p53, DNA damage, and NAD+ homeostasis

The AsiDNA™ decoy mimicking DSBs protects the normal tissue from radiation toxicity through a DNA-PK/p53/p21-dependent G1/S arrest

AsiDNA™, a cholesterol-coupled oligonucleotide mimicking double-stranded DNA breaks, was developed to sensitize tumour cells to radio- and chemotherapy. This drug acts as a decoy hijacking the DNA damage response. Previous studies have demonstrated that standalone AsiDNA™ administration is well tolerated with no additional adverse effects when combined with chemo- and/or radiotherapy. The lack of normal tissue complication encouraged further examination into the role of AsiDNA™ in normal cells. This research demonstrates the radioprotective properties of AsiDNA™. In vitro, AsiDNA™ induces a DNA-PK/p53/p21-dependent G1/S arrest in normal epithelial cells and fibroblasts that is absent in p53 deficient and proficient tumour cells. This cell cycle arrest improved survival after irradiation only in p53 proficient normal cells. Combined administration of AsiDNA™ with conventional radiotherapy in mouse models of late and early radiation toxicity resulted in decreased onset of lung fibrosis and increased intestinal crypt survival. Similar results were observed following FLASH radiotherapy in standalone or combined with AsiDNA™. Mechanisms comparable to those identified in vitro were detected both in vivo, in the intestine and ex vivo, in precision cut lung slices. Collectively, the results suggest that AsiDNA™ can partially protect healthy tissues from radiation toxicity by triggering a G1/S arrest in normal cells.

The new chimeric chiron genes evolved essential roles in zebrafish embryonic development by regulating NAD+ levels

The origination of new genes is important for generating genetic novelties for adaptive evolution and biological diversity. However, their potential roles in embryonic development, evolutionary processes into ancient networks, and contributions to adaptive evolution remain poorly investigated. Here, we identified a novel chimeric gene family, the chiron family, and explored its genetic basis and functional evolution underlying the adaptive evolution of Danioninae fishes. The ancestral chiron gene originated through retroposition of nampt in Danioninae 48-54 million years ago (Mya) and expanded into five duplicates (chiron1-5) in zebrafish 1-4 Mya. The chiron genes (chirons) likely originated in embryonic development and gradually extended their expression in the testis. Functional experiments showed that chirons were essential for zebrafish embryo development. By integrating into the NAD⁺ synthesis pathway, chirons could directly catalyze the NAD⁺ rate-limiting reaction and probably impact two energy metabolism genes (nmnat1 and naprt) to be under positive selection in Danioninae fishes. Together, these results mainly demonstrated that the origin of new chimeric chiron genes may be involved in adaptive evolution by integrating and impacting the NAD⁺ biosynthetic pathway. This coevolution may contribute to the physiological adaptation of Danioninae fishes to widespread and varied biomes in Southeast Asian.

Combined treatment with acetazolamide and cisplatin enhances chemosensitivity in laryngeal carcinoma Hep-2 cells

The aim of the present study was to determine whether acetazolamide (Ace) treatment enhances the chemosensitivity of Hep-2 laryngeal cells to cisplatin (Cis). At the logarithmic growth phase, Hep-2 cells were treated with Ace, Cis or both, and cell viability was detected using an MTT assay. The degree of apoptosis was detected using flow cytometry. Expression levels of apoptosis-related proteins, including BCL2 apoptosis regulator (bcl-2), BCL2 associated X (bax) and caspase-3, and of proliferation-related proteins, including proliferating cell nuclear antigen (PCNA) and tumor protein p53 (P53), were detected using western blotting. mRNA expression levels of aquaporin-1 (AQP1) in each group were detected using reverse transcription-polymerase chain reaction. Compared with the drugs used alone, treatment with both Ace and Cis displayed synergistic effects on the growth inhibition and apoptosis induction in Hep-2 cells. The Ace/Cis combination decreased the expression of PCNA but increased the expression of p53. In addition, the combination treatment decreased the ratio of bcl-2/bax and increased the expression of caspase-3, as well as decreased the expression of AQP1. These results demonstrated that the combined use of Ace and Cis enhanced the chemosensitivity of laryngeal carcinoma cells.

Redox homeostasis protects mitochondria through accelerating ROS conversion to enhance hypoxia resistance in cancer cells

Mitochondria are the powerhouses of eukaryotic cells and the main source of reactive oxygen species (ROS) in hypoxic cells, participating in regulating redox homeostasis. The mechanism of tumor hypoxia tolerance, especially the role of mitochondria in tumor hypoxia resistance remains largely unknown. This study aimed to explore the role of mitochondria in tumor hypoxia resistance. We observed that glycolysis in hypoxic cancer cells was up-regulated more rapidly, with far lesser attenuation in aerobic oxidation, thus contributing to a more stable ATP/ADP ratio. In hypoxia, cancer cells rapidly convert hypoxia-induced O(2˙)(-) into H2O2. H2O2 is further decomposed by a relatively stronger antioxidant system, causing ROS levels to increase lesser compared to normal cells. The moderate ROS leads to an appropriate degree of autophagy, eliminating the damaged mitochondria and offering nutrients to promote mitochondria fusion, thus protects mitochondria and improves hypoxia tolerance in cancer. The functional mitochondria could enable tumor cells to flexibly switch between glycolysis and oxidative phosphorylation to meet the different physiological requirements during the hypoxia/re-oxygenation cycling of tumor growth.

TAp73 transcriptionally represses BNIP3 expression

TAp73 is a tumor suppressor transcriptional factor, belonging to p53 family. Alteration of TAp73 in tumors might lead to reduced DNA damage response, cell cycle arrest and apoptosis. Carcinogen-induced TAp73(-/-) tumors display also increased angiogenesis, associated to hyperactivition of hypoxia inducible factor signaling. Here, we show that TAp73 suppresses BNIP3 expression, directly binding its gene promoter. BNIP3 is a hypoxia responsive protein, involved in a variety of cellular processes, such as autophagy, mitophagy, apoptosis and necrotic-like cell death. Therefore, through different cellular process altered expression of BNIP3 may differently contribute to cancer development and progression. We found a significant upregulation of BNIP3 in human lung cancer datasets, and we identified a direct association between BNIP3 expression and survival rate of lung cancer patients. Our data therefore provide a novel transcriptional target of TAp73, associated to its antagonistic role on HIF signaling in cancer, which might play a role in tumor suppression.