Fragmentation level determines mitochondrial damage response and subsequently the fate of cancer cells exposed to carbon ions

Polyphyllin II Induces Apoptosis in Fibrosarcoma Cells via Activating Pyruvate Kinase M2

Aerobic glycolysis is a metabolic reprogramming of tumor cells that is essential for sustaining their phenotype of fast multiplication by continuously supplying energy and mass. Pyruvate kinase M2 (PKM2) has a vital role in this process, which has given it high interest as a target for anticancer drug development. With potent toxicity to many types of cancer cells, polyphyllin II (PP2), a steroidal saponin isolated from the herbaceous plant Rhizoma paridis, brought to our attention that it might interfere with the PKM2 activity. In this study, we discovered that PP2 was a novel agonist of PKM2. PP2 activated recombinant PKM2 and changed the protein's oligomeric state to activate intracellular PKM2. At the same time, PP2 suppressed its protein kinase function by decreasing the content of nuclear PKM2. The mRNA levels of its downstream genes, such as Glut1, LDHA, and MYC, were inhibited. In addition, PP2 induced oxidative stress by downregulating the expression and activity of antioxidant proteins such as NQO1, TrxR, and Trx in HT-1080 cells, which in turn led to mitochondrial dysfunction and ultimately induced apoptosis. Moreover, PP2 reduced the proliferation and migration of HT-1080 cells. Thus, targeting the glycolysis pathway offers an unprecedented mode of action for comprehending PP2's pharmacological impacts and advances PP2's further development in fibrosarcoma therapy.

NEAT1 Confers Radioresistance to Hepatocellular Carcinoma Cells by Inducing PINK1/Parkin-Mediated Mitophagy

A long noncoding RNA, nuclear paraspeckle assembly transcript 1 (NEAT1) variant 1 (NEAT1v1), confers radioresistance to hepatocellular carcinoma (HCC) cells by inducing autophagy via γ-aminobutyric acid A receptor-associated protein (GABARAP). Radiation induces oxidative stress to damage cellular components and organelles, but it remains unclear how NEAT1v1 protects HCC cells from radiation-induced oxidative stress via autophagy. To address this, we precisely investigated NEAT1v1-induced autophagy in irradiated HCC cell lines. X-ray irradiation significantly increased cellular and mitochondrial oxidative stress and mitochondrial DNA content in HCC cells while NEAT1v1 suppressed them. NEAT1v1 concomitantly induced the phosphatase and tensin homolog-induced kinase 1 (PINK1)/parkin-mediated mitophagy. Interestingly, parkin expression was constitutively upregulated in NEAT1v1-overexpressing HCC cells, leading to increased mitochondrial parkin levels. Superoxide dismutase 2 (SOD2) was also upregulated by NEAT1v1, and GABARAP or SOD2 knockdown in NEAT1v1-overexpressing cells increased mitochondrial oxidative stress and mitochondrial DNA content after irradiation. Moreover, it was suggested that SOD2 was involved in NEAT1v1-induced parkin expression, and that GABARAP promoted parkin degradation via mitophagy. This study highlights the unprecedented roles of NEAT1v1 in connecting radioresistance and mitophagy in HCC.

Flourish of Proton and Carbon Ion Radiotherapy in China

Proton and heavy ion therapy offer superior relative biological effectiveness (RBE) in the treatment of deep-seated tumors compared with conventional photon radiotherapy due to its Bragg-peak feature of energy deposition in organs. Many proton and carbon ion therapy centers are active all over the world. At present, five particle radiotherapy institutes have been built and are receiving patient in China, mainly including Wanjie Proton Therapy Center (WPTC), Shanghai Proton Heavy Ion Center (SPHIC), Heavy Ion Cancer Treatment Center (HIMM), Chang Gung Memorial Hospital (CGMH), and Ruijin Hospital affiliated with Jiao Tong University. Many cancer patients have benefited from ion therapy, showing unique advantages over surgery and chemotherapy. By the end of 2020, nearly 8,000 patients had been treated with proton, carbon ion or carbon ion combined with proton therapy. So far, there is no systemic review for proton and carbon ion therapy facility and clinical outcome in China. We reviewed the development of proton and heavy ion therapy, as well as providing the representative clinical data and future directions for particle therapy in China. It has important guiding significance for the design and construction of new particle therapy center and patients’ choice of treatment equipment.

