Overexpression of the human ubiquitin E3 ligase CUL4A alleviates hypoxia-reoxygenation injury in pheochromocytoma (PC12) cells

CUL4A expression is associated with tumor stage and prognosis in nasopharyngeal carcinoma

Cullin 4A (CUL4A) is a protein of E3 ubiquitin ligase with many cellular processes. CUL4A could regulate cell cycle, development, apoptosis, and genome instability. This study aimed to analyze the expression of CUL4A in nasopharyngeal carcinoma (NPC) tissues and the associations of CUL4A expression with prognostic significance. A total of 115 NPC patients were collected to assess the protein expression of CUL4A by immunohistochemistry, so as to analyze the relationships between CUL4A expression and clinicopathological and prognostic parameters. All patients were followed-up until death or 5 years. The results showed that high expression of CUL4A was significantly associated with larger primary tumor size (P = .026), higher nodal status (P = .013), more distant metastasis (P = .020), and higher TNM stage (P = .005). Kaplan-Meier curves showed that patients with higher CUL4A expression had significantly shorter overall survival (OS) and progression-free survival (PFS) (both P < .001). In multivariate Cox analysis, CUL4A is an independent prognostic factor for OS (P = .016; hazard ratio [HR] = 2.770, 95% CI: 1.208-6.351) and PFS (P = .022; HR = 2.311, 95% CI: 1.126-4.743). In conclusion, high expression of CUL4A was associated with advanced disease status of NPC, and might serve as an independent prognostic factor.

Suppression of CUL4A attenuates TGF-β1-induced epithelial-to-mesenchymal transition in breast cancer cells

Transforming growth factor-β1 (TGF-β1) plays a vital role in the process of epithelial-to-mesenchymal transition (EMT) in breast cancer and the cullin 4A (CUL4A) gene is overexpressed in primary breast cancer. However, whether TGF-β1 signaling can induce CUL4A expression has not been investigated to date, at least to the best of our knowledge. In this study, using breast cancer cell lines, we found that the CUL4A expression level was increased following EMT induced by TGF-β1. Silencing CUL4A expression or CUL4A inhibition by thalidomide suppressed the EMT process induced by TGF-β1. We also found that CUL4A was associated with the expression of zinc finger E-box-binding homeobox 1 (ZEB1) which was induced by TGF-β1. These results suggest that CUL4A is upregulated in TGF-β1-induced EMT, and has a regulatory function in this process. The identification of CUL4A as a downstream target of TGF-β1 represents a critical pro-survival mechanism in breast cancer progression and provides another point for therapeutic intervention in breast cancer.

Allele-specific expression in the human heart and its application to postoperative atrial fibrillation and myocardial ischemia

BACKGROUND

Allele-specific expression (ASE) is differential expression of each of the two chromosomal alleles of an autosomal gene. We assessed ASE patterns in the human left atrium (LA, n = 62) and paired samples from the left ventricle (LV, n = 76) before and after ischemia, and tested the utility of differential ASE to identify genes associated with postoperative atrial fibrillation (poAF) and myocardial ischemia.

METHODS

Following genotyping from whole blood and whole-genome sequencing of LA and LV samples, we called ASE using sequences overlapping heterozygous SNPs using rigorous quality control to minimize false ASE calling. ASE patterns were compared between cardiac chambers and with a validation cohort from cadaveric tissue. ASE patterns in the LA were compared between patients who had poAF and those who did not. Changes in ASE in the LV were compared between paired baseline and post-ischemia samples.

RESULTS

ASE was found for 3404 (5.1%) and 8642 (4.0%) of SNPs analyzed in the LA and LV, respectively. Out of 6157 SNPs with ASE analyzed in both chambers, 2078 had evidence of ASE in both LA and LV (p < 0.0001). The SNP with the greatest ASE difference in the LA of patients with and without postoperative atrial fibrillation was within the gelsolin (GSN) gene, previously associated with atrial fibrillation in mice. The genes with differential ASE in poAF were enriched for myocardial structure genes, indicating the importance of atrial remodeling in the pathophysiology of AF. The greatest change in ASE between paired post-ischemic and baseline samples of the LV was in the zinc finger and homeodomain protein 2 (ZHX2) gene, a modulator of plasma lipids. Genes with differential ASE in ischemia were enriched in the ubiquitin ligase complex pathway associated with the ischemia-reperfusion response.

CONCLUSIONS

Our results establish a pattern of ASE in the human heart, with a high degree of shared ASE between cardiac chambers as well as chamber-specific ASE. Furthermore, ASE analysis can be used to identify novel genes associated with (poAF) and myocardial ischemia.

Oxygen regulates molecular mechanisms of cancer progression and metastasis

Oxygen is the basic molecule which supports life and it truly is "god's gift to life." Despite its immense importance, research on "oxygen biology" has never received the light of the day and has been limited to physiological and biochemical studies. It seems that in modern day biology, oxygen research is summarized in one word "hypoxia." Scientists have focused on hypoxia-induced transcriptomics and molecular-cellular alterations exclusively in disease models. Interestingly, the potential of oxygen to control the basic principles of biology like homeostatic maintenance, transcription, replication, and protein folding among many others, at the molecular level, has been completely ignored. Here, we present a perspective on the crucial role played by oxygen in regulation of basic biological phenomena. Our conclusion highlights the importance of establishing novel research areas like oxygen biology, as there is great potential in this field for basic science discoveries and clinical benefits to the society.

Knockdown of CUL4A inhibits invasion and induces apoptosis in osteosarcoma cells

Cullin4A (CUL4A) is implicated in many cellular events including cell survival and growth. However, the specific function and underlying mechanisms of CUL4A in cancer invasion have not yet been elucidated. In this work, we were focused on investigating the role of CUL4A in human osteosarcoma (OS). The expression level of CUL4A was evaluated by immunohistochemical (IHC) assay in human OS tissues. Lentivirus-mediated CUL4A shRNA (Lv-shCUL4A) constructed by us was transfected into OS cells for assessing its effects on cell proliferation and invasive potential, respectively detected by MTT and Transwell assays. It was demonstrated that the expression of CUL4A protein was markedly increased in OS tissues compared with the adjacent non-cancerous tissues (ANCT) (57.8% vs. 25.6%, P = 0.019), and was associated with the distant metastases in OS patients (P = 0.016). In vitro, silencing of CUL4A gene inhibited OS cell proliferation and invasion, and induced cell apoptosis, followed by increased expression of p27 and p53 and decreased expression of MMP-2. Therefore, these findings indicate that elevated expression of CUL4A is positively correlated with distant metastases in OS patients, and knockdown of CUL4A suppresses invasion and induces apoptosis in OS cells, suggesting that CUL4A may serve as a potential target for the treatment of OS.

Tumor hypoxia as a driving force in genetic instability

Sub-regions of hypoxia exist within all tumors and the presence of intratumoral hypoxia has an adverse impact on patient prognosis. Tumor hypoxia can increase metastatic capacity and lead to resistance to chemotherapy and radiotherapy. Hypoxia also leads to altered transcription and translation of a number of DNA damage response and repair genes. This can lead to inhibition of recombination-mediated repair of DNA double-strand breaks. Hypoxia can also increase the rate of mutation. Therefore, tumor cell adaptation to the hypoxic microenvironment can drive genetic instability and malignant progression. In this review, we focus on hypoxia-mediated genetic instability in the context of aberrant DNA damage signaling and DNA repair. Additionally, we discuss potential therapeutic approaches to specifically target repair-deficient hypoxic tumor cells.

Pathogenic Role of the CRL4 Ubiquitin Ligase in Human Disease

The cullin 4-RING ubiquitin ligase (CRL4) family employs multiple DDB1–CUL4 associated factors substrate receptors to direct the degradation of proteins involved in a wide spectrum of cellular functions. Aberrant expression of the cullin 4A (CUL4A) gene is found in many tumor types, while mutations of the cullin 4B (CUL4B) gene are causally associated with human X-linked mental retardation. This focused review will summarize our current knowledge of the two CUL4 family members in the pathogenesis of human malignancy and neuronal disease, and discuss their potential as new targets for cancer prevention and therapeutic intervention.