wild-type PLK4. These findings suggest that HIF1α induces CA by directly upregulating PLK4 and could help us risk-stratify patients and design new therapies for CA-rich cancers.

IMPLICATIONS

Hypoxia drives CA in cancer cells by regulating expression of PLK4, uncovering a novel HIF1α/PLK4 axis.

A New Antitumor Direction: Tumor-Specific Endothelial Cells

Targeting tumor blood vessels is an important strategy for tumor therapies. At present, antiangiogenic drugs are known to have significant clinical effects, but severe drug resistance and side effects also occur. Therefore, new specific targets for tumor and new treatment methods must be developed. Tumor-specific endothelial cells (TECs) are the main targets of antiangiogenic therapy. This review summarizes the differences between TECs and normal endothelial cells, assesses the heterogeneity of TECs, compares tumorigenesis and development between TECs and normal endothelial cells, and explains the interaction between TECs and the tumor microenvironment. A full and in-depth understanding of TECs may provide new insights for specific antitumor angiogenesis therapies.

A Genome-Wide Analysis of the Gene Expression and Alternative Splicing Events in a Whole-Body Hypoxic Preconditioning Mouse Model

Exposure to specific doses of hypoxia can trigger endogenous neuroprotective and neuroplastic mechanisms of the central nervous system. These molecular mechanisms, together referred to as hypoxic preconditioning (HPC), remain poorly understood. In the present study, we applied RNA sequencing and bioinformatics analyses to study HPC in a whole-body HPC mouse model. The preconditioned (H4) and control (H0) groups showed 605 differentially expressed genes (DEGs), of which 263 were upregulated and 342 were downregulated. Gene Ontology enrichment analysis indicated that these DEGs were enriched in several biological processes, including metabolic stress and angiogenesis. The Kyoto Encyclopedia of Genes and Genomes enrichment analysis showed that the FOXO and Notch signaling pathways were involved in hypoxic tolerance and protection during HPC. Furthermore, 117 differential alternative splicing events (DASEs) were identified, with exon skipping being the dominant one (48.51%). Repeated exposure to systemic hypoxia promoted skipping of exon 7 in Edrf1 and exon 9 or 13 in Lrrc45. This study expands the understanding of the endogenous protective mechanisms of HPC and the DASEs that occur during HPC.

Spotlighting the hypoxia-centrosome amplification axis

The abysmal success rate of anticancer drugs in clinical trials, is in part, attributable to discordance between cultured cancer cells and patient tumors. While tumors in vivo, display a lower mitotic index, patient tumors portray much higher centrosomal aberrations, relative to in vitro cultured cells. The microenvironment too differs considerably between the in vitro and in vivo scenarios. Notably, another hallmark of cancer, hypoxia, is not recapitulated in cell lines cultured under normoxic conditions. These observations raise the possibility that hypoxia may be the missing link that explains the discordance between cell biological phenomena in vitro versus physiological conditions. Further, the interplay between hypoxia and centrosome amplification (CA) is relatively understudied. Recent research from our laboratory, geared toward examining the biological link between the two, has uncovered that hypoxia induces the expression of proteins (Plk4, Aurora A, Cyclin D) implicated in CA, in a hypoxia-inducible factor 1α (HIF-1α)-dependent context. Our studies evidence that hypoxia fuels CA that underlie intratumoral heterogeneity and metastatic potential of cancer cells. Given the advent of HIF-1α inhibitors, this research has ramifications in aiding patient risk stratification and designing new cancer drug therapies to facilitate clinical decision-making.

Excess centrosomes induce p53-dependent senescence without DNA damage in endothelial cells

Tumor blood vessels support tumor growth and progression. Centrosomes are microtubule organization centers in cells, and often up to 30% of tumor endothelial cells (ECs) acquire excess (>2) centrosomes. Although excess centrosomes can lead to aneuploidy and chromosome instability in tumor cells, how untransformed ECs respond to excess centrosomes is poorly understood. We found that the frequency of primary human ECs with excess centrosomes was quickly reduced in a p53-dependent manner. Excess centrosomes in ECs were associated with p53 phosphorylation at Ser33, increased p21 levels, and decreased cell proliferation and expression of senescence markers, but independent of DNA damage and apoptosis. Aspects of the senescence-associated phenotype were also observed in mouse ECs that were isolated from tumors with excess centrosomes. Primary ECs with excess centrosomes in vascular sprouts also had elevated Ser33 p53 phosphorylation and expressed senescence markers. Our work demonstrates that nontransformed ECs respond differently to excess centrosomes than do most tumor cells-they undergo senescence in vascular sprouts and vessels, which suggests that pathologic outcomes of centrosome overduplication depend on the transformation status of cells.-Yu, Z., Ruter, D. L., Kushner, E. J., Bautch, V. L. Excess centrosomes induce p53-dependent senescence without DNA damage in endothelial cells.