Role of Mitochondria in Radiation Responses: Epigenetic, Metabolic, and Signaling Impacts

Until recently, radiation effects have been considered to be mainly due to nuclear DNA damage and their management by repair mechanisms. However, molecular biology studies reveal that the outcomes of exposures to ionizing radiation (IR) highly depend on activation and regulation through other molecular components of organelles that determine cell survival and proliferation capacities. As typical epigenetic-regulated organelles and central power stations of cells, mitochondria play an important pivotal role in those responses. They direct cellular metabolism, energy supply and homeostasis as well as radiation-induced signaling, cell death, and immunological responses. This review is focused on how energy, dose and quality of IR affect mitochondria-dependent epigenetic and functional control at the cellular and tissue level. Low-dose radiation effects on mitochondria appear to be associated with epigenetic and non-targeted effects involved in genomic instability and adaptive responses, whereas high-dose radiation effects (>1 Gy) concern therapeutic effects of radiation and long-term outcomes involving mitochondria-mediated innate and adaptive immune responses. Both effects depend on radiation quality. For example, the increased efficacy of high linear energy transfer particle radiotherapy, e.g., C-ion radiotherapy, relies on the reduction of anastasis, enhanced mitochondria-mediated apoptosis and immunogenic (antitumor) responses.

Mitochondrial dynamics, a new therapeutic target for Triple Negative Breast Cancer

Triple Negative Breast Cancer (TNBC) is an aggressive tumour with patients survival rarely exceeding five years. TNBC tumours are larger in size, more chemoresistant, highly proliferative and usually more enriched in stem and immune cells comparing to other breast cancer subtypes. Functionally, these changes are dependent on a high-quality mitochondrial pool. Mitochondrial health is constantly assessed and appropriately improved by mitochondrial dynamics (cycles of mitochondrial fusion and division). Recent advances in understanding of mitochondrial dynamics in TNBC has demonstrated its critical importance in tumour growth and metastasis. This review explores current knowledge of mitochondrial dynamics in TNBC and discusses targeting this pathway clinically to improve outcomes for patients.

Mitochondrial Fission Protein 1: Emerging Roles in Organellar Form and Function in Health and Disease

Mitochondrial fission protein 1 (Fis1) was identified in yeast as being essential for mitochondrial division or fission and subsequently determined to mediate human mitochondrial and peroxisomal fission. Yet, its exact functions in humans, especially in regard to mitochondrial fission, remains an enigma as genetic deletion of Fis1 elongates mitochondria in some cell types, but not others. Fis1 has also been identified as an important component of apoptotic and mitophagic pathways suggesting the protein may have multiple, essential roles. This review presents current perspectives on the emerging functions of Fis1 and their implications in human health and diseases, with an emphasis on Fis1's role in both endocrine and neurological disorders.

The Regulatory Mechanisms of Dynamin-Related Protein 1 in Tumor Development and Therapy

Background: Various types of tumors are likely to acquire drug resistance over time. Hence, the development of novel therapies to overcome drug resistance is critical. Studies have demonstrated that drug resistance is closely associated with the dynamic regulation of mitochondria in tumor cells. The dynamin-related protein 1 (Drp1) is involved in the regulation of mitochondrial fission and plays an important role in maintaining mitochondrial morphology, function, and distribution. It is a key protein in mitochondrial quality control. Drp1 is a GTPase localized to the cytoplasm and is a potential target in cancer therapy. A variety of drugs targeting Drp1 have shown great promise in reducing the viability and proliferation of cancer cells. The dynamic regulation of Drp1-mediated mitochondria is closely associated with tumor development, and treatment. Aim: In this article, the authors reviewed the occurrence and progression of mitochondrial fission regulated by Drp1, and its influence on cell cycle, autophagy, apoptosis, migration, invasion, the molecular mechanism of tumor stemness, and metabolic reprogramming. Targeted inhibition of Drp1 and mitochondrial fission could reduce or prevent tumor occurrence and progression in a variety of cancers. Drp1 inhibitors could reduce tumor stemness and enhance tumor sensitivity to chemotherapeutic drugs. Conclusion: Research into identifying compounds that could specifically target Drp1 will be valuable for overcoming drug resistance in tumors.

CircRNA CBL.11 suppresses cell proliferation by sponging miR-6778-5p in colorectal cancer

BACKGROUND

Radiotherapy (RT) is considered an important therapeutic strategy in the fight against colorectal cancer (CRC). However, the existence of some radioresistance factors becomes the main challenge for the RT. Recently, non-coding RNAs (ncRNAs) have shown an important role in modulating cancer cell responses to ionizing radiation (IR). It is therefore of great significance to elucidate the exact mechanisms of ncRNAs in IR-mediated responses to CRC.

METHODS

Microarrays were used to identify specific miRNAs that may be altered in response to IR. Bioinformatics, luciferase reporter analyses were used to explore the targets of miR-6778-5p. CircRNA CBL.11 was identified to bind with miR-6778-5p by bioinformatic analysis, AGO2 immunoprecipitation and biotinylated RNA pull-down assay. Functional experiments, including CCK-8 assay, cell colony formation assay and EdU incorporation were conducted to investigate the biological roles of miR-6778-5p and circular RNA CBL.11.

RESULTS

MiR-6778-5p was suppressed in CRC cells after irradiation. Results of functional experiments indicated that miR-6778-5p promoted the proliferation of CRC cells. Luciferase reporter analyses showed that YWHAE was a target of miR-6778-5p, which mediated the function of miR-6778-5p in the proliferation of CRC cells via the p53 pathway. Furthermore, we have noticed that after carbon ion irradiation, circRNA CBL.11 was increased in CRC cells and could function as a competing endogenous RNA (ceRNA) to regulate YWHAE expression by sponging miR-6778-5p, resulting in regulation the proliferation of CRC cells.

CONCLUSION

CircRNA CBL.11 may play an important role in improving the efficacy of carbon ion RT against CRC.

Silibinin-induced apoptosis of breast cancer cells involves mitochondrial impairment

Mitochondria are dynamically regulated by fission and fusion processes. Silibinin induces apoptosis of MCF-7 and MDA-MB-231 human breast cancer cells. However, whether or not mitochondria dysfunction is involved in the apoptosis induction with silibinin of both types of the cells remains unknown. We here report that silibinin decreases the mitochondrial mass in terms of MitoTracker Green staining in both breast cancer cells. Silibinin induces morphological changes of mitochondria from oval to truncated or fragmented shapes accordingly. Condensed crests are observed in mitochondria by transmission electron microscopy. Silibinin causes mitochondrial membrane potential reduced. The expression of mitochondrial fission-associated proteins including dynamin-related protein 1 (DRP1) is up-regulated, whereas expression of the mitochondrial fusion-associated proteins, optic atrophy 1 and mitofusin 1, is down-regulated. In addition, silibinin treatment down-regulates ATP content as well as the levels of mitochondrial biogenesis-regulators including mitochondrial transcription factor A, peroxisome proliferator-activated receptor gamma coactivator 1 and nuclear respiratory factor 2. Moreover, treatments with DRP1 inhibitor, mdivi-1, or with DRP1-targetted siRNA efficiently prevent silibinin-induced apoptosis in the breast cancer cells, whereas inhibition of DRP1 phosphorylation with staurosporine increases apoptosis furthermore. Taken together, we conclude that silibinin impairs mitochondrial dynamics and biogenesis, leading to apoptosis of MCF-7 and MDA-MB-123 cells.

Different mitochondrial fragmentation after irradiation with X-rays and carbon ions in HeLa cells and its influence on cellular apoptosis

Although mitochondria are known to play an important role in radiation-induced cellular damage, the mechanisms by which ionizing radiation modulates mitochondrial dynamics are largely unknown. In this study, human cervical carcinoma cell line HeLa was used to demonstrate the different modes of mitochondrial network in response to different quality radiations such as low linear energy transfer (LET) X-rays and high-LET carbon ions. Mitochondria fragmented into punctate and clustered ones upon carbon ion irradiation in a dose- and LET-dependent manner, which was associated with apoptotic cell death. In contrast, low-dose X-ray irradiation promoted mitochondrial fusion while mitochondrial fission was detected until the radiation dose was more than 1 Gy. This fission was driven by ERK1/2-mediated phosphorylation of Drp1 on Serine 616. Inhibition of mitochondrial fragmentation suppressed the radiation-induced apoptosis and thus enhanced the resistance of cells to carbon ions and high-dose X-rays, but not for cells irradiated with X-rays at the low dose. Our results suggest that radiations of different qualities cause diverse changes of mitochondrial dynamics in cancer cells, which play an important role in determining the cell fate